Alright, I think it's time to start Good morning, everyone. Welcome to notice GSA will start our session by it's about the tectonic evolution of eastern North America from rocks seismic data experiments and models.
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We have 12 presentation this morning, 10 of them are all presentations, and two posters.
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But all presenters are going to be live here for your questions before we start to listen. Awesome talks ranging from the surface geology to seismic works on the eastern North America.
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Yes. All right, let's start slowly, our first talk is titled Magnum Magnum mingling and contact metamorphosis during an onsite manager I China guy Brown Eyed suits and placement is to another one Doc Martens New York by Peter rally and Greg wash and peak
peak is going to deliver this talk, Pete, go ahead.
Alright. Thanks sir can get my screen going here.
There it is.
And I'm on
it starting the slide show it says,
Okay, everybody see the screen.
Yes, it's okay. Um, so, Greg and I have been mapping in the eastern Adirondack Mountains. And just a fantastic place to work.
So much geology to see, despite the like in this around.
You can find lots of great outcrop with some very interesting geologic processes going on, just to give an overview of the project. We are mapping theyre in eastern Adirondacks is part of a multi year project to map much of the Eastern Adirondacks one
to 24,000. Despite people working there for 130 years hundred and 40 years, there are very few one to 24,000 max.
Only some really tiny detailed maps that people have done.
We're there to evaluate the geologic structures metamorphosis of, and especially the origins of magnetite appetite deposits that have associated rare elements with them, and the appetite.
The field mapping is done using some awesome new LIDAR that we have.
We have airborne geophysics, and we have some folks in Colorado, who are describing your deposits.
If I could pick any tool to use outside of a compass. It's the lighter boy, it saves so much time, you can see where every single outcrop is you know have to go searching through the woods.
And finally, we'd like to say something about the tectonic evolution of Eastern Adirondacks, there's not been a lot of work done on sheer zones and, and much of the structure.
So we'd like to get some answers for that.
Just a quick background for the eastern Adirondacks Adirondack Mountains or extension of the Granville province exposed in Quebec and Ontario.
the Adirondack lowlands and the Adirondack Highlands along something called the Carthage Colton shear zone, which or con is done some work on.
And the highlands were metamorphose by both the show and again and auto in phases of the Granville Rajini.
But the lowlands have only seen show in again defamation and metamorphosis.
So here's where we're working.
This red box is a big overview of the Eastern Adirondacks northern New York, and are nine quads, that we have in plan to do the bottom three here paradox leg Eagle Lake and Crown Point are completed in one form or another, I think.
Crown Point is just about ready to go and Greg will be talking about that.
I'm working up here and poor Henry, which is one of the central locations for a lot of the historical iron mining that was going on in the area.
If you've never been to the eastern Adirondacks. I really recommend it. It's.
I think Greg and I both feel are incredibly lucky to get to go out there, even during covert I got to do at least five or six weeks of mapping.
It's just spectacular. So, the eastern Adirondacks themselves, they're dominated by this 1100 and 60. million year old approximately a Northside Andre, China Kate granite suite that intrudes an older meta sedimentary see plants.
These rocks have been metamorphose to upper amphibious lighter grainy light bases. We recognize four distinct periods of information in the map area.
But despite much of this metamorphosis and information, a lot of the intrusive contacts are preserved by a big metamorphic over. and that's what I'm going to talk about today.
Just a quick overview of the units that I see in the map area.
There's a get broken Northside Gabrielle on northeast say this is part of the white face faces named by camp in 1898, start to be a border faces of the big Marcy and North the site.
I see no mercy at all important Henry.
The Rock varies from being a nice to completely under form, magnetic textures, their mutual cross cutting relationships between the Gabrielle and the in order to say next June is China kite nice, which.
Overall I would describe it as a horn blend granite. It probably had a lot more appeared see minute to start with a subsequent metamorphosis over printed in.
It's really a series of rocks.
Hearing seeing granite court cyanide cyanide.
True Charnock a Monterey, and Garnet granite and almost always and treats the gap row North the site, but it was rarely observed to see the Gabrielle and truth the churn two units that I won't talk about today are the line mountain granite nice, this
is the host all the magnetite deposits are the majority of magnetite deposits.
It has magnetite everywhere.
It's been affected by fluid alteration around the number of your deposits, and it has intrudes all of the units.
And then there's a meta sedimentary sequence of making attack nice Marvel prophetic marvel of course site and film.
So general contact relationships.
We see evidence for Magnum mixing their intrusion branches, can't describe that as lock structure. So strap assimilation is mineral live mineralization along context, the context can be razor sharp inner fingered creation know obviously tectonic, and
sometimes you just can't tell.
you just can't tell. As a general sequence from oldest to youngest or Northside is the oldest gab bro, followed by Charnock I, and then line mountain.
Great. Nice.
So here's some field shots of the North the site gap bro. You can see in the upper left the top of that outcrop is Lupo Gabrielle. The bottom is Garnet Baron North the site.
And you can, you can see that the boundary is very diffuse, you can see Garnett's that are put this in quotation marks, raining out of gab row.
On the right hand side you can see some big flash.
For for blast or output for blast but Xena list from the north the site, better that have been trained within the gap.
And then in the lower left, you can see that the rocks do get get pretty good for music, you can see some asymmetric tails on those garnets.
So the Charnock I Gabrielle contact, which is what I'll be talking about today.
The turncoats generally younger, and the contact itself can be quite complex, it's great emotional over the distance of maybe 60 or 70 meters.
Starting in, what it would be the true China Kate Rog, you go through a sequence, at least in this particular area where I looked at it, the chocolate cake goes to manager I may think China kite or cyanide.
Which that actually might be part of the gap row now after living in sections.
There's a magnet to eliminate CPE x rock, and then you get into a true gab.
And that sequence is all inner layer with other little things, small granite layers granite segments I say make make mistake felt and rarely north.
So there's a lot going on at the contact between the China guy, and the gap.
But textures within the outcrop, they can be shared in that section iraq that's a foot long, and then be completely uninformed right next to it, there's you know lists of get broke rocks in China guy.
But the one I'll go through a number of thin sections today is about a mile away from the one listed above, and that will be contact from Monterey through a mix pregnant type rock.
An iron rich iron rich piercing Gabrielle, and fill it and then gap.
I was really lucky that the town of Port Henry was retrenching or retrenching ditch that went right across these contacts and so here's the contact almost hundred percent expose which is pretty rare.
So here are some field shots of the Charnock Chi, and the Gabrielle and the transitions in the upper left, you can see a fairly sharp boundary of the charges against the Gabrielle Gabrielle either has lots of Lucas zones or less a little fingers of China
K and treating it.
I'm not sure which which of those is the case in the upper right, you can see China k shooting into the lower left and Xena lip.
Garnet bearing Gabrielle and chocolate cake.
Another Xena live with lots of swirly bits and making minerals in China.
So, here is more of the town for Henry was retrenching The road is still the Shire road and SOS.
The main place I'll talk about is this contact with the Charnock I on the southwest side, and the Gabrielle and the North East Side, the red line, marking the approximate contact the field shots are from near this yellow circle.
Today I'll be going through in sections where the Green Star is.
And I'll. Originally I was going to go through what the site looks like along the sheer sounds. And I'll show one of those at the end.
But I didn't have the time to cover all of it.
So, here. This is another fun thing and working from home as all my thin section photos are from my iPhone putting pointed down.
I hold the microscope.
So I'm on the left cross polarized light, a pretty typical Charnock I rock period seen this op x.
The forum Garnett pathetic felt spar and, and pledge.
So, but as you get close to the contact with the camera, things start to change.
So here we are.
We're in the gap row and we're going to make it transept off to the north, east of Britain the charter guy, we're going to make a trade off to the north, east to the Gabrielle.
This is the gap row right at the contact so here you're about a meter away, or where you get into a big mix.
And unfortunately this rock it was really hard to say a whole lot about all the, all of what used to be period seen an affable is all late chloride.
One thing that did get preserved.
These garnets with Big Magic plays halos around them.
So that was interesting that'll be part of our metamorphic story i think i. It was really hard to tell any effects from the intrusion, because of the, the low grade over print.
But moving along the first rock at the contact is a pigment a very mixed pigments sports magic plays horn Lynn by it site, and then oxides are a mixture of illuminate and magnetite
it. To me, it looked like a hybrid rock between the charter K, in the gap bro.
It could possibly be late.
Late segment tight that just happened to us, the contact as a conduit.
I'll have to take a closer look at that.
When we get back to the field.
The second rock, which is three meters from the contact. It's very interesting because the period scenes, and this is without doing any sem or micro probe analysis. They appear that they're going to be very iron rich, either even better guy or iron rich,
which is a bit unusual for the gab row.
And there's this strange orange alteration that I can't quite identify maybe it's your ally.
Some of it is chloride I can tell this is quite bright orange.
Not sure why.
So this rock three meters from the contact has some big iron rich pyrrhic scenes, you can see rim net coronas or coronas around Garnet Garnet array Corona pelagic plays.
It also has little inclusions oxides horn blend. And then there will be an outer rim of horn blend. And the gap bro i sorry, the pyrrhic scene is kind of in a layer all by itself, going through the middle.
So that is three meters from the context, continuing on to Iraq, we're about seven meters away, 20 feet. I have an amphibious like. So it's almost all horn blend mixed up sides again with element AI and magnetic has budget plays and loads of appetite.
Rock is just full of appetite.
I believe it was the Gabrielle at one point, because they're altered minerals with little bits and specs of client appeared seen in the PC.
And there's no garden. So, the Garnet is not for whatever reason, I attributed to contact metamorphic ism, the calcium would be going into appetite. It's not making Garnett, it's a bit unusual because almost every rock has gone in it, in this area.
One thing I forgot to say is that, I'm going to show you lots of observations and not have a lot of answers.
That's, that's what this summer will be four key, that's about 20 feet from the contact.
And then, finally, because, you know, a mapping I can't collect the sample every two meters unless something really interesting comes up, which now has been about 40 meters from the contact of the Charnock a start to get back into what I would consider
the true Gabrielle surely Gaborone door right with lots of period scenes, this photo micro graph up in the on the left hand corner.
That's all client appeared seen in that in section view so pure UK scene is quite happy here. Garnet is very happy.
So, just looks like a pretty typical gab bro.
It's Gabrielle nice.
It is a bit deformed here.
So, just approve or I think prove to you that these relationships are in related to intrusion.
I went through and I found thin sections progressing from almost completely under formed in the gab row to proto mile a night in the gap row. And so these three sections are from the sheer zone on the northeast and build a Shire road, and you can see
here's a nice coordinated gab row with, as described by Whitney and McClellan and 73.
There's couldn't find all have been in it, there might be at least where we're working it seems to be the rocks have eliminated, most of the all of the, maybe one, if I get on the SEM I can find some, but here you see nice coronas with spin owl or eliminate
magnetite cores, surrounded by horn bland. And then the matrix says this beautiful flash laugh in it.
Some partially replaced by Garnet bent a little bit, but as you go to the northeast and you start to deform this rock, you can see here in the right upper right side, that the mineralogy is basically the same.
But everything's getting getting flattened out and shared out.
And then finally, the sample, that's closest to the sheer zone, it's just it's just pretty hammered.
That being said, there's still a period scene in the rock.
Even after undergoing all that information.
So, you have almost two minutes left, so Okay, start to wrap up so maybe we can have a quick question.
Sure.
I'll just show you on the map there where we were working, here's a big shear zone I've mapped. This is where those last samples are from this is where the, What I believe is the intrusive contact is from.
And I'll just skip through the information.
So, we're mapping in the Adirondacks, there's the preservation of igneous processes related to AMCGMCG sweet intrusion, despite a big metamorphic and tectonic over print.
So I'll just leave it at that and we can have a quick question.
Thank you very much.
We have one minute, maybe a one quick question for Pete anyone has a question, please raise your hand, or you can actually type your questions on the chat box.
After the top.
Pete can answer that, see if there's any questions,
see any, I have a quick question.
You mentioned these two types of roles are they, I'm sure they are different from each other, is it possible to discriminate them in the field at a more diverse.
dB in the pyrrhic scenes that iron rage period scene. Yeah, the alpha balls in those rocks versus the, you know, like pragmatists of honorable in it as well.
You cannot, in fact it's even difficult to tell the difference between the horn blend and the period scenes in the field because it's all black.
I was that bluish green color in the pyrrhic scene and I was really surprised to see, I have not seen that before. Because typically the climate pyrrhic scenes just clear.
Probably RJ.
So you cannot tell it in the field.
Thank you.
There's some question on the chat box so go ahead and answer that. But we'll move on to the second talk we have the second talk, it will be staying in other index integrated that bedrock logic mapping in the Adirondack highlands of New York, by Gregory
was laying off. Ryan Taylor, and Anjana show.
Greg is going to give the talk. I will give you a heads up when you have done your 15 minutes. Okay, good thank you Larkin, and good morning everybody.
Happy Friday. I think you can see my screen I hope you get off to my left here, and I'll probably turn off my video for a second while I go through the talk, will be talking about mostly bedrock geologic mapping results over the past couple years and
the Adirondack Highlands.
This project is focused mostly on one to 24,000 scale mapping in the Adirondack Mountains funded from the USGS national cooperative geologic mapping programs and the mineral resources programs.
When I say integrated bedrock mapping I'm talking about different tools that we're using in the field and the first and foremost is boots on the ground but we're also able to use LIDAR new airport into physics, chemistry metrology economic geology geology
and some strategic fi and paleontology, most of the work I'm going to be talking about today all the work and be talking about today is in the area and right here in Southern Essex County, the Adirondacks so this large area right here and Essex County
in white and the air area of the new airborne geophysical survey is this blue footprint right here. Most of us know where the Adirondacks are here they are they're an extension of the Grenville province which extends for thousands of kilometers on the
edge of Lorenza
in the Adirondack Mountains. All the colored units here are basement rocks, middle presented basement rocks at the Adirondack Mountains in the Adirondacks are divided into the lowlands in the highlands the Adirondack lowlands occur to the northwest in
in the upper plains of the Carthage Colt shear zone there and fibber light faces rocks here, and then all the rocks down here are called the Adirondack Highlands they consist of complexity to form Meza present granulated faces rocks that have experienced
at least three grade high grade organic phase is called a wriggle at the Auto and show when again from about 1.2, to 1.0 ga. The basic rock types in here the colors in blue and pale blue are paradises marbles and some in FB light and then they are interested
by a suite of igneous rocks and Pete was referring to the AMC g sweet and or the site and yellow manager right charter kite in green and orange and and then a grant that's coming in later on those of the line mountain grants tweet here in red that extend
down around the eastern side of the Adirondacks above these rocks are unconfirmed Lee overlain by lower Paleozoic sedimentary rocks along the great unconformity.
This is what the great nonconforming looks like sometimes it's quite spectacular here's the Cambrian Potsdam sandstone unconformity on top of a biotech paradise.
And then here you can see it also in Putnam create this is the Potsdam sandstone and this is the basement rocks down below.
There's about one kilometer of lower Paleozoic section that it's early Cambrian the late Ordovician Great American carbonate bank on the eastern margin of Florencia, the area that I'm gonna be talking about today it was last map it over 60 years ago six
ago, bye bye well being Vermont at one to 62,500. And last map in New York by none other than john Rogers 70 years ago, and Matt Walton, and they they did the mapping at one to 20,000 but one to 21 to 24,000, but none of the mapping is published and this
sort of highlights a problem. If you look at the National geologic map database there's essentially no bedrock geologic map information for the Adirondack Karlin's.
And I think if you can see this picture right here see this right here this is a, this is the cut out of the one to 250,000 scale geologic map of New York.
This is a seven half minute quadrangle, this is the Crown Point quadrangle. This is all the published geologic map information for this area, and about 200 quadrangles in in the Adirondacks and we're trying to improve on that.
Why are we mapping in eastern Adirondack Highlands well they'll ever index have long and recognized as as a location for mineral resources, their historical iron mines and tailings in eastern Adirondack Highlands called the iron ore district, and these
have rare earth element potential, the rare earth elements occur in Corona type iron oxide appetite or Iowa deposits that are either magnetic north fiber thermal, and there's an established link between these Iowa deposits and the line mountain granite
nice this area here in red, will focus again on this area down here.
Here's mine Ville mine Ville is probably one of the larger areas for iron extraction and Eastern Adirondacks iron mining took place from the Revolutionary War Two, but the 1970s.
At one point appetite was extracted from mine Ville and a byproduct was produced called red sand which is used for phosphorus fertilizer.
This is where we're doing active geologic mapping and about eight seven and a half minute quadrangles in southern Essex County.
We specifically target the rocks or most complexity to form, where there are high number of iron minds.
There is no one to 24,000 published geologic maps and all these areas are considered high priority areas for mapping by the New York State Geological Survey, mostly focused about this area down here in Crown Point.
Just adjacent to that this is an example from the Eagle Lake quadrangle, if we're going to study the mines well it's very important to know where they are right fundamental question Where are the minds well if we look at the geologic maps or the total
graphic maps actually these aren't geologic maps, through time we see that in this area is called Hammond Ville back in the 1890s there was a town that were railroads.
Later on the number of the mines were shown on the map and then later on into the 1970s fewer minds were shown. And if we look at the MR DS database, there's only one.on the map so there's a disconnect here between where the actual minds are and what
they're shown on the, on different levels of mapping.
And this is what the area looks like now Hammond Ville is gone, it's a ghost town The area has been taken over by the forest so finding mines in this area is a little bit of a challenge.
Fortunately we have LIDAR light our first became available for the Adirondacks and in 2016 right when the project was getting going, and most of the Adirondacks now have qL to data.
Light we're using LIDAR to map minds outcrops abandoned mine roads, abandoned railroads tailings piles waste rock piles and the bedrock structure in the Hammond Ville area alone, we found over 50 different pits, and for the most part we're using a percent
slope map for most of the LIDAR applications, seems to work well for finding outcrops and some of the features. This orange polygon right here is in the next picture, this is what some of the waste rock piles look like there's a geologist back there.
