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新发现的永珠席状岩墙群位于西藏北部班公错-怒江缝合带与雅鲁藏布江缝合带之间。永珠席状岩墙群规模之大、结构之完整在国内尚属罕见。岩石由蚀变辉绿岩、辉长岩和辉绿玢岩岩墙组成,向上与枕状玄武岩呈渐变过渡和侵入接触关系,发育有单侧或双侧冷凝边,具高CaO、Al2O3、MgO、FeO、Fe2O3,低TiO2、P2O5的特点,为亚碱性系列岩石。微量元素主要显示MORB的特征,部分判别图显示MORB和岛弧拉斑玄武岩(IAT)的过渡特征,推测可能产于弧后盆地环境。依据上覆放射虫硅质岩的时代和枕状玄武岩、岩墙群同位素年龄,确定永珠席状岩墙群形成的时间可能为中侏罗世—早白垩世。这一发现为中特提斯海时期古海底扩张提供了新的证据。
The newly discovered Yongzhu mafic dyke swarm is located between the Bangongchu-Nujiang suture in the northern part of Tibet and the suture zone of the Brahmaputra. The size and structure of the large-scale dyke group of the Yongzhu mast are rare in China. The rock is composed of altered diabase, gabbro and dacite wall, and is upwardly transitional and intrusive contact with pillow-shaped basalts, with unilateral or bilateral condensation, high CaO, Al2O3, MgO , FeO, Fe2O3, low TiO2, P2O5 characteristics for the sub-alkaline series of rocks. Trace elements mainly show the characteristics of MORB. Partial discrimination maps show the transitional features of MORB and island arc tholeigenic basalts (IAT), suggesting that they may be produced in the back-arc basin environment. Based on the age of overlying radiolarian cherts and the age of the pillow-shaped basalt and dykes, the time of formation of the Yongzhu matted dyke swarms may be from Middle Jurassic to Early Cretaceous. This finding provides new evidence for the ancient seafloor expansion during the Middle Tethys Sea.