52 Provenance of the Eastern North American Margin: From Triassic Rifting to Modern Sedimentation

Sunday, 22 March 2020
8:00 AM - 12:00 PM
Lake Fairfax

SPATIALLY VARIABLE BURIAL AND EXHUMATION HISTORY OF THE CENTRAL APPALACHIAN MOUNTAINS FROM ZIRCON (U-TH)/HE THERMOCHRONOLOGY

Paper number: 52-3
Program: Theme Sessions
Time: 8:25 AM – 8:45 AM

Authors

Abstract

Recent geophysical, geomorphic and geochronologic work along the Eastern North American Margin (ENAM) has generated a debate about the timing, mechanism(s), and magnitude of post-rift topographic evolution. Our research constrains the mid-temperature evolution of the Central Appalachian Mountains using zircon (U-Th)/He (ZHe) thermochronology (closure temperature ~150-220°C), where ~1400 m of topographic relief is co-located with a low-velocity seismic anomaly, thermal springs, Eocene volcanics, drainage re-organization, and topographic disequilibrium. Our goal is to document the timing and magnitude of post-orogenic exhumation and assess the role, if any, mantle anomalies have in driving uplift.

Previous studies report ~900-300 Ma zircon fission track (ZFT) dates (closure temperature ~220-260°C) and ~200-100 Ma apatite fission track (AFT) dates (closure temperature ~110°C), both of which young to the east and have been interpreted as evidence for westward escarpment retreat following rifting. We systematically employ ZHe thermochronology across a 200-km-long transect orthogonal to the Appalachian orogenic front, which covers >1000 m of relief in West Virginia-Virginia, to bridge the gap between ZFT and AFT data and assess the regional pattern of foreland basin (modern Appalachian Plateau and Valley and Ridge) burial and erosion and the post-orogenic exhumation of the orogenic core (Piedmont).

ZHe results display an eastward younging trend, from ~450 Ma in the Appalachian Plateau to ~150 Ma in the Piedmont. The westernmost ZHe dates pre-date depositional ages, whereas central and eastern ZHe dates post-date depositional ages. In the foreland. Eastward younging suggests greater burial and exhumation towards the east, while ZHe data in the Piedmont reflect significant post-rift exhumation. Inverse thermal modeling using HeFTy (1) limits western burial to 170˚C, (2) imposes minimum post-depositional reheating of 220˚C on eastern samples, (3) suggests an earlier onset of exhumation in the Valley-Ridge than the Appalachian Plateau, consistent with Alleghenian uplift, and (4) provides only limited constraints on potential Cenozoic exhumation that may be associated with mantle anomalies.

Geological Society of America Abstracts with Programs. Vol. 52, No. 2

doi: 10.1130/abs/2020SE-344484

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