Abstract:

The South Shetland Trench and Islands and the Brandsfield Trough form a trench-are-trough system which is only one around Antractica, and is a high neotectonic activity area in Antarctica. the Bransfield Trough is a deep trough under 1300-2600m deep water. Its eastern part is deeper than the western. Topographically its both sides are obviously asymmetric. Analysis of data on gravity, geomagnetism, volcanism and seismicity indicates that the Bransfield Trough is a Cenozoic rift. The morphology and geotectonic characteristics of the Bransfield Trough are similar to that of Okinawa Trough, though its formation machenism is different distinctly form later. The trough has developed in two stages: 1) The subduction has caused the back-arc spreading, and 2) after the large-scale subduction and spreading of Drack Passage, the mantle upwelling led the lithosphere to be extended, thinning and rifting, and then a series of grabens and horsts were formed. Mafic magma from the mantle has gushed out along the axis of the rift. The spreading centre was magrating toward the ocean, thus an asymmetirc rift was formed. The trough is spreading and where a new oceanic crust is formed.