PRELIMINARY U-PB, 40AR/39AR AND FISSION-TRACK AGES SUPPORT A LONG AND COMPLEX TECTONIC HISTORY IN THE WESTERN BLUE RIDGE IN NORTH CAROLINA AND TENNESSEE

New 40Ar/39Ar analyses of muscovite and hornblende, one U-Pb analysis of sphene, and zircon fission-track (FT) data from Mesoproterozoic basement and Neoproterozoic cover rocks suggest that the rocks in a 40 by 150 km area of the western Blue Ridge province in North Carolina and Tennessee experienced peak metamorphism in the late Ordovician and early Silurian, were retrograded and deformed in the early Mississippian, and transported westward to higher crustal levels at ~ 280 Ma in the Alleghanian orogeny. A single hornblende cooling age of ~ 450 Ma records cooling from peak Taconian amphibolite-facies metamorphism. Other hornblende data yield a younger age of ~ 430 Ma, and U-Pb sphene results are 433±7 Ma. 40Ar/39Ar cooling ages of muscovite from mylonitic rocks range from ~ 355 to ~ 330 Ma. Muscovite cooling ages and zircon FT ages of ~ 350 Ma are most likely related to deformation and retrograde greenschist-facies metamorphism in the late Devonian to early Mississippian. In the central highlands of the Great Smoky Mountains, cooling through zircon FT closure temperature occurred at ~ 280 Ma. In the northwestern part of the field area the metamorphic grade was not high enough to thermally reset detrital muscovite in the Neoproterozoic sedimentary cover rocks.