内蒙古阿拉善地区二叠纪曼德林乌拉岩体年龄、成因及其地质意义  

Geochemical, age and Hf-in-zircon isotopic characteristics and geological significance of granite and MME from the Mandelinwula pluton, northern Alxa block, Inner Mongolia

作　　者：张建军[1] 张磊[1] 王涛[1,2] 史兴俊 ZHANG Jianjun;ZHANG Lei;WANG Tao;SHI Xingjun(Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources/Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Beijing SHRIMP Center,Beijing 100037,China;School of Urban and Environmental Science,Xinyang Normal University,Xinyang 464300,He'nan,China)

机构地区：[1]自然资源部深地动力学重点实验室/中国地质科学院地质研究所,北京100037 [2]北京离子探针中心,北京100037 [3]信阳师范学院城市与环境科学学院,河南信阳464300

出　　处：《地质通报》2019年第10期1675-1690,共16页Geological Bulletin of China

基　　金：科技部国家重点研发计划项目《北方东部复合造山成矿系统深部结构与成矿过程》(编号:2017YFC0601301)和《深地资源勘查开采理论与技术集成》(编号:2018YFC0603702);中国地质调查局项目《阿拉善、藏东南等关键地段地壳圈层物质与演变基础地质调查》(编号:DD20190001)、《全国陆域及海区地质图件更新与共享》(编号:DD20190370)、《基础地质学科(岩石)数据库建设与共享应用》(编号:DD20190685)、《地质云系统集成与共享服务》(编号:DD20190397);国际地学计划项目《Orogenic architecture and crustal growth from accretion to collision》(编号:IGCP662);国家自然科学青年基金项目《中蒙边界亚干地区前寒武纪变质火山岩的岩石学、年代学及其构造意义》(批准号:41802239)

摘　　要：内蒙古阿拉善地块北缘及其邻区广泛出露早古生代—早中生代侵入岩,其时空分布、源区物质组成及成因对研究阿拉善北部地区构造演化乃至整个中亚造山带南缘晚期的演化具有重要意义。曼德林乌拉岩体位于阿拉善地块北部雅布赖-诺尔公-洪古尔玉林带西段,岩体以二长花岗岩为主,广泛发育岩浆暗色包体。这些镁铁质包体为岩浆结构,大多具有塑性外形,并具有多种不平衡结构和矿物组合,如斜长石环带、针状磷灰石等。LA-ICP-MS锆石U-Pb测年结果显示,曼德林乌拉二长花岗岩年龄为271±3Ma,花岗岩中发育的包体年龄为271±2Ma,表明该岩体形成于二叠纪,而非之前认为的中生代。二长花岗岩的锆石εHf(t)值为-18.4^-10.1,相应的二阶段Hf模式年龄为1.8~2.3Ga;暗色包体中的13颗二叠纪锆石相应的εHf(t)值为-23.6^-9.1,相应的二阶段Hf模式年龄为1.7~2.5Ga。锆石Hf同位素特征表明,形成花岗岩和镁铁质暗色包体的这2种岩浆均来自以古老地壳物质为主的源区,这与东段诺尔公—红古尔玉林地区的中酸性侵入岩相同。曼德林乌拉岩体花岗质岩和镁铁质暗色包体的岩石学、地球化学及同位素研究表明,它们可能也具有岩浆混合成因。这为阿拉善地块北缘区域在二叠纪发生广泛的壳幔相互作用提供了进一步证据。Early Paleozoic to Early Mesozoic intrusive rocks are widely distributed in northern Alxa region,Inner Mongolia.The temporal and spatial distribution,magma source components and petrogenesis for these rocks are important for studying the tectonic evolution of northern Alxa,and even for studying the late stage evolution of the southern Central Asian orogenic belt.Mandelinwula pluton,located in the west part of the Yabulai-Nuoergong-Honggueryulin tectonic belt,is mainly composed of granite and monzogranite,and mafic microgranular enclaves(MME).The identified MME has fine-grained textures,sinuous margins and diffuse contacts with the host monzogranites,and various disequilibrium textures and mineral assemblages indicate mingling or mixing processes.LA-ICP-MS zircon U-Pb dating yielded ages of 271±3Ma and 271±2Ma for the monzogranite and MME,respectively,indicating that the Mandelinwula pluton was emplaced in Permian instead of in Early Mesozoic as suggested by previous researchers.ZirconεHf(t)values of the monzogranite and enclaves show a wide range and significant overlap from-18.4 to-10.1(with TDM 1.8~2.3Ga)and-23.6 to-9.1(with TDM 1.7~2.5Ga),respectively.The source characteristics are similar to those of the intermediate-felsic plutons in the east part of the Yabulai-Nuoergong-Honggueryulin belt of the northern Alxa block.Combined with petrology,geochemistry and Hf-in-zircon isotope studies,the authors propose a plausible magma mixing interpretation for the Mandelinwula monzogranite and MME.

关 键 词：锆石U-PB年龄 HF同位素 阿拉善 岩浆混合 

分 类 号：P534.46[天文地球—古生物学与地层学] P597.3[天文地球—地质学]