The margins of the South Orkney microcontinent

Marine geophysical studies of the South Orkney microcontinent show two intersecting tectonic fabrics of different age. The older fabric is oriented E-W, and represents the magmatic arc and fore-arc created by subduction-related processes at the Pacific margin during the Mesozoic. The younger, oriented NNW to SSE, comprises half-graben related to E-W rifting at both the eastern and western margins of the microcontinent. Both fabrics provide constraints on a 40 Ma reconstruction, which shows a highly systematic distribution of arc and fore-arc provinces and points to the importance of E-W strike-slip in regional tectonic evolution. The rifting, apparently of Oligocene age, is associated with back-arc extension which created the oceanic basins to either side of the microcontinent. This strongly supports the existence of subduction with the same orientation as the present South Sandwich arc as far back as 35 or 40 Ma.