I think that's peak Valley.
This is what some of the mines look like they're just small holes expose on the surface and some trenches is Ryan cliff and Caitlin now LIDAR is fantastic and and, but sometimes outcrops are hard to find even when you do have LIDAR.
So here, here's some outcrops underneath this tree fall and LIDAR of course is fantastic but it doesn't tell us what kind of rocks are on the ground so we still need boots on the ground and go collect samples is Pete showed in great detail and his presentation.
This is an example of the Crown Point quadrangle. This is a map that's in progress right now, and I'm going to focus mostly on on these LIDAR application here these green lines are near partners like dykes on the northern side of Bulldog a mountain, I'll
I'll explain the geology here in a little bit with some examples. And these northeast trending dikes extend for several kilometers and if we look on the LIDAR you can see these long lineaments that extend across the country site now if you just have the
LIDAR you know that there's a crack in the ground, but you don't know what that is, is that a fault is that a joint, or is it, is it a dike, and you don't know well now we know that these, these areas here are underlined by metric dykes, you can also
see lineaments that are parallel to the fully ation on the liner and you can see a nice humbling experience that there's a vast amount of outcrop in the area and will only be able to get a look at some of it during the course of our mapping.
This is what these lineaments look like from the ground we're in the Champlain Valley looking to the west and you can see these, these ravines here, and this is what they actually look like in the forest.
And so I'll talk a little bit more about the bedrock geology of the Crown Point quadrangle here's a status map from the mapping program that shows the number of one to 24,000 maps and the scale maps in the Adirondacks.
This is the current point quadrangle again and here's Lake Champlain that that divides the quadrangle into New York on the west and Vermont and the East the area of Paleozoic rocks are shown in pinks and purples and a little bit of green here I'm not
going to talk about those. But most of the focus today is on these basement rocks, this major medicine elementary rock in the area is a magnetic biotech ports pledge it plays nice you can see it all throughout here that's the brown unit on the map.
inner layer and with the paradises you have marbles and FB lights is an example of a graphite Baron calcite marble. And that was mine for both graphite and some places the marble was used for flux in the iron furnaces.
This unit here on red on the map is the line mountain granite nice it's a furrow and alkali felt spark granite and consists of several different phases microclimate granites micro perfect granite and quartz Albert rocks were there altered.
Here it's assimilating some infinity light and it's got a very weak fully ation.
These granites occurrence sheets parallel to the existing fully ation in the area. that's the areas here and read and cross section from across this area right here.
You can see where the full ation is gently dipping with sheets of granite that are intruding a pre existing pre to form, and FB light here.
And in cross section this this flat areas affiliation or because the light up right during the dome stage folds are found all throughout the Adirondacks in three dimensional model you can see this, this late gentleman here on this southern part of the
Crown Point quadrangle.
This is what the or seems look like most of the orders occurs either sales or cross cutting veins or dikes these in Iowa type deposits and their most common in line mountain granite nice but they do occur within some of the other units as well.
Here, we can see that the seams are folded by these domes stage folds.
Pete Valley for his PhD did some cutting edge Zurich on geo chronology to determine that the zero con and the or seems was about 1042 1000 ma and it was younger than the host granites that he dated between about 1062 and 1033, we've continued to do some
additional geo chronology using high resolution CL imagery to reveal highly complex zircons and granular like faces zircons are quite complex, and this has been a little bit controversial but we've got a paper that's impressed right now Precambrian research.
These are not your zircons that you see in lower grade rocks. This is an example from New Hampshire and green shoes face these blue icons. These icons in the Adirondacks are much more complex.
The results from the paper show that the Zurich encores represent the igneous age of the rock they're not the inherited age the age of the line mountain granted it's about 1162 1140, the rims represent a period of auto and metamorphic ism this these results
will overturn about 30 years of conventional thought the line mountain granite nice is the G part of the AMC g sweet, and that it's about 100 230 million years older than the Iowa deposits that it contains.
Just some highlights some of the first modern rank one airborne geophysical surveys that have been completed in the Adirondacks much of this work and cooperation and done and led by Angie show and Denver, you can see the old era magnetic ad on the left
and the new era magnetic data on the right.
Magnetic highs correspond to Luca granites, the line mountain granite nice and some meta gab rose and lows correspond to enormous sites and marbles and some meta sedimentary rock.
This is another example of the era of magnetic data using a high pass filter to highlight some of the structures in the area. Pete was talking about the sheer zones here's an example where the highly magnetic rocks are are left laterally offset and in
the field we see often these magnetites in these dilate and dilate and share zones intruding in these in these in these planes.
Another example of arrow magnetic data using band pass filter analysis shows that the highs correspond to known deposits, these are known mines these white dots and also highlight some places where there are no known deposits that might indicate potential
shallow sources.
Angie and Jeff Phillips made this three dimensional model of the magnetic susceptibility that show the projected Lyon mountain granite dipping to off to the east underneath Lake Champlain in fact underneath the Paleozoic rocks into, into subterranean
Vermont. It's kind of a neat application of the of the air magnetic data.
Ryan Taylor has a paper that came out a couple years ago and he's got another one on the geochemistry of these deposits. Looking at the or the waste rock and the tailings show that the light rare, rare earth ratios in these rocks are relatively high and
they're more enriched than some other well known global resources such as boy an oboe and mountain pass the Oren waste show enrichment in Europe, Terbium UTM neodymium and a positive correlation between sorry im and rare earth elements, the airborne radio
metric equivalent thorium and uranium anomalies show large tailing files you can see these highlighted here these are some of these large scaling piles, and that the waste rock and the tailings are a potential resource.
So just in summary, we have rare that element potential exists at all iron minds, the bedrock characterization is very old and inadequate we're in the process of updating that significantly.
New geophysical data are available LIDAR is here. Right, right.
The mines are not adequately located but we can find them now and that the waste rock and tailings are a potential resource, and just In conclusion I really want to acknowledge a large number of people are that are involved with this, this project.
Specifically, the folks that UMass a number of students have worked with and Mike Williams, their advisor and number, number of other folks at the USGS and the funding from the USGS and the early work by Matt Walton in the area.
So thank you very much and I'll take some questions now.
Thank you Greg, we have some time for questions. I have one question coming from the chat. What's IOA stands for iron oxide appetite, it is a is an end member of iron oxide copper, gold deposit.
It's a specific specific type of mineral deposit but the iron oxide is magnetite in this case and then appetite so these are magnetite appetite deposits.
And that's an acronym sorry we throw those acronyms out all the time. Honor oxide appetite is IOA have one more question. What was the previous unpublished detailed mapping of any use or they just have started to over.
Oh, that's an excellent question. Matt Walton and john Rogers did some mapping in the area and their mapping was useful specifically for determining what destructive graffiti was in the area so they identified the major units the line mountain granite
and some of the parent ISIS.
But some of the details in terms of where they actually mapped like where the outcrop locations were some of those pieces of information were not available.
And so, the maps were are available from the New York State Geological Survey if anybody's interested in in previous mapping in the Adirondacks that's not published I urge you to contact the New York State survey because they have a series of archive
manuscript. Open File reports that are publicly available upon request. You have to ask them specifically, but since they were never peer reviewed and published they're not.
They're not available on their website so Matt Waltons maps have been very very useful and john Rogers as well so we we are not starting from ground zero we do have, we do have something to work on so they've been very helpful.
Thank you.
One more question. How do you know the age of Neoproterozoic may think, oh, that's it, that's a good question, um, for the most part they're not very well constrained to Jeff Karen's le and Shawn reagan did a, a St Lawrence University field trip a couple
years ago and Jeff had dated one of these dikes I think he got about 640, ma.
Most of them are correlated with the, the age of drifting that's been dated in the, in the Tippett Hill volcanic sand volcanic sand in Canada and the volcanic that I worked on in Vermont that there are about 570 So somewhere between 640 and 570 is about
the age, but we've known for a long time it's very been very well demonstrated that the Neoproterozoic dikes are cut by the great unconformity, they don't actually pass up into the Potsdam so that we know that they're older than.
Then, then cambrin.
Well, thank you, Greg I think we're going to move on to the next. All right.
If you can share your screen, I'm going to do that. Yes. All right.
Yep. Alright, our next speaker is Jeff Pollock, and his talk is on the tectonic inheritance in the North Atlantic consequence of episodic organic collapse.
Jeff, it's your turn.
Okay, I'm trying to turn on my camera here.
Okay, good morning.
Can you hear me.
Yes we can hear you but we can't see you can't see me okay.
It's not sharing.
We can see the screen, Jerry can see the screen so you know okay here we go.
Excellent. Okay, so I'm really kind of more of a large scale not a regional talk that we've seen from the first year but looking at North American the geology, North America, USGS map here.
The distinction between how North America is unique as a content there's no other continent. On Earth, that is like North America.
And it's not readily apparent from this map here but we see that uniqueness when we look at the age.
Separate rocks by age, and so that ranch in North America.
It consists of a core
of our key and continents, that were welded together by protozoa origins. And what makes it unique is that surrounding the central core of the continent.
We have much younger origins which kind of formed this ring like structure, we don't see this anywhere else on earth. And these younger origins of course are several Wilson cycles and it's best demonstrated here in eastern North America where we move
from the Precambrian superior the Mac of Vicki in the Grenville Ian and the the Appalachian origin that surround these surround the older core.
And it really represents. We're content riffed on old mountain belts, this was first demonstrated by Tuesday Wilson.
50 years ago and his famous paper in nature, showing that new oceans will always open up, parallel to old organic belts and just figure here shows.
Wilson's now color diagrams, from these 1966 paper nature.
And, you know, the modern reconstruction in the ocean here from Pangea, and it's not surprising that mountains riffed on old or oceans riffed on old mountain belts because the old mountain belts have inherent weaknesses in them, they have old faults they
focus fluids. So they partition strange these zones of weakness.
And we see in eastern North America from the two mountain belts, the Appalachians are a two sided mountain system, which shows us that the origin.
After it refers to form the Atlantic, it must have drifted outboard of the suture because we see exotic pieces of Africa gun wanna stuck on North America, where's the Grenville is a one sided orgy which means that it must have resulted in board of the
suture, but ultimately we see this you know this is part of Nancy and Murphy supercontinent cycle where we see this repeated riffing and mountain building occurring on the same location at the around the margins of the continent, and its really the concept
of tectonic inheritance, where we guide deformation along pre existing structural deformities nominally in the crust. And that inheritance takes two forms we can either reactivate old structures, which is usually controlled by the mechanics, mechanical
properties of the structures which is compositionally controlled and that dominant in the crust, which we see here, and then deeper we get into more reworking, which you know example of metamorphosis.
Dr. Information recrystallization. These are dominated by the thermal history of the list of sphere. And we see that in the mantle and then that zone we get in between this transitional zone.
Really good example of this. You go to the Bay of Islands off the lake and you can see right at the motorhome.
There's an alga nice has these transposed fully Asians, and these these folds in the mountain top that have applicants and four and five kilometers.
So the question that comes out and we look at tectonic inheritances where's where's the construction, where is the structural control of this. Are they held in the crust or they held in the mental what is dominating and here it is what is focusing focusing
this strain partitioning.
And as an example for tectonic inheritance or tectonic mimicry, we see that just in the shape of the origin continental margins are not straight but they take this zigzag shape and when we brought up just outcrop some Grenville crust, we see that the
old margin of the Neoproterozoic continent through here takes the shape, and it's parallel by the Appalachian origin and then again it's parallel by the modern Atlantic and this is Bill Thomas's reconstruction, showing that this tectonic mimicry is a
result of transforms and riffs in new oceans that parallel transforms and reefs in old continents, old continental margins and old mountain goats.
This is, you know, first recognized by Bill Thomas and his famous American journalist science paper where he talks about per month trees and reinsurance controlling the deposition of sentiments in the Appalachian origin.
So we look in more detail, where I want to talk today in the Appalachians.
It is the type example of a mountain belt it's the most studied mountain belt in the world I think it's the best mountain belt, it's characterized by a series of Paleozoic accretions of arc terrains that culminated in a cotton cotton collision, and then
subsequent Mesozoic drifting open up the Atlantic. But what's key about that Mrs o drifting is that the North Atlantic spreading access moves.
North the south, but it has this bifurcation that cross cuts the origin and opens up the Labrador see. And that's kind of unique and that's where I want to focus talking today on two real main structures in the Appalachians and the Grenville.
And these are the two most important features we zoomed in on the USGS map here. The Grenville structural front and the Dover fault.
And the default is often overlooked but it is. I think the most important structure in the Appalachians especially in accretionary structure.
So the Greenville front.
It's mostly, this is summarize work mostly Toby rivers and effort at and dares.
It is the limit of the tectonically reworked Greenville it's kind of analogous to the Appalachian structural front. It extends all the way from Labrador from Ontario into the southwest and central us.
It crosses older structural boundaries in the Canadian shield across the superior province.
And in eastern the Labrador on the coast, it's a three kilometer wide dr fault zone but what's unique about and then what's kind of odd is that is a very very abrupt metamorphic change and metamorphic fancies decreases to the northwest, so that we zoom
much deeper much higher grade metamorphic rocks, along the south of the Granville front that are then juxtaposed against all the rocks in the Canadian shields.
And then looking at the Dover fault.
This is the boundary between Gandy area and of a loja. And much like the Grenfell fault it juxtaposes essentially low grade Apollonian volcanic sequences against high grade nice and metamorphic rock critic rocks again Derrida through here.
It has multiple periods of motion, ranging from sinister all the extra little Obree motion in the salary and then the Devonian or its final displacement has an extension phase in the Mississippi.
It has one of the world's classic stitching futons the actually granted at the 377.
But what's kind of interesting about the Dover faulty seismically.
It shows up, extremely well from Alyssa pro data. It is a vertical structure that penetrates rates through the mobo and into the entire lifted sphere.
And it projects offshore, we see this from both from a Lister pro beta, but from the oil exploration data we see offshore the Dover false. Again, sense, right to the edge of the Continental margin book penetrates, all the way through to the mobile it
is a major, major cross the boundary.
a major, major cross the boundary. So, when we extend both of these features offshore they are the major features from both of these origins, they line up very well with two features in the modern oceanic crust.
The Grenville structural front lines with the current rate fracture zone and Dover false aligns with the Charlie gives fracture zone.
So starting, let's look at the heart rate fracture zone. This is a fossil transform fault form from opening of the Labrador see essentially Greenland breaking off from the rest of North America, in the lake Cretaceous.
It's restored using EUPOL rotations, and it continuous with the Julian odd fracture zone on the opposite side of the extinct reef down the Labrador See, but only look at the very edge for the current rate fracture zone comes ashore we see this expression
morphologically on the margin call the current rate urge, and that is the C word extension of the Greenville front is a major change in morphology, but more importantly a very major change in the geophysical data and I'll show that on a map.
In a second and then the other major oceanic feature is the Charlie gives for x zone.
This is the largest fracture zone in North Atlantic. It extends all the way from the New Zealand margin to the Irish margin. It offsets the Ricky and his range, and the Mid Atlantic spreading rage.
It's very similar to other long offset slow slick. So it's less than two centimeters per year transform faults.
And it was first interpreted by Richard Howorth geophysicist with the gic to be the refund offsets from the opening of the Atlantic, and it extends right to the edge of the Continental American and correlates directly with the Dover fault at orphan know
which is very similar morphologically to the current rate urge.
So this is the GC map will receive that extension here the map of Canada the Dover falls extends offshore to the two more familiar with the edge of the margin and lines up with the child gets fracture zone, and then the Greenville front is co linear with
with the current rate fracture zone and we see this in the geophysical data here, where the Charlie gives fracture zone extends to the oceanic offsets the magnetic anomalies comes on short at the orphan know and then extends right in here with the magnetic
lows we see in Gandy area along the Dover fault and the Grandville structural front correlates with the current right arch this low negative anomaly here and then into the current radar, again we see that same magnetic offices.
So the question that comes in is are, you know, again, we want to get back to what is controlling the structure here. Is it the crust or is it the mantle and there's four observations, really that show it's not just Crossley derive the fabric and the
origins in this case is parallel to the direction of transform motion and see for spreading which is very unique.
We don't see any other pre existing faults reactivated in border the merging the transforms line up with the two major structures in both origins, but transforms do not extend out from old suture zones and either origin.
So, the question really is is the rift in control, not in across the by the mantle, some sort of mental with a sphere of structure. And I think the observation that explains this best is organic collapse.
Without summarizing. This is Toby rivers work from a paper in 2012, the gravel front records significant collapse of the hinterland he model this looking just like the Himalayan collapse but the origin develops this large organic plateau, that has core
complex is doomed and very very well constrained to the earliest Neoproterozoic, and we see the same thing in the Appalachians on the Dover fault.
We see this rapid uplift in the Devonian on the Dover fault there's a inverted metamorphic gradients on the betas fault zone so is out of sequence rocks and green shoots look for group rocks in the hanging wall and fibula a beta Nord group rocks in the
foot wall.
Becky Jamison's work in the beaver peninsula shows the means by complex is an out of sequence Devonian core metamorphic core complex, we see uplift from the structure from the sedimentation the pools co formation shows this rapid uplift it's a mega boulder
conglomerate that contains gigantic boulders again Darien derived granites that are loaded onto Ghandi area and that unconformity is regional extends all the way off shore into the margin and is picked up in the drill wells off.
Sure.
And then lastly, uplift in the Devonian, we see these very very high geothermal gradient these pure Auckland intrusions like the act and granted, and these massive land preferred dates along fortune bay for the longest time these gradients, the grants
were thought to be the cause of the gradient but I think it's the reverse it's the high gradient causes these intrusions. So we see evidence for a late, latest Devonian appellation collapse on the Dover fault, much like the Granville front.
So if the controlling mechanisms are in the crust.
As is demonstrated in the Mozambique belt. The watch across in the US, and then East Greenland, all of these features here are thought to be structurally controlled in the crust,
showing that reactivation from old structural weaknesses, and that's not unexpected because the crust is inherently weaker because it's the courts very mineral contains all the stress in the crust and it is weaker than the all of the rich metal.
