东昆仑东段纳赤台岩群变火山岩锆石U-Pb年龄、地球化学特征及其构造意义  

Zircon U-Pb age,geochemical characteristics and tectonic significance of metavolcanic rocks from Naij Tal Group,east section of East Kunlun

作　　者：陈有炘[1] 裴先治[1,2] 李瑞保[1,2] 李佐臣[1,2] 裴磊[3] 陈国超[1] 刘成军[1] 李小兵[1] 杨杰[1] 

机构地区：[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

出　　处：《地学前缘》2013年第6期240-254,共15页Earth Science Frontiers

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;2013G1271092);青海省国土资源厅-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)

摘　　要：纳赤台岩群主要为一套变质火山-沉积岩系,是东昆仑东段早古生代构造演化的重要物质记录。变火山岩的锆石U-Pb年代学研究结果显示,年龄具有较宽的年龄谱（459~2 729Ma）,可划分为2 559Ma、1 341~1 472Ma、918~1 142Ma、557~595Ma、459~497Ma 5个年龄段,前4组为继承锆石年龄,反映研究区早期构造-岩浆事件,459~497Ma年龄谱段的锆石具有较好的生长韵律环带,为典型的岩浆成因锆石,206Pb/238U加权平均年龄为（474±7.9）Ma（MSWD=0.59,n=11）,代表纳赤台岩群变火山岩形成时代,即形成于奥陶纪。地球化学研究表明,纳赤台岩群变火山岩原岩均为玄武岩,可以划分为两个岩石系列,斜长角闪片岩和角闪片岩为亚碱性拉斑玄武岩。Mg#介于43.09~46.44,反映岩浆经历了一定程度的结晶分异演化;绿帘绿泥钠长片岩属于碱性玄武岩;Mg#介于57.20~76.00,相对接近原始岩浆成分。微量元素特征显示前者具有岛弧火山岩特征,而后者具有E-MORB和OIB特征,其岩浆源区更富集。锆石U-Pb年代学和地球化学研究表明,纳赤台岩群火山岩形成于早古生代弧后盆地,是原特提斯洋洋壳向北俯冲导致东昆仑地区拉张成弧后小洋盆的物质记录。Naij Tal Group is a metamorphic volcanic-sedimentary series in East Kunlun.It is also the important material record of the Early Paleozoic tectonic evolution.The zircon U-Pb age spectrum of meta-volcanic rock from Naij Tal Group is evidently divided into five groups：2559 Ma,1341-1472 Ma,918-1142 Ma,557-595Ma and 459-497Ma.The former four groups recorded the Precambrian tectono-magmatic events in this area.The zircon grains of the fifth group are of clear oscillatory zonation indicating their magmatic origin.The206Pb/238 U weighted average age of these zircon grains is 474±7.9 Ma（MSWD=0.59,n=11）,which indicates that the forming age of the meta-volcanic rocks is the Ordovician.The major element data show that the protolith of meta-volcanic rocks are basalts which can be divided into two series：tholeiite（including plagioclase hornblende schist and hornblende schist）of lower Mg#（43.09-46.44）and alkali basalt（including epidotechlorite albite schist）of higher Mg#（57.20-76.00）.These suggest that the tholeiite magma has undergone crystallization differentiation of femic minerals,whereas the alkali basalt magma is similar to primitive magma.Trace element data show that the tholeiite is of characteristic of island arc volcanic rocks,while the alkali basalt is similar to E-MORB and OIB.Zircon U-Pb dating and geochemical study indicate that these meta-volcanic rocks were formed in the early Paleozoic back-arc basin environment,it is the material record of the pull-apart of East Kunlun to form the backarc small basin caused by the northward subduction of Proto-Tethys oceanic crust.

关 键 词：锆石LA-ICP-MS U-PB定年 地球化学 构造环境 变火山岩 纳赤台岩群 东昆仑造山带 

分 类 号：P588.1[天文地球—岩石学] P597.3[天文地球—地质学]