POST-OROGENIC THERMAL HISTORY AND EXHUMATION OF THE NORTHERN APPALACHIAN BASIN CONSTRAINED THROUGH LOW-TEMPERATURE THERMOCHRONOLOGY

The Northern Appalachian Basin, located in Pennsylvania (PA) and New York (NY), contains a well-preserved sedimentary record as well as significant unconventional reserves of gas. Our goal is to constrain the post-orogenic thermal history and exhumation of the Northern Appalachian Basin by application of low-temperature thermochronology. We also address the significance of an enigmatic Cretaceous (~120 Ma) rapid cooling event that is observed on the eastern side of the basin, as well as many locations along the eastern US and into Canada. Apatite fission-track (AFT) data (i.e. ages, track lengths, composition proxies) were collected from Devonian strata, typically sandstones (stratigraphically close to the Marcellus Shale) along an east-west transect straddling the NY-PA border. Combined with existing stratigraphic and maximum paleo-temperature constraints (i.e. conodont alteration index and vitrinite reflectance), inverse thermal models with resultant best-fit time-temperature envelopes constrain the post-orogenic thermal history and the correlative tectonic events that the sample has experienced. AFT ages range from 170-125 Ma, with mean confined tracks of 14-13 µm. All samples reached temperatures higher than the retentivity of fission tracks in apatite (i.e., >~110-120 °C). Thermal maxima in basin samples was reached during the Alleghenian Orogeny (mid-Pennsylvanian). Samples resided at depth until relatively quick cooling began during the mid-Triassic until early Cretaceous. The most rapid period of cooling is near-coincident with the intrusion of kimberlite dikes at ca. 150-120 Ma. Of significance, the onset of cooling from maximum temperatures for our basin samples began earlier in the west (ca. 220 Ma) and gets younger to the east. This may be due to sediment thickness or effects from the passage of the Great Meteor hotspot, however the mechanism for differential onset of cooling in the Northern Appalachian Basin is still to be determined.