LEAVING PERI-GONDWANA: MIDDLE CAMBRIAN (SERIES 2) AND YOUNGER KINGS MOUNTAIN TERRANE, CAROLINIA, SOUTH CAROLINA-NORTH CAROLINA, U.S.A

Recent isotopic data refine the Carolinian Rheic margin model for the Kings Mountain terrane presented by Dennis and Baker (2012). Near the base of the upper, epiclastic part of the Battleground Fm, about half the detrital zircons from the Dixon’s Gap metaconglomerate member are Meso- or Paleoproterozoic in age, and the remainder are Ediacaran-Cambrian. Recent single grain ID-TIMS studies show that the youngest of these grains is 521 ± 3 Ma (2σ). Above the Jumping Branch Manganiferous Member, detrital zircons from the Draytonville metaconglomerate member yield almost exclusively (>99%) grains of Mesoproterozoic-Archean age. Thus, the Jumping Branch Mn mbr is interpreted to represent subsidence and burial of the rifted Carolina arc accompanying subcrustal delamination and the transition from rifting to drifting, or at least to a more Basin and Range geometry/geography whose detrital component is sourced wholly within the Gondwanan shield. Current efforts in the overlying Blacksburg Fm seek a younger limit to the rift-drift sequence age with a crystallization age for granodiorite to dacite porphyries that cut the base of the Blacksburg section, and Sr isotopic stratigraphy to complement existing C isotope stratigraphy for the Gaffney marble and the marble member at Dixon’s Branch near the top of the Blacksburg Formation. C isotope values range from 0 — -2 per mil (PDB), typical of Middle Cambrian (Series 2), pre-SPICE values. Amphibolite sills within the marble member at Dixon’s Branch are interpreted to reflect the mafic component of bimodal volcanism accompanying ridge incision, opening of the Rheic Ocean, and departure of Carolinia from peri-Gondwana.