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Bransfield Basin
The Bransfield Basin is a back-arc rift basin located off the Northern tip of the Antarctic Peninsula. The basin lies within a Northeast and Southwest trending strait that separates the peninsula from the nearby South Shetland Islands to the Northwest. The basin extends for more than 500 kilometers from Smith Island (South Shetland Islands) to a portion of the Hero Fracture Zone. The basin can be subdivided into three basins: Western, Central, and Eastern. The Western basin is 130 kilometers long by 70 kilometers wide with a depth of 1.3 kilometers, the Central basin is 230 kilometers long by 60 kilometers wide with a depth of 1.9 kilometers, and the Eastern basin is 150 kilometers long by 40 kilometers wide with a depth of over 2.7 kilometers.〔 The three basins are separated by the Deception Island and Bridgeman Island.〔 The moho depth in the region has been seismically interpreted to be roughly 34 kilometers deep.
==Tectonic development==
The Bransfield Basin is considered to be a back-arc basin that is located behind the South Shetland Islands. The Islands are believed to have formed from a period of subduction that occurred between the Phoenix plate and the Antarctic plate starting roughly 200 million years ago during the Mesozoic.
It is believed that the Phoenix plate stopped subducting under the Antarctic plate at least 4 million years ago during the Pliocene.〔〔〔〔 Once the subduction ceased, it is believed that the extension that created the basin was initiated. Aeromagnetic surveys have provided evidence that the extension occurred 1.8 million years ago during the Pleistocene at a rate of 0.25 to 0.75 centimeters per year.〔
It is widely accepted that the Bransfield Basin formed from extension caused by slab rollback.〔〔〔〔 New geophysical and structural data contradicts previously believed theories about slab rollback being the main mechanism for the opening of the basin.〔〔 A newer theory for the opening of the basin is attributed to sinistral strike-slip motion between the Scotia plate and Antarctic plates.〔 It is theorized that the trench between the Phoenix and Antarctic plates is locked in place and there is not any motion within the trench. The new data suggests trench retreat is not attributed as a mechanism for extension because there is a lack of seismic activity in the South Shetland Trench area, and that slab rollback is not a mechanism for extension either because if it were then Northwest-Southeast extension should be observed in the entire South Shetland region but instead compression can be observed. It is proposed that the motion between the Scotia plate and Antarctic plate are pushing the Phoenix plate to the Northwest creating compression.〔〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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