Inferences regarding initiation of oceanic crust formation from the U.S. East Coast margin and conjugate South Atlantic margins

Abstract

Listen

Translate article

The U.S. East Coast volcanic continental margin is compared and contrasted with volcanic continental margins of the South Atlantic (Pelotas and Walvis basins). Seismic reflection data acquired by the EDGE project off the US East Coast, supplemented by wide-angle reflection and refraction surveys, provided the best data across this margin. One important geophysical feature associated with this margin is the presence of a very prominent Total Intensity magnetic anomaly that lies over the Continental Slope. The East Coast Magnetic Anomaly may be associated with the seaward dipping reflectors (SDR's) along the US East Coast and this wedge is interpreted to be a part of the Initial Oceanic Crust. Migration of the seismic reflection data suggested that the strongly reflecting continental crust ended abruptly at an interface with a steep landward slope. It seems that the dipping reflectors, the underlying intrusive material, and the high velocity material lying further below (interpreted earlier as underplated material) actually constitutes the earliest crust and upper mantle generated at the time of the initial opening of the ocean. The volcanic complex of the Parana-Etendeka continental flood basalts and the SDR's of the Pelotas and Walvis basins are the result of the rifting and subsequent breakup of the South American and African plates under an initial influence of the Tristan da Cunha hotspot. The SDR's wedges of Pelotas and Walvis basins were emplaced after continental breakup at least partially over an extended continental crust. Two major SDR's provinces characterize the South Atlantic: Santos-San Jorge (South America) and Walvis-Orange (Africa) provinces. These provinces form a broad and symmetrical volcanic complex. It is proposed that these SDR's provinces were emplaced as a subaerial oceanic ridge that would represent the initial stage of formation of the oceanic crust in most passive margins.