东昆仑造山带早中生代镁铁质岩墙群LA-ICP-MS锆石U-Pb定年、元素和Sr-Nd-Hf同位素地球化学  

LA-ICP-MS zircon U-Pb dating,elements and Sr-Nd-Hf isotope geochemistry of the Early Mesozoic mafic dyke swarms in East Kunlun orogenic belt

作　　者：熊富浩[1] 马昌前[1,2] 张金阳[3] 刘彬[1] 

机构地区：[1]中国地质大学地球科学学院,武汉430074 [2]地质过程与矿产资源国家重点实验室,武汉430074 [3]中国地质大学资源学院,武汉430074

出　　处：《岩石学报》2011年第11期3350-3364,共15页Acta Petrologica Sinica

基　　金：中国地质调查局计划项目(1212010918002;1212011121270)资助

摘　　要：东昆仑造山带白日其利镁铁质岩墙群以苏长辉长岩为主,含少量含斑辉绿岩,LA-ICP-MS锆石U-Pb年代学指示该套岩墙群结晶侵位年龄为251±2Ma。岩石具有中等的Mg#(31～50)和高铝(16.25%～19.49%)的特征,整体属于钙碱性玄武岩系列岩石(Na2O+K2O=2.75%～3.51%;FeOT/MgO=1.02～2.22);微量和稀土元素方面,岩石具有较低的稀土总量、轻稀土轻微富集和Eu正异常特征(∑REE=52.16×10-6～99.81×10-6,(La/Yb)N=2.08～5.49,δEu=1.0～1.3),所有岩石富集LILE(如Rb、Ba和Pb等)而亏损HFSE(如Nb、Ta、P和Ti等),且具有显著不同于地壳的不相容元素组成(如Nb/Ta比值)。岩墙具有富集的Sr-Nd同位素组成((87Sr/86Sr)i=0.71103～0.71502,εNd(t)=-7.4～-3.6),具有相对集中且显著不同于地壳岩浆的Hf同位素组成(εHf(t)=-2.37～1.07)。元素地球化学和同位素研究指示镁铁质岩浆起源于流体交代的富集地幔II,并未受到显著的地壳混染。构造环境分析表明,岩石具有岛弧和洋中脊玄武岩双重特征。结合区域构造演化分析,我们认为,在晚二叠世-早三叠世时期,在俯冲环境下,板片流体交代使上覆地幔楔发生富集,形成富集地幔II,随着该区伸展作用的加强,在早三叠世,进一步诱发了富集地幔的部分熔融并产生镁铁质岩浆,最终侵位结晶就形成了白日其利镁铁质岩墙群。The Bairiqili mafic dyke swarms in East Kunlun are principally composed of noritegabbro,with minor porphyritic diabase.The LA-ICP-MS zircon U-Pb dating indicates that the mafic dykes were emplaced with age of 251±2Ma.The mafic dykes are characterized by moderate Mg#（31～50） and high alumina（16.25%～19.49%）,belonging to calc-alkali rocks（Na2O＋K2O=2.75%～3.51%;FeOT/MgO=1.02～2.22）.The rocks have lower total REE,with slightly enriched LREE and positive Eu anomalies（∑REE=52.16×10-6～99.81×10-6,（La/Yb）N=2.08～5.49,δEu=1.03～1.30）,besides,all rocks are enriched in LILE（eg.,Rb,Ba and Pb,etc.） and depleted in HFSE（eg.,Nb,Ta,P and Ti,etc.）,and have significantly different ratios of incompatible elements to that in the crust（such as Nb/Ta ratio）.Dykes have enriched Sr-Nd isotopic compositions（（87Sr/86Sr）i=0.71103～0.71502,εNd（t）=-7.4～-3.6）,with the relative concentrated and significantly distinguished εHf（t） ratio（-2.37～1.07） when compared to that derived from the crust.Geochemical and isotopic studies show that the mafic dykes were derived from EM2 that have been metasomatized by fluid.Tectonic setting analysis shows that the rocks have characteristics of island arc and/or mid-ocean ridge basalts,combined with the tectonic evolution of East Kunlun,we propose that the Bairiqili mafic dykes were derived from EM2 in a subduction environment,which was metasomatized by fluid and then,triggered to partial melting to form the mafic magma,at about 250Ma,it took place back-arc extension in the north of the subduction zone,and then the mafic magma was rising to upper crust along the fissure to form the mafic dykes.

关 键 词：基性岩墙 锆石U-Pb年代学 SR-ND-HF同位素 弧后伸展 东昆仑 

分 类 号：P588.122[天文地球—岩石学]