西藏茶巴拉地区晚白垩世角闪辉长岩与石英闪长岩年代学、岩石地球化学与成因  

Geochronology,Geochemistry and Petrogenesis of Late Cretaceous Hornblende Gabbros and Quartz Diorites in Chabala Area of Tibet,China

作　　者：吕娜 郎兴海[1] 王旭辉[1] 何青 邓煜霖 杨同山 董咪 LYU Na;LANG Xing-hai;WANG Xu-hui;HE Qing;DENG Yu-lin;YANG Tong-shan;DONG Mi(College of Earth Science,Chengdu University of Technology,Chengdu 610059,Sichuan,China)

机构地区：[1]成都理工大学地球科学学院,四川成都610059

出　　处：《地球科学与环境学报》2022年第1期42-64,共23页Journal of Earth Sciences and Environment

基　　金：成都理工大学珠峰科学研究计划项目(2020ZF11407);四川省科技计划项目(2020JDJQ0042);国家自然科学基金项目(41502079,41972084);国家重点研发计划项目(2018YFC0604105);西北大学大陆动力学国家重点实验室开放基金项目(18LCD04);自然资源部深地资源成矿作用与矿产预测重点实验室开放基金项目(ZS1911);中国地质调查局地质调查项目(DD20190167,DD20160346)。

摘　　要：青藏高原南部拉萨地体晚白垩世岩浆岩的岩石成因及地球动力学机制仍存在争议。以拉萨地体南缘曲水县茶巴拉地区西部的角闪辉长岩和石英闪长岩为研究对象,在野外地质调查基础上,开展了岩相学、地球化学和LA-ICP-MS锆石U-Pb年代学研究,查明了角闪辉长岩和石英闪长岩的形成时代及岩石成因,进一步约束了南部拉萨地体晚白垩世的构造演化。结果表明:角闪辉长岩侵位年龄为91~87 Ma,石英闪长岩侵位年龄为81 Ma。角闪辉长岩具有低SiO_(2)含量(质量分数,下同)(48.16%~51.05%),高MgO含量(4.54%~11.13%)、Co含量((31.2~46.8)×10^(-6))、Ni含量((1.79~82.70)×10^(-6)),(^(87)Sr/^(86)Sr)_(i)值为0.703925~0.704380,ε_(Nd)(t)值为2.50~3.96,表明角闪辉长岩来源于受俯冲板片流体交代的亏损地幔楔的部分熔融;石英闪长岩普遍具有高SiO_(2)含量(62.45%~62.90%)、Al_(2)O_(3)含量(15.94%~16.22%)、K_(2)O+Na_(2)O值(6.36%~6.46%)、Mg^(#)值(43.77~44.65)的特征,属于准铝质Ⅰ型花岗岩,其来源于下地壳的部分熔融,并有少量幔源岩浆的加入。两类岩石均显示岛弧岩浆的特征,富集轻稀土元素及大离子亲石元素(Rb、Th、U、Sr等),亏损重稀土元素及高场强元素(Nb、Ta、Ti等)。结合区域资料,晚白垩世早期(100~80 Ma)发生在南部拉萨地体的岩浆爆发事件可能是新特提斯洋洋脊北向俯冲的结果。洋脊俯冲使软流圈物质通过板片窗上涌,并发生减压熔融形成基性岩浆,这些基性岩浆提供的热量促使地幔楔和下地壳岩石发生部分熔融,从而导致南部拉萨地体晚白垩世早期岩浆爆发。The petrogenesis and geodynamic mechanism of Late Cretaceous magmatic rocks in southern Lhasa terrane,Tibet,are still controversial.The hornblende gabbros and quartz diorites in the west of Chabala area,Qushui county of southern Lhasa terrane were selected as the research object,and based on field geological surveys,the petrography,geochemistry and LA-ICP-MS zircon U-Pb geochronology were analyzed to identify the formation ages and petrogenesis of hornblende gabbros and quartz diorites,and further constrain the tectonic evolution of southern Lhasa terrane during Late Cretaceous.The results show that the hornblende gabbros emplace at 91-87 Ma,and the quartz diorites emplace at 81 Ma.The hornblende gabbros have low contents of SiO_(2)(48.16%-51.05%),high contents of MgO(4.54%-11.13%),Co((31.2-46.8)×10^(-6))and Ni((1.79-82.70)×10^(-6)),and(^(87)Sr/^(86)Sr)_(i) value is 0.703925-0.704380,ε_(Nd)(t)value is 2.50-3.96,indicating that the hornblende gabbros are generated by partial melting of a depleted mantle wedge that have been metasomatized by slab-derived fluid,and suffer from no obvious crustal contamination.The quartz diorites are generally high SiO_(2)(62.45%-62.90%),Al_(2)O_(3)(15.94%-16.22%),K_(2)O+Na_(2)O(6.36%-6.46%)and Mg^(#) value(43.77-44.65),thus can be grouped into quasi-aluminous I-type granite.The quartz diorites are generated by partial melting of the lower crust and mix with a little mantle-derived magma.Both rocks show the characteristics of arc magma with enrichment of LREEs and LILEs(such as Rb,Th,U and Sr),and depletion of HREEs and HFSEs(such as Nb,Ta and Ti).Integrating regional data,the“flare-up”event in southern Lhasa terrane during the early Late Cretaceous(100-80 Ma)is likely the result of the northwards subduction of an oceanic ridge of Neo-Tethys.The ridge subduction would have resulted asthenosphere material upwelling through a slab window and decompression melting to form a basic magma,which provides heat to cause partial melting of the mantle wedge and lower crustal rocks,result

关 键 词：角闪辉长岩 石英闪长岩 地球化学 岩石成因 晚白垩世 洋脊俯冲 拉萨地体 

分 类 号：P581[天文地球—岩石学] P597[天文地球—地质学]