|Northeastern Section - 36th Annual Meeting (March 12-14, 2001)|
|Paper No. 15-0|
|Presentation Time: 8:30 AM-12:00 PM|
THE COASTAL VOLCANIC BELT (CVB), EASTERNMOST MAINE: GEOCHEMISTRY AND TECTONIC SETTING
LLAMAS, Aranzazu Piņan and HEPBURN, J. Christopher, Department of Geology and Geophysics, Boston College, Chestnut Hill, MA 02467-3809, firstname.lastname@example.org|
The Eastport-Machias area of easternmost Maine contains a thick sequence of well preserved and well dated Silurian and Early Devonian volcanic rocks generally assumed to have peri-Gondwanan affinities. Forty-nine samples of the volcanic members of this sequence, as well as the overlying Perry Fm., have been analyzed for both major and trace elements. The rocks range from basalts to rhyolites and give a bi-modal distribution on an alkalis vs. silica plot as previously noted by Gates and Moench (1981). However, immobile trace element concentrations (Zr/Ti vs. Nb/Y) of the samples indicate these rocks form a continuous sub-alkalic sequence between basalt and rhyolite, with the majority of the more mafic samples lying in the basaltic andesite and andesite fields. Silurian mafic rocks from the Dennys, Edmunds and Leighton Fms. contrast with those from the Early Devonian Eastport and Late Devonian Perry Fms., having generally lower contents of Nb, Zr, Y, Ti and P and higher values of Cr and Ni. The Silurian basaltic to andesitic samples are high-alumina, calc-alkalic rocks that plot in the volcanic arc fields on various tectonic discrimination diagrams. Likewise, the Silurian felsic rocks also indicate volcanic arc affinities on granitic discrimination diagrams. In contrast, the post-Acadian Perry Fm. yields a clear within-plate geochemical signature. However, the tectonic environment in which the volcanics of the Eastport Fm. erupted is more difficult to establish and may be somewhat transitional in nature. While felsic rocks from the Eastport give within-plate signatures, characterization of the mafic rocks is less clear. We interpret the geochemistry of the volcanic rocks of the CVB in the Eastport-Machias area as pointing to volcanic arc activity throughout the Silurian. By Early Devonian, the tectonic setting was changing from an arc to likely one of extension or transtension. By Late Devonian, the CVB was clearly in a within-plate tectonic setting.
Northeastern Section - 36th Annual Meeting (March 12-14, 2001)
General Information for this Meeting
|Session No. 15--Booth# 6|
Hydrogeology and Geochemistry (Posters)
Sheraton Burlington: Lake Champlain Exhibition Hall
8:30 AM-12:00 PM, Tuesday, 13 March 2001
© Copyright 2001 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.