内蒙古苏莫查干敖包萤石矿区流纹岩锆石SHRIMP定年及地质意义  

Zircon SHRIMP U-Pb Dating on Rhyolite Samples from the Xilimiao Group Occurring in the Su-Cha (Sumoqagan Obo) Fluorite District,Inner Mongolia

作　　者：聂凤军[1] 许东青[1] 江思宏[1] 胡朋[1] 

机构地区：[1]中国地质科学院矿产资源研究所,北京100037

出　　处：《地质学报》2009年第4期496-504,共9页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号40573025);国家科技支撑课题(编号2007BAB25B02)资助的成果

摘　　要：内蒙古苏-查(苏莫查干敖包)萤石矿区晚古生代火山-沉积岩分布广泛,主要岩石类型有碳泥质板岩、结晶灰岩、凝灰岩、千枚岩、英安岩和流纹岩,其中碳泥质板岩和流纹岩为苏-查特大型萤石矿床的顶和底板围岩。采用锆石SHRIMPU-Pb铅法分别对底板围岩中蚀变流纹岩和顶板围岩中未蚀变流纹岩样品进行了同位素年代测定,所获数据分别为276±10Ma和271±8Ma。蚀变和未蚀变流纹岩的形成时间均为海西晚期(早二叠世)。苏-查萤石矿区早二叠世流纹岩是华北陆台与西伯利亚板块从碰撞挤压到松弛张裂转折期,酸性岩浆喷发活动的产物,其成岩物质来自壳、幔混合源。早二叠世流纹岩的出现不仅标志着苏-查到西里庙地区海西期构造-岩浆活动的终结,同时也为苏-查特大型萤石矿床的成矿作用提供了动力、热力和物质来源。早二叠世流纹岩成岩时代的厘定不仅为阐明华北陆台北缘西段构造演化历史提供了科学依据,而且对于查明流纹岩的原岩性质和圈定新的萤石矿床找矿靶区也具有重要意义。The Su-Cha （Sumoqagan Obo） fluorite district, located on the northern margin of the North China continental massif, is the largest fluorite-only district in the world. Fluorite mineralization occurs mainly within in Late Paleozoic volcano-sedimentary sequences of the Xilimiao Group. Previous studies show that the geological setting for the Su-Cha fluorite district is a late Paleozoic rift basin along the convergence zone of the Northern China continental massif and Siberian platform. The whole Xilimiao Group can be divided into 9 sections, with a total thickness of 5667 m. The No. 4 and No. 6 sections constitute the hanging wall and foot wall of the fluorite bodies located in the Su-Cha district, respectively. The two sections of the Xilimiao Gropup consist of mainly rhyolite （porphyritic rhyolite）, rhyolitic tufflava, tuffaceous sediments, sandstone, marble, limestone, carbonaceous and argillaceous slates, with a certain amount of skarn lens. Locally, the volcano-sedimentary sequences of the Xilimiao Group have been intruded by a number of Mesozoic Yanshanian granitoid stocks. Both fresh rhyolite samples from the hanging wall and altered rhyolite samples from the foot wall of the fluorite bodies have been selected for the isotopic age dating. The SHRIMP U-Pb analytical data for the zircon grains both from the fresh and altered rhyolite samples are presented in this paper. The zircon grains separated from the fresh rhyolite sample give an average SHRIMP U-Pb age of 271±8 Ma, with MSWD value of 1.8. Meanwhile, the zircon grains separated from the altered rhyolite samples have yield an average SHRIMP U-Pb age of 276±10 Ma, with MSWD value of 1. 9. Based on the zircon SHRIMP U-Pb age data mentioned above and combined with other geological evidences, it has been suggested that the rhyolite and its related fluorite deposit were formed within an Early Permian rift basin located along the collision zone of the Northern China continental massif and Siberian platform. The rhyolite is believed to be a product of

关 键 词：流纹岩 锆石SHRIMP定年 早二叠世 苏-查(苏莫查干敖包)萤石矿区 内蒙古 

分 类 号：P597.3[天文地球—地球化学] P619.215[天文地球—地质学]