Tectonics of the Southern Ocean Passive Margins in the Africa–East Antarctica Region

Аннотация

Based on geological and geophysical data for the conjugate Africa–East Antarctica margins, the peculiarities of preparation of the breakup of central Gondwana are discussed. When using the historical approach, a significant inheritance of the Middle-Upper Jurassic tectono-magmatic development from the preceding time is shown. The first location of tectono-magmatic activity in zones of weakness on the proximal margin, its subsequent migration to distal margins, and further opening of the ocean is established. The geochemical features of magmas of the region and their sources are discussed. Evidence is presented for the decisive influence of the Karoo–Maud plume on the development of magmatism. A significant feature of plume manifestation is considered: the presence of high-magnesian ferruginous picrites, formed by melting of a pyroxenite source with specific composition, coinciding with the central part of the plume and corresponding to the earliest eruptions. We determined the source of magmatism at the initial stage could have been the substance of a rising plume, and magmas reached the surface through existing fractures without interacting with the lithosphere. In the course of evolution, the admixture of pyroxenites in the source decreased and the melts acquired the features of melting lithospheric mantle, which was reflected in the isotopic characteristics of melts with a predominant enriched EM2 component. The structure and magmatism of the Southern Ocean and South Atlantic are compared. Also discussed the locations of the Mesozoic Karoo–Maud and Tristan plumes, as well as the zones of subsequent breakup of Gondwana, above the margins of the African superplume, indicating a relationship between surface and deep-seated events.