坦桑尼亚西南部乌本迪带内Nsamya镁铁-超镁铁质杂岩体的锆石U-Pb年龄、地球化学特征及构造意义  

Zircon U-Pb age,geochemistry and tectonic significance of the Nsamya mafic-ultramafic complex in the Ubendian Belt,southwestern Tanzania

作　　者：许康康 刘晓阳 孙凯 龚鹏辉 吴兴源 何胜飞 孙宏伟 XU Kangkang;LIU Xiaoyang;SUN Kai;GONG Penghui;WU Xingyuan;HE Shengfei;SUN Hongwei(Tianjin Centre,China Geological Survey,Tianjin,300170;North China Center for Geoscience Innovation,China Geological Survey,Tianjin,300170)

机构地区：[1]中国地质调查局天津地质调查中心,天津300170 [2]中国地质调查局华北科技创新中心,天津300170

出　　处：《地质学报》2021年第4期1174-1190,共17页Acta Geologica Sinica

基　　金：中国地质调查局项目(编号DD20190439+121201006000150014+1212011220910);商务部援外项目“援赞比亚东北地区航空物探和地质地球化学综合填图”([2015]352)资助的成果。

摘　　要：在坦桑尼亚西南部的乌本迪带内首次发现了阿拉斯加型(岛弧型)镁铁-超镁铁环状杂岩体,对约束区域构造演化历史具有重要的意义。Nsamya杂岩体主要岩性为单辉橄榄岩和辉长岩,单辉橄榄岩位于杂岩体的中部,而辉长岩主要位于北部边缘,表现出环状岩体特征。锆石U-Pb年龄表明杂岩体的形成年龄介于1874~1944Ma之间,为古元古代晚期。岩石地球化学显示,杂岩体具有低SiO_(2),高MgO、FeOT、Cr和Ni含量,富集LREE和Ba、Pb、U等大离子亲石元素,不同程度的亏损HREE和Nb、Ta、Zr、Hf和Ti等高场强元素特征,为具有岛弧构造背景的阿拉斯加型岩体。综合区域地质背景资料,认为其形成于古元古代乌本迪造山作用晚期的岛弧盆地闭合阶段,玄武质岩浆来源于受俯冲流体交代的岩石圈地幔,并在上升过程中遭受下地壳基底的混染作用。The Nsamya mafic-ultramafic complex of Alaskan type was discovered for the first timein the Ubendian Belt.The study of the origin of mantle-derived magmatism is of great significance to the tectonic evolution history.The Nsamya complex has ring-shape characteristics,clinopyroxene peridotite and gabbro occur from central to northern edge.Zircon U-Pb age is between 1874 Ma and 1994 Ma,indicating formation in the Late Paleoproterozoic.All the rocks are characterized by low SiO_(2),high MgO,FeOT,Cr and Ni,enrichment of LREE and LILE(Ba,Pb,U),depletion of HREE and HFSE(Nb,Ta,Zr,Hf and Ti)suggesting that the Nsamya complex is the Alaskan-type formed in anarc setting.Based on the regional geological background,it is suggested that the rocks were formed during the closure of the intra-arc basin inthe late stage of the Ubendian orogeny in the Paleoproterozoic,the magma came from the lithospheric mantle metasomatized by subduction fluid and experienced the crustal contamination of lower crust during underplating.

关 键 词：Nsamya杂岩体 锆石定年 地球化学 阿拉斯加型 乌本迪带 

分 类 号：P597.3[天文地球—地球化学] P587[天文地球—地质学]