柴北缘阿木尼克山北坡蛇绿混杂岩的发现及地质意义  

The Discovery and Geological Significance of the Northern Amunike Ophiolitic Mélange in the Northern Qaidam Basin

作　　者：李建兵 孟军海 万世昌 Li Jianbing;Meng Junhai;Wan Shichang(Qinghai third exploration institute of geology and mineral resources,Xining,Qinghai,810008,China;Sichuan Zhongcheng Mining Co Ltd,Chengdu,Sichuan,610047,China)

机构地区：[1]青海省第三地质矿产勘查院,青海西宁810008 [2]四川省众成矿业有限公司,四川成都610047

出　　处：《新疆地质》2018年第3期386-392,共7页Xinjiang Geology

基　　金：青海省都兰县阿木尼区地区1:5万区域矿产地质调查项目研究成果(1212011221146)

摘　　要：阿木尼克山北坡蛇绿混杂岩是柴北缘蛇绿岩带的重要组成部分,具备较完整的彭罗斯型蛇绿岩结构,从下至上依次为堆晶超镁铁质杂岩、辉长杂岩、镁铁质席状岩墙杂岩群、喷出岩,深海沉积物有条带状放射虫硅质岩、页岩、结晶灰岩,蛇绿混杂岩带广泛发育英安岩、英安质凝灰岩、流纹岩。侵入岩、火山岩TiO_2含量低,玄武岩富Al_2O_3,LREE和HREE分异明显,大离子亲石元素Rb,Sr,Ba,Th富集,高场强元素Ta,Nb亏损,为岛弧玄武岩。斜长花岗岩富碱,相对富Na2O贫K_2O,w(Al_2O_3)含量较低,属于火山弧花岗岩。结合地质特征及岩石地球化学特征可判定,蛇绿岩类型属火山弧型(VA)。在蛇绿混杂岩的灰岩岩块中采集到了化石扭心珊瑚属(Streptelasma corniculum)、为正形贝(Orthis sp.),在斜长花岗岩中获得的锆石206Pb/238U年龄为(485.6±2.4) Ma,据此可确定阿木尼克山北坡蛇绿混杂岩的活动时代为早—中奥陶世。The northern Amunike ophiolitic melangeis an important part of ophiolitic belt which located in the northern Qaidam basin.It has a relatively complete ophiolite architecture identical to the Penrose ophiolite,with an ophiolite sequence consists,from bottom to top,of cumulated ultramafic complex,gabbroic complex,mafic sheeted dikes swarms, mafic lavas, silicalite with braided radiolarian, shale and crystal limestone. The ophiolitic melange is widely developed with dacite,rhyolite and dacite tuff. The contents of TiO2 in intrusion and lava are low. Basalts are rich in Al2O3 and have distinct REE fractionation with enrichment of Rb,Sr,Ba,Th and depletion of Ta and Nb, which are typical to the ispletion related basalts.The plagiogranites belong to VAG with the characteristics of enrichment of alkali and Na2O, depletion of K2O and low Al2O3.Combined with the comprehensive research of local geologic feature and geochemical characteristics of the studied ophiolite, the studied ophiolitic melangecan be determined to VolnaicArc type. We gath- ered fossils of Streptelasmacorniculum andOrthisin limestone rock and also obtained the zircon ages of 485.6nnd in the plagiogranite.Thus we propose that the formation age of the northern Amunike ophiolitic melangeis early to middle Ordovician.

关 键 词：柴北缘 蛇绿混杂岩 地球化学 时代 

分 类 号：P588.3[天文地球—岩石学] P597[天文地球—地质学]