伊犁盆地蒙其古尔砂岩型铀矿床源区体系与构造背景分析--来自碎屑锆石U-Pb年代学证据

Provenance and Tectonic Setting of Sandstones in the Mengqiguer Sandstone-type Uranium Deposit, Yili Basin: Evidence from Zircon U-Pb Chronology

针对伊犁盆地蒙其古尔砂岩型铀矿区中生界露头剖面,重点通过8个砂岩样品的碎屑锆石LA-ICP-MSU-Pb同位素分析,解析了其年代学、物源特征及源区构造等信息,初步探索了研究区对应的源区位置、母岩形成时代及性质、源区构造演化机制。研究表明,矿区中生界不同地层中碎屑锆石年龄分布范围及峰值相似,峰值年龄集中于300～350 Ma、350～400 Ma、400～450 Ma,另有少量碎屑锆石年龄为前寒武纪。通过与盆地周边岩体及地层的年代对比推测其物源主要来自于盆地南缘乌孙山大哈拉军山组火山岩及南部那拉提地区的古生代花岗岩;前寒武纪锆石主要来源于伊宁-中天山板块巴伦台地区和那拉提地区的一套中深变质岩系。结合西天山造山带构造背景,初步将源区划分为4个构造演化阶段,其中700～350 Ma时期的新元古代晚期-石炭纪古生代天山洋盆演化阶段最为突出,为整个西天山造山带的主要形成阶段。

Eight sandstone samples were collected from the Mengqiguer sandstone-type uranium deposit in the Yili Basin. LA-ICP-MS U-Pb dating results of detrital zircon grains are used to constrain the age, provenance and geological setting of their sources. The results showed that the age distribution of detrital zircon from different Mesozoic strata are similar, and the peak ages concentrate on 300 – 350 Ma, 350 – 400 Ma and 400 – 450 Ma, with a small portion of detrital zircon with Cambrian ages. Comparison with ages of intrusions and strata in the peripheral areas, the provenance of the sandstones is mainly the volcanic rocks of the Dahalajunshan Formation in the Wusun Mountain in the southern margin of the basin and the Paleozoic granites in the southern Nalati area. The Precambrian zircons mainly come from a set of middle to high grade metamorphic rocks in the Bailuntai and Nalati area in the Yining-middle Tianshan plate. According to the tectonic setting of the West Tianshan Orogenic Belt, the tectonic evolution of the source area is divided into four stages, and the late Neoproterozoic-Paleozoic Carboniferous Tianshan Ocean Basin(700 – 350 Ma) is the most important stage in the formation of the Tianshan orogenic belt.