DETRITAL-ZIRCON PROVENANCE ANALYSIS OF NEOACADIAN GLACIAL DIAMICTITES FROM THE CENTRAL APPALACHIAN BASIN: TESTING FOR INNER-PIEDMONT-TERRANE DEXTRAL TRANSLATION USING CLAST GEOCHRONOLOGIC AND PROVENANCE ANALYSIS

Neoacadian orogenesis primarily involved dextral transpressional collision of outboard terranes (Inner Piedmont [IP]) with the eastern Laurentian margin. The IP in the southern Appalachians is one of the largest sillimanite-grade terranes in the world and was the Neoacadian metamorphic core, but it was purportedly not in its current position along strike when it experienced peak conditions at the Devonian–Mississippian boundary. IP peak metamorphism is ca. 365–355 Ma while peak metamorphism in the adjacent Eastern Blue Ridge is ca. 465–455 Ma (Taconian) and correlates with formation of the Ordovician clastic wedge of central Tennessee. However, little to no clastic response was recorded in the stratigraphic record due to IP exhumation in the southern Appalachians. Hence, it has been proposed that the IP’s original docking point was farther northeast in the central to northern Appalachians, where deposition of the Devonian Catskill clastic wedge correlates closely with the time of peak crustal thickening in the IP and in central New England. The IP was likely translated ~400 km to its current position during deposition of the Lower–MiddleMississippian Borden-Grainger-Price-Pocono clastic wedge in the northern and central Appalachians, the deposition of which also migrated southward in time. Part of this wedge, the Devonian–Mississippian Rockwell Fm. of the east-central Appalachians, is a glaciogenic sequence containing first-cycle plutonic and recycled sedimentary clasts. If palinspastic restoration of the IP restricts its location to a position between the NY and VA promontories and links uplift, resulting from ca. 360–345 Ma orogenesis in the IP with Devonian–Mississippian clastic wedges, it is possible that this glaciation was sampling exotic highlands of the IP. To test this hypothesis, we will conduct U-Pb geochronologic analysis of magmatic zircons from large granitic clasts and detrital zircon in their enclosing diamictite matrices. Also analyzed as “detrital” will be two bulk samples comprising 28 small granite clasts as an estimate of the source age profile (each clast is too small to yield significant zircon crystals for dating individual clasts). Granite clasts from diamictites are more accurate provenance indicators as they are first cycle material reflecting the immediate source.