GEOCHEMISTRY AND PROVENANCE OF INNER PIEDMONT PARAGNEISSES, NC AND SC: EVIDENCE FOR AN INTERNAL TERRANE BOUNDARY?

The southern Appalachian crystalline core remains one of the least studied and possibly most over-interpreted subdivisions of the Appalachian orogen. Recent geochemical and geochronologic work has focused on Grenville basement and Paleozoic intrusives while largely ignoring the crustal affinity of the areally extensive and structurally complex paragneisses. Our work represents the first detailed analysis of crustal affinity for numerous lithotectonic units within the Blue Ridge (BR) and Inner Piedmont (IP). Rocks within the BR and IP crystalline core are polydeformed and regionally metamorphosed up to granulite facies, with the IP representing a sizeable area of sillimanite (I and II) grade assemblages. Geochemistry and ion microprobe data from IP and eastern BR paragneisses supports the correlative nature of psammitic paragneisses across the Brevard fault zone. Zircon rim growth in the crystalline core is either Grenville (~1.0-1.1 Ga) or Paleozoic (~350 Ma). A major structural boundary, the Brindle Creek thrust, has been identified in the central NC IP. This fault separates mostly NE-SW trending structures in the footwall from E-W trending structures in the hanging wall with no change in metamorphic grade (sillimanite and migmatitic on both sides). Preliminary data from the central NC IP suggest that the Brindle Creek thrust may separate rocks solely containing Middle Proterozoic (Grenville) zircons in the hanging wall from rocks containing Grenvillian and Neoproterozoic zircons in the footwall. Based on the lithologic and structural characteristics, the NC Brindle Creek thrust is roughly correlative to the SC Six Mile and GA Toccoa Falls-Shorts Mill thrusts and the NC-SC Mill Spring fault is roughly correlative to the Walhalla thrust sheet. SHRIMP analyses of zircons from samples in the SC Six-Mile and Walhalla thrust sheets will further delimit the provenance and crustal affinity of several major lithotectonic units within the IP. Additionally, monazite ages from samples within the eastern BR and IP will constrain the timing of Paleozoic metamorphism in the crystalline core.