South Shetland continental margin

The South Shetland continental margin occupies the north-eastern tip of the Pacific margin of the Antarctic Peninsula (Fig. 4), and it represents the only remnant of the former Palaeozoic to Mesozoic Gondwana's subduction margin (de Wit, 1977; Grunow et al., 1992). Because the Antarctic-Phoenix ridge, located seaward of the South Shetlands margin, ceased spreading about 4 Myr ago, present day convergence between the continental domain of the South Shetland platform and the oceanic crust of the Phoenix microplate is ensured by a mechanism of roll-back of the hinge of the subducting plate in response to gravitational sinking and opening of the Bransfield strait (Barker & Dalziel, 1983). The margin is delimited by the Hero Fracture Zone to the S-W and by the Shackleton Fracture Zone to the N-E. The Shackleton Fracture Zone, the South Shetland trench, and the South Scotia Ridge, form a triple junction (Klepeis & Lawver, 1996; Aldaya & Maldonado, 1996) in which continental blocks and relatively young oceanic crust become part of a structurally complex geological environment (Gambeta & Maldonado, 1990; Maldonado et al., 1994; Kim et al., 1995).

60»» 59"W 5X"\V 57"\V 56»W 55»»' 54"W

60»» 59"W 5X"\V 57"\V 56»W 55»»' 54"W

South Shetland Trench
Fig. 4 - Bathymetry of the South Shetland continental margin, with location of the seismic profile presented in Fig. 7 (thick segment). Contours every 250 m. Bathymétrie data taken form Klepeis and Lawver (1996).

On a regional scale, the analysis of the seismic profiles has shown the co-existence of two different tectonic styles on the margin, clearly related to distinct deformational regimes. An older regime (active since Late Paleozoic-Early Mesozoic), was responsible of the build-up of the accretionary prism as a consequence subduction of Panthalassa oceanic lithosphere. More recently during the Cenozoic, another tectonic style, superimposed on the older one, affected the margin producing mostly normal faults, which in many cases reach the sea floor. These are particularly well developed in the middle continental slope, where significant extensional basins, with more than 700 m of sediments, are present.

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