中蒙边界英巴地区元古宙杂岩的时代及其对南戈壁微陆块分布范围的限定  

The age of the Proterozoic rocks in Yingba area in western Inner Mongolia:Constraints on the distribution of the South Gobi micro-continent in the Central Asian orogenic belt

作　　者：周印章[1] 韩宝福[1] 徐钊[1] 任荣[1] 苏犁[2] 

机构地区：[1]北京大学地球与空间科学学院/教育部造山带与地壳演化重点实验室,北京100871 [2]中国地质大学(北京)地学实验中心,北京100083

出　　处：《地质通报》2013年第2期318-326,共9页Geological Bulletin of China

基　　金：国家重点基础研究发展计划(973计划)<兴蒙造山带构造叠合与大规模成矿作用>(编号:2013CB429806);国家自然科学基金项目<华北克拉通中生代地壳减薄的机构变形机制;时限及动力学背景>(批准号:90714006);中国地质调查局项目<兴蒙造山带花岗岩演化与成矿耦合关系综合研究>(编号:1212011085474);<兴蒙造山带基本构造格局综合调查和研究>(编号:1212011085476);<中国和亚洲不同造山带花岗岩年代学格架;岩浆序列及其与成矿关系的对比>(编号:1212010611803);<中国北方增生造山过程;陆壳生长及其对找矿的作用>(编号:1212010611817)

摘　　要：中亚造山带可能存在具有前寒武纪基底的微陆块。中国境内亚干地区新元古代片麻状花岗岩的存在可能表明南戈壁微陆块延伸到了中国境内,但南戈壁微陆块在中国境内的分布范围还不能准确限定。在内蒙古西部靠近中蒙边界的英巴地区可能存在元古宙变质杂岩,岩性主要有片麻岩、石英岩、云母石英片岩和碳酸盐岩等。其中产出在岩体内部的一个花岗质片麻岩岩块主要由斜长石、石英和黑云母组成,LA-ICP-MS锆石U-Th-Pb定年给出复杂的年龄结果,岩浆成因的锆石核的年龄分散,207Pb/206Pb年龄在2.5-1.0Ga之间,暗色锆石幔给出的206Pb/238U加权平均年龄为417.2Ma±3.5Ma,可能代表早古生代晚期一次构造热事件。花岗岩体内另外一处片麻岩岩块主要由斜长石、黑云母和石英组成,206Pb/238U加权平均年龄为905.2Ma±6.1Ma,与亚干新元古代片麻状花岗岩的时代非常接近。并且,亚干和英巴地区元古代杂岩具有相似的岩石组合。表明南戈壁微陆块向南至少延伸到中国境内的亚干—英巴一带,显生宙强烈的构造-岩浆活动对微陆块产生了重要的改造或破坏,造成了目前不连续出露的状况。Micro-continents with Precambrian basement are developed in the Central Asian orogenic belt. In southern Mongolia, the Toto Shan and South Gobi miro-continents are characterized by Neoproterozoic magmatism. The South Gobi micro-continent might extend into China, as evidenced by the discovery of Neoproterozoic granitoid in Yagan area. However, the distribution of the South Gobi micro-continent is not well constrained in China. Regional geological data reveal that there are some Proterozoic rocks in Yingba area of western Inner Mongolia. They are regarded as the relict blocks in and around the Yingba granitoid pluton and are mainly composed of gneiss, quartzite, mica and quartz schist and carbonate. In a Proterozoic block, the felsic gneiss composed ofplagioclase, quartz and biotite gave complex U-Pb age results from the LA-ICP-MS zircon dating. The zircon cores with the igneous origin provided a wide range of ^207Pb/^206Pb ages from 2.SGa to 1.0Ga, while the igneous zircon mantles generated a weighted mean ^206Pb/^238U age of 417.2Ma±3.5Ma, indicating an early Paleozoic tectonic event. In another block, the gneiss is crosscut by leucogranite veins, one of which gave a weighted mean ^206Pb/^238U age of 905.2Ma±6.1Ma. The age is close to the emplacement time （916Ma±16Ma） of Neoproterozoic gneissic granite pluton in Yagan. Therefore, the South Gobi micro-continent extended southward at least to the Yagan- Yingba area in China and were strongly modified and destroyed by the Phanerozoic tectonic-igneous activities.

关 键 词：南戈壁微陆块 新元古代 锆石U—Pb定年 英巴地区 中蒙边界 

分 类 号：P534.3[天文地球—古生物学与地层学] P597.3[天文地球—地质学]