TRACKING ACROSS THE SOUTHERN APPALACHIANS: EASTERN TENNESSEE AND WESTERN CAROLINAS

Fission-track (FT) ages have been determined on apatite and zircon from rocks along a transect extending from eastern Tennessee through western North Carolina into northwestern South Carolina, and from the Great Smoky Mountains northeast to the Grandfather Mountain area.

In the central highlands of the Great Smoky Mountains, zircon FT data from the upper plate of the Great Smoky fault indicate that the rocks underwent rapid cooling through the zircon closure temperature (~235°C) at ~280 Ma (early Permian). This cooling most likely was related to rapid uplift and denudation of upper plate rocks associated with emplacement of the Great Smoky and related thrust sheets during the late Paleozoic Alleghanian orogeny. Most rocks yield significantly older zircon FT ages in all directions away from the central highlands, suggesting that the central highlands is a paleothermal dome, formed during or after emplacement of the Great Smoky thrust sheet. Neoproterozoic and Paleozoic rocks in the northwesternmost Blue Ridge and in the Valley and Ridge have never been buried to temperatures sufficient to totally anneal fission tracks in zircon; in some of these rocks, zircon may have undergone little if any postdepositional annealing.

The FT data indicate that the entire study region, with the possible exception of the northwestern Blue Ridge and the Valley and Ridge, was still at temperatures >100°C in the early Mesozoic. Beginning no later than Late Triassic or Early Jurassic, the region has undergone uplift through the apatite closure temperature (90-100°C) and denudation at rates that, on average, are very slow (~20 m/m.y.). Apatite FT data record similar slow regional uplift in the northern Blue Ridge in Virginia. The one known exception in this regional pattern is the Grandfather Mountain window, which shows significant Cretaceous cooling.

In the Great Smoky Mountains, the apatite data suggest that continuing uplift has been accompanied by Late Cretaceous or younger offset (southeast side up) on one or more faults in the upper plate of the Great Smoky fault, most likely including the Gatlinburg fault system. In contrast, neither the apatite nor the zircon ages show any detectable change across the Brevard fault zone, suggesting there has been no significant vertical displacement on the Brevard fault since the late Paleozoic.