But along this case what we don't see here, one observation here is that none of these extension features in the cross, extend across into the ocean and show that here.
These two extension structures the lake novel grabbing is he.
I happened in riff structure and then the funding base and it'll antic restructure showing that when the oceans riff they ripped over abroad zone.
And so that both of these structures, even though the funding grabbing is close to the Greenville front, they are tracking the cross, they do not extend into the ocean.
So it's unlikely I think that crystal structures are controlling the tectonic inheritance and more recent work by Bill Thomas and Phil here and shows this.
So Bill Thomas's work in the southern Appalachians says that the transfer vaults and across their inherited from the sheer zones in the mantle and Phil parents work in the southern US says that for old fossils subduction zones are held in the manual but
in the Labrador see we don't see that because only cross the boundaries with organic collapse are involved in inheritance the old suture zones in the Appalachians and there's four of them.
None of those are involved the reading the line the favorite line, the grub line the dog Bay line none of those are reactivated in the modern crust.
So the importance i think is on the left is for Eric mantle, close to finishing here I know my time is almost up, because there's a lot of observations and organic collapse provides the mechanism, really to transfer gravitational potential energy from
the crust of the upper mental, so we replaced the week crust with strong ultra basic mental than the mental becomes the stress during part of the cross, and we induce a strain in the mantle, in all of it and we see this, both from seismic data but more
importantly if you've been to the Bay of violence ofili, you see these mental tech tonight's that have this all been aligned orientation within them. And then here from the SKS measurements of share ways is Bill Thomas's reconstruction the southern US
US showing that the fast direction and sky measurements is parallel to the structural trends in the vector plate of the North Atlantic and the vector direction of the North Atlantic plate, which he tributes to the Ori or orientation have all been in the
mantle and just to finish. We, in the North Atlantic we see difference, ESKS measurements is not as many, but they are parallel to the structural trends which suggests that the mental fabrics developed during collapse or here who by the oceanic crust.
And so to conclude that alignment of all faults and the modern transforms is not I think a coincidence. We don't reactivate all of these structures in the cross.
It's only the two major ones that have evidence of collapse are reactivated and transferred from the mantle, to the upper layer of the oceanic little sphere.
Ocean was determined by tectonic patterns in the medicine protozoa, and the Granville front. billion years ago determines what the modern Atlantic looks like.
And then just to finish some people. Thanks for comments on this, especially Toby rivers and Gene Hibbert. And I guess I'm over my time but I can take some questions.
Thank you. Thank you, Jeff.
That was really interesting. Any questions for the Jeff, you don't have anything on chat box but you can raise your hand, or unmute yourself.
See,
Jeff. This is Craig. Yeah.
Have you looked at any high resolution Digital Elevation models on on land to see if the modern fracture zones had that are in the ocean actually do extend into the continental crust on either side.
My guess is that, if you had LIDAR or at least, even some, some of the radar data that's available from the shuttle you might be able to see some of these.
These fractures, showing up in the bedrock even though there might not be a whole lot of displacement they might show up in the bedrock. have you looked at those.
off the localized margin is that you know the margin is mostly underwater when you get offshore from that.
I haven't looked at because some of the data just doesn't exist, interesting though, after senior LIDAR talk, maybe take a look at some of the radar data that's publicly available I know it's sort of course but Shuttle Radar data.
There is global.
Digital Innovation models for the entire planet. It might be worthwhile to see you might get, you might see bigger structures that are sub parallel to these zones.
Okay, thanks. Yeah.
Thank you Greg Thank you, Jeff.
The move on to the next talk, which is hundred million years of metamorphosis in western Maine to build in pull the metamorphic tie tonight by Jesse Walters, Alicia Cruz Europa john wounds on Joshua stone.
Hannah Brooks and Kimberly Baylor and Jessica will deliver it from Germany.
Thank you.
Okay, thanks for the opportunity to speak today I'm going to be sharing a little bit about this project I worked on with one of my undergraduate students while I was a PhD student at the University of Maine.
And we're going to see what tight night can reveal it to us about metamorphosis and main.
So main is a classic example of Pauline metamorphosis.
On the left is the updated metamorphic map of Maine from Charlie good Doughty 1985. So you've seen, I've shrank the Sebago futon appropriately and I've changed the extent of the big midnight terrain
in the northwest the rocks are sub green just bases. And in the southwest, they are magnetites.
So there's this large metamorphic gradient across the state, the widespread regional metamorphosis and defamation is thought to have occurred at 400, ma and fell sick pollutants and die crystallization ages range from 422 260 ma 420 being some of the
oldest stages of the coastal futons and 260 being the famous main Jim magnetites, although it seems from a.
The later magnetic session that that age range should be expanded a bit. Having looked at some of the abstracts.
So following this earlier Acadian metamorphosis at 400 ma there was a metamorphosis, and then Neo Acadian and Allegheny in. And this is thought to be post informational and largely driven by the intrusions and contact metamorphosis and pressures and addition
to temperatures do vary and rocks across the state.
So, and the northern end of the Lexington futon here, the pressures are 235 mega Pascal's, and they increase to the south, just south of the Sebago futon there are varying metre political rocks and the pressures of those rocks are thought to be 550 to
640 mega Pascal's my undergraduate and I collected samples of calc silicate rocks, just outside of Lewiston, Maine on the Andrew Scott and River. Here is the local geologic map this green unit here and the sub unit of the Sanger Ville formation is the
calc silicate bearing sub unit and just below this and above it is the political unit. This is collected in this arm of this large northeast Southwest trending anti Klein.
I would like to just warn everyone, you never know when Google is watching you. We went to this outcrop in this quarry only once, and that just so happened to be the day that there weren't any clouds and satellites were taking pictures, and you can see
that we are here looking at our maps on the hood of my truck, before we went to collect samples which was a little unnerving.
So these rocks have mineral assemblages consistent with upper ma blight to learn regulate face use conditions shown on the left are some
polarized light images and then we also have some backscatter electron images. These rocks have dioxide pleasure place and calcite along with tremble light and quiet so site, which are texturally late.
The project place shows a wide range of textures and annotate contents from a an 82 and 20 so most of the range that you get in place, and the calcium affable the tremble it is replacing their upside.
And the point is though site, often has Alan eight cores, and over print earlier dioxide.
Tight nights and big place. This assemblage of the upside and calcite tight night is stable over a wide range of co2 conditions and occurs between 550 and 850 degrees Celsius, this upper temperature limit is the lower temperature limit of SCAP alight
which is not observed in these rocks.
So we collected uranium lead.
Tight night data by laser ablation industrially coupled mass spectrometry at the University of Maine.
And I group these data into four domains or four populations based off of their textures and compositions. On the left is a terrible suburb diagram with the random lead ratio on the x axis, the lead, lead ratio on the y axis, And you can see the for ice
icons that I have groups and calculated these ages from.
There was one at 408 376 ma 342 Ma, and 300 and to me, the oldest domains these 400 ma domains are BSc dark Corps.
Then there are BSc bright mantels which have 376 and 340 GMA. And then, the youngest domains are these BSc dark rims.
These each have unique birth element patterns, and I've pulled out the analysis into these four groups on the y axis, this is the concentration of these elements in tight night normalize to a see icon right in the 400 ma domains.
These have a slightly steeper middle to heavy birth, negative slope and a small Europium anomaly.
The 376, ma domains, have a slightly less steep middle to heavier earth to almost no middle to have your earth slope, and also a small Europium anomaly.
Now the 376 and 342 ma domains, these are both BSc bright and they looked extremely similar but they're chemically quite different.
And these 342 ma domains, have no Europium anomaly.
And these youngest rims, they have a relatively flat middle to heavy birth pattern, a quite large, European monopoly negative European monopoly and they have a depletion in the light rare earths.
So I wanted to know what were the drivers of the trace element village variability and what can it tell us about the metamorphic history of these rocks.
To begin, I noticed that the tight nine zones, exhibit increasing get run through time, and there's a large jump between these BSE dark cores, and the bright mantle domains between 400 and 376 ma.
Now there's only a handful of minerals in these rocks that contain get them. One of them being kind of pyrrhic seen these two images here are from the program x map tools so these regenerated and quantified from FEMA X ray maps.
The upper is a phase map, and we can see dioxide here is an orange, and these grains are highly fractured and then healed.
We can see that the dioxide grains here are in filled by play filled spar, and then rims by kind of oversight in this map here which is the mall fraction of dioxide from 50 to 70%.
These blue domains, which are were brutally fractured and represent the earliest phase of dioxide crystallization were higher in iron in aluminum and lower and magnesium, and then they were revealed by
by more Diop Siddiq Plaza place. Sorry, more Diop CITIC quite a pure, clean, and possibly multiple generations of that.
If we look at the atrium concentrations between the older dark side and the younger dioxide domains, we see that the older ones which are higher and aluminum are also higher in the atrium.
And then there is a decrease to almost no yet.
probably between these two metamorphic events.
Then what about the light rare earth depletion well it's caused by the partitioning between this texture little late. Alan night, and quite associate with tight night.
So, Alan night, having a light rare earth elements like Syria as a major constituents that the weight percent level, the partitioning of those elements is really strong between Elena and tight night, so it causes this rare earth, a lightweight earth element
depletion.
And the point is, is I was formed in response to the infiltration of hydro fluids. The earlier three metamorphic events occurred at a relatively elevated Exeo to conditions in this field here.
And then the Hydra is fluid infiltrated formed coin so science Alan night and tremble lights, and we crossed over this Allen night plus calcite goes to a sorry, and worthless calcite goes to point a suicide reaction at an SEO to have less than 5%.
And the temperatures remains quite hot.
So if we actually look at the temperatures through time from the draconian and tight night thermometer.
On this reveals that there were multiple high temperature events all spanning between 850 degrees to 750 degrees Celsius. We have the best constraints from this latest one, because that's the only one in which courts was stable and you have to have courts
to use this thermometer.
These earlier events these represent minimum temperatures, but given these rocks don't have satellites, and there was limited or no by a tight dehydration melting in the P lights, it's unlikely that these rocks were much hotter than this.
So what are the implications of that then well there's two hypotheses. One is that you have 100 million years in which these rocks right 800 degrees Celsius, and then you just have periodic phases of mineral growth triggered by fluid pulses.
I think it's unlikely that you have 800 degrees 400 million years in the mid crust and these rocks, it's inconsistent with the textural observations in p lights in the surrounding area which suggests you have multiple phases of pro grade and retrograde
metamorphosis.
So it's instead, more likely that these are four separate metamorphic events each followed by a cooling.
So to conclude tight night may reliably record and preserve many phases of metamorphosis.
The trace element chemistry is a powerful tool, Patrick chronology, we were able to pick out brutal defamation and revealing of the quarter pyrrhic scene, and the change in the co2 content in response to an influx in Hydra fluids.
And this lead.
This study leads me to a few open questions we don't have any idea about how pressure might have changed over each phase of metamorphosis them, whether the crust was thickening at not would be really important to understanding the tectonics of the situation.
Whether the crust was thickening or not would be really important to understanding the tectonics of the situation. It's not really clear what the heat sources for each phase was in this region.
And it's not clear which of the phases would correspond to partial melting or all of them be given that there are such high temperature, and they're surrounding magnetite.
And it's also not clear. Because the type of the the calc silicon don't really show much in the way of defamation textures, with the exception that brutal fracturing, which of these phases were accompanied by defamation.
And with that, I'd like to thank everyone for listening and I would love to hear any thoughts and any questions about this study.
Did you just see it was very interesting. You have your own questions that's also good spies remind everyone you can either raise your hands and ask your questions live or write in the chat box, which I have one question, but is there any evidence of
brittle deformation in the nearby p lights, do you think it was a very local or potentially larger event that you might look entirely really crystallized.
In, and thin section.
From what I see in their textures and their compositions of the minerals are really only see evidence of that 300 ma event.
I do see that there there is no Sullivan night in the matrix, but there's so many inclusions in Garnett.
And we do see evidence that Soma night was replaced by Muscovite during this this last hydro this fluid infiltration which also affected the P lights, but we don't see much evidence, other than that for any of these earlier phases of defamation which
the calc silicate seemed to preserve.
Yeah.
Any other questions, please, do we have some time actually just you have a question, this is my gray. Hi. One of the things I've wrestled with is the timing of the Neo Katie and Rodney literature seems to get fairly wide range of ages on that.
And I'm interested to see that you had an age of about 340. Yeah.
So you go with 372 and 340 300.
Yeah. What's going on about 340, that seems young even for the New York area. I know I was surprised to get that age, and unfortunately you know there's no clear textures or anything to to really link that to any specific processes.
And as far as I know, there's no.
I don't know what the heat source of that is I actually don't know why there's no Europium anomaly, either. Which is quite mysterious because the plaid you place in these rocks have no Europium at all, which I was surprised at so that that is one of the
things that keeps me up at night about this project and I'm sorry I don't actually have a good answer for you it's quite cryptic. How about the 300 billion year age is there other evidence of, I guess there is a button so Katie Allegheny and in the area.
Yeah, yeah, there's others that are pretty young.
So that it does.
It does link up pretty well with with. I mean it overlaps in on with uncertainty of the ages of the Sebago futon.
So that's, that's okay.
Great, thank you. Yeah.
So, questions.
I have a question named Bob winch.
Right.
It looks like your, your assemblages are far from equilibrium with logic lasers, hardly zone, the fracture and fillings, all the minerals are zone so I wonder how you use the pseudo sections to it for PT conditions when
you only use are chromium and tight in the, in the tight night to to get temperature and you haven't shown that serotonin was saturated.
My bigger question is, how you you have cores, in this image that you just showed us. Thank you.
Record that's 400 million but it looks like the by volume much more of the tight night is younger than that. Yeah. And so my question is, where was the titanium.
Where was the rest of the titanium at 400 million.
Where did it live, you talked about the rare earths but the big budget problem is titanium.
Where was it before it was 15.
Yeah, so we do see some titanium depletion, and the upside for example between those two phases but it's it's relatively small, most of this, and all the samples that I've looked at here and, and some of the work that I've done the Himalaya as well on
tight night. Is that a lot of it is driven just by dissolution and re precipitation, you know cannibalism of the, the Titan night that was already there.
And this sample doesn't show it nearly as well as one of the other ones.
So it's, it's, yeah it's mostly just dissolution re precipitation and tight, tight, tight seems to be very susceptible to that.
In terms of zircons saturation.
There's these bright phases here, a lot of those are pure uptight but the bright phase here in the tight nights and and one of these here in the matrix is recon.
And this is one of the only samples where we actually observed frequencies work on inclusions and tight night.
So this is about as good as you could hope for or potential Zurich on tight night equilibrium.
Also the, the pseudo what I showed earlier there was a Patrick genetic grids not pseudo sections and I shied away from doing any student sections of these rocks because the bulk rock is not an equilibrium.
And there, that's also why that I placed the highest confidence on that last phase of
tight night crystallization and that the earlier ones are really just possible minimum temperatures.
So, one quick follow up like you're a was asking about two 340, can you go back to your terrible loss of bird please.
Yeah. The, you really don't have much information on that cord for the three four to you have a few spots there a little way up the cord. And then you just run it up to seven six ratio that seems to, to be the average one but the confidence to, it seems
on the 340 is much less than the 302, you have at least one analysis that matches up the cord.
340 i think is the least robust.
Yeah, so the, the, the common lead composition was actually measured and uranium four phases such as pelagic place and alkali felled spar and kind of pick seen.
Also, there was a little bit of variability but that is propagated into the these ages. And I also compared that with the model.
lead composition, and they gave identical ages and these, the common lead is so little in these compared to what we often see for tight night where we're at like 50% common lead that the contribution is quite small in terms of the uncertainty.
So, even though there are only a handful of agents at 342 I'm actually quite confident that in them.
Thank you. Alright thanks Jesse.
We're gonna move on with a pre recorded presentation by Ian Hillenbrand Mike Williams and Microsoft of itch, and they're going to continue on this theme of Petra chronology.
In the Appalachians. So I'm just going to hit play on Ian's presentation. And again, just want to remind everyone that we can continue to ask questions in the chat and during the break that's coming up in about 30 minutes
up Hold on a sec.
Can people hear
my computer.
I can hear your mouse clicks.
When you said sharing there is an option for you to share volume as well so maybe you should unshared and start sharing again, and make sure that you select that option.
Oh I got it here. All right, I think it's gonna work now.
One of the great challenges for scientists is concerning the for scientists is concerning the tectonic incremental evolution of areas that have experienced multiple phases of mountain building.
One example of this is the Appalachian Khaled night origin or multiple phases of Paleozoic mountain building. I recorded the forms that are created terrains, and Polydor formed and metamorphosed rocks.
This is particularly true in southern New England, but the terrains are highly telescope at least four phases of mountain building are presently recognized the earliest event is the Ordovician to connect progeny associate the creation of the gun one and
derived more town to me Laurentian margin. This was followed by the Syrian. So let me go Raj me a somewhat enigmatic event in New England, associate the creation of a gander terrain to compile a rancher, then.
This was followed by the lead Syrian to Carboniferous Acadian Rodney associated with the creation of the Avalon, and Bakula terrains, and perhaps the formation of a high elevation organic plateau.
And finally, there's the Carboniferous to Permian alligator progeny associate with the collision of adventure and Gondwana not final formation and Pangea affects the Allegheny and are largely recognized in southeastern most New England.
This complex multistage history is reflected and equally complex array of tectonic elements in southern New England, notably the red line in this map, marks the interpreted suture between rock solid ranch and affinity to the west and included gone one
and derived terrains to the east.
Interestingly, this interpreted suture appears to follow the trend of a large offset and crystal thickness in Western New England.
The crust things dramatically in Western New England. From 40 to 45 kilometers to as little as 30 kilometers over a short distance of 10 to 15 kilometers, leave it out, 2018 term this feature, the Mohawk step recent analysis of thermal project data suggests
the areas of the west and east of the most experienced very different thermal histories, as well.
Rocks the West Coast up in the record cooling to comic or Rodney well those to the east record cooling from the Acadian Rodney.
