THE CAROLINIAN RHEIC TRAILING MARGIN

A detrital zircon study was made at four sites in the Battleground and Blacksburg Formations in the Kings Mountain terrane of the Carolina composite terrane. At Dixon’s Gap (DG) and Stepp’s Gap, the oldest metaconglomerates contain detrital zircon populations that are dominated (ca. 50%) by grains Ediacaran to Cambrian in age; the youngest grains are 503.2 ± 11.7, 509.8 ± 7.1, 510.7 ± 7.6, 514.8 ± 4.5, 516.7± 10.1, 517.6 ± 12.2 Ma (1σ, 89-110% concordant). Near the top of the Battleground Fm at Draytonville Mtn (DV) the youngest two grains are 607.8 ± 17.4 Ma and 906.3 ± 32.6 Ma. The sandstone at Whitaker Mtn, the stratigraphically highest member of the Blacksburg Fm yields entirely almost entirely Mesoproterozoic ages with no grain younger than 927.9 ± 37.4 Ma. We interpret the Kings Mountain t to preserve the Rheic rift-drift sequence formed as Carolinia rifted from the Amazonian craton in the Middle to Late Cambrian. Between DG and DV times, the Ediacaran-Cambrian volcanic sequence was uplifted, eroded, subsided and covered by sediments derived from the Amazonian craton. The dramatic change in provenance of the DV member with the virtual disappearance of Ediacaran–Cambrian grains records the advent of Rheic drift sequence. We place the rift-drift transition at the very fine-grained rocks of Jumping Branch Mn Member between DG and DV, and ascribe the fine grain size of this unit to transgression accompanying subsidence. The Mesoproterozoic detrital zircon age spectrum for all three units is consistent, with peaks at ≈ 1200, 1230, 1335, 1500, 1550, 1775 and ca. 2000 Ma. Archean grains are present, and the oldest grain measured is 3254.9 ± 1.6 Ma. We expect the age of hypabyssal intrusive rocks (dacites) on either side of the Kings Creek shear zone to be Furongian. Our data is consistent with the conclusion of Horton et al (1987) that the metamorphic fabric of these rocks is Upper Mississippian. The Tinsley Bridge fault juxtaposes the Kings Mountain and Charlotte ts and is crosscut by the Pacolet granite.