Thermal and Structural Reconstruction of an Eroded Foreland Basin: Central Appalachian Basin, USA

Abstract

The Appalachian Basin is an archetypal foreland basin system. However, the timing, rates, and magnitudes of orogenic loading, fold-thrust belt (FTB) exhumation, and foredeep burial and exhumation are not well constrained. Here, we present a new suite of low-temperature thermochronometric and vitrinite reflectance (%R_o) data from a ~350 km transect through the Virginia-West Virginia Valley and Ridge and Appalachian Plateau. The dataset includes new zircon fission track (ZFT), zircon (U-Th)/He (ZHe), and apatite fission track (AFT) ages from Devonian, Mississippian, Pennsylvanian, and Permian strata. Following deposition of the sampled units, most ZFT grain ages were partially reset with single-grain ages spanning 1850–275 Ma, whereas ZHe and AFT grain ages were fully reset and record mostly Permian–Triassic to Cretaceous cooling. Inverse thermal history modelling (time–temperature and time-depth) coupled with structural restoration suggest that the FTB was exhuming prior to significant Pennsylvanian-Permian sedimentation. We infer burial depths ranging from 3.6 km in the western foredeep to 11 km in the FTB. Results indicate the western foredeep experienced elevated temperatures beyond what would be predicted by burial. Time-depth models support a pulse of elevated heat flow in the western foredeep in the Mesozoic, driven by crustal thinning and mantle-derived rock emplacement associated with the Rome Trough, or potentially blanketing and insulation by Permian strata. A Permian–Triassic structural reconstruction suggests that, even in Permian–Triassic time, this part of the Alleghanian orogenic wedge retained a critical taper angle of 6°–7°. The new thermal data and analyses presented here help constrain the thermo-tectonic conditions of the Appalachian foreland basin system during late Palaeozoic orogenesis, late-stage relaxation of the orogenic wedge, and Mesozoic rifting.