Further, they suggested that this step formed during the collapse of an Acadian organic plateau named a Kayden on the piano.
To better constrain the tectonic and cross evolution of how the New England and test hypotheses regarding the co host up and organic plateau.
We integrated geo chronology, and geochemistry and method called Petra chronology.
One important Petric project relationship is that between the element get trim.
And then minerals and Manas like in Garnett is commonly interpreted and Manas I, it goes early metamorphose in Israel to being ripped and nutrient Howard and crystal thickening Garnet become stabilized and citizen matrix atrium sink.
Hence, Manas a growing the presence of stable Garnett is often highly depleted, and the atrium.
Then proportionate collapse. Garnet becomes unstable. During decompression or cooling, and releases get them to form thin rims on mana site and alternate scenario is when Xena time extreme phosphate Stiebel along with Manas a Garnet, there's somewhat
more complex scenario, however, can help place additional constraints on the thermal evolution. Wednesday to time and stable, the atrium contents and monitors like become high temperature dependent, does that get from contents which can only increase
as temperatures increased or incremental thickening further Garner become stabilized, Its YouTube content can be used as a thermometer, as well.
When this is combined with the geo chronometer and Manas like Xena time, they become powerful thermo chronometer.
The timing of gossip breakdown, can also be constrained by Xena time, which often forms halos around resort but Garner, identify these relationships, again train these reactions.
We first begin by mapping the entire thing section, through this, we can identify monitor in Xena time in their life or structural context.
After finding the grains. We then map them in detail, identify their internal zoning.
We then date these zones or domains. He's in the chemical opera electron micro probe to maximize spatial resolution in this talk. These will be presented as internal data domains plotted against a compositional parameter, such as the atrium and Manas
eight for the Terbium disclosing ratio of Xena time.
We also investigate major phases, like Garnet, and what you can map and quantify major increased element zoning.
Finally, we integrate these distinct data types to constrain the samples pressure, temperature time history. This can include major increase element Philip Brahma tree as well gives modeling of his own garnets further insights can be gained from modeling
of major and trace phases, which together can be used to constrain the PT history.
The absolute ages of this PT path can then be constrained with Manas light and Xena time Patrick ology.
We applied these techniques to a suite of samples across southern New England crossing tectonic and structural boundaries. Individual samples analyzed, or one of the diamonds on the map.
In this talk, the group the samples bays and tectonic and geologic histories.
First start in the east central Massachusetts, and then work our way West and complicated and older rocks.
The image of the right is a full section magnesium map a sample from the central Massachusetts metamorphic Hi, this sample contains both Manas late and Xena time, but they occupy distinct Microsoft domains Xena time, it's about an incarnate cores on Manas
light is found in Garnet rims and the matrix.
is found in Garnet rims and the matrix. Now, will tell us more in this Garnet, and the lower right.
Detailed X ray maps, highlight complex zoning in this Garnet, The core is enriched and get trim and moderately mentioning calcium, the mantle is highly enriched in calcium and moderately enriched in nutrients and the rim is low and both calcium and get
them over Rama tree, and modeling, along with existing studies suggest an overall counterclockwise path. We've released suggest a looping style of path, followed by ice and Barrett cooling
Manas light from this area are systematically zone with high gear dream corps logo tree mantels, and higher trim rims, these colors remains correspond distinct ranges of dates pipe dream Corps, and I on the order three eight and they are older, low nutrient
mantels on the order 372 340 million years old, and higher chat rooms are 339 years old or younger, we interpret the high atrium cores grew before Garnet, while the logo to him mantels could remain stable Garnett, and finally rims, could drink on a breakdown.
This interpretation is supported by the dates of Xena time incarnate corps as your time on fractures, that form drunk on a breakdown.
From the status that have interpreted pressure and temperature time histories. Throughout the talk, temperature time history, especially on the top panel, well pressure time history is will be shown below.
Now, let's move west to look at the rocks of the Pelham dome, a large double structure in North Central Massachusetts, we examine two samples from all locality describe that Peter Robinson, one sample preserves and simulate k felt spar assemblage typical
the Katie and metamorphic Hi.
One other sample records, a leak kinda over print associated with dome formation is still my apparent sample has a very similar PT history to that of the central Massachusetts metamorphic high.
In contrast, the kind of bearing sample large records decompression Patrick on a logic analysis of a nightmare and sample facilitated by abundance of models like inclusions and Garnett Chi night and store like.
Together, these tightly constrained record of loading, and then rapid explanation. Between round 310 and 289 years ago.
Now, let's continue pushing further west and examine rocks of the Amherst block. Pete Robinson interpret the embers block to represent a down drop block, preserving higher Acadian crystal levels, not observed elsewhere in central Massachusetts them a
Brahma tree supports this hypothesis has calculated pressures are lower than those from Central Massachusetts, although they suggest a complicated PT history, this complexity is further suggested by wild spectacular zoning and Manas like and Xena time
Manas IDs correspond to both the Aquino progeny 400 years ago, as well as the new Acadian phase around 360 million years ago.
And you go to thermo Brahma tree and geo chronology test and initial pressure, temperature high or on forward, ma felt like rapid cooling and decompression.
This was followed by a second period of loading thermal high around a million years ago, fall by very slow cooling.
Now, let's continue pushing West into the rocks of Western Connecticut, but your interpreted experience both Peconic and Acadian protectionism consistent with this hypothesis garnets from Western Connecticut, nice stoves, and a cover sequence, Connecticut
Valley belt to complex zoning, both in major and trace elements.
These rocks who evidence for early event in the lower end public face she's probably a subsequent event at higher PT conditions. Note at the increase in pressures from quarter cover rocks increases with structural level Manas in Xena time also show complex
zoning suggesting multiple days of Garner growth and breakdown.
Our results, just an early event, picking on 450 to four and 40 million years ago, after this metamorphic peak, the rock experience at two stage cooling history, rapid and then slow cooling the rocks then experience second metamorphic high around 382 360
million years ago, followed by slow cooling. all rock to Evan for garment breakdown around 340 million years ago.
Interestingly, the rocks that formed the mantle and rim of the Knights of the washing Connecticut record distinctly different PT pass on the Connecticut Valley belt and the quarter the nice stones.
The sweetheart mountain, member of the Collinsville foundation mantels and number of Washington again nice stones records high pressure conditions of up to 16, to 18 kilowatt hours at temperatures of 750 to 100 degrees Celsius.
Before we are collaboration in the mid crust. The streets chest, which remains many nice terms in Western New England also has a distinct PT history.
Peak conditions are approximately 10 to 11 kilowatt hours, and 700 degrees Celsius. Interestingly, both these units show evidence for only single metamorphic event.
In contrast, the overlying underlying units interpreted pressure, temperature and time temperature paths are shown here, for these two units. Interestingly, these paths to not converse with those are the nice stones, until around 380 375 million years
ago.
Finally, let's hop across the Mohawk step and examine rocks at a comic belt, where a classic Peruvian metamorphic sequence is preserved.
These rocks are interpreted to have only been metamorphosed and the motivation to conquer Rajini bus, they present interesting contrast but Polly metamorphic rocks, a Western Connecticut, and can therefore be used to contrast thermals and tectonic histories
across the mobo step, be observed a dominant population of Manas I can for 40 and four and 29 years ago.
The single low your trimaran is around three guiding Ma, I think of a low temperature Manas I growth femoral grounders just slow cooling after the 440 metamorphic peak, with an increase in the cooling rate between 390 and 369 years ago.
Now, let's compare PTT path to the New England, along with Joe chemically derived crystal thickness proxies to evaluate and constrain the crystal tectonic evolution of this area.
The oldest event in Western New England. Is that a conical Rajini so through the collision of a more countering Florencia around for 25 million years ago.
Interestingly, minimal Garnet growth is observed from form 25, ma, the major paid of current growth and crystal thickening postdates timing of collision by 20 to 30 million years to explain this, you consider several scenarios.
One possibility is that the collision between more tunnel Rancho, the soft, or strike slip and did not result in significant Garnet growth. Alternatively, it may have taken 10s of millions of years for Hugin metamorphosis to occur as it as it by some
thermal models.
Another possible explanation considers the effect of seduction polarity reversal an episode of flat slab Indian or learn mind style subduction could lead to Crystal thickening in southern New England could explain the sweeping of magnetism westward into
Western Connecticut. At this time, however, it this model is correct, it may be spatially limited as similar crystal thickening and magnetism are not observed in Massachusetts or New Hampshire.
This could be explained by differences in the depth of the subducting slab along strike. However, this could require a slab tear. Interestingly, a slab tear could explain the alcohol and magnetism, of the Cortland beam Ravel belt in such a position against
Louisville calc alkaline raw in western Connecticut.
A final possibility for this event that it represents crystal thickening associate the creation of the game returning the Salonika Rajini after this colossal thickening episode, we can see a two stage cooling history in Western New England with the rapid
cooling likely examine these rocks the mid crust, where the rocks called very slowly.
However, the tectonic belt has evidence for very slow cooling and very distinct thermal history, beginning around 430 million years ago.
Next, we can see the rocks New England show evidence from major crystal thickening episode, 400 and 389 years ago associated with the occasion or progeny this crystal thickening event is observed and all rocks, East at the Mohawk step further.
After the cross picking this region, it stayed thick for 40 to 50 million years, supporting the hypothesis of a long lived organic plateau in southern New England, we speculate.
The slightly higher initial pressures and slightly faster cooling rates in western Connecticut, any record structural siding and these rocks and then retro wedge, the origin, as opposed to the order NET Core of Central Massachusetts.
hours east of the mo host our present evidence for a major appear on Garnet breakdown at 340 330 million years ago, interpret a current breakdown, or cards or tenant collapse of a cadence Altiplano.
It's in this period around 322 300 million years ago that we see thermal histories of rocks at the West and East Nemo host up converge. This suggests that rocks, a West and East them all hooked up for juxtaposed at this time.
This suggests that the Mohawk Step. Research present state, and the collapse of the Kayden Altiplano.
Finally we see evidence for rapid reloading, and then unloading the Pelham dome printer 20, and Twitter 18 million years ago, this timing suggested association with the Allegheny progeny, or perhaps complicated stages of Pato collapse.
However, this must have been a very localized event planning question about the tectonic siding and much that occurred in this talk, we've shown that monetarily and Xena time are powerful Patrick nanometers, that can turn the pressure, temperature time
paths across distinct tectonic domains.
Thank you.
All right, so, um, thanks again for presenting that we are running short on time a little bit.
And so, actually we have, like, a minute so actually does anyone have a question for end.
All right.
Oh, Allie, yes.
I'll just ask this quickly and maybe we can chat more about at the break, I was just a little curious and how you were able to constrain those like multiple looped PT path I thought that was really cool but I'd like to know a little bit more about like
I guess yeah how you're able to actually do that for sure yeah so it's a mix of really great zone garnets, and then integrating that with a monolithic record and, and the cricket trace element from from from modeling Sophie Garnett is really a big get
rid of sync. And that pop like for example of the abundance of Garnet, I think most of Garnet on their highly pressure dependent. So if you're crossing that path you'd like to be consuming a lot of Garnet and creating retrograde product that we see the
reactions and break down reactions to monetize Xena time.
So it's a matter of integrating both everything from the Garnet to them about the trees phases and bring back together to interpret the bat bat and if we're going to talk about in more detail.
I'm happy to actually do that at a later point.
And there's more. Thank you.
Yeah, thanks to you and again for the wonderful,
where we have a break.
Sorry, Bob.
We have a break after the next talk so for if you have questions for in. I encourage you to ask them during the break.
So coming up next is Eliza Folsom and Leia is going to be telling us about the geology geo chronology and tectonic history of the Bronson Hill belt in northern New Hampshire so lies if you want to share your screen and take it away.
Go ahead.
Yeah, thank you. So today I'll be talking about my year long senior thesis project on the bedrock geology geology and tectonic history of the Bronson Hill antiquorum in northern New Hampshire, which I completed as part of the USGS and New Hampshire Geological
Survey state map program. And this project is definitely still in progress, I'm still working on my conclusions, but I'll be done with it. By the end of May.
So, in this talk, I'll start by introducing the Boston Hill into Canaria and its relationship to the greater Appalachians.
Then I'll talk about some previous mapping of the Berlin, seven and a half minute quadrangle. And then following that, I'll show the bedrock geologic map that I created using data collected this past summer, and then also discuss it's relevant units,
and then talk about the phases of defamation that are relevant to the study area before talking about the igneous and two titles are con gu chronology, that I completed for three samples found in the study area.
And then finally all really my work to previous work.
So, this project intends to study the Bronson Hill and tomorrow, as part of the Berlin set and a half minute quadrangle in northern New Hampshire, using bedrock mapping structural analysis and geo chronological techniques.
And these methods will help us to understand the spatial distribution and contact relations of the rocks, and then defamation history.
In the Bronson Hill antiquarian as, and then related to the greater Appalachians. And this. Additionally, the study area includes part of the Central Maine belt, along with the north eastern end of the largest have many all Varian domes including the
backlit, and it's man telling me music mechanics. And this study is important because no detailed mapping of the area exists, and there's little igneous gu chronology, completed in the area in general and no to title analyses on the shamanistic volcanic,
which are prevalent unit in the study area.
So, the Boston Hill and Canaria is thought to be a series of volcanic arcs that erupted along a plate boundary during the Ordovician. And then after erupting the volcanic accreted to Lorenza during the two car garage and Bronson Hill and decorum is made
of the about 470 million year old eMusic volcanic that formed on the quantum side of the apparatus and the about 450 million year old all variant photonic sweet rocks that formed after the volcanic, and then intruded into them in the form of the Jefferson
backlit.
So Caribbean's at all and 20 in 2017 and Dora, all in 2012, believe that the Oliver include tonics feet rocks were abduction abducted and then subduction polarity flipped.
To the west which created a continental arc, as seen in these two figures and Caribbean house at all determined that the reversal and seduction clarity occurred between 40 and 66 and 455 million years ago, and that this reversal resulted in a West dipping
seductions down under both the Russia and the more town terrain that have recently created to it.
And then they also suggest that many for 955 to 440 million year old magnetic arc rocks in the Bronson Hill Ark formed above the subduction zone, and that arc itself formed along the eastern edge of the mortality rate.
that the domes that formed when the all green platonic suites and treated the shamanistic volcanic are found in the core of the Boston Hill antiquorum, which suggests that the amnesty for Catholics were thrust westward over the lunch and margin.
So that launched and basement rock sit under the Bronson Hill and to Canaria, then we have another model by Valley at all from 2020 with which suggested the flip in polarity.
That was suggested by carabiners and Dre might not actually be necessary since to contact information, was found to be 10 to 15 million years younger in certain places than what was originally thought.
So instead, Valley at all suggest that the Bronson Hill antiquorum is part of one long lived composite Arc System, and that it shows a continuum of ages rather than two separate arcs which carabiners or up the shell born in France and Hill.
So now getting into some previous mapping of the area. The area has been mapped several times but never in detail. It was first mapped or the Brooklyn seven half minute quadrangle was first map as part of the Gorham 15 minute quadrangle which is this
larger map the Berlin, seven and a half minute quad is this northern half.
But it was first mapped by Billings and Fowler Billings throughout the 1940s and 50s, and they then publish their map in 1975.
Following that, the same area was mapped by Mitch at all in 1996, as part of a bedrock map that stretched from Sherbrooke Quebec to Lewiston, Maine. And as you can see image changed some of this part of the map which is the Central Maine belt from Billings
this map mentioned at all then map the area again in 1999.
And additionally, the Mount Washington Jefferson and the mount Crescent seven half minute quadrangles that lie adjacent to the Berlin quadrangle have been mapped in detail by used in in 2010 Baker in 2016 used it in 2017 and neither in 2018.
And then, as you can see on the, or I'll show you on these maps so these, this line here on the Billings map and here on the mesh map is the McKusick fault, which separates the Bronson Hill and to connect them to the west and the Central Maine belt to
the east. And then in the Billings map this orange color is all very include tonic sweet, the green is the shamanistic volcanic, and the yellow unit is the solar hand Perry mountain formation of the Central Maine belt.
And then in the Manage map. The light brown is all around photonic sweet the dark brown is the m&e sick volcanic, and this blue part was mapped as little information which is just part of the Central Maine stratigraphy.
So now moving on to the map that I created based on data collected this past summer by me deck used in, Tommy shields and Peter Galloway and died recently and for me that my legend is backwards but I'll get there by the end of May.
So, going and getting into the unit. The first one I'll talk about is the Ordovician and when you say volcanic or Om. And this unit was found in the center and the south of the study area to the west of them who's at fault in the process and hell and
area. And we saw in 52 different outcrops and it shown on the map in purple. And this unit was dark green color, as you can see this picture, can be found on its own in many outcrops but also as in the form of intrusion into the automation all green biotech
or an aunt or OBG which I'll talk about in the next slide.
So OEM has several different variations that we saw in the field.
That will go through the first was a my acacias court site that we called OMQ. We found this unit in three outcrops in the north of the study area. And this unit had never been seen before in the southern half of the quad that was mapped last summer,
or in any of the surrounding quads.
And this unit is gray and finding medium grain and texture.
Then another variation of OEM was a conglomerate that called AMC.
We found this unit six different outcrops in the northwest of the study area, and it's shown in hot pink on the map.
Oh EMC is dark gray like OEM but it has white and like great class and.
And then another variation is OMF, which is a fell sick variation of Om.
We found it at 12 different outcrops in the center of the study area. And this was also a new unit.
And it's white and pale orange in color and shown on the map in blue.
Then a rusty variation of a lamb was found at 25 outcrops in the north and the south of the study area. And this unit was seen and always seen in contact with oh I am in a red dark brown, red, and a dark red brown color, and it shown on the map and brown.
And then finally, the last variation of OEM was a CT site or granite fells with magnetite and amicable, which we call it OMDQ for dark cord site.
We, it was dark gray and color and medium green at texture and it's this light pink unit on the map.
So now getting into the Jefferson bath with or the hologram Teutonic sweet units.
