Structure of the Lithosphere and Conditions of Formation of Oceanic Rises in the Sub-Antarctic Sector of the South Atlantic Using Density and Physical Modeling

Abstract

The kinematic reorganization of plate boundaries, accompanied by the cessation of old spreading centers and the formation of new ones, and manifestations of plume magmatic activity in the southeastern part of the Antarctic sector of the South Atlantic led to the formation of a complex structural plan of the region. As a result of these processes, a system of ridges, rises, and plateaus with varying morphological expressions and different geophysical characteristics were formed. Results of density modeling of the crust and lithosphere structure along profiles extending from the Falkland Plateau to the Mozambique Ridge and crossing a series of rises and ridges separated by deepwater basins showed that rises have different crustal structures, indicating different origins. The conditions for the formation of different types of submarine rises were studied based on physical modeling. A new experimental model of lithosphere and submarine rises formation in the region was constructed, in which the fracture of the large Agulhas magmatic province into the Agulhas Plateau and the Northeast Georgia rise played an important role, as did the accretion of oceanic crust on the Agulhas spreading ridge and subsequent jump of the spreading axis, leading to the cessation of spreading on this ridge and the formation of the southern segment of the Mid-Atlantic Ridge and its associated Meteor and Islas Orcadas rises. Jumps of spreading axes, accompanied by the periodic activity of hotspots, played an important role in the formation of submarine rises of different genetic types, which determined the different structures of their crust.