Small ocean basin development along the Scotia-Antarctica plate boundary and in the northern Weddell Sea

The oceanic crust of the northern Weddell Sea and Scotia Sea contains the following principal morphostructural elements: (1) the South Scotia Ridge and the South Orkney Microcontinent, both with continental crust; (2) the oceanic Powell and Jane basins; and (3) Jane Bank, which belongs to an island arc. The analysis of MCS profiles and of gravimetric and magnetic data from Russian, Italian and Spanish cruises, supplemented with satellite gravimetric data, has enabled us to determine the relationship between these elements and to propose a model for the main stages of Cenozoic evolution in the area. During the early Cenozoic, the Weddell Sea oceanic crust was subducted under the southern margin of the South Orkney Microcontinent. The subduction probably ended westwards at the South Powell Ridge, a submarine extension of the Antarctic Peninsula. A major transcurrent fault zone is identified in the northwestern Weddell Sea, bounding oceanic crust of Mesozoic and Cenozoic ages. This fault zone was probably active at least to the Miocene. The drifting of the South Orkney Microcontinent from the Antarctic Peninsula during the late Eocene to early Miocene originated the Powell Basin. Jane Basin developed as a backarc, related to the subduction of the Weddell Sea oceanic crust below Jane Bank. The seismic stratigraphy of the depositional sequences in these two basins indicates that spreading in Jane Basin started simultaneously with the end of the opening in Powell Basin. The active spreading ridge of the Weddell Sea collided with the trench and was subducted below Jane Bank at 15-20 Ma. Drifting in Jane Basin and subduction below Jane Bank ended shortly thereafter, in the middle Miocene, and the boundary between the Antarctic/Scotia plates migrated north of the South Orkney Microcontinent, along the South Scotia Ridge. Present tectonic activity in the region is minor.