内蒙古西乌旗地区寿山沟组流纹质砾石锆石U-Pb年龄及其意义

为研究兴蒙造山带中部早二叠世构造背景，探讨古亚洲洋闭合时限，本文以内蒙古西乌旗浩热哈达地区寿山沟组流纹质砾岩及大石寨组流纹岩为研究对象，开展了沉积地质学分析及锆石 U-Pb同位素研究。结果显示，寿山沟组流纹质砾石锆石U-Pb年龄为（280.0±1.9）Ma，大石寨组流纹岩锆石U-Pb年龄为（276.0±1.9）Ma，指示西乌旗浩热哈达地区寿山沟组流纹质砾岩沉积时限介于280～276 Ma，属早二叠世Kungurian期；寿山沟组流纹质砾石年龄、流纹质砾岩沉积时限与研究区南部大石寨组流纹岩同位素年龄高度一致，表明南部大石寨组火山岩是寿山沟组碎屑岩的物源之一，二者属同期异相。岩石组合及沉积构造特征指示寿山沟组流纹质砾岩为浊流成因；根据寿山沟组源区岩石时空分布特征，综合前人资料，认为寿山沟组为弧后盆地沉积产物，证实古亚洲洋东段在早二叠世尚未闭合。

The zircon U-Pb age of rhyolite gravel from Shoushangou Formation in Xi Ujimqin Banner， Inner Mongolia and its geological significance

In order to study the Early Permian tectonic setting in the middle of Xing’anling-Mongolian Orogen and discuss the final closure time of the Paleo Asian Ocean， the rhyolitic conglomerate of Shoushangou Formation and the rhyolitic rocks of Dashizhai Formation in the Haorehada area of Xi Ujimqin Banner， Inner Mongolia， were studied by sedimentary geological analysis and zircon U-Pb isotopic geochronology. The zircon U-Pb age of the rhyolite gravel is （280.0±1.9） Ma， the age of the rhyolite is （276.0±1.9） Ma， indicating that the sedimentary time limit of the rhyolitic conglomerate of Shoushangou Formation in the Haorehada area of Xi Ujimqin Banner is between 280 and 276 Ma， with the main deposition epoch being the Kungurian stage of Early Permian； The age of rhyolite gravel and sedimentary time of rhyolitic conglomerate in the Shoushangou Formation are highly consistent with the rhyolite of Dashizhai Formation in the southern part of study area， indicating that the volcanic rocks of Dashizhai Formation in the south area are one of sources of Shoushangou Formation， and they are contemporaneous difference facies. The characteristics of rock assemblage and Sedimentary structures indicate that the rhyolitic conglomerate of Shoushangou Formation is turbidite；According to the temporal and spatial distribution characteristics of the sources of Shoushangou Formation and the previous data，considering that the Shoushangou Formation is the sedimentary product of Back-arc basin， which confirms that the eastern section of the Paleo Asian Ocean was not closed in the Early Permian.