Peri-Gondwanan Lithospheric Fragments In the Southern Appalachian Orogen

Peri-Gondwanan lithospheric fragments spalled from their source areas following the break up of Rodinia were accreted to the southern Appalachians during closure of the Iapetus Ocean, a step towards the amalgamation of Pangea. Their distribution has yet to be fully delineated because the juncture of Laurentian and Gondwanan lithospheres, the main Iapetan suture (MIS), has not been identified in the southern Appalachians.

South of the Virginia promontory, Neoproterozoic to earliest Paleozoic, peri-Gondwanan magmatic arc rocks of composite Carolinia are juxtaposed against peri-Laurentian rocks along the late Paleozoic central Piedmont shear zone (cPsz); here, the MIS is likely buried beneath the cPsz. Although the MIS is unexposed, most workers concur that Carolinia accreted to Laurentia by the Late Ordovician on the basis of paleomagnetic data, timing and style of penetrative deformation, and the stratigraphic record on the Laurentian margin. The departure of Carolinia from its Gondwanan source is likely recorded by Early Cambrian-Middle Ordovician gabbro of the Stony Mountain suite, which intrudes all younger arc units, predates regional tectonism, and is geochemically consistent with an arc rift setting.

North of the Virginia promontory, the Chopawamsic magmatic arc (Cma), of unknown affinity, intervenes between Laurentian and Carolinian elements; stratigraphic and Pb-isotope data indicate that the Cma may be of peri-Gondwanan origin. The arc is sutured to peri-Laurentian rocks along the Chopawamsic fault, which appears to be stitched by the 444 Ma, Ellisville pluton; this fault may represent the MIS. The Smith River allochthon, once hypothesized to represent a peri-Gondwanan fragment, is now recognized to be Laurentian on the basis of detrital zircon data.

Carolinia is conventionally viewed as the southerly extension of Avalonia; however, the two differ in terms of timing of magmatic arc cessation and Paleozoic tectonic histories. Rather, Carolinia shares more similarities with the northern Appalachian Ganderia.