对雅鲁藏布江结合带形成演化的再探讨

Further discussion on the formation and evolution of the Yarlung Zangbo suture zone, Tibet

通过1∶5万区域地质调查和收集相关资料的综合研究,本文对雅鲁藏布江结合带的形成演化作了进一步的探讨。雅鲁藏布江特提斯洋具有弧后扩张洋盆的性质,在早三叠世至中三叠世中期洋盆初步形成,中三叠世晚期至晚三叠世洋盆全面形成,从早侏罗世至晚白垩世洋盆逐步萎缩,到古新世至始新世关闭。南带的蛇绿岩主要为洋中脊扩张型(MORB型),形成于中三叠世晚期至晚三叠世。北带的蛇绿岩主要为与洋内俯冲相关的俯冲带上盘型(SSZ型),形成于早中侏罗世。带内侏罗纪至白垩纪其他岩浆岩主要为前弧玄武岩类(FAB型)。显示雅鲁藏布江特提斯洋从早侏罗世开始发生了洋内俯冲,并同步向北向冈底斯带之下主动俯冲消减和向南向喜马拉雅地块之下被动俯冲消减,持续发展到晚白垩世,在古新世至始新世俯冲碰撞消亡转化为结合带。

Based on a comprehensive study of 1∶50000 regional geological survey and relevant data collection, this paper further discusses the formation and evolution of the Yarluzangbo suture zone. The Tethys Ocean in the Yarlung Zangbo had the nature of the back-arc expanded ocean basin. From Early Triassic to mid Middle Triassic period, the oceanic basin was formed preliminarily,completely formed in late Middle Triassic to Late Triassic period, then gradually shrank from Early Jurassic to Late Cretaceous period, and was finally closed in Paleocene-Eocene period. The ophiolite in the southern belt was mainly of the mid oceanic ridge dilatation type(type MORB) formed in late Middle Triassic to Late Triassic period. The ophiolites in the northern belt seem mainly to have been the upper plate of the subduction zone(type SSZ) related to intra-oceanic subduction, formed in the early Middle Jurassic period. The other Jurassic-Cretaceous magmatic rocks in the belt were mainly fore-arc basalt rocks(type FAB). It is shown that the Tethys Ocean in the Yarlung Zangbo began its intra-oceanic subduction in the Early Jurassic, and synchronously subducted actively northward under the Gangdise belt, subducted passively southward under the Himalaya landmass, and then continued to develop until the Late Cretaceous. The Palaeocene-Eocene subduction and collision and extinction were transformed into a binding zone.