西藏西南部达巴-休古嘎布蛇绿岩带的形成与演化

Origination and Evolution of Daba-Xiugugabu Ophiolite Belt in the Southwestern Tibet

该蛇绿岩带的岩体由地幔橄榄岩组成,主要岩石类型是方辉橄榄岩和纯橄榄岩,缺少典型蛇绿岩剖面中的洋壳单元。微量元素和稀土元素特征显示蛇绿岩形成于类似洋中脊的构造环境。笔者提出该区蛇绿岩来源于印度大陆北缘洋盆的洋壳碎片,这个陆缘洋盆与新特提斯洋主体的形成和演化准同步。洋盆的演化模式是:早三叠世,随着印度(冈瓦纳)大陆向南漂移,其北部边缘因引张裂解产生裂谷,于晚三叠世向东开口与新特提斯洋主体连通,洋盆初具洋壳性质,北侧形成阿依拉-仲巴微陆块。侏罗-白垩纪为洋盆洋壳演化期,处于类似洋中脊的构造环境。晚白垩世末洋盆开始闭合。在新特提斯洋板块向北俯冲消减过程中,阿依拉-仲巴微陆块、陆缘洋盆和印度大陆一起随着向北漂移,在印度大陆向北挤压作用下洋盆逐渐收缩以致最终闭合。

The Ophiolite massifs are composed of mantle peridotite that is mainly harzburgite and dunite, and lacked of crust magmatite within the typical ophiolite suite. Characteristics of trace and rare earth elements suggest that Ophiolite originated from the setting similar to mid - ocean ridge. The authors put forward that Daba-Xiugugabu ophiolite belt originated from an ancient oceanic crest fragment of India continental northern marginal ocean basin, that was approximately synchronous with the formation and evolution period of the Neo - Tethys ocean. The marginal ocean basin＇s formation and evolution model may be as follows： early Triassic, rift was formed by extension and splitting in India （Gondwana） continental margin during it was drifting southward; late Triassic, the rift had been joined in the Neo -Tethys ocean in the east and convetted into initial ocean basin, and AYiLa-Zhongba micro-continental was formed in north of the rift. Jurassic and Cretaceous, the marginal ocean basin was in the stage of ocean crest evolution and had a setting similar to mid- ocean ridge. By the end of Cretaceous the marginal ocean basin began to close. During subduction northward of Neo-Tethys oceanic plate, Ayla-Zhongba micro-continental, the marginal ocean basin and India continental drifted northward all together, the marginal ocean basin was gradually contracted and closed by compressed of India continental.