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

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.