PROVENANCE OF POLYMICTIC CONGLOMERATES IN THE CATSKILL-POCONO CLASTIC WEDGE: IMPLICATIONS FOR THE INNER PIEDMONT OF THE CAROLINAS AND DEVONIAN-MISSISSIPPIAN COLLISIONAL TECTONICS IN THE CENTRAL APPALACHIANS

The Inner Piedmont of the Carolinas, Georgia, and Alabama has a tectonothermal history that is different and distinguishable from the adjacent Carolina terrane, and the eastern Blue Ridge. The IP of SC-NC-GA enjoyed peak metamorphic conditions (up to granulite facies) at the Dev-Miss boundary, ca 355-365 Ma. Recent U-Pb geochronology for the central BR, east of the Hayesville f., indicates eclogite and granulite facies conditions ca. 458-459 Ma. The composite Carolina terrane in SC experienced peak metamorphic conditions at the Camb-Precamb boundary ca. 540 Ma. All three composite terranes record effects of the Carboniferous continental collision. While a Middle Ordo clastic wedge is well known in the TN-AL-GA Appalachians, the evidence for a Dev Southern Appalachian wedge is less obvious. Evidence supports very high dextral shear strains in the eastern BR and western IP. Nominal shear strains of g³20 across a belt not less than 20 km wide restore the IP to the central Appalachians. The Catskill and Pocono-Price wedges record deposition of detritus of a collisional orogen. Detrital zircons and sandstone petrology of the Catskill rocks suggest a recycled orogenic provenance. At the Dev-Miss boundary, between the Catskill and Pocono rocks an unusual lithology is preserved. The Spechty Kopf (PA) and Rockwell (MD-WV) Fms include diamictites and laminites (varved claystones?) with dropstones. It is clear that formation thickness is highly variable in MDsk, and is suggestive of deposition in valleys incised into the underlying Catskill delta. Some clasts of the MDsk diamictites are striated, and some represent igneous and metamorphic clasts that are uncommon in the overlying or underlying units. These relations, with other regional data, have led to the interpretation that MDsk represents a glacial interval that samples exotic Acadian highlands. Thus the hypothesis that the Dev-Miss wedges may be derived from higher structural levels of the IP during dextral IP collision with Laurentia may be testable. Such a approach requires indirect methods because U-Pb monazite ages (ca. 359 Ma, 6/8 TIMS) and Ar-Ar mineral ages from the Alto Allochthon indicate the western IP cooled through hornblende blocking temperatures by ca. 350 Ma but did not cool through the blocking temperature for muscovite before ca. 315-316 Ma.