So the most prevalent unit or the most prevalent rock in the study area was the automation all very invited tight granite, or OBG, which you found in 90 outcrops in the northern and central parts of the study area.
And this unit is light and light and dark gray and color, and is finding medium grain and texture and is this light blue unit on the map. And then the second most prevalent unit in the study area was the Ordovician all Varian biotech field spar granite
or OBKG, which was pink, pink grey and color with medium to coarse grained textures and it's this dark green color on the map.
And then, as I mentioned before, we also saw a lot of OBG with OMZ analysts, as OBG intruded into om before the before the two were folded as the m&e see volcanic for thrust westward over the Laurentian margin.
And in this photo on the bottom right you can see the lighter unit as OBG and the darker unit as the OMZ analyst.
So now moving on to the sequence of defamation seen in the study area.
So the first phase of defamation began with the normal McKusick fault juxtaposing the Bronx and hell antiquorum and the central main belt, as the Acadian organic front moved Northwest.
And this was followed by D one folding in the early Acadian Rodney that consisted of Ne, ne really trending ISO carnal folds of s zero bedding and layering with strong as one fully Asians and less common a one linear nations.
And those were seen in both the Bronx and hell and to Korea, and the central main belt. And then during the Stephen folding them who's at fault was folded I sequentially.
So falling that we have DTD to folding in the mid Devonian late Acadian Rajini, and these folds were.
And this, and due to falling was characterized by open and again ne trending folds with a week or non existent as to axial planar cleavage that deformed the s one and SEO fabrics, in the Bronson Hill and Gloria, and the central main belt.
Following that, doping occurred in the weight Devonian Neo Acadian Rodney, and this is visible as a change in s one and zero re don't dip from northwest to southeast which effectively reverses the dip, of the moose at fault.
And then after that finally is northeast breaking your vertical specified zones resulted from late Mesozoic Mesozoic brittle normal faults. So in this picture here on the left of the D one folds.
We can see OBGNOIM shown with an ISIS final fold, with an axial plane full Asian us one. And then, In this picture here.
We see OBG and Oh am again as a D to open fold.
And then the stereo net here shows the ivector value of three is original fold hinge line trending northeast.
So, moving on to the chronology part of my thesis.
So I'll do chronology work was completed at the Arizona laser current center. During this past December and remotely. And so three so three samples were sent to the lab, including the fell sick OMF CT site OMQ and dark work site OMDQ because those three
samples had never been seen before in the field in the southern half of the quad or the surrounding quadrangles. And it's important to determine the ages of all of the varieties of ammunition for Catholics in order to stand, understand the exact sequence
of formation and defamation events. So the sample OMF is a fell sick meta tough with zircons containing facilitated zoning. And so I filtered out the extremely discord and samples with a 20% discord and filter, and then also constraint it between ages
442 40 and 60 million years based on the peak of this population density plot. And then this resulted in an age of 1452 plus or minus 8 million years.
Then the next sample.
The OMQ, the courtside sample, which is a sedimentary volcanic plastic unit. We wanted to get its maximum depth positional age, as well as it's trained fingerprint in order to correlate it to one of the trends.
So the sample is filtered for 30% discordance with ages, from four between the ages of four and 50 to four and 80 million years, also based on the peak of the population density plot.
And then this resulted in an age of 465 plus or minus 6 million years.
So, the data from the Arizona laser comm center produced a unit total population density plot as you can see here, which means that the zircons that make up this sediment were derived from about 460 million year old are crocs without any old basement
signatures. And that is different from the dark court site sample OMDQ, which is another sedimentary volcanic plastic unit.
And so we were unable to get a maximum depth as a channel age for the sample because of the large amounts of appetite and magnetite and the few amounts of zircons.
However, this sample does allow us to see some interesting terrain fingerprints, with more basement type orders or cons, as opposed to the unit model arc signature of OMQ.
So now we're leading to my work to some previous and also current work.
So my advisor diet used in and also in Hillenbrand have been looking at the same samples as I have, and also samples from the hologram Pathak suite, including OOBGNOBKG, as you can see in the finger on the left, and their work with the hologram platonic
platonic sweet confirms that the units are about 10 to 20 million years younger than I am.
And then they also looked at the same OMDQ and OMQ samples, as I did, and they believe that they show really different sources with OMDQ having more basement related zircons and OMQ being more arc sorcerer cons, and so this figure on the right is a way
to show the different samples based on their source with the sample here in the Arctic dominated source section, being OMQ and then OMDQ being here.
And so this is showing that how the source change between OMQ and OUOMDQ, even within the timeframe of the shamanistic volcanic so I went from an arc source to a basement dominated source.
And then also, Valley at all the ages that valley at all found in their 2020 paper, or the ages for the fall sick meta tough that they talked about our within air of the ages that I found for the OMF sample.
And then my ages also fill out previously unknown Avenue six volcanic ages, while also fitting in with the known ages from Valley.
So from my study so far, bedrock mapping of the Bronson Hill and consortium has revealed that the platonic rocks within the Ordovician all very improved tonic sweet or has revealed rocks within the automation hologram protonix feed and also several variations
of the Ordovician m&e sick volcanic.
Which leads us to believe that the MA civil clinics were interested by then to formed with all very include tonic sweet rocks, then.
Yes, sir. On June chronology.
For sample OMF gave us an age of foreign 52 plus or minus 8 million years. While the titles are kanji of chronology.
sources. And then do titles or come to your chronology for sample OMDQ reveals train fingerprints and also shows is that the orders are cons are likely from basement rocks.
So then finally from this we can understand that the source regions for the MDC volcanic has changed over time.
Thank you.
Alright, thanks, guys, that was an excellent presentation. Thank you for sharing your work with us.
Before I open up the floor for questions. There was one question that was posted in the chat from Marianne for your CT site, OAMQ, and OANDQ. What structural or strategy graphic information tells you that they are or division and not solution.
Um, I that's or sorry I'm trying to go back and this is based on. From what I know like previous readings and research and previous work that has been done.
All right, thank you. So if anyone has any other questions from Isaiah, we can open up the floor now.
Hello, so this is my great. Have a good question for you, what are the ages you came up with was about 410 is that rank for 10. He
was this later than us.
Keep going.
Okay, maybe I missed, maybe I didn't see it correctly. Okay, I thought so one is for 10 as I will maybe that's kinsmen granted direct but obviously I was this reading Sorry about that.
Yeah, no that's I think that's a little out of my ballpark. Okay,
unless it is Greg, I'll ask a question.
Your, I did a great job by the way it's it's really nice results.
I did a great job by the way it's it's really nice results. One of your analyses you have an age, which was your fell sick rocket OAMF.
And in the age, you got for 52 plus or minus eight you showed a population density plot, but you also have zircons that you analyzed in there that look like they're metamorphic, you've got 360s and for hundreds.
Did you include those younger grains in your calculation of the age or did you exclude those.
Um no i i excluded those so in order to make the way to mean and get the final age, I think I are Yeah, I can strained it between 40 and 40 and 40 and 60 million years so nothing earlier, or nothing later than that.
Okay. All right. Good. Thank you. Thanks. Nice job.
Thanks,
Bob which I had a question as well.
The sample I think before the one you're showing was also.
They had the trial yeah this is the one you propose an age of 465.
But that's the age of detritus zircons is that correct.
Um, yeah. So, you do have ages, you do have zircons that dropped to 450 and there's even received six or eight zircons that looked like they're about 430 million.
Why did you exclude those as potential youngest
potential deposition no grains, you're looking at the peak. But that's the that's the that tells you where most of those guns came from it doesn't have to say that the age of deposition, I think,
um, yeah I just, I think it was just a decision I made to go with where the peak was and where most of the zircons were so yeah like the previous sample is constrained it to 450 to four and 80 million years.
Okay, would be it would be interesting to see whether the peak that looks like it's at about 410, that has about seven grains and I'm looking at the upper upper right diagram.
I'm going to try and see what else I can come up with but this is just what I have right now I'm still going to do a little bit more with it. That would be very interesting to see how those are cons looked in in human vessels.
Oh yeah, I have those pictures I should have put them on. But thank you that's a great talk I hope you go on to grad school. Thanks.
Alright thanks lies.
And this point, we are in a break, we're actually running four minutes behind schedule so if, if you want to reload on tea or coffee or whatever.
Go ahead and we'll reconvene at 1015 to hear more interesting research about the tectonic history of northeastern North America.
If you want to ask any of the previous presenters, any questions, you can feel free to do so now.
Between now and 1015. So,
are you still there.
Well, Bob.
That was a spectacular talk by the way.
Thank you. Appreciate it.
Very very impressed. Hello. I wonder if we could lower you into eastern Connecticut where we have some momentum and your, your kind of study would really hammer some of our issues.
And you're welcome I'm no longer at UMass I'm with.
I sort of I, I graduated, and I'm sort of, I'm with the USGS now so we're actually working on now but I'm sure you can reach out to Mike or, or you know Mike Williams are like genetic to see they're interested in, potentially collaborate with with working
with entrepreneurs.
So you're a USGS Well congratulations.
Thanks.
Ian, I might continue. I have a question actually that was really interesting and very very
important work.
You mentioned the overall concept is collapsing of the plateau. And what we know from the modern examples or geologically under examples when this happens, we see a very dominant extension of structures that is closing metamorphic core complex kind of
structures coming in some of them might have nice stones in the centers.
So I was wondering, with that perspective, any of these classic nice stones that we see in New England might be reworked in the in similar fashions is just showed that timber Brahma tree from the pattern Damn it, I can you mentioned that it has the compression
melting and very rapid cooling at the beginning. So, are those extension a little late It's essential structures are there.
I think I think so, the calendar is interesting because they see the extra period of loading.
Before that, and then it gets zoom really quickly we don't see that signature elsewhere. But I think that there's that sort of exclusion of the domes and sort of a, maybe a core complex like scenario is is a good option we talked about it a bit in our
EP SL paper, so I can send that to you, you going to copy.
And so it's for example, one of the good example is the the the Chester Dominic Vermont can see that there's Paul carabiners his friends and evidence for us are low angle detachment around it, extrusion and are gone for 39 data converges with sort of
the core rocks are much are a little bit hotter.
And, and they reach the same temperatures that cover rocks around 325, which is when we see this Garner breakdown signal, some work goes on there by gateway at all saw that there was that same time period, there's a lot of Xena time halos around garnets
and really spectacular ones.
So I think there's a ton of these domes, probably the complex history, like we can we can see from those really interesting, different different levels.
But the pie the final stage is maybe a core complex like structure, I think that the.
The Kentucky group has also done some some similar work from the base from a structural standpoint.
Yeah.
I had a question for eons.
Did you.
I did you ever think of, like, what the topography of the Altiplano was and how it might relate to like later Pennsylvania and for Ireland deposition you know the coals and cycle themes and stuff.
To the west.
Yeah, so we can sort of again, sort of like, there's two ways we can gain some insight into that one is from the thermal thermal barometer You're right, which sort of an average of what the pressure that we see those, those broad pressures over over really,
really, we see six kilo bar we calibration Western Connecticut and he's the 66 kilo bar pressures throughout Central Massachusetts and across a large north south area and that sort of implies to me sort of a muted muted typography, maybe around three
to 390 when we see those.
The first part of the extrusion or Western Connecticut, they may have generated some, some large some more Jagat topography. The other thing we could look at as the chemical crystal thickness proxies.
And they suggest that the early occasions about about elevations about one to two kilometers from a sort of a ridge that progressed, and the sort of siloed badly at all.
And then in the neocon medium, we see a big pulse across with beckoning in southern New England, that doubles the crystal thickness.
And instead of seeing a progression in the direction crystal beckoning we see the whole area sort of just inflates and I just sort of distributed manner.
And we end this this record that we see from the crystal thickness proxies, based on whole rock stars and get your implant and b2b and you give me my isotopes.
Those suggest that we had elevation some around five kilometers in southern New England.
Those are.
And that's the signal thickening tracks with other crop the fallen basin.
Right.
So I hope everyone had a nice break for those few minutes there.
Now we are going to transition from a metamorphic and tetra chronology, and geo chronology theme to structures in northern New England, and for this first talk after the break we have Paul Washington and Stephen Chizik who have uploaded a pre recorded
presentation, called deciphering the internal structure of the silicon Champlain mega grabbing in the central Champlain Valley.
Hi, I'm Paul Washington, Steve and I have been working on this area since the mid 1970s and working together since the mid 80s, or work rests on the shoulders of two centuries of previous workers, beginning with Edwin Jameson 1819.
We are especially indebted to Augusta swing for deciphering the strategic graffiti in the 1860s, and to the late Brewster Baldwin of Middlebury College who patiently spent many hours helping us better distinguish the strategy in the field.
Today we are going to show the results of our recent efforts to define the relative vertical movements of various box within the mega group and that underlies the Champlain Valley in Vermont New York.
This picture shows the western surface of this area with the deformed camber division carbonate bank Strout of the valley, extending westward to the boundary faults of the Adirondacks depth the basement is approximately six kilometers under the valley.
So there's about seven kilometers of vertical throw across the boundary falls, with most of that displacement having occurred in the saurian during the formation of the mega Robin.
Just to give context, we are talking about a half degree by half degree area in western Vermont in northeastern New York on the outer edges of the deformed northern Appalachians.
This area is about 55 kilometers north south and 40 kilometers east west.
The specific area lies between the northern end of the mechanics and the southern end of the continuous champagne thrust sheet. It is an area dominated by the Campbell division carbonated shelf strata, which is what we really have been studying most of
this time, and includes the reference section for the Beekman town.
We have chosen the 1961 state map for the enlarge version since the 2011 state map mostly copied this area from the earlier map, and the color scheme of the 61 map makes critical and it's clearer.
This portion of the 61 map was compiled by while he Katie, and over half of it is personal mapping, mostly pose masters and doctorate.
This is the area that includes Katie's Middlebury synchronous Aryan with the Green Mountain had a glorious towards east, the south end of the Champlain thrust with the Orwell thrust is the login sign continuation southward.
The northern termination of the mechanics in the northern end of the commercial marble belt.
Just to give you some visual perspective. This is a view looking south from Apollo promontory on the Champlain thrust a few miles north of the area show house mountainous the northern limit of the study area.
Most of the areas relatively low lying, with only the champion thrust pieces, make mountain being the southern most, and the mechanics providing significant relief between the Green Mountains to the east, and the Adirondacks to the west, except for a
few large drug one such as Chipman Hill by Middlebury Vermont.
To understand this area, we have been forced to get brutally honest about what can be seen, large portions of the area have no outcrop thanks to major modern Robbins and accompanying thick return recover.
We'll be talking about the grub into our second talk. Often we don't even have water well data as bad as that is to guide us in these areas. By removing these areas from the state map, you can see that the poles of the Middlebury centenarian disappear.
It should be noted that even this view is problematic because Katie ports, the number of this strategy graphic assignments to make them fit the map pattern.
The superficially repetitious nature of this particular fee and the paucity of fossil data allowed him to believe this model despite the obvious need for the DLR to complete the pattern.
Nick Ratcliff created some additional skill art in assembling the current state map, but it's just as invalid.
We have been forced to produce our own map of the area correct in Australia graphic assignments, we have grouped strata to make the map pattern possible to see at the scale.
This map attempts to be correct in location at the outcrop level throughout the area, know that we have not attempted to map into the Green Mountains accepted to constrain the East edge of the Cheshire, and we have included the limited outcrop data from
the New York side of Lake Champlain.
This slide would be just a strat reference slide, except that we have also recognize each and certainly three elements.
One the main marble belt, as far as we know no fossil data constraints its age.
The Caitlin's and included iron deposits, these are obviously deeply weathered case silicate in proven a strata possibly latest Niels protozoa shifts and delights in Brandon, they are associated within a legacy, or Miocene late night.
And finally a truly enigmatic block of and false slippers state, a strata on the southeast corner of snake mountain, that is not compatible with any part of the Kimbo deficient stratigraphy district take her feet divides up nicely into a serious the tectonic
packages with the champagne and Green Mountain thrust sheets containing only lower and middle Cambrian strata, and the rest of the thrust sheets containing nothing older than late Cambrian.
However, to be quite accurate. We need to look at the structure graffiti is an online sequence that was no more than about a kilometer taken any Park, and was stepped up more than six kilometers stick by slick thrusting, meaning that it had to extend
more than 300 kilometers eastward that would put it in Augusta, Maine today.
This view of the thrust stack is not intended to be anything more than a cartoon.
After the Salonika thrust stack was created. We then have the formation of our mega Grubin to have a connected folder thrust structure, such as that standard have been proposed for the Middlebury synchronicity underlined by the champagne thrust.
The Maven Robin would have had to have held together internally during grabbing collapse.
But we know that Robbins don't collapse that way, especially if they are experiencing significant extension in vertical motion, such as the seven kilometers seeing here.
So the internal structure of the Robin must include significant relative vertical displacements.
So, we are trying to decipher the box vaulting within the mega grabbing, so we can start to really understand the solidity thrust information to the same for the story and grabbing structure, we must first remove or account for the subsequent affirmations,
other than the active extension event that has produced the modern Robbins hit hide the rocks. We have to deal with a new gene thrusting event that gives us most of our current mountain typography.
Genesis. The remaining events are much less important for this analysis. The Neo gene events produce relatively small displacements, so we can ignore them except for not being confused by their persons.
So the Green Mountains were raised in the weight near gene above the Green Mountain frontal thrust that comics were raised by sub iconic East virgin thrusts as well as lesser West virgin thrusts.
The picture was taken from my family home just northwest of Middlebury and Wogan's line was created as a topographic feature by late in Eugene trusting in the underlying strata.
These features can be seen as major features on the map.
It is the Acadian structures that present the most difficulties. The Acadian thrust sheets, that is the champagne Rashid.
The Taconic Alarcon's, the sheets in an adjacent to the Green Mountains containing Cheshire and Dunham, along with the meta carbonate naps in Sudbury and Weybridge.
