内蒙古白音查干地区莫斯图花岗岩锆石U-Pb年代学、岩石地球化学及其地质意义

莫斯图岩体位于大兴安岭中南段西坡成矿带,属于锡林浩特杜什业吐岩体晚古生代侵入岩。通过对莫斯图岩体花岗岩系统开展锆石LA-ICP-MS U-Pb年代学、岩石地球化学等综合研究,两种岩性(二长花岗岩、浅色花岗岩)测年结果显示为(322.9±3.9)Ma、(321.8±8.1)Ma,表明莫斯图花岗岩侵位于晚石炭世,属海西期。岩石地球化学特征显示,莫斯图花岗岩具有高硅、中—高钾钙碱性特征;富集Rb、Ba、Th、K等大离子亲石元素,亏损Nb、Ta、Ti等高场强元素;低Sr低Yb,中等负铕异常;具有高分异花岗岩特征。莫斯图岩体具有火山弧岩浆作用成因特点,指示了海西期该区域经历了一次强烈的构造岩浆事件。

U-Pb chronology of zircon, petrogeochemistry and its geological significance of the Mositu granite in Baiyinchagan,Inner Mongolia

The Mositu granite is located in the metallogenic belt in the western slope of central and southern of the Da Hinggan Mountains area, which belongs to the late Carboniferous intrusive rock of the Tushiyetu pluton in XilinHot. The U-Pb chronology of zircon by using LA-ICP-MS and rock geochemistry are systematically studied for the Mositu granite. The results show that the crystallization ages of two kinds of granites, i.e., monzonitic granite and light-colored granite, are (322.9±3.9) Ma, (321.8±8.1) Ma respectively, which indicate that the granite intruded in late Carboniferous intrusive rocks. The rock geochemical characteristics show that the Mositu granite is rich in SiO₂, and moderate to rich-K calc-alkali. It is rich in Rb, Ba, Th, K and other large ion lithophile elements, low in Sr and depleted in Nb, Ta, Ti and other high field strength elements. The granite has middle negative Eu, and characterized with highly fractionated granite. The results indicate that the granite pluton has a volcanic arc setting genesis and there has been an intensive Hercynian tectonic-magmatic event in this area.