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 f ollowing principal morphostructural elements: (1) the South Scotia Ridge an d the South Orkney Microcontinent, both with continental crust; (2) the oce anic Powell and Jane basins; and (3) Jane Bank, which belongs to an island are. The analysis of MCS profiles and of gravimetric and magnetic data from Russian, Italian and Spanish cruises, supplemented with satellite gravimet ric data, has enabled us to determine the relationship between these elemen ts 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 subducte d under the southern margin of the South Orkney Microcontinent. The subduct ion probably ended westwards at the South Powell Ridge, a submarine extensi on of the Antarctic Peninsula. A major transcurrent fault zone is identifie d in the northwestern Weddell Sea, bounding oceanic crust of Mesozoic and C enozoic ages. This fault zone was probably active at least to the Miocene. The drifting of the South Orkney Microcontinent from the Antarctic Peninsul a 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 depositiona l sequences in these two basins indicates that spreading In Jane Basin star ted simultaneously with the end of the opening in Powell Basin. The active spreading ridge of the Weddell Sea collided with the trench and was subduct ed 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 boundar y between the Antarctic/Scotia plates migrated north of the South Orkney Mi crocontinent, along the South Scotia Ridge. Present tectonic activity in th e region is minor. (C) 1998 Elsevier Science B.V. All rights reserved.