MISSISSIPPIAN-DEVONIAN DEXTRAL COLLISION IN THE CENTRAL APPALACHIANS: EVIDENCE FROM THE CATSKILL-POCONO CLASTIC WEDGE AND THE SOUTHERN APPALACHIAN INNER PIEDMONT

The S Appalachian Inner Piedmont has a different tectonothermal history from adjacent Carolina and the eastern Blue Ridge. The IP of SC, NC and GA enjoyed peak metamorphic conditions (up to granulite) at the Dev-Miss boundary, ca 355-365 Ma. While a Middle Ordo clastic wedge is well known in the TN-GA-AL App's, the evidence for a Dev SA clastic wedge is scant, even as a pre-Chattanooga Shale unconformity has been well known for many years. Additionally very high dextral shear strains are recorded in the eBR and western IP: γ=20 across a belt not less than 20 km wide restore IP to the central Appalachians. At these latitudes detritus shed from a collisional orogen is preserved as the Catskill and (younger and to the south) the Pocono-Price clastic wedges. Black shales preceding deposition of Catskill rocks migrate south indicating ongoing dextral translation at the Laurentian margin between the NY and VA Promontories. At the Dev-Miss boundary, between Catskill and Pocono rocks is preserved the Spechty Kopf Fm. The MDsk includes diamictites and laminites (varved claystones?) with dropstones; it is clear that formation thickness is highly variable, in valleys incised into the underlying Catskill delta. Some clasts in the diamictites are faceted and striated, and some are igneous and metamorphic clasts that are uncommon in the overlying or underlying units. These relations have led to the interpretation that these rocks represent a glacial interval that samples exotic Acadian highlands, interpreted here to be the highest structural levels of the IP. Subsequent terrane dispersal brought the IP (+/- the eBR) to its current position along strike and final late Paleozoic emplacement as a thin composite crystalline thrust sheet. I hypothesize that these wedges are derived from Laurentian-IP collision, uplifting an earlier fold and thrust belt formed from the Cambro-Ordo margin, and that clasts in the diamictites preserve the highest structural levels of the colliding IP.