EXPLORING THE EXTENT OF CENOZOIC CENTRAL APPALACHIAN EXHUMATION USING TARGETED LOW-TEMPERATURE APATITE (U-TH)/HE THERMOCHRONOLOGY

The debate over the timing, extent, and mechanism(s) driving Eastern North American margin (ENAM) Cenozoic topographic evolution has been reignited in light of recent and continued research on: (1) Cenozoic Virginia volcanism, (2) identification of the Central and Northern Appalachian low-velocity seismic anomalies (CAA, NAA), (3) ENAM lithospheric structure, (4) characterization of thermal springs, (5) the Cenozoic sedimentation record, and (6) Appalachian landscape disequilibrium and variable erosion rates. Despite these advances from a variety of fields, no substantial Cenozoic exhumation has been documented in the low-temperature thermochronologic record from the Central Appalachians.

Low-temperature apatite (U-Th)/He (AHe) and apatite fission track (AFT) thermochronometers access temperatures of ~70°C and ~100°C, respectively, and are used to constrain rock cooling, commonly via exhumation, through the upper ~2-4 km of the crust. Previous studies report spatially variable dates from ~200-100 Ma, which are interpreted as evidence for westward escarpment retreat following passive margin initiation, and limit Cenozoic exhumation to <2 km. No AHe data exist from within the CAA footprint, and limited AFT data are from high elevations, which are least likely to record Cenozoic exhumation.

We collected and processed 16 samples for AHe analysis from a ~200-km-long transect, oriented perpendicular to the axis of the Central Appalachian orogen in Virginia and West Virginia (primarily along U.S. Route 250). The transect crosses the CAA, zones of Cenozoic volcanism, and major physiographic provinces including the Piedmont, Blue Ridge, Valley and Ridge, and Allegheny Plateau. Samples from the Valley and Ridge and the Allegheny Plateau provinces access >1000 m of relief with particular focus given to sampling deeply incised gorges from both the east and west side of the highlands. Deeply incised, low elevation samples are most likely to record previously unidentified Cenozoic exhumation, if indeed enough exhumation has occurred to capture it using AHe thermochronology.

Preliminary AHe results will be shared in September.