东昆仑西段阿确墩地区白沙河岩组锆石U-Pb年龄——对前寒武纪基底演化的约束

    Zircon U-Pb geochronology of the Baishahe Formation in the western part of East Kunlun Orogenic Belt: Constraints on Precambrian basement evolution

    • 摘要: 对东昆仑西段阿确墩地区金水口岩群白沙河岩组片麻岩进行了LA-ICP-MS锆石U-Pb年代学研究。结果显示,片麻岩中锆石的年龄范围为2400~410 Ma,峰值范围为1650~1400 Ma,其中存在少量新元古代(1.0~0.9 Ga)和早古生代(410 Ma)的变质锆石,从而限定了原岩的最早沉积时代,为中元古代末期,指示片麻岩先后经历了新元古代和早古生代变质作用。片麻岩锆石含有大量早古生代变质的信息,考虑到片麻岩中的榴辉岩形成于早古生代(450~410 Ma),推测该地区片麻岩也经历了早古生代榴辉岩相变质作用,片麻岩与榴辉岩为原地关系。结合区域研究资料,表明东昆仑早古生代可能存在1条上千千米的高压变质岩带,可能为俯冲折返后的产物。

       

      Abstract: The geochronology of the detrital zircons of the gneiss in the Aquedun region, western part of the East Kunlun Mountains was studied by LA-ICP-MS method.The ages of the detrital zircons of the gneiss vary between 2400 Ma and 410 Ma with a peak ranging from 1650 Ma to 1400 Ma.Minor metamorphic zircons was dated as 1.0~0.9 Ga (Neoproterozoic) and 410 Ma (Early Paleozoic).The dating results imply that the protolith of the gneiss was deposited in Late Mesoproterozoic, and had undergone Neoproterozoic and Early Paleozoic metamorphism.Based on eclogite in gneisses formed in Early Paleozoic (450~410 Ma).Combined with a lot of Early Paleozoic metamorphic information from zircons in gneiss, it is speculated that the gneiss in this region also underwent Early Paleozoic eclogite-facies metamorphism, and gneiss and eclogite is in situ relationship.Combined with regional studies, it is suggested that there may exists a high pressure metamorphic belt of nearly 1000 km long in Early Paleozoic in East Kunlun, which may be the product of subduction and reentry.

       

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