东昆中构造带清水泉地区变沉积岩碎屑锆石U-Pb年龄及其地质意义

Detrital Zircon U-Pb Age and Geological Significance of the Meta-sedimentary Rocks from the Qingshuiquan Area in the Central Tectonic Mélange Belt of East Kunlun

东昆中构造混杂岩带主要由构造混杂岩块、古老基底岩系及原地沉积岩系组成,前人对其做了大量的研究。都兰县清水泉地区的东昆中构造混杂岩带中出露了一套变质沉积地层,作为清水泉蛇绿构造混杂岩的基质岩系,研究其形成时代、构造归属以及沉积物源,对于了解东昆中构造混杂岩带的时代归属及构造演化具有重要的意义。通过对变质沉积岩的碎屑锆石LA-ICP-MS U-Pb同位素年代学研究,获得碎屑锆石年龄范围为1847~437Ma,可进一步划分为1847~1729Ma、1 558~1400Ma、1 295~1 112Ma、965~749Ma、552~437Ma 5个年龄段。通过年代学、岩相学和区域对比研究,将浅变质沉积岩的形成时代限定为(490±2.6)^(427±4)Ma,为早古生代,归属于下古生界纳赤台群,同时进一步限定东昆中构造混杂岩带的基本构造格架形成于早古生代末期。

The central tectonic melange belt of East Kunlun is mainly composed of tectonic melange blocks, ancient basement rock series and autochthonous sedimentary rocks. Predecessors have done a lot of research on this tectonic melange belt. A series of meta-sedimentary strata are outcropped in the central tectonic melange belt of East Kunlun, Qingshuiquan area, Dulan County, which serve as the basement rocks of Qingshuiquan ophiolitic melange. Thus, the studies on the forming time, tectonic attribution and sedimentary source have important significant to understand the age assignment and tectonic evolution of the central tectonic melange belt. According to the detrital zircon LA - ICP - MS U - Pb geochronology analysis,the yielded detrital zircon ages vary from 1 847Ma to 437Ma, which can be further divided into five age groups： - 1 847 - 1 729Ma;② 1 558-1 400Ma;③ 1 295-1 112Ma;④965-749Ma;⑤552-437Ma. After comparing and analyzing the chronological data, petrography and regional evidences, the forming age of these low metamorphic sedimentary rocks has been delineated within （490 ± 2. 6）-（427 ± 4） Ma, which belongs to Early Palaeozoic Era, and these rocks have been classified as Lower Paleozoic Naij Tal Group. Meanwhile, the basic tectonic framework of the central tectonic melange belt in East Kunlun has been defined, which was formed in the end of Early Paleozoic.