RELATIONSHIPS BETWEEN ACADIAN/NEOACADIAN TECTONISM (DEVONIAN-MISSISSIPPIAN) ALONG THE EASTERN MARGIN OF LAURUSSIA AND COEVAL SEDIMENTATION IN THE APPALACHIAN FORELAND BASIN

Structural and terrane analyses in the Appalachians, along with patterns of black-shale distribution in the Appalachian basin, now permit more direct correlations between Devonian-Mississippian tectonic events along the eastern margin of Laurussia and sedimentary events in the Appalachian foreland basin. Black-shale deposition is especially telling in this regard because the shales are thought to represent the timing of major deformation loading in the orogen. The tectonic events at this time are related to the northwestward convergence of the Carolina terrane with eastern Laurussia. The docking of Carolina began in Early Devonian time near the New York promontory and ended in Late Devonian time with an oblique, transpressive, zippered collision between Carolina and Laurussia. This convergence resulted in the development of Appalachian black-shale basins, as well as their subsequent southwestward migration during the zippering collision. These black-shale basins and the accompanying Catskill clastic wedge developed during three Acadian tectophases with a total duration of about 51 Ma. In latest Devonian time, the tectonic regime changed as the northern end of Carolina apparently collided with the New York promontory and the Avalon and Meguma terranes, which were being “ejected” southwestwardly along dextral faults in a pincer movement between Gondwana and Laurussia. This event, the Neoacadian orogeny, created a major metamorphic/deformational complex in southern New England around the New York promontory, and by earliest Mississippian time initiated the Sunbury-Riddlesburg black-shale basin and the overlying Price-Pocono-Borden-Grainger clastic wedge. As terrane ejection continued, dextral shear was transferred to the newly accreted Carolina terrane, causing it to move in a southwestward transpressional regime that generated new deformational loading and clastic sources at the Virginia promontory. The southwestwardly expanding Sunbury basin and overlying clastic wedge developed during the fourth tectophase, which lasted about 36 Ma until the end of Mississippian time. The long duration of the fourth tectophase during Neoacadian orogeny may reflect the fact that dextral lateral translation from the central to the southern Appalachians involved the entire 650-km length of Carolina.