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东昆仑东段纳赤台岩群变沉积岩地球化学特征及构造意义

ISSN号：1000-8527
期刊名称：《现代地质》
时间：0
分类：P588.37[天文地球—岩石学;天文地球—地质学]
作者机构：[1]长安大学地球科学与资源学院,陕西西安710054, [2]西部矿产资源与地质工程教育部重点实验室,陕西西安710054, [3]中国地质大学(北京)地球科学与资源学院,北京100083
相关基金：国家自然科学基金项目（41172186,40972136,40572121）;中国高等学校博士学科点专项科研基金项目（20110205110004）;中央高校基本科研业务费专项资金项目（CHD2011TD020,2013G1271091）;青海省国土资源厅一中国铝业公司公益性区域地质矿产调查基金项目（中铝基金200801）.致谢：一起参加野外工作的有丁仨平高级工程师、郭俊锋副教授、刘战庆博士、冯建赞博士等,在此表示诚挚感谢.

作者：陈有圻[1], 裴先治[1,2], 李瑞保[1,2], 李佐臣[1,2], 裴磊[3], 刘成军[1], 杨杰[1]

关键词：东昆仑, 东昆南构造带, 纳赤台岩群, 变沉积岩, 地球化学, 构造意义, East Kunlun , south tectonic belt of East Kunlun , Naij Tal Group , meta-sedimentary rock , geochemistry , tectonic significance

中文摘要：

东昆仑东段出露的下古生界纳赤台岩群为一套变沉积－火山岩系，是该地区早古生代构造演化的重要物质记录。岩石学及地球化学特征表明，纳赤台岩群变沉积岩主要岩石类型有绢云石英片岩、二云石英片岩、长石石英片岩和绿泥绢云片岩，局部夹有少量大理岩、片麻岩和石英岩，其原岩主要为砂岩、杂砂岩及少量泥质岩。岩石具较高的SiO2（平均为69.82%）、Sr（平均为559.60×10^-6）、Ba（平均为194.68×10^-6）含量，微量元素含量与大陆上地壳丰度很相近，轻重稀土分异明显、轻稀土富集而重稀土亏损、有明显的负Eu异常，反映出源区的物质成分主要为长英质，来源于上地壳，很少有地幔物质的加入。化学蚀变指数为49.70-75.95、成分变异指数为1.32-2.01，表明物源区风化程度较低，处于寒冷、半干旱的气候区，是活动构造带的首次沉积。变沉积岩形成于活动大陆边缘－大陆岛弧环境，与共生的变火山岩地球化学特征所指示的构造环境一致，共同记录了早古生代原特提斯洋向北俯冲导致东昆仑地区拉张形成弧后小洋盆的地质过程，进一步证实东昆南构造带的早古生代板块体制应该属于活动大陆边缘。

英文摘要：

Naij Tal Group mainly consists of metamorphic volcanic-sedimentary series, which is the important material records of Early Paleozoic tectonic evolution in East Kunlun. Petrologic and geochemical characteristics indicate that the meta-sedimentary rocks from Naij Tal Group are mainly composed of mica-quartz schist, chlorite sericite schist, feldspar quartz schist, sericite quartz schist. Additionally, marble, gneiss and quartzite were occasionally outcropped in some area. The geochemical characteristics are very similar to upper continental crust, with high SiO2 （average 69.82%）, Sr （average 559.60×10^-6） and Ba （average 194.68×10^-6）. The meta-sedimentary rocks have high quantity of LREE （（La/Yb）N=7.18） with obvious negative Eu anomalies （δEu=0.44-0.66）, which is similar to active continental margin. The upper continental crust-normalized trace elements diagram shows that their protoliths are dominatly felsic rocks （e.g., sandstone, greywacke, and pelite） from upper continental crust. Tectonic discrimination based on geochemical data of meta-sedimentary rocks, as well as the CIA （49.70-75.95,Chemical Index of Alteration） and ICV （1.32-2.01, Index of Compositional Variation） reveal that the provenance of meta-sedimentary rocks are characterized by low degree weathering, and lied in the cold or semiarid zone. Based on the previous regional data, we conclude that the Naij Tal Group formed in the backarc basin relating to the Proto-Tethys northward subduction, and that the southern tectonic belt of East Kunlun was in the avtive continental margin in Early Paleozoic.