甘孜-理塘蛇绿混杂岩带理塘地区硅质岩地球化学特征及沉积环境探讨

Geochemical Characteristics and Sedimentary Environment of Siliceous Rocks in the Litang Area of the Ganzi-Litang Ophiolite Melange Belt

理塘地区擦岗隆洼岩组硅质岩的w(SiO2)为81.27%~92.71%,Si/Al比值为11.69~37.22,表明硅质岩的泥质成分相对较多,硅质岩样品的稀土元素总量较低,多介于22.61×10-6~41.67×10-6之间,轻稀土元素富集。硅质岩的w(V)为10.718×10-6~38.14×10-6,Ti/V比值为10.5~89.0,与大陆边缘硅质岩相应值相近。对硅质岩岩石学和地球化学的研究表明理塘洋盆于早三叠世就已经进入到洋壳俯冲消减、岛弧发育的活动陆缘演化阶段。

Major,trace elements and REE（rare earth elements）are presented for siliceous rocks of the Caganglongwa petrofabric in the Litang area.In these samples,w（SiO2）is 81.27%-92.71% and ratio of Si/Al is 11.69-37.22,indicating that they contain high content of politic detritus.The REE content in these siliceous rock samples from 22.61×10^-6 to 41.67×10^-6 is low.The REE curves incline to the enrichment of LREE（light rare earth elements）and lack of HREE（heavy rare earth elements）.In these siliceous rocks,w（V）is 10.718×10^-6-38.14×10^-6,and the Ti/V is 10.5-89.0,which are similar to those in the siliceous rocks formed in the continental margin regimes.The research on petrological and geochemical of siliceous rocks suggests that Litang ocean basin already entered the oceanic crust subduction and the development of the island arc active epicontinental evolutionary stages in Early Triassic.