THE CAROLINA TERRANE IN NORTHWESTERN SOUTH-CAROLINA, USA - LATE PRECAMBRIAN-CAMBRIAN DEFORMATION AND METAMORPHISM IN A PERI-GONDWANAN OCEANIC ARC

The Carolina terrane comprises an exotic island are in the hinterland of the Southern Appalachian orogen. The western portions of the Caroli na terrane consist of zoned mafic-ultramafic plutonic complexes intrud ed into a pile of basalts and basaltic andesites. This sequence of coc ks has been interpreted to represent an episode of intra-are rifting p rior to regional metamorphism and deformation. New U-Pb zircon ages fr om the Mean Crossroads complex in northwestern South Carolina along th e central Piedmont suture confirm relative ages inferred from detailed mapping. Two foliated metadiorites yield U-Pb dates of 579+/-4 and 57 1+/-16 Ma, interpreted to be crystallization ages, A foliated metaquar tz diorite yields a U-Pb date of 538+/-5 Ma interpreted to be a crysta llization age. An undeformed, unmetamorphosed diorite intruding these metamorphosed zoned complex intrusive rocks yields an age of approxima te to 535 Ma. Hence we believe that intra-arc rifting and regional met amorphism and foliation development both occurred between approximate to 580 and 535 Ma, While petrographic and hr-Ar studies support subseq uent middle to late Paleozoic regional metamorphic overprint(s), or at least static recrystallization and/or uplift through hornblende-bioti te-muscovite blocking temperatures for Ar, the 535 Ma, undeformed, unm etamorphosed intrusion suggests late Precambrian-Early Cambrian region al metamorphism and deformation was the event responsible for the regi onal metamorphic fabric in this area of the Piedmont, These observatio ns contradict the idea that this metamorphism and fabric development a re related to presumed early Paleozoic accretion of the Carolina are t o Laurentia as well as correlations with Middle Ordovician fabric elem ents in the eastern Piedmont. Instead, this fabric is interpreted to r ecord a changing plate kinematics (e.g., migration of triple junction or change in relative motion vectors) during semicontinuous, diachrono us development of an island are on the Gondwanide margin.