布兰斯菲尔德海槽——新生代裂谷

THE BRANSFIELD TROUGH-A CENOZOIC RIFT

对重力、地磁、火山和地震活动资料的分析表明,布兰斯菲尔德海槽为一新生代形成的裂谷系,其形态和特征同冲绳海沟有相似之处,但形成机制不同。它经历了两个阶段:(1)俯冲活动引起的弧后扩张;(2)大规模俯冲活动停止后,由于地幔物质上隆造成岩石圈拉张、减薄和破裂,形成一系列地堑、地垒,地幔基性岩浆在裂谷轴部涌出,扩张中心向大洋迁移,形成不对称裂谷。该海槽目前仍在扩张,将形成新的大洋。

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.