RIFTING, DRIFTING, MAGMATIC ACTIVITY, AND BASIN INVERSION ON THE PASSIVE MARGIN OF EASTERN NORTH AMERICA

The tectonic development of the passive margin of eastern North America between the Carolina trough and Scotian basin was considerably more complex than the classical two-stage, rift-drift model. Firstly, the transition from rifting to drifting was diachronous. In the southeastern United States, the rift-drift transition occurred after Late Triassic synrift deposition and before CAMP (Central Atlantic Magmatic Province) magmatism in earliest Jurassic time (~200 Ma). In maritime Canada, the rift-drift transition occurred after CAMP magmatism and synrift deposition in Early Jurassic time and before postrift deposition in early Middle Jurassic time (~185 Ma). Secondly, on both the southern and northern segments of the margin, the deformational regime changed substantially after rifting. Generally, NW-SE postrift shortening replaced NW-SE synrift extension. NE-striking reverse faults formed, and many of the rift-basin boundary faults had reverse displacements (inversion). In the southeastern United States, the change in the deformational regime occurred in Late Triassic/Early Jurassic time during the rift-drift transition. Simultaneously, diabase sills and dikes, many striking perpendicular to the trend of the rift basins, intruded the attenuated continental crust, and a massive wedge of presumed volcanic or volcaniclastic rocks developed near the continent-ocean boundary. In maritime Canada, the change in the deformational regime occurred during or after Early Jurassic time and before or during Early Cretaceous time (i.e., during the rift-drift transition and/or early stages of seafloor spreading).