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Abstract

Field, seismic, and drill-hole data provide a wealth of information about the tectonic processes associated with rifting, breakup, and the early stages of seafloor spreading for the passive margin of eastern North America. The onset of rifting, from Florida to the Canadian Grand Banks, was approximately synchronous, occurring by Late Triassic time. The cessation of rifting (and presumably the onset of drifting) was diachronous, occurring first in the southeastern United States (latest Triassic), then in the northeastern United States and southeastern Canada (Early Jurassic), and finally in the Grand Banks (Early Cretaceous). The Central Atlantic Magmatic Province developed simultaneously (earliest Jurassic, ~200 Ma) throughout eastern North America. This magmatic activity occurred after rifting in the southeastern United States, and during rifting in the northeastern United States and maritime Canada. The passive margin, from Florida to southern Nova Scotia, is volcanic, characterized by seaward-dipping reflectors (SDRs) near the continent-ocean boundary. The remainder of the passive margin lacks SDRs and is, thus, non-volcanic. In the continental crust, most rift-related structures parallel preexisting zones of weakness created by Paleozoic and older orogenies. Few transfer zones exist, and these also parallel the pre-existing fabric. In the oceanic crust, fracture zones parallel the direction of relative plate motion. Thus, the trends of the fracture zones in the oceanic crust differ from the trends of the rift-related structures in the continental crust. The deformational regime changed substantially after rifting throughout eastern North America: post-rift shortening (inversion) replaced syn-rift extension. Detached structures associated with salt movement also developed after rifting, especially on the Scotian shelf and Grand Banks.

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