INTEGRATING OBSERVATIONS OF ALLEGHANIAN PLUTONISM, THRUST FAULTING, LITHOSPHERIC DELAMINATION, AND THE FINAL CLOSURE OF THE RHEIC OCEAN IN THE CAROLINAS AND GEORGIA

Two discrete subcrustal lithospheric delamination events occurred within accreted Carolinia on the Laurentian margin in the Upper Pennsylvanian and Upper Mississippian during the penultimate stages of Pangaean assembly. The timing and location of asthenospheric slab windows formed during these delamination events, and the dimensions of the removed delaminated lithosphere are preserved in two linear belts of Alleghanian granite plutons intruded at 326-323 Ma (older, western belt) between Hyco Lake, NC and Whitmire, SC, and 310-305 Ma (younger, eastern belt) between Rockingham, NC and Juliette, GA. The western and eastern belts of plutons formed by in-situ melting of Carolina terrane crust as that crust came in contact with rising asthenosphere; we estimate the depth of this melting at 44 km. The asthenospheric window opened at the site of what would become the Rheic suture, along the Charleston terrane -Carolina terrane boundary. Removal of subcrustal lithosphere permitted thin-skinned thrusting of the Carolina terrane nominally 80-140 km northwest following the intrusion of the western belt of plutons. Between the 326-323 and 310-305 events there was 500 km of dextral slip. An additional nominal 50-120 km of northwest transport followed intrusion of the eastern belt of plutons; we use the location of the Rheic suture to pin these displacements. Thus, we interpret the dimensions of delaminated slabs to have been 360 km (along-strike) x ≥100 km (displacement along overthrust) x 100 km (thickness of subcrustal lithosphere) in the Upper Mississippian, and 480 km (along-strike) x ≥100 km (displacement) x 100 km (thickness) in the Upper Pennsylvanian. We interpret the discrete difference in timing between the two events to be the result of a large inherited fracture zone (ca 520 Ma) internal to the Carolina terrane, roughly orthogonal to the suture. This model reconciles the dextral, northeast-to-southwest closure of the Rheic Ocean with timing and location of the western and eastern granite belts, and coeval thin-skinned thrusting in the Piedmont with that in the Valley-and-Ridge. Additionally, this hypothesis may provide better understanding of the location of the Rheic rift-drift stratigraphy of the Kings Mountain terrane well west of comparable basement and cover stratigraphy of the eastern Piedmont.