张广才岭地块早侏罗世晚期花岗闪长岩及其闪长质包体的岩石成因及构造意义  

Petrogenesis of late Early Jurassic granodiorites and associated dioritic enclaves in the Zhangguangcai Range and its tectonic implications

作　　者：冯光英[1] 牛晓露[1] 刘飞[1] 刘燊[2] 杨经绥[1] FENG Guangying;NIU Xiaolu;LIU Fei;LIU Shen;YANG Jingsui(Center for Advanced Research on Mantle(CARMA),Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing,100037;Department of Geology,Northwest University,Shaanxi,Xi’an,710069)

机构地区：[1]地幔研究中心,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]西北大学地质学系,西安710069

出　　处：《地质学报》2019年第10期2598-2616,共19页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号41773029、41672063、41573022、41720104009);中国地质调查局地质调查项目(DD20190060)资助成果

摘　　要：对松嫩-张广才岭地块早侏罗世晚期北长岗花岗闪长岩及其暗色包体开展了详细的岩石学,地球化学及年代学研究。结果表明,北长岗花岗闪长岩中含有大量闪长质暗色微粒包体,包体具有典型的岩浆结构,并发育针状磷灰石,同时斜长石斑晶从核部到边部显示复杂的成分和结构不平衡。寄主岩与包体均为准铝质,高钾钙碱性或高钾钙碱性-钙碱性过渡岩石,两者具有基本一致的稀土元素及微量元素组成,同时都具有正的εNd(t)和锆石εHf(t)值。主微量元素-SiO2协变图中,包体成分的两端分别向寄主花岗闪长岩及该区时代略早的基性岩延伸,三者具有良好的线性关系。以上特征表明北长岗花岗闪长岩中暗色包体为岩浆混合成因,且其原始岩浆可能为受到俯冲沉积物熔流体交代的软流圈地幔。寄主花岗闪长岩原岩主要为中-新元古代新生基性下地壳,并有少量亏损地幔物质的加入。寄主岩和暗色微粒包体具有基本一致的锆石U-Pb年龄(分别为173±2.0Ma和173±1.5 Ma),显示岩浆混合作用发生在早侏罗世晚期。区域构造演化显示,早侏罗世(~185Ma),张广才岭地块处于古太平洋西-北西向俯冲到亚洲大陆之下形成的弧后伸展环境,北长岗花岗闪长岩及其暗色包体的形成暗示早侏罗世晚期(~173Ma)依然存在幔源岩浆活动,该区仍然处于弧后伸展环境,幔源物质的底侵诱发下地壳部分熔融形成研究区长英质岩浆,同时也说明该区早侏罗世晚期仍然存在地壳增生,且增生方式为垂向增生。The petrology,whole rock geochemistry and geochronology of the late Early-Jurassic Beichanggang(BCG)granodiorite and its dark microgranular enclaves in the Songnen-Zhangguangcai Range were reported in this paper.Abundant mafic magmatic enclaves(MMEs)are contained in the BCG granodiorite.The MMEs are characterized by typical magma structure and long prisms of apatite.The plagioclase crystal in the MMEs shows obviously compositional and structural imbalance.Both the host rock and MMEs are metaluminous,high-K calc-alkaline series or high-K calc-alkaline series to calc-alkaline series rocks.They have similar rare earth element patters and primitive mantle-normalized trace element variation patterns.Both of them show positiveεNd(t)and zirconεHf(t)values.In the Harker diagram,a good linear relationship is showed in the host rock,MMEs and the earlier mafic rocks in this area.The above characteristics indicate that the MMEs are products of magma mixing and derived from partial melting of asthenospheric mantle which have been metasomatized by the slab-derived fluids or melts.While the host rock were derived from the partial melting of the Meso-neoproterozoic mafic lower crust,combined with minor part of depleted mantle materials.The host rocks and the MMEs yield consistent zircon U-Pb ages(173±2.0 Ma and 173±1.5 Ma,respectively),which is interpreted as the magma mixing age.Tectonically,Zhangguangcai Range represents an incipient continental back-arc tectonic setting which resulted from the palaeo-Pacific slab subducting W-NW beneath East Asia in Early Jurassic(~185Ma).The occurrence of Beichanggang granodiorite and MMEs suggests continuous mantel derived magmatism and an extensional environment in the late Early-Jurassic(~173Ma).Subsequently,mantle magmatic underplating resulted in partial melting of the lower crust and formation of the studied granodiorite,which indicates a lateral crustal growth event.

关 键 词：张广才岭地块 花岗闪长岩 暗色微粒包体 岩浆混合作用 早侏罗世晚期 地壳增生 

分 类 号：R28[医药卫生—中药学]