PRELIMINARY P-T-T INVESTIGATION OF RUTILE-BEARING PELITIC SCHISTS IN THE SOUTHERN APPALACHIAN BLUE RIDGE

Over the past decade, geochronology studies in the southern Appalachians have focused on zircon, monazite, and mica ages to confirm the occurrence of a major Taconic event (~460-450 Ma) affecting the Western and Central Blue Ridge, followed by a younger NeoAcadian (~360-345 Ma) event affecting the Eastern Blue Ridge and Piedmont. Peak conditions of granulite facies metamorphism are estimated at ~850°C (garnet-biotite) and 7-9 kbar (GASP) for sillimanite schists at Winding Stair Gap (WSG), but thermobarometric studies of metasedimentary rocks in the region are limited and consequently P-T-t-D paths are poorly understood. Further, relating zircon U-Pb dates to petrologic context is challenging, adding complexity to the interpretation of the ages. Many details of the orogenic processes in the region remain unanswered, such as the depth of burial, rates of burial, cooling, & exhumation of various terranes, and variation of ages along strike. Rutile provides a robust, high-temperature U-Pb geochronometer that forms during metamorphic reactions and is a key phase for applying several thermobarometers (e.g., GRAIL, GRIPS) in the determination of P-T conditions. We have begun a study of rutile-bearing metapelitic schists in the Blue Ridge, and our goal is to obtain U-Pb isotopic and trace element analyses on rutile for age constraints as well as major element mineral data for thermobarometric constraints; here we report initial results of our investigation. Initial sampling indicates that rutile-bearing schists are somewhat sparse across the orogen, but have been confirmed in the Great Smoky Group of the Western Blue Ridge as well as in the Cartoogechaye & Cowrock terranes of the Central Blue Ridge, all of which were metamorphosed to high grades during the Taconic Orogeny. Rutile is found in both kyanite- and sillimanite-grade rocks, primarily as a matrix phase associated with biotite. Common assemblages in these rocks include garnet, biotite, muscovite, quartz, opaques, plagioclase, ±kyanite, ±sillimanite, and ±staurolite. Rutile is especially common in the shooting creek schist and in lithologies at Winding Stair Gap.