They were all fresco for the denuded block vaulted strata within the mega grabbing the Mesozoic extension mostly reactivated earlier grabbing structures, further complicated you have evaluation of the late pillars so contractual features by juxtaposing
the Acadian thrust sheets with Sonic blocks within the mega Robin. That's the champagne thrush eat at snake mountain was dropped into a Mesozoic Robin so it now sits adjacent to and Portland word of strategy edited overwritten
by removing these Acadian thrush sheets from the map, we can highlight the grub and killing strata, and the structures that preceded the Acadia.
We then need to distinguish the subtle strata graphic patterns in the rocks such as limestone those stone ratios, sand content strategy graphic thicknesses and similar face she's issues.
We also need to recognize the subtle differences in the lowest and metamorphic grades as they are expressed in the carbonate syncing stones that make up the bulk of the strata working these patterns out has been the most difficult part of this project
because the box or no longer range linearly.
Being juxtaposed and interspersed by the box vaulting.
We should note that the Providence Island issues that is the building's vs spread port where the buildings has inner bedded limestone Cinderella stones in the breadboard is almost all those stone
I is one of these issues. The buildings, also is metamorphose to marble on the eastern portion of the area, but there is a non metamorphosed built in between it and the Bridgeport, in many areas in the middle Beekman town.
There's sand content differences, so that Eastern blocks tend to be Eastern that is Eastern and higher.
Structural levels have a higher sand content to chase the Black River Cretans sequence becomes cleaner and more popular for us from farther Western original sources.
The picture in the lower left shows my co author Steve in the early 80s, he wishes he was surprised today as he was then.
We then need to assign the strategy to their pre grabbing position in the Salonika press step by integrating the strata graphic and metamorphic patterns into the regionals cartographic patients patterns in the standard input it in hinterland increasing
metamorphic gradients.
Note that the increasing metamorphosis.
It goes not just hinterland word but upward. There's basically an inversion of metamorphosis in a trust stack.
From this we get a rough stacking sequence for the various identifiable box noted the higher box identified in brighter reds and the lower sheets or darker blues.
We then apply this to the map, replacing star trigger fee, the sheet level assignments.
As expected, the box step up and down, as we proceed eSports across the area. And there are abrupt changes as different attitudes had different block vaulting patterns.
Also, as expected.
There is a general progression to hire sheet levels toward the east.
We should note that the marble belt is the eastern most exposed stratum, and has the highest metamorphic grade, what underlies the Green Mountain sheets however is an interesting question.
Since more than 10 kilometers of additional Robin is hidden.
We can now identify and label a number of internal forces and Robin's within the Meg Robin.
You can see more than I have labeled, but this is just for reference.
We can now add the salary and normal bolts on tour geologic map.
Their presence explains why so many of the strata graphic contacts are so very linear over such long distances.
They aren't normal context.
Rather, they are normal false to to juxtapose strategy that wasn't originally together, though they are often roughly consistent with the strategy graphic sequence.
If you ignore the details.
We also provide a map showing the false and labeled horse and Robbins, to give some perspective on their density, since we couldn't come up with a color scheme that would make them stand out on the colored map.
In conclusion, we have shown a block faulting structure for the Campbell our division strategy in the Champlain Valley.
The pattern is consistent with that expected for the interior of oak Robin, we may not have all the details yet, but we're getting a lot closer.
So we can honestly say that the Champlain Valley has its faults and lots of them at that.
But the area is really good at hiding them.
All right. Thank you, Paul.
Does anyone have any questions for Paul,
certainly have time for some.
make a comment at this point.
Absolutely.
Uh, I was interested in the collapse that was being proposed in one of the earlier talks.
The collapse of the Altiplano so to speak that Ian was talking about. And this is what the primary grabbing structure would be the collapse and the Soria that he was that you're seeing the exclamation that the there and then you have the rebuilding of
the wedge, the rebuilding of the islands in the Soria with, in my case I'm out on the floor one, I'm seeing the thrusting of the new tectonic wedge over the old deformed material that has been done.
I'll walk halted in the extension in between.
Hey, that's really cool it's a really any of the great to sort of build comparisons between what we know what we can think of country that's going on in the hinterland and that has connections to, you know, better preserve upper crust will record in the
fall and I think that's super, super useful going forward often interpreting events that happen. Deep in the cluster, somewhat cryptic to interpret the tectonic signature and sometimes that's the better preserve like a graph and it's a great example of
you know extension, I can see if I see rapid cooling.
In the salary and that might suggest explanation. But if you can see a good Robin forming that's great, great evidence for, you know, or essential tectonics.
You may think that you're seeing cryptic signatures in the hinterland. Well, shall we say, it isn't much less cryptic out in the portal and.
After all, I'm talking about, we're talking about blocked vaulting in an area that has been considered just simply thrust faulted for.
Well, gosh 150 years in fact the champagne thrust that snake mountain is the first description of an older thrust in the literature.
So, really interesting, really. Yeah, to some really eaters and really really careful work and really interesting. Thanks so much for sharing it.
All we have a question from Yvette.
She says isn't a Syrian a little early for ends Altiplano collapse.
Well, that's the say you're talking about the second collapse the Altiplano collapse that you're talking about is the one that happened I guess Mississippian early Mississippian.
The one I'm talking about is the post salinity collapse because he had a building of a high Highland in the clinic, and then he had that that collapsed and then you build another Highland in the Devonian.
Yeah, exactly. So we see crystal thickening like for me for starting before 440 peeking around for 14 is rapid cooling within 444 30.
In the rock seem to hang out in the mid crushing cool slowly prior to Acadian reloading.
So it's not seen anywhere else in the distillery and we have person grabbing.
Then there's a belief in small mm message model, they'll fit together so you have like lateral escape along critical faults in med message model.
There's also some sort of extension horizontally and there's a nice little does it all fit together. Do you think I'm having a really hard time, I had around that.
I look, I look at it from the floral and so I head out the other direction westward, and in this area and you have in the latest motivation you have this wonderful Winston Delta, or shall we call it a mass wedge built out onto the continent.
And then it suddenly collapses in you build carbonate shelf out onto the platform to the west in the story and then into the early Devonian, and then that gets overrun by the next, which which is the capital Delta.
So we see the effect to the west of this. And we see this, the same structures have been being identified in northwestern New Jersey by some good careful mapping being done there.
There isn't much being seen in between because people haven't been looking at it that way.
And so what's going on internally, I leave that to you are. So, I have enough to deal with just dealing with the sets.
All right, 35. Oh, sorry. go ahead.
No, I was just gonna say okay so.
So thank you all for the questions for Paul.
So, the next talk is actually going to be by Paul again.
He's uploaded a second pre recorded presentation, in which he's going to discuss some of the structures he just talked about.
But how they may record the do texting ism in the Champlain Valley.
Hi, this is the second of our two papers on the central Champlain Valley, with those of you who are not attending my last talk, I am Paul Washington.
Stephen I have been reevaluating the Champlain Valley structure based on our work there over the last 40 plus years.
The picture here is looking eastward across the Southwest end of the lemon fair Valley in northeastern Shoreham.
This is an active grabbing, and the hills slope facing us across the valley is a series of cliffs hidden among the trees that are the east side false carp for the grabbing that underlies this valley in the distance, or the Green Mountains.
They were uplifted on West Virginia thrusts in the late Nia chain.
For reference, we are working primarily in the central Champlain Valley, I have to agree by half degree area on the New York for my border.
The area is underlined by multiple deformed Camborne division strata, and is bounded by the mechanics to the south and the continuous champion thrust sheet to the north.
I discussed the bedrock geology in my previous talk, so I will spare you the pain of repeating it this talk will focus on the active block faulting that affects the area, and how it relates to subsurface structures.
Just to prove to you that there is active normal faulting I show you a couple of pictures of these faults. The upper picture is along the Adirondack front, which has been recognized as a series of normal thoughts since the 19th century, the geo morphology
of this scarf tells you it is extremely recent.
The lower picture is a picture of a an eight meter waterfall and relatively soft limestone.
Note that there is almost no incision into the limestone even though the stream is cut a 15 meter deep Kenyan through a slight Ridge, just upstream.
The rock at the base of the Falls is the same as that of the falls itself, the Champlain Valley has been affected by numerous tectonic events. This may not be a complete list, but it is the best we can do at this point in this talk, we are trying to understand
the earlier events, by looking at the features being formed today.
This is where I ended the last talk with our map of the geology of this area with the identifiable story and exceptional faults overlaying the structural complexity of the area means that the subsurface projections that we would all like to do are questionable
at best,
as we pointed out in the last talk, order is the Champlain Valley have no outcrop leading others to generate amazing geo work by projecting strata graphic units faults and folds across these areas, sometimes for more than 20 kilometers between outcrops.
In many cases, they are not even any water wells to give us a clue as to what might be down there.
The large blank areas within the map area are mostly Robbins with ticket trim refill. So the question is whether we can use the grub and geometries to understand what is going on down below.
So, let's talk Robin theory, we can specify grabbing mechanics in a stratified system.
But the pre existing structure of an organic belt inserts an overwhelming kinematic control. So nearly all of the Robbins in this area will form above ramps on former thrust surfaces with the thrust detachments being reactivated as extension of detachments.
This means that if we figure out what the grabbing detachment, looks like we are defining the subsurface for a structure as well.
We first need to understand that a grumpiness a collapse feature created in response to the divergence of the bounding box. This collapse creates a void at the surface, which we see as a valley, the cross sectional area of this void must equal the displacement
area created by the movement of the downtown grabbing wall. Of course, defining the void can be problematic. Thanks to original on the Robin walls in deposition on the Robin for.
Please note that the nature of the collapse above a dipping ramp will produce a more definable scarf on the uptick wall than on the down dip wall.
This is significant because it tells us dip direction on the underlying ramp.
Because grabbing sir downward tapering wedges wider Robbins generally had deeper detachments. However, there is no unique relationship between grabbing geo morphology and depth or displacement.
Rather, grabbing void volume can be defined as a function of the interaction of depth and displacement.
This means that we need to apply knowledge of the subsurface in order to solve the nature of the subsurface under Robin.
A nice circular reasoning problem.
Fortunately, Robbins or bounded by Hyland's were outcrop is often available to help us out.
It should be noted that the depth displacement controls on grabbing Jim morphology are essentially independent of ramped up. So any analysis needs to assume a dip.
Note also that the shallowest available depth places the top of the ramp at the base of the void, essentially creating the mythical half crop and they do exist but only in more flexible strata, the deepest possible depth occurs where the bounding faults
would have met prior to any displacement.
So let's try applying this theory to the Champlain Valley. I believe a labeled several, but not all of the major Robbins for reference.
Each of these large province Mark some ramp on or the splaying off of a through going detachment surface, the detachment surfaces are reactivated thrust attachments from earlier current correctional events.
So what might we figure out from the Brahmins, hopefully depth of the detachment, and ramp projects.
We will begin by applying the theory to the northern part of the women fear of Robin, where we have excellent surface geologic information on both sides.
The green line marks the location of the transcript, we will use in this analysis.
The differences in land use, make the ground and stand out on Google Earth views of the area.
labeling the map shows that the test site in the lemon paragraph Robin is northwest of Middlebury and just east of snake mountain, which is topped by the south end of the Champlain thrust sheet.
The transept we chose runs from the village of labor chill to Central snake mountain.
This is a view from waiver chill westward across the lemon fair Valley to snake mountain.
Basically the line of the concept, the distance from the cliffs at the base of Weybridge hill to the bounding Paul for snake mountain, it's just about three kilometers.
The etymology of the name lemon fair which is the name of the slow moving river within the grabbing is unclear, but it's likely an English mangling of a French name.
The Valley has held a large Native American settlement during the French occupation of Crown Point in the mid 18th century that settlement lay right next to the cliffs at the near side of the valley directly below us, the nearby bittersweet falls and
a high volume perennial spring at the base of the cliffs provided the dependable water source for the settlement.
I must thank my nephew Chris for this photo taken this sweater.
The scarves on the east side of the lemon paragraph and are quite dramatic, but there are virtually no scarves visible on the west side.
As stated previously this difference indicates ramp slope, with the east side, obviously being the apocalypse carb in the west side, being the down dip bounding fault.
Returning to the Google Earth view, we see the continuous line of the legends, the local name of the line of cliffs fit on the east side scarf.
I have marked the location of our cross section fansite for reference.
Starting with a couple graphic profile, we have constructed a theoretical Robin which assuming that there has been some erosion on the edges. We have constructed a probable pre extension surface at the elevation of labor chill quarterly sediments partially
partially filled Robin, we have chosen to assume an average depth of about 250 people the central portion in the valley poor based on water well information from a kilometer north of the line with a width of about three kilometers, and an average boy
depth of 165 270 meters.
The Void area is just about a half a square kilometer fault depths of 25 degrees were assumed this step is based on observed fault tips in the area, the subsurface strata graphic control on the depth of the profitable detachment comes from our knowledge
of this particular fee of the saurian horsebox exposed to the south and projected northward to this cross section line that block is represented at this latitude only by isolated outcrops on internal horse within the graphic.
As we can see by marking the ledges on a close up view of the geologic map the horse block contain the middle Beekman town. That is the to or dark greenish blue on the map is cut obliquely by the Robin wall.
But the opposing dip directions of the saurian and modern Robin vaults means that the saurian horse block occurs in the subsurface of the Eastern grasp and bonding block.
This horse block originated in a thrust sheet derived from the lower structural levels of a, of the Salonika organic which thrust sheets from this portion of the wedge will usually have Potsdam sandstone basal units, with nearly complete strata graphic
sections in the underlying press sheets.
sections in the underlying price sheets. I have pinned the vault to a projected thrust surface under the next lower Potsdam basal unit.
So, as we conclude with a view across the western Champlain Valley. From the top of the mountain.
We can identify the dead Creek Robin.
Through its, Jim morphic expression, though that's most easily seen at ground level in numerous impounded portions of the creek within the wildlife refuge, the geo morphology is much less dramatic than that of the lemon paragraph and just find us on the
east side of snake mountain.
Note that the dead Creek grabbing is once and a half the width of the lemon paragraph and, meaning it probably has a deeper detachment than that of the lemon paragraph and this progressive narrowing of hearts grabbing c squared and these are just two
points in that pattern suggests and East climbing detachment system, which strongly suggests it originated as an East Virginia trust system, cutting through the previously blocked vaulted, making Robin, Bill.
So, I will leave you with the question was the late Nia Jean uplift of the Adirondacks caused by an East virgin thrust system that in placed Grenville Roxanne to Kimbo division strata within the champagne makeup Robin fill the active Robbins would seem
to be suggesting that this is so.
Thank you.
All right. Thank you, Paul. That was really interesting.
So we have six minutes for questions for Paul,
yes to that.
Oh, there's one in the chat from Marianne.
How much near gene movement on the Green Mountain thrusts what tectonic or stress of it caused the Neo gene thrusting.
Well the new gene thrusting would start with the event.
The new gene signature and East West signature are seen across all of northeastern North America.
It's mostly hidden, because it's reactivating by older structures, but it's, you can actually define it pretty well out in Ohio, and actually in the plateau of the New York State.
How much shortening enough to take what was a flat structure across to lift it to a kilometer and plus high, and it's probably you're probably talking about five to 10 kilometers so of shortening their.
Anyone have any other questions for Paul.
I would love to have the USGS upon drilling a hole in Crown Heights, in the show is here at Port Henry down through the Precambrian and to see if I'm right that there's some camera division underneath it since they're mapping there right now.
I know the answer to that is Yeah right.
Yeah.
I'll just answer your Now Paul boy if we could get some funds to drill holes that there's lots of places we'd like to drill but yes, you know your your observation that the Champlain Valley is is hiding a lot of its faults and a lot of it's a crops is
accurate it's a, it's been a challenge for a lot of people working there. Well, we did a pretty good job of describing that back in 1961 and saying, you know, any connection of this particular view across a lot of these suppose at fault is it is a hazard
undertaking so we appreciate your efforts and try to unravel it because it's it's a problem, but I don't see anybody spending any money to drill any holes in any point in time, unfortunately.
Yeah, well, well be was the one who really first try our recognize that block bolting extended into the valley. And what we're doing is we're taking it all the way to the Green Mountains and I can tell you I see it affecting the Green Mountain, shall
we say, Jim morphology, very odd as well so.
And in fact, all the way down into all the way the whole Champlain Valley Hudson River belt seems to be a block faulted belt.
So,
well do we know what forces are driving the extension during that period of time, while the extension is active.
It's the same extension that is affecting the Adirondacks the Adirondack current block vaulting in the Adirondacks is.
And then, if you want a great grab and just go to Lake George.
That is active, the Champlain Valley is active as well.
I don't think anybody has a good model for what's going on, Neo tectonically in the in northeastern North America right now anyway.
Very interesting. Do we have any additional questions from the crowd.
Oh, I would like to add one last thing.
When I have gone across the, the classic Ruby and metamorphic section down by Poughkeepsie, I am seeing that a lot of the metamorphic boundaries are across active Robbins or two more quickly apparent.
Robbins.
So, not having mapped it carefully I can't say for sure but they sure as heck look like what I'm looking at up in the Champlain Valley.
So be careful of your metamorphic boundaries in your metamorphic progressions.
Very good, thank you so much for the warning.
Thank you for your presentations that we can now move on to the next one, which is also structural geology base with Jeanne crispy and her colleagues is studying the kinematic modeling of string variation in the evenings, Brooke thrust sheet of the Taconic
allocate them, and the implications for the development of the key back salience.
Thank you Sarah you handled that well.
Um, yeah let me get my presentation, up here hopefully it'll work.
I'm actually does anyone mind, I would prefer to present it in this mode. Oh, Let's do this.
Okay. Um.
First off, I just want to thank the convener of this session and let's see your presentation though you can't know are you sharing. Oh, sorry, sorry, know that I'm eating up a valuable time here.
Sorry I'm in the ozone, apparently.
How about now.
Yeah, that looks good if you make it full screen, yup, yup, yup, yup, yup.
There we go. Okay, my head is in this now. All right, so, um, I did, I already said this, but let me say it again now that I'm in the groove is, first off I just wanted to thank you all for convenience for organizing this session, it really has been a
great morning so far.
