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1 地质背景乔治工岛是南极南设得兰群岛中最大的岛屿,面积约1200km~2,大部分地区长年被冰雪覆盖.全岛广泛分布第三纪火山岩,也零星出露相应侵入岩及晚中生代和第四纪火山岩.南设得兰群岛是一发育于硅铝质基底之上的、时代为侏罗纪-第三纪的陆缘火岩弧,其岩浆活动受太平洋板块向南极大陆板块的俯冲所制约;它曾是南极大陆西部濒太平洋边缘的一部分,直到约2Ma前,在俯冲作用停止和边缘盆地布兰斯菲尔德海峡张开后才从南极半岛西北部分离出来(图1).
Geological Background Georgetown Island is the largest island in the southern Shetland Islands in Antarctica, with an area of about 1,200 km2, most of which is covered in snow and ice for many years. Tertiary volcanic rocks are widely distributed throughout the island and sporadic outbreaks of corresponding intrusive rocks Late Mesozoic and Quaternary volcanic rocks.The southern Shetland archipelago is a continental margin fire rock arc dating from the Jurassic to the Tertiary and developed over the Si-Al basement, It was once part of the Pacific margin of the western Antarctic continent until about 2Ma before its subduction stopped and the Bransfield Strait opened up in the marginal basin (Figure 1) .