Constraints on the Tectonic Setting of the Andaman Ophiolites, Bay of Bengal, India, from SHRIMP U-Pb Zircon Geochronology of Plagiogranite
Constraints on the Tectonic Setting of the Andaman Ophiolites, Bay of Bengal, India, from SHRIMP U-Pb Zircon Geochronology of Plagiogranite
复制标题
斜长花岗岩 SHRIMP U-Pb 锆石年代学对印度孟加拉湾安达曼蛇绿岩构造环境的约束
DOI：
10.1086/656354
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发表时间：
2010
期刊：
影响因子：
--
通讯作者：
N. McNaughton
中科院分区：
文献类型：
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作者：
D. Sarma;S. H. Jafri;I. Fletcher;N. McNaughton
安达曼蛇绿岩在安达曼群岛中出露良好，安达曼群岛是印度孟加拉湾巽他-缅甸双链弧系的一部分。产于南安达曼岛南部东缘的斜长花岗岩呈石英和斜长石的蠕虫状和微相混生体。它们的成分为英云闪长岩至奥长花岗质，Rb、Yb、Ta和Y的丰度具有火山弧亲和力的特征。对安达曼蛇绿岩中斜长花岗岩进行了高分辨率离子探针U-Pb测年，得到206 Pb/238 U加权平均年龄为Ma，这是其结晶年龄。与俯冲有关的斜长花岗岩侵入了安达曼蛇绿岩的辉长岩单元以及东海岸火山的喷出物。由于安达曼蛇绿岩早于斜长花岗岩，它们不可能产生于目前活跃的晚中新世安达曼-爪哇俯冲带，最有可能是在早白垩世俯冲活动的早期阶段被仰冲到欧亚大陆的前缘。
The Andaman ophiolites are well exposed in the Andaman group of islands, which is part of the Sunda-Burmese double-chain arc system in the Bay of Bengal, India. Plagiogranites occurring on the eastern margin of the southern part of South Andaman Island appear as interstitial vermicular and micrographic intergrowths of quartz and plagioclase. They are tonalitic to trondhjemitic in composition, and their Rb, Yb, Ta, and Y abundances are characteristic of a volcanic-arc affinity. Sensitive high-resolution ion microprobe U-Pb dating of zircons from a plagiogranite within the Andaman ophiolite has yielded a weighted mean 206Pb/238U age of Ma, interpreted as the age of its crystallization. The subduction-related plagiogranite has intruded a gabbro unit of the Andaman ophiolites as well as extrusives of the East Coast Volcanics at this time. Since the Andaman ophiolitic rocks predate the plagiogranite, they cannot have been generated in the currently active Late Miocene Andaman-Java subduction zone and were most likely obducted onto the leading edge of the Eurasian continent at an earlier phase of subduction activity during early Cretaceous time.