So to get started with this talk, I think some of you in the audience know that I've been working for well really more than a few years in the mechanical lockdown of Vermont and New York.
And what I want to do in this talk is to present a synthesis of some of that work in the context of shall we say some covert inspired or some you can't get out in the field and do any field work inspired kinematic modeling and weekly metamorphose rocks
and thrust sheets and Portland fold and thrust belts, have been studied quite a bit in this respect as have medium to high grade metamorphic rocks in the more internal parts of organic wedges and low grade metamorphic rocks like those in the mechanical
lock bond really are understudied. And so what overall goal with all of this is to try to get a more complete picture for an organic wedge.
So, um. This map shows where we've been working in the getting spark thrust sheet, and the mechanical oxen, and I first wanted to draw your attention to the north arrow, which is pointing to your left, rather than up.
And I also wanted to draw your attention to the fact that I forgot to include a location map. But I do have labels for you for Vermont and New York here, so that'll give you some sense of where we are in the world.
And to be honest, for better or worse this really is a process oriented talk. And so it really won't matter where we are, until we get to the very last slide of the presentation.
So, on this map. There are two main features to notice before we move on.
And the first is that you can see that there isn't a long strike change in the overall age of the strata graphic units, as we move from north to south where we see generally older units in the north, and generally younger units in the south, and we interpret
that as indicating that the getting spring thrust sheet is inclined ever so gently with maybe an inclination in the neighborhood of one to two degrees to the south.
And then the other main feature to notice is that the axes of the regional scale folds are curved, and they define a salient here in the north, and a small recess here in the south.
And so what we've done is we've used these two features to define three structural domains and northern domains central domain and southern domain and the northern the northern domain is the structurally lowest domain, as a result of that southward inclination
of the thrust sheet so the northern domain is is structurally lowest domain, and it has fold axes that trend north northeast are parallel to the overall trend of the conical lock fine if we slide down here to the southern domain.
The southern domain then of course would be at the highest structural levels, and you can see that it also has north northeast trending fold axes parallel to the overall north northeast trend of the Taconic alongside the central domain here in the middle
is at intermediate structural levels, and it's described by these anomalous North north northwest trending folds and
then on this map, I've included strain ellipses, that represent the strain data we've collected over the years from string fringes around sub spherical rigid core objects such as pyrite Fran Boyd's.
And in this particular map I'm showing you the xy plane of the strain ellipses.
And so in terms of strain magnitude let's just focus on string magnitude first, you can see that that is fairly constant in each of the structural domains, and that the strain magnitude is highest in the northern domain.
If we think about this in terms of orientation, you can see that strain ellipses are very nicely behaved in the northern, and in the southern domain and the x axis or the long axis of the strain of the strain ellipses is perpendicular to those regional
scale folds so that's the case, we can see that beautifully here in the northern domain and in the southern domain. But that's not the case in the central domain.
And if you look closely at the central domain, you'll see that the x axis or the long axis of those strangelet slide a moderate, and in some cases not a few cases you can see one here that those long axes slide a very low angle to the structural grain.
So, I'm
so that has really been a conundrum for us and that's what a lot of this talk is going to focus on. Let's move away from the map to the law of all structural geologists stereo nets.
And we can see the same pattern here on these three staring at so I'm going to use red throughout the talk for the Northern domain. Blue for the central domain and purple for the southern domain.
And so, um, what we can see here is that, in terms of the rate. Maybe we'll go down to this table in the southern domain in terms of the rake of the x axis on the cleavage domain.
That's essentially down dip in the southern domain, and it's nearly down to it but not quite in the northern domain that'll be coming important in a little bit.
And then, in our anomalous central domain, we have a moderate rate of the x axis on the cleavage plane. And the other thing I wanted to call your attention to with the steering nuts is orientation of the Y axes, and the Y axes are again well behaved in
the northern domain in the southern domain. They're just as we would expect in a thrust sheet with a horizontal orientation. If you go over here and look in the central domain.
You can see that the y axis plunges 20 to 25 degrees to the north north east.
And that's going to become important in in just a few slides. So let's.
This is in terms of lines let's think about planes that cleavage plane before we leave our steering that's. And what we see in, in terms of the orientation of the cleavage.
Is that compared to the northern domain, and to the southern domain. The central domain. The cleavage in the central domain strikes North North West, rather than North north east, and it also dips moderately rather than generally.
So then if we just step back and summarize all of that structural information I just ran past you kind of quickly. What do we see in the central domain.
Well, basically we see an x axis that trends to the south, east, rather than to the east southeast.
And we see a Y axis. That's plunging to steeply.
And we see a Z axis, that's trending to the south of West, rather than to the north of West. And that's also plunging to shallowly.
So if you put all that together, that is really starting to smell like there is a distributed component of left lateral wrenching or strikes slip motion in the central domain.
So what we've done to evaluate that is we've modeled the strain patterns in the getting spark thrushes using different combinations of simultaneous simple share and pure sheer in three dimensions.
And I've included information matrix for the math oriented people in the crowd and some more simple steps are sketches here at the bottom if you'd rather have a visual for the math.
And so what do we have here is I've included a thrusting component of simple shares shown here by the effect of sheer strain in the defamation matrix.
And you can visualize that here are thrusting simple share component with a top to the to 90 direction we've set up the coordinate system such that the x axis is parallel to the sheer direction, and I've set that with a trend of to 90 and I won't get
the reasons for that in this talk that will take too long. And then we've also included, what we've gotten suspicious about is left lateral wrenching component shown here in the defamation matrix by this effective shear strength entry in the matrix and
that's represented down here now this is not a cross section view like we saw over here. This is a map view so you're looking down on the earth here to appreciate the wrenching component of simple shear.
And we're really trying to keep the information matrix as simple as possible. So we have got the sheer direction for the wrenching component. Also parallel to the x axis or the x coordinate access or in the 290 direction.
so so these are the two big things going on some minor things are that we're going to have no change in length parallel to the x coordinate axes. And I'm just doing that because that will allow us to easily maintain compatibility along strike between
those three structural domains that we've got a little bit of action here on the rest of the diagonal in the matrix. And that's a very small amount of pure sheer, and I'm including that because in the central domain and in the southern domain, we see
a small amount of fiber growth in the y direction.
So we need to have that component as well.
So, so that's the game plan and I'm going to walk through each of the three domains. And I thought about starting with the simplest domain and then I realized there really isn't a simplest domain so let's start with the most interesting domain which is
the central domain.
And it's always kind of tricky when you're working with three dimensional data to think about how to display the results. And so what I have for you here is a diagram I came up with that is plotting the wrenching shear string against the strain ratio
in the xe plane. And then you can see curves of constant thrusting sheer strain on the plot.
And I've stopped those curves, where the.
Here we would have a thrusting shear strength Oh point one so I've stopped those curves, where the thrusting sheer strain is the same as the wrenching cheer strain and I think that kind of makes sense right because we're in it over thrust, or cheat environment.
And so, we would expect to have more thrusting than mentioned sheer string. Anyway by stopping the curve there that's what gives this plot this to me It always looks like the top half of an angel fish.
So that half Angel fish plot here that you're looking at. So the bottom line is, you're in this plot we're really thinking about that strain magnitude data that you looked at on the map but the strain ellipses, and this blue bar here shows the range of
options we have for the relative amounts of thrusting and wrenching in the central domain based on strain magnitude. So how could we translate this into words.
We could say that oh we could be down here on the bar, and we would have a small, or we would have a thrusting share strain of say about 4.8 and a small wrenching cheer strain of about oh point one, or we could be up here on the top part of the bar, and
we would have a thrusting cheer stream of about oh point six and a wrenching share screen about oh point five. Or we might be somewhere in the middle with, say, a thrusting sheer strain of 4.7 ish and a wrench into your strain of maybe Oh point three
ish. So what I'm going to in the next three slides is show you those three options. First we'll look at the bottom of the blue bar, then we'll look at the top of the blue bar and then we'll look at the middle of the blue bar, and we're going to jump from
stream magnitude and we're going to look at the orientation of the strange ellipse sides. So basically we're going to take our string magnitude data and make some predict or we're going to take, make some predictions of what the orientations should be.
And then we're going to compare that to what we actually observed from our strain ellipses.
So here we are now to get you oriented again we've moved on, we're talking about orientation so this now is a plot of plunge against trend, and I were first that I think will first think about the y axis of the strain and flip side because that's the
that's intuitively, the most easy to understand. You'll remember I pointed out a few minutes ago that the y axis in the central domain plunges about 20 to 25 degrees to the north northeast. So, if we had a zone that was only undergoing thrusting.
I think it's pretty easy to visualize that your y axis is going to be horizontal and we saw that in the northern in the southern domain stereo minutes.
And if we have a zone that's just described by wrenching or strikes slip motion. Then we're going to have a Y axis that sub vertical. And if we have some combination between thrusting and wrenching, then we're going to have a Y axis, that's somewhere
in between. So that's the thinking, and we've got our bottom of our blue bar here without rabbit route relatively large thrusting shear strength Oh point eight and the smaller wrenching share screen.
And you can see the predictions I put in the yellow circles. So this would predict for our sheer strain here of Oh point one that we would have a Y axis with a plunge have less than 10 degrees.
And so that doesn't agree very well with what we observed from our strain data. And you can also see that the x axis and the z axis are not the best of fits the, the blue squares here are our observed orientations for the x axis and the z axis, the y
axis kind of fun to work with because we don't have to deal with the fact that it's a long strike so we don't have to deal with the fact that we really don't know what the dip is of the getting spreadsheet What is it, the base will thrust.
We do have to worry about that with the X and Z axis so that's why I've got two boxes here, the solid boxes if the Bazell thrust is flat and the open boxes if that basis for us dips about 10 degrees to the east.
Okay, so that's plot one, let's go to the top of the blue bar, and you'll remember at the top of the blue bar we have a thrusting sheer strain of about oh point six in a wrenching sheer strain of about 8.5 so they're about the same.
And if we do that, let's go over to the y axis that's easiest one to understand, you can see if we have this relative combination of thrusting wrenching shear strength.
We're going to predict that our Y axis the prediction again is shown by the yellow circles, we're going to predict that our Y axis has a plunge of almost 40 degrees.
And that of course is much deeper than our observe 20 to 25 degrees. And if you look over at the X and Z axes, you can see that on the model, the yellow circles represented the model overshoot in both cases, the actual observed orientations of the x and
the z axis. So this is another particularly good combo of thrusting and wrenching either so I think you probably can guess where I'm going with number three.
Number three, we're in the middle of that bar and we've got a thrusting cheer strain of about 8.75 and a wrenching cheer strain of 4.3 and why was I surprised when I applauded this, because we've got our Y axis right in here with a plunge of 20 to 25
degrees justice we observe with our arms, all those strange lips Lloyd's in the central domain. And we also have just a beautiful fit with the orientations of the xn.
Well, these are interrelated right because the axes are mutually perpendicular but we, we have a beautiful fit for for the other stream axes, as well.
So, um, so. So what this is telling us is basically that what well what have we done here is we've done probably set up the simplest kinematic model that we possibly could to describe the central domain, and we've done a pretty good job of actually matching
the strain data that we see in the field. And we've done this, almost completely with simple sharing, there is only a very very small amount of pure sharing here you can see that with the ky value of just a little bit above one is only a very small amount
of pure sharing.
In this model, if you're thinking about the big picture which I'll get into in a, in a little bit, is what this is telling us if we just have a zone of simple sharing with no pure sharing, it's telling us that as this threshing was deforming internally,
it wasn't changing its thickness of course that's going to feed into the development of a critical, critical wedge, which I'm not going to go into in this talk.
So let's, I'm just a warning us.
I had a feeling I was going to run out of time so then I said, you probably I was going to say if I ran out of time that you've probably all had enough structural geology by now. And so we're going to skip through the northern domain and the southern
domain and I'm just going to run through my conclusions, which are that I'm conclusion number one is that you thought we remember we had much higher
elliptical higher strain magnitude in the northern domain and so what we figured out in the northern domain is we have a much higher component of thrusting shear strength in the northern domain.
And that makes sense because the northern domain is a structurally lowest domain. And so we're just right above the Bazell thrust in this area so we would expect to have a high thrusting share screen in that area.
Sorry about that.
Conclusion to is this curvature that I alluded to, at the beginning of the talk. The reason that curvature is there we believe is because in the central domain, we have a relatively high component of of this wrenching share string.
And then finally, if we step back and put the getting's Brooke thrust sheet into its position relative to this grand sweep of ceilings and recesses in the Appalachians which I think is so well displayed by the original 1978 lipo tectonic map, you can
see that that left lateral wrenching component is really easy to interpret, in terms of the development of salience and recesses, and the curvature of the correct salient as Bill Thomas has shown is most likely inherited from the app and rift architecture.
And so we would interpret the convex salient as a primary arc, and a what our work in this little postage stamp of the getting's book thrust sheet is telling us then is that the Quebec salient probably evolved from a primary arc to a progressive arc during
to Conan, or a Genesis, such that the curvature of the ceiling was amplified as the various threats sheets were in placed.
Thank you for giving me a couple extra minutes there Sarah. That's all right. Thank you very much, but a very interesting talk and review of the structure of geology, we are out of time so if you have any question you can go ahead and post them in the
chat or you can all love and ask them in about half an hour when we have a little bit of time for a break.
Thank you.
Thank you Sarah. My pleasure.
Alright, so our next talk is by $1 Lou, which is going to talk to us about high resolution receiver function profile beneath Connecticut, and its implications for the tonic is three of suffering New England.
Thank you. Okay guys see this light. Yes, we can see them if you want to put them full screen.
Perfect. Thank you.
All right, thank you. So I will get started on southern New England exit is diverse geologic features resulting from past tectonic events in this study we conducted a seismic survey across a longer profile in the northern Connecticut, denoted as the black
broken line on this bedrock geology map, our profile traverses many surface geological units, including an orange and units in the West, several down to one are derived Turing's to the east, and the Mesozoic riveting basin in the central part of the array.
array. There is a gun one and derived two rings were created to lunch during different episodes of the play Gen Genesis.
These Turia creation events as well as the following formation breakup Pangea resulting the diverse surface geology of selves in New England.
As a seismologist, I am interested in how did these tectonic events, modify the structure of Christ and this experimental deep beneath the surface. And how does present a deep structure corresponds to the surface geology.
Also I wonder how features image by seismology can in turn, put constraints on the tectonic history of cells in New England.
In this day, we use p to ask and receive a function analysis, receive function analysis is based on identifying seismic waves that are converted and structural discontinuities with seismic impedance contrast caused by changes in material properties.
In the case of PJs residual function, we are interested in the ass wave converted from incoming P wave at an interface that separating two mediums, with different show but Asti end or different densities by measuring the time difference between the direct
PR rival, and converted as that rival, we can estimate to the depth, where this conversion happens. However, as you can see on this resume function seismograph is, it is not so trivial to pick out the converted acid waves, which is buried in like a train
of noises. And that's why we need to stack, our residual functions.
When, when we only have a single station, or when the station separation is large, calculated residual functions are being at each single stages.
When we have a dense array of size programs, I say some more meters and the station station is small enough that seismic waves, two different stations intersect at so called common conversion points at the depth.
We can then stack, our reserve functions at those common conversion points to achieve better resolution, a previous large scale p to s3 so function study, based on the earth scope transportable array shows that drastic mobile depth offset, but needs the
boundary between Lorenza and our creative Turing's.
However, as we can see on this trends, we can see on this profile. The station spacing for the transportable array is large, and the distance between the station to the west of the staff and the station to the east of the staff is at least 100 kilometers.
In this way we cannot resolve detailed geometry and the sharpness of this mo step. Also, detailed structures within crust and the little experimental associated with the past tectonic events, cannot be accurately constraint.
In this study, we use data from size calm, the seismic experiment for imaging structure but nice Connecticut, the size count deployment consisted of 15 sizable stage.
Nancy. Yes, there are one, two cs 15 from west to east denoted as red triangles on this station map. They are deploying a dense linear array with 150 kilometer total length and brought about 11 kilometer average stations basic.
In addition to size constellations. We also incorporate data from other stations denoted as black, black rectangles in this station map to produce our common conversion point images.
We use earthquakes, with magnitude, with a magnitude of at least 5.5, and a distance from 30 to 100 degree, away from our seismic stations.
Here is our calculated a common conversion point profile radicals indicate pasta velocity ingredient, where the seismic velocity is increasing with death blue colors indicate an active velocity gradient, where the velocity is decreasing with steps, kind
of skills shows the amplitude of the converted waves as a fraction of P waves amplitude with deeper colors suggesting a strong, a stronger velocity contrast across the discontinuities in this profile, we can very easily identify the mobile discontinuity,
which is shown as a very strong horizontal positive velocity gradient, sit at about 40 to 45 kilometer bunnies station 123, and at about an at about 30 to 35 kilometer police station for to station 15, and we observe prominent step like change have more
depth between station three and the station for. In addition to the mobile features. We also observe a strong positive velocity gradient bunny's station seven, eight and nine and a couple of elongate West dipping positive velocity gradient in both crust
and the least experimental and also some traces of negative velocity ingredients in the mental combining seismic profile with surface jewel with surface geology, we can start to interpret these seismic discontinuities in light of constraints provided
by surface geologic geological units.
So, our first, the feature number one is the mobile step, we can see that it is located directly beneath the boundary between Lorenza and our creative terrains on the surface and feature number two is the possible velocity ingredient, located directly
bunnies Hartford basin, which provides It was a very straightforward explanation.
harmful basin, which provides it with a very straightforward explanation. This positive allows the gradient is likely to represent the interface between the slow sedimentary rock in the hardcore basin and the fat and the faster crystal and basement rocks
beneath.
And the feature number three is the West keeping positive velocity gradient in the crust, and we can see that the eastern end of this feature kind of connects to the Western margin of Avalon during the force of feature is the West dipping positive velocity
ingredient in the list of spark mental.
