柴北缘果可山岩体的岩浆混合作用:来自岩相学、矿物学和地球化学证据  

Magma mixing identified in the Guokeshan pluton, northern margin of the Qaidam basin: Evidences from petrography, mineral chemistry, and whole-rock geochemistry

作　　者：牛漫兰[1] 赵齐齐[1] 吴齐[1] 李秀财[1] 闫臻[2] 李继亮[3] 孙毅 苑潇宇 NIU ManLan;ZHAO QiQi;wu Qi;LI XiuCai;YAN Zhen;LI JiLiang;SUN Yi;YUAN XiaoYu(School of Resources and Environmental Engineering,Hefei University of Technology,Hefei 230009,China;Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Institute of Geology and Geophysics,Chinese Academy of Scienees,Beijing 100029,China)

机构地区：[1]合肥工业大学资源与环境工程学院,合肥230009 [2]中国地质科学院地质研究所,北京100037 [3]中国科学院地质与地球物理研究所,北京100029

出　　处：《岩石学报》2018年第7期1991-2016,共26页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41272221;41672221);中国地质调查局地质调查项目(DD20160201-04;DD20160022-02)联合资助

摘　　要：青海南山岩浆岩带沿柴达木盆地和西秦岭造山带北缘分布,主要由与古特提斯洋俯冲-碰撞相关的晚二叠世-三叠纪花岗岩组成。本文对柴北缘东段果可山石英闪长岩及其中镁铁质微粒包体开展岩相学、矿物学、地球化学和Sr-Nd同位素综合研究及成因约束,为探究壳-幔相互作用提供新信息。LA-ICP-MS锆石U-Pb定年结果显示,果可山石英闪长岩与镁铁质包体形成于～247Ma。石英闪长岩属中钾钙碱性I型花岗岩,具有中等K_2O含量(1.43%～2.18%)和高Mg~#值(48.9～52.4),还表现出富集轻稀土元素、大离子亲石元素(如U、K、Pb),亏损重稀土元素和高场强元素(如Nb、Ta、Ti)和弱Eu负异常特征(Eu/Eu~*=0.71～0.85)。Sr-Nd同位素组成和矿物不平衡结构(如斜长石韵律环带和突变环带及角闪石包裹黑云母)表明,石英闪长岩主要源自镁铁质下地壳部分熔融并伴有富集地幔来源镁铁质组分的参与。镁铁质微粒包体呈椭球状,发育冷凝边和特殊的显微结构(如针状磷灰石、斜长石反环带和斜长石含刀刃状角闪石),具有更低的SiO 2含量(56.68%～59.28%)、更高的ε#Nd(t)和Mg值(58.5～62.2)以及更平坦的稀土配分曲线,暗示果可山镁铁质包体和寄主花岗岩是由源自遭受俯冲交代地幔的镁铁质岩浆与古老下地壳(古元古代晚期)来源的长英质岩浆不同比例混合形成的。结合前人对区域沉积学和构造解析研究结果,本文认为青海南山早-中三叠世岩浆活动与古特提斯洋向北俯冲诱发的幔源岩浆底侵和岩浆混合作用有关。The Qinghai Nanshan magmatic belt,located along the northern margin of the Qaidam basin（ NQB） and West Qinling Orogen,is mainly composed of Late Permian to Triassic granites that are genetically linked to subduction and collision of the PaleoTethys ocean. To constrain their origins and provide new insights on the curst-mantle interaction,an integration of methods including pertrology,mineralogy,geochemistry and Sr-Nd isotopes is performed on the mafic microgranular enclaves（ MMEs） and their host quartz diorites from the Guokeshan pluton in the eastern segment of the NQB. Zircon LA-ICP-MS dating reveals that the Guokeshan quartz-diorites are coeval with their MMEs（ 247 Ma）. The quartz diorites are medium-K calc-alkaline I-type granites that exhibit moderate potassium（ K2 O = 1. 43% 2. 18%） and high Mg#（ 48. 9 52. 4）. They are also characterized by arc-type enrichment of LREEs and LLIEs（ e. g.,U,K,Pb）,depletion of HREEs and HFSEs（ e. g.,Nb,Ta,Ti） and weakly Eu depletions（ Eu/Eu＊=0. 71 0. 85）. Their evolved Sr-Nd isotopic compositions,coupled with disequilibrium textures of oscillatory-zoned plagioclases,spike zone in plagioclase and biotite enclosed within amphibole,indicate precursor magmas were mainly produced by partial melting of mafic lower crust with additional input of a mafic component derived from an enriched mantle. In contrast,the MMEs possess lower SiO2（ 56. 68% 59. 28%）,and higher εNd（ t） and Mg#values（ 58. 5 62. 2）,and flatter REE distribution patterns. In combination with field and petrological observations,such as chilled margins,spheroidal shapes,acicular apatite,reverse-zoned plagioclase,bladeshaped amphibole in plagioclase,the MMEs and host granitoids were inferred as products by different percentage mixing of subductionrelated metasomatized mantle-derived mafic and ancient（ Late-Paleoproterozoic） crust-derived felsic magmas. In association with previous sedimentological research and tectonic analysis,in this paper,we propose that the Early

关 键 词：镁铁质微粒包体 早-中三叠世 斜长石复杂环带 岩浆混合 果可山岩体 柴北缘 

分 类 号：P588.122[天文地球—岩石学] P588.124[天文地球—地质学]