塔里木克拉通库鲁克塔格下寒武统底界年龄:锆石LA-ICP-MS U-Pb定年

Dating of the basal Cambrian in the Kuruktag area of the Tarim craton:LA-ICP-MS zircon U-Pb age of tuffs

制约塔里木克拉通下寒武统的精确锆石U-Pb年龄稀少,最近笔者于库鲁克塔格北区下寒武统西山布拉克组底部硅质岩中发现一层10~20 cm厚的凝灰岩夹层,对其锆石斑晶进行LA-ICP-MS U-Pb测年,结果显示该凝灰岩的就位年龄为520.3±2.9 Ma(MSWD=0.11)。首次获得塔里木克拉通下寒武统精确锆石U-Pb年龄数据,构建了该区下寒武统以精确锆石U-Pb年龄为基础的时间框架雏形。参考华南下寒武统黑色岩系沉积速率,库鲁克塔格北区且干布拉克达坂剖面下寒武统西山布拉克组可能于532.1±2.9 Ma开始沉积;结合区域地层对比,受西大山运动影响库鲁克塔格北区埃迪卡拉系—寒武系可能存在约50 Ma的沉积间断。

Precise zircon U-Pb ages that constrain the Lower Cambrian strata in the Tarim Craton are rare.Recently the authors identified a layer of 10~20 cm tuff interbedded at the bottom of the siliceous rocks of the Xishanbulake Formation in the northern Kuruktag area,located in the Tarim Craton.The LA-ICP-MS zircon U-Pb age of crystal tuffs yielded a depositional age of 520.3±2.9 Ma(MSWD=0.11).The accurate zircon U-Pb age data of the Lower Cambrian strata in the Tarim Craton are provided for the first time,and a prototype of the time frame based on the zircon U-Pb age is constructed.Using the deposition rate of the Lower Cambrian of the black rock series in South China,the sedimentation of the Xishanbulake Formation may have begun at 532.1±2.9 Ma in the Qieganbulakedaban section of northern Kuruktag.Combined with regional stratigraphic correlation,the Ediacara-Cambrian sedimentary discontinuity in the northern Kuruktag area at 50 Ma was affected by the western Mountain Movement.