东昆仑造山带早古生代—早中生代构造演化的沉积地球化学记录

摘要

东昆仑地区发育一套显生宙碎屑岩地层,包括下寒武统沙松乌拉组、中—上奥陶统纳赤台群、上石炭统—下二叠统浩特洛哇组、下三叠统洪水川组、中三叠统希里科特组以及上三叠统八宝山组.研究区砂岩的CIA值反映沙松乌拉组砂岩源区化学风化程度较高,其余各组砂岩源区化学风化程度较低.主量和微量元素研究结果表明各组砂岩源区以长英质岩石为主,包含少量中性成分.La、Ce、Th、U、∑REE含量和La/Sc、Th/Sc、Sc/Cr、La/Y比值指示沙松乌拉组和纳赤台群砂岩沉积环境为大陆岛弧或活动大陆边缘,浩特洛哇组砂岩形成于被动大陆边缘环境,洪水川组砂岩沉积环境为活动大陆边缘,希里科特组砂岩的微量元素含量及其比值接近于活动大陆边缘和被动大陆边缘,八宝山组砂岩沉积环境为活动大陆边缘.综合分析认为沙松乌拉组和纳赤台群砂岩形成于原特提斯洋俯冲阶段,浩特洛哇组砂岩形成于古特提斯洋持续扩张阶段,洪水川组砂岩形成于古特提斯洋俯冲阶段,希里科特组砂岩形成于陆(弧)陆初始碰撞阶段,八宝山组砂岩形成于陆陆全面碰撞—碰撞后阶段.%There are six Phanerozoic clastic rock strata distributed in the East Kunlun orogenic belt,including the Lower Cambrian Shasongwula Formation,the Middle-Upper Ordovician Nachitai Group and the Upper Carboniferous-Lower Permian Haoteluowa,the Lower Triassic Hongshuichuan,the Middle Triassic Xilikete and the Upper Triassic Babaoshan formations.Chemical index of alteration (CIA) values of the sandstones indicate the source rocks of the sandstones from the Shasongwula Formation underwent significant chemical weathering,while the other formations were opposite.Major and trace element characteristics suggest that the sandstones in the study area were primarily sourced by felsic rocks with minor intermediate igneous rocks.Moreover,through systematic comparison of the La,Ce,Th,U,∑REE contents and the La/Sc,Th/Sc,Sc/Cr,La/Y ratios,it is suggested that the sandstones from the Shasongwula Formation and the Nachitai Group were deposited in an active continental margin setting produced by the subduction of the Proto-Tethyan oceanic crust,whereas the sandstones from the Haoteluowa Formation were deposited in a passive continental nargin setting related to the rifting between the East Kunlun and Bayanhar terranes.The detritus of sandstones from the Hongshuichuan Formation were mainly derived from continental margin arc volcanic rocks that were produced by the subduction of the Paleo-Tethyan oceanic crust.Due to the both active and passive continental margin-related geochemical affinity,the sandstones from the Xilikete Formation are considered to be deposited during the initiation of the continental collision.The sandstones from the Babaoshan Formation were deposited in an active continental margin setting caused by the complete continental collision and post-collision.