| Detrital apatite grains separated from Carboniferous sandstones of the Pottsville and Mauch Chunk groups exposed on the surface in central West Virginia yield (U-Th)/He apparent ages of 70 +/- 30 Ma to 132 +/- 7.4 Ma. Multi-sample means yield regional average ages of 93 +/- 12 to 95 +/- 8 Ma. These ages are interpreted with three-dimensional heat flow forward models, constrained by published fluid inclusion, vitrinite reflectance, and apatite fission track data from the region. Several exhumation scenarios are considered, each producing a surface distribution of calculated thermochronometric ages for an area around the New River Gorge. Calculated ages resulting from a simple-case, constant exhumation rate of ∼16 m/Ma from maximum burial to the present match measured apatite helium ages, but over-estimate published apatite fission-track data, suggesting a more complex exhumation history with a steeper geothermal gradient or faster exhumation during the Mesozoic. A thermal model containing time-varying exhumation rates of ∼10, ∼30, and ∼25 m/Ma with inflection points at ∼150 and ∼100 million years ago (after Reed et al., 2005) produces a compromise between apatite (U-Th)/He data from this study and published fission track ages. Topographically-dynamic exhumation models that incorporate proposed incision rates of the New River result in calculated ages that vary from 79 Ma at the base to 96 Ma at the top of the Gorge. This spread fails to be resolved in the measured samples due to abnormally high data dispersion. In lieu of compelling elevation or spatial variations in apparent ages, approximations of the timing and rate of incision of the New River Gorge remain unattainable. It is apparent that regional exhumation rates and sample quality are controlling factors in thermochonometric age determinations. These characteristics overshadow any effects due to topographic development in this slowly-exhuming, tectonically-quiescent region, which is likely dominated by erosional denudation. |
