东天山大白石头南新元古代片麻状花岗岩锆石U-Pb年代学、岩石地球化学及地质意义  

Zircon U-Pb Age,Geochemistry and Tectonic Implications of Neoproterozoic Granite from South of Dabaishitou,East Tianshan

作　　者：孟勇[1,2] 唐淑兰[3,4] 王凯 李艳广[1,2] Meng Yong;Tang Shulan;Wang Kai;Li Yanguang(Xi'an Center of Geological Survey,China Geological Survey,Xi'an 710054,China;Orogen Research Center,China Geological Survey,Xi'an 710054,China;College of Management,Xi'an University of Finance and Economics,Xi'an 710010,China;School of Earth Science and Resources,Chang'an University,Xi'an 710054,China)

机构地区：[1]中国地质调查局西安地质调查中心,陕西西安710054 [2]中国地质调查局造山带地质研究中心,陕西西安710054 [3]西安财经学院管理学院,陕西西安710010 [4]长安大学地球科学与资源学院,陕西西安710054

出　　处：《地球科学》2018年第12期4427-4442,共16页Earth Science

基　　金：中国地质调查局项目(Nos.1212011120473,121201232000167711);西安财经学院项目(No.16FCJH05)

摘　　要：对东天山大白石头南片麻状花岗岩的研究,可以为新元古代早期Rodinia超大陆汇聚事件提供约束.在野外调查和岩相学研究的基础上,对该片麻状花岗岩开展了LA-ICP-MS锆石U-Pb定年、全岩地球化学和锆石原位Hf同位素分析.研究显示,片麻状花岗岩LA-ICP-MS锆石U-Pb年龄为922.7±7.9Ma.岩石富SiO2(70.04%~71.60%)、碱(Na2O+K2O=5.93%~6.58%)、Al2O3(13.88%~14.91%)和低MgO(1.13%~1.29%).岩石Al2O3/TiO2(25~27)小于100,CaO/Na2O(0.7)大于0.3,K2O/Na2O(1.6~2.2)大于1.0,富集大离子亲石元素Rb、Th、K及La等,亏损Ba、Ta、Nb和Sr等,(La/Yb)N(7.29~8.11)小于10,δEu小于0.5,均显示出S型花岗岩特征.锆石εHf(t)均为正值(3.22678~13.72746),二阶段模式年龄为920~1598Ma,表明新元古代花岗岩形成于大陆边缘构造环境.综合已有研究结果,可以推断天山地区出露的该期构造岩浆事件可能对应于新元古代的罗迪尼亚(Rodinia)超大陆汇聚事件.Researches on the south of Dabaishitou gneissic granite can provide constraints on early Neoproterozoic Rodinia supercontinent convergence in the East Tianshan.In this paper,zircon LA-ICP-MS U-Pb dating,in-situ Hf isotope and whole-rock geochemical composition analyses are presented for the gneissic granite.The results show that the LA-ICP-MS zircon U-Pb isotopic dating on the gneissic granite yields a mean U-Pb age of 922.7±7.9 Ma,which approximately represents the intrusive age of the granite.Geochemical characteristics of major elements of the granite exhibit high SiO2(70.04%-71.60%),Na2 O+K2 O(5.93%-6.58%)and Al2O3(13.88%-14.91%)contents,and low MgO(1.13%-1.29%)contents.Al2O3/TiO2(25-27)ratios are less than 100,while CaO/Na2 O(0.7)and K2 O/Na2 O(1.6-2.2)ratios are more than 0.3 and 1.0,respectively.The gneissic granite is characterized by relativeenrichment in Rb,Th,K,La,and depletion in Ba,Ta,Nb and Sr.All the samples are slightly enriched in LREE with(La/Yb)Nratios ranging from 7.29 to 8.11(less than 10),and all the gneissic granite show clear negative Eu abnormalies(δEu<0.5).These characteristics are similar to values of typical S-type granite.Additionally,zirconεHf(t)values fall in the range of 3.226 78-13.727 46,with the two stage mode age from 920-1 598 Ma.Based on the chemical characteristics and Hf isotopic compositions,the Neoproterozoic gneissic granite was likely generated in a continental margin tectonic setting.With consideration of the age information on the ancient terranes from several areas,we suggest that the Tianshan ancient blocks probably formed a part of Rodinia during early Neoproterozoic period.

关 键 词：东天山 片麻状花岗岩 同位素年代学 HF同位素 地球化学 

分 类 号：P59[天文地球—地球化学]