As we can see, this feature actually cuts across the entire profile and all the surface Joe geologists features and the feature five and six.
Natural velocity green and in the mental the likely represents either made the list asparagus continuity, or the list of sphere as sinister boundary.
In the following, I will focus on feature one three and four, which may have multiple potential explanations that have important implication on the tectonic history of cells in New England.
There are three potential origins of the large mobile step we observe. The first is pre existing differences in the Laurentian cross and the crust of the credit rings, said several previous studies have shown that the orange.
the orange and cross, cross is overall thicker than the crust of a creative rings, and also the P word velocity to ask way velocity ratio in the Laurentian crust is larger and larger P wave velocity to as we've been asking ratio will resulting shallow
mo hole. Then we then we observe in this profile.
However, although although there is.
Although this effect can by no means fully explained the existence of the mobile step, it can partially contribute to the large size of the mobile step.
The second plus the second origin is the oldest rustling apple, orange, during that two car garage any.
So during the creation of the more countering to Lorenza. The seduction polarity is likely to be Eastern dipping, and the Orange is the lower plate. So it is possible that during the during creation, the orange.
The third origin involves the collapse of the Acadian Altiplano. The Acadian Altiplano is a proposed
organic plateau produced during Acadian or progeny after Acadian progeny reduced tectonic stress, resulting gravitational collapse off this organic plateau, which largely things, the crust of the creative terrains, which may produce or amplify amplify
this mobile step.
step. Another interesting feature is the West the deepening possible velocity gradient in across, which is denoted as a feature number three on this feature.
This feature can be explained by crust assure zones, creating during sharing occasions, the largest share defamation may lead to Crystal graphic preferred orientation of cross the minerals, resulting seismic anisotropy shown as discontinuities in our
image. This feature can be up one continuous feature, or like two separate features with a western portion connects to the surface and how round the eastern margin of hospital basin and and Bronson to arc.
And, and the eastern portion connects to the surface and around the western margin of the Avalon jewelry, then it is possible that the western portion of this PVG me represents the Selenium suture associated with the creation of the cafeteria.
And the eastern portion of it, then represents the occasion surgeon associated with the creation of Avalon touring.
However, it is also possible that the feature number three is one continuous feature associated with occasional progeny, and it's geometry is distorted by younger tectonic events like the collapse of origin plateau, or Mesozoic corrupting.
And the feature number four is kind of counterpart of the feature number three in the least experimental.
It's also a wet gentle a West dipping passive velocity ingredient, given its steps continuation and gentle a dipping geometry, it likely correspond to the mobile have a relic slap from pastors adoption events.
Since the eastern end of this feature. Similarly, extends further to the east to the Avalon terrain.
It is intuitive to assume that this abduction event associated with this relics lab is younger than the Acadian origin, then it may represent a broken off slab during the new Acadia Rajini, but it is, it is contentious whether new Acadian or Rajan exists
as the latitude of southern New England. The other possibility is that it's um it's a Radek slab.
Due to the production of the Reich ocean, leading to the Anakin your progeny. Although the subduction polarity during Anakin Dr. Rajan is also contentious, but in order to make the granite slab of this size.
We only need 10 million years, assuming a typical, a typical production rate of four or five centimeter per year.
And then so it is possible that at least during some period of time save 10 million years. During the closure of like oceans of action proudly made be West opinion and which produced this Radek slap, we seeing our image.
Yet another interesting possibility is that the feature number four, may actually be a continuation of feature number three, given that we have so similar dipping slope.
And then the feature number three and number four war one single continuous feature associated with Acadian or progeny and but it was later displays and a separated, then it is kind of intriguing that what kind of tectonic process can decouple and displays
cross and mental by 150 kilometer. It may be an interesting future topic to further investigate this possibility.
In conclusion, we conducted the PTS research function analysis our dense seismic array across northern Connecticut to investigate little sparks structures, and we observe a sharp mobile step, and several others that make these discontinuities in the digital
sphere with high resolution.
We have suggested several potential explanations for these features, but seismology only provide a snapshot of present day structure with no temporal information.
So our major future challenges to fully integrate seismic imaging with complimentary analysis that have better cut time constraints on these features.
And thank you for listening out your questions.
Thank you very much for a great talk, if there are any questions, you can go ahead and ask them live, or you can write them in the chat.
Bill, I see your hand.
Alright, thanks for the great talk. I'm looking at the dipping, a number three reflection dipping West. And I noticed that that job that you address going up right under the Hartford basin, and then back down again and I'm wondering if that job couldn't
just be an effect of Mesozoic drifting.
Yeah, as I mentioned, like so.
If there are two possibilities. One possibility is that this feature number three's was one continuous feature, and it was this geometry was like later just thought it danza master interesting, maybe one candidate to like kind of distort the geometry
of this feature. Okay, Thank you, and I just while I'm on just, you know, refuting versus arrived uni it just seems like they would produce such different things and yet we can't distinguish them and I guess I'm biased against major refuting producing
major I'm biased for that, that major, major features are, are caused by major crystal refining.
But I'm not an expert in so thank you yeah it's like as I said, we only have a kind of the president in present day like snapshot so it's kind of integrate integration of like all the past events is kind of hard to like separate the effects from different
time period.
Yeah, is Roger block.
Your, your comment that three and four might have been the same feature offset perked my ears. And I looked at a poster that Doug Roche and I put together for any gsa.
2019. And we postulated a similar geometry for the salinity suture offset in the Acadian and suggested there could be 200 kilometers of offset on that.
So, what you were saying all of a sudden reminded me of ourselves.
Couple years ago. And it'd be interesting to maybe perhaps follow up with you on that. Yeah, sure, of course, and also like eager to buy know is, is either like you know, special feature like in this region or it's more like a universal stuff that is
other like regions you know the origins. You're right. Right, exactly and preserving it also by the way, for that long is seems a bit odd but anyway.
It looked like our cartoon, or cross section that we put together.
Thank you. Thank you.
Another couple of questions in the chat, maybe you can go ahead and start answering them through the chat directly and then we can keep the conversation going after our poster session.
Sure, thank you very much for your presentation.
If you don't mind, stop. Yeah. Excellent.
So the following two presentations are posters. So I'm gonna share them they will run for five minutes and then we have five minutes for discussion.
So, hello everyone, thank you for coming to my talk.
So today I'm going to be talking about the main results from the seismic experiment for imaging the structure beneath Connecticut, or size con for short.
So, New England's complicated superficial geology reflects millions of years of tectonic processes where there have been several drifting mountain building events.
However, the way that these tectonic events that have shaped the deeper story remains fairly elusive. So, we are interested in learning more about the past, and ongoing processes that have shaped and are still shaping the latest peer and upper mantle
sudden the deep Earth structure may provide further insights to new influence formation.
So, little bit about size con in general, was it appointments of 15 seismic stations that collected data for about four years.
Stations traversed number of tectonic boundaries along Connecticut, in a relatively short distance, the seismic data that the station's collected is the way that we're able to probe deeper than the first place.
So we use the principles of seismic anisotropy or the directional dependence of seismic waves to constrain deform structure.
So, how it works, is that waves passing through and and ice tropic medium, who gets split and fast and slow components.
And usually it's the greater the delay time between the fast and slow, the stronger the anisotropy is.
Additionally, the direction that weighs want to travel the fast track to travel is known as the past polarization direction.
And in our process of analysis used a specific type of seismic waveform, known as SKS, which is important because it's a means that we're sampling the earth directly underneath the observer.
So, in our analysis we use the methods transverse component minimization, which is an event by event basis, and the other being the multi channel, which is more collective.
So for the transverse can put them in position. Most of the observations that we found for Knowles, meaning that they were seismic ways that didn't display splitting.
So, the ones that were split were able to see them on stereo plots, which is a function of back as myth that direction from which the seismic wave came from an incidence angle.
And so what we see here is that some size but there's stereo plots have different fast polarization directions for the same plot meaning that there are multiple layers of anisotropy present.
And then for the multi channel method here, we're able to see that we can see the results through scientific data plots, which is a function of back as Smith and splitting intensity.
So this is just another way of getting the same two parameters that polarization direction and delete time.
The amplitude corresponds to the delay time, and the areas where it crosses the x axis are the fast polarization direction.
And so to put this board and a geological context.
We overlay the results on geological maps.
And so, for the transverse component here, we see that even though there's a bit of scattering, there's still some patterns that emerge, such as here in the West, where they're the same on the same terrain.
The station's display north east, South West passport ization directions. And an interesting one here is that station six here.
It's parallel to the trend of the Hartford basin, being that there's some correlation there. And then for the multi channel method, there's less variability, and that's polarization direction but there's definitely a significant amount of a delay time
where there's longer in the West and short in the east. And so, to explain this we propose two different results and, is this the spirit differences. And the other thing that there are let this period differences that contribute to these contributions.
And so,
thank you very much, and to learn more, please see our paper
stuff.
Excellent.
Sorry I completely forgot to read the title.
But if you are here if you could please unmute yourself.
Yeah. Hi, I'm here.
Sorry that it was so quiet.
That's okay, that happens. And I can go back and show you the game but if there are any questions please go ahead and ask
the. Any questions for Ethan.
Done. Is there anything that you want to add, given that the volume was a little low and people might have missed some parts of your presentation, right yeah so feel free to go back and listen to the presentation again.
Hopefully the audio would be better but a balloon part of the video that I wasn't very happy. Just because of time constraints was just talking about the discussion.
And so, I just want to elaborate that the main points from the studies were that there's
consistent fast polarization directions where you're taking long averages but there's a lot more scatter when you're looking at just individual events, meaning that the dominant force is from the stratosphere, and that there are secondary effects from
the lip is fear. And so to explain this, and explain why there is such a big difference and delay times between the size constellations from west to east.
There's two different models that are proposed. So one is that the reason that there's such a big delay time is that there is a region known as the northern Appalachian normally.
So it's a region of low upper mental velocity and so it's possible that that's dipping into the eastern portion of the cycle size Connery, meaning that it's going to decrease the delay times.
And the other possibility is that it's within the lettuce beer, so it's that there's more destructive interference going on there stronger but the Spirit components towards the east.
And so those are going to cancel out the main plate motion, sharing effects that we see. So that's mostly what I wanted to say thank you.
Absolutely, thank you for clarifying that.
Are there any questions. Yes, a quick question from Bob when you speak of the MSRP, and the waves you're looking at our nearly vertical. So, is this an integrated to refer orientation over the whole spirit mantle, or is, is it affected by
more shallow or more deeper parks.
Right. So, I guess, mostly what we see comes from the upper mantle, even though there are.
I guess Maureen's pregnancy had something else what sorry. Um, so, the largest components coming from the upper mantle of the reduces some contributions for the crust, except the crust is so small, it's just going to be about like, I'd say like 10% of
the total anisotropy that we can see.
So it's mostly deeper within the earth that we're seeing this anisotropy.
So the. I was wondering about the Olympus very manual which might go from 30 or 40 kilometers to more than 100 over that range, is there any localization.
Yeah, I guess.
There's localization when you're looking at just individual places but if you're looking at it more long term, why back asthma three inches. Then we see less variability.
And we see that it's pretty consistent and it's pointing along plate motion sharing with some counter clockwise.
Patterns going from west to east.
Okay.
Thank you.
So we're moving on into the last poster of this session, which is by medicine Rosen which is going to present the evidence of trash sheet thickening in a region of out of sequence thrust folding in the Taconic progeny wedge.
Again, I'm going to play her video and then we will have time for discussion.
Hopefully my internet will allow us.
Unfortunate unfortunately we cannot download this presentation so thank you for checking out my poster. My name is Madison Muslim, and I'm a master student at University of Connecticut.
Today I'm presenting about evidence for a spreadsheet thickening in a region of out of sequence stars faulting and the mechanic organic which.
Here's the geologic map of the northern region that to clinical oxygen and getting big spreadsheet, which is located in New York and Vermont.
The mechanical Auckland develops during the order division to connect progeny, and is comprised of three structural demands northern central and southern these domains under one regional folding the development of sweetie cleavage.
And out of sequence dress vaulting. Today I'm specifically going to be talking about the central domain which consists of two sub domains, an area of high street in the east and a larger area of relatively low straight in the West.
Looking from west to east and the central domain, out of sequence thrust faulting become more prevalent and criminalization cleavage locally develops here.
As we can see, these are staring at this show site mean orientation data collected from the low Street and high stream subdomains the light blue color represents the low strain sub domain and the blue color represents the highest rates of domain, black
lines is just means.
As you can see from the steering that's the high street is characterized by north northeast striking cleavage which is similar to the overall trend of the mechanical oxen.
In contrast, the lowest rate and sub domain is characterized by north northwest striking cleavage.
Now we're going to look at the history games for the site mean orientation data. This data shows that the stretching delineation for the low string sub domain is ranking to the south while in the high street sub domain, the situation is dumped it.
Now, this contrast is important because it shows that the low strain subdomain has a complex 3d defamation whereas the down deep searching limitation and the high stream so domain is really going to allow for an in depth 2d analysis using our versus data
Prep diagrams.
Now, if you look at these are vs data prime diagrams for the high stream sub domain, you're going to see two different scenarios. The first is simple share plus volume change, and the second we're going to be looking at a simple shear and peer share with
no volume change designs represent present work with solid lines for horizontal threads she while dashed lines have a 10 degrees east of being spreadsheet.
The red circles represent password with solid circles is horizontal spreadsheet and open, open circles account for a 10 degree east of being fresh sheet.
So, for the simple sheer and volume change graph you can see that it's internally inconsistent with all the one site plotting in the volume game field.
Now if you look at the simple sheer and peers here with no volume change graph you can see that most of the stream data is putting in a thickening shares.
So the high stream subdomains strain data really suggest that the getting broke stress she underwent thickening in order to maintain the critical taper angle of the origin neck which in this interpretation is really supported by the prevalence of out
of sequence trust falls in the highest strand sub domain.
So now we're going to look at this cross section here and the cross section of the conical oxen has the central domain labeled, you can see the low and high strain sub domain and context and also where the bird mountain thrust fault is which is similar
to all the other thrust falls in the area.
in the highest ranked subdomains specifically.
So, according to critical wedge theory, we know that the critical table angle of the chronic, Oregon, organic wedge was most likely maintained through this balance and dynamic relationship of out of sequence.
mountain trustful, and, and, in sequence thrust falls in the 12, the wedge. We know that out of sequence thrust faults they thicken the wedge while in sequence them.
So we have this dynamic important balance.
So, looking at all the stream data that was collected so far you can also see that the penetrative stream also supports this idea that the high street and sub domain is a ticketing shares them.
So the combination of the artists egos thrust faults that are characteristic of this area the stream data that's collected, it really solidifies this notion that the thickening of the organic wedge was localized to this area of the getting Brooks spreadsheet.
I would really like to thank, Jennifer Cooper Bumbles for her assistance in the field, and with this project, and this work was supported by a Geological Society of America, student research grant, and really thank you so much for listening to my presentation.
Excellent.
So I'm just going to stop sharing so that we can see each other but any question for this presentation are welcome nice presentation.
Yeah, sorry, um, I hope you guys can hear me but sorry about the resolution, I'm guessing that there was a second internet connection problem. So, I promise it's high quality resolution.
But if you guys have any questions you can just ask me or I can actually just show the poster and what it really looks like.
Yeah, if you want to go ahead and show your screen you're definitely welcome to do that. Oh, I don't have a pulled up right now, but, um, I don't know why the internet connection but it looked fine on my computer but it's totally possible that through
the, you know, the transition between my screen, and the internet.
I apologize for that.
Madison.
This is called Washington.
Is it your direction of motion was more or less consistent between the out of sequence and in sequence, our motion.
Yeah. Everything is dipping east. So, um, if you looked at the field area. I'm throughout the central domain, everything is dipping east.
Throughout the central domain, everything is dipping east. We just have see this strange difference.
As you can see on the R vs data prime diagrams, versus the high street and low strand sub domain so even though there's a string difference there was dipping east as you can see from the steering that's okay.
Thank you.
Alright so we have five more minutes, and then they will cut us out so I guess I would like to open the floor for questions of previous stocks for the next couple of minutes if there are any.
Okay.
Yeah, I think if Greg is still around. I don't know if either Greg here.
I had a question about the Adirondacks.
Seems like he might be gone.
I question is going to be kept for later.
I think that everybody has always had questions about the Adirondacks.
And that is an option to keep the conversation going by using the any GSA web page that is a space for chopping question in them page that you use to log into the zoom session.
I had a question for young cow,
which is with your refined data that would move the mo whoa step over a little to the east relative to the earlier maps.
I'm sorry the moat move the mobile step to the east, work with a surface expression on the previous maps where you would draw the most step is it with your refined data doesn't move a little bit to the east, as you would draw on a map.
Oh yes so it's not like directly beneath the surface boundary, like between the Lauren show ended up creating stories, so the boundary as the depth is not is there as a little like sub longitude to offset.
Thanks.
Are there any other questions.
Seems like there's not but I think what I want to sell is, thank you very much for all the contributors, for their great submissions great presentations, and thank you for all of you to coming to this online meeting.
We all wish to see each other next time in person, so that we can have lengthy conversations and real drinks together.
Yeah.
They're really good discussions and sessions this afternoon and tomorrow, please check them out as well. And we have three more minutes. Feel free to express your thoughts before we cut out.
Thanks everybody.
Oh, go ahead.
No, I was just saying thanks, great session, lots of fun.
I might say for the Lancaster meeting next year that Gail Ashley is I think in charge of the technical sessions, and may have already been sending out emails encouraging people to propose sessions, so I'll say that on her behalf
to convene as well it's, it's fantastic that you did this for such a remote session and and Three cheers to you for keeping it going.
Well thank you all for participating is always nice to have is such a in their disciplinary session, those are very interesting to hear from all of you and learn so much.
It's always good to see you ball.
Everyone thinks so.
Alright guys, feel free to disengage and leave.
There's a great session this afternoon. If you're interested in hard rock, as most of the people who are here, madman magma mingling, so I'm sure I'll see most of you there, this afternoon.
Have a great rest of the day.