THE ROLE OF DELAMINATION IN PANGAEAN ASSEMBLY IN THE SOUTHERN APPALACHIANS AND THE CRYPTIC RHEIC SUTURE

Recognition of 1) deformed and undeformed upper Mississippian (western) and middle to upper Pennsylvanian (eastern) granites and 2) an allochthonous crystalline Piedmont above the Laurentian margin are the most significant discoveries in the southern Appalachians in the past fifty years. The two observations can be reconciled with a hypothesis that two subcrustal lithospheric stubs were delaminated from accreted Carolina at the times of pluton emplacement. Removal of rigid lithospheric mantle 360 km long x >100 km (across strike) x 100 km thick at 326-323 Ma resulted in partial melting of lower-middle crustal Carolinia and emplacement of Bald Rock, York, Clover, High Shoals, Mooresville, Landis and Churchland plutons, and emplacement of a composite Inner Piedmont-Charlotte terrane – Kings Mountain terrane thrust sheet. Ca 323 Ma retrogression along the Brindle Creek unconformity within the Inner Piedmont was part of this event. We interpret that a ca. 520 Ma fracture zone inherited from the rifted Rheic margin of Carolinia separated these rocks from a 500 km long Eastern Piedmont – Carolina slate terrane that underwent 500 km dextral translation prior to a second delamination event at ca 310 Ma. Partial melting of mid-lower crust Carolinia yielded the Dames Ferry, Rockville, Siloam, Sparta, Meriwether/ Clarks Hill, Winnsboro, Columbia, Liberty Hill Pageland, and Lilesville plutons. An additional 50-120 km of northwest thrust transport followed intrusion of the eastern belt. We use the Carolina terrane – Charleston terrane boundary to pin each delamination event, and estimate dimensions of delaminated subcrustal lithosphere and check against overthrust estimates. The boundary between the two overthrust blocks is nominally the Carolina slate-Charlotte terrane boundary. This agrees with the changing character of this boundary along its strike. These two delamination events adjacent to the Carolina-Charleston terrane boundary are interpreted to have destroyed rocks that might be recognized as the Rheic suture.