PALEOZOIC THROUGH CENOZOIC UPLIFT, EROSION, STREAM CAPTURE, AND DEPOSITION HISTORY IN THE VALLEY AND RIDGE, BLUE RIDGE, PIEDMONT, AND COASTAL PLAIN PROVINCES OF TENNESSEE, NORTH CAROLINA, VIRGINIA, MARYLAND, AND DISTRICT OF COLUMBIA

Fission-track (FT) analysis of zircon and apatite is helping define the Paleozoic through Cenozoic history of the Valley and Ridge (VR), Blue Ridge (BR), Piedmont (P), and Coastal Plain (CP) provinces of the Eastern United States. The oldest zircon FT ages from the VR and western BR are significantly older than those of the eastern BR and P provinces. This is apparent in the ranges of both sample ages and single-grain ages.

Some VR and western BR rocks were never buried deeply enough during the Phanerozoic to obtain temperatures sufficiently high (>~225°C) to totally reset their zircon FT ages. In contrast, most zircon ages from the eastern BR and P show significant cooling from >225°C at ~300-280 Ma, most likely related to emplacement of major Alleghanian thrust sheets. Apatite FT data suggest that BR and P rocks underwent relatively slow, continuous cooling during the Mesozoic and Cenozoic, passing through the apatite FT closure temperature (~90-100°C) at a rate of about 16 m/m.y.

FT ages of detrital zircon in shallowly buried (<411 m) rocks in the CP reflect FT ages in the source terrain. The data suggest that the P and eastern BR were the major source of detritus from Cretaceous through Oligocene time. Old zircons comparable in age to those in the western BR and VR do not appear in CP rocks until early or middle Miocene. Preliminary interpretation is that major drainage from the western BR and VR was to the west prior to the Miocene--major east-flowing Mid-Atlantic rivers did not breach the Blue Ridge until early or middle Miocene time.