藏南冈底斯岩基晚白垩世构造岩浆作用：以拉萨白堆复合岩体中-基性岩脉群为例  

Late Cretaceous tectonics and magmatism in Gangdese batholith,Southern Tibet: A record from the mafic-dioritic dike swarms within the Baidui Complex,Lhasa

作　　者：高家昊 曾令森[1] 郭春丽[2] 李秋立[3] 王亚莹[1] GAO JiaHao ZENG LingSen GUO ChunLi LI QiuLi WANG YaYing(Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China)

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]中国地质科学院矿产资源研究所,北京100037 [3]中国科学院地质与地球物理研究所、岩石圈演化国家重点实验室,北京100029

出　　处：《岩石学报》2017年第8期2412-2436,共25页Acta Petrologica Sinica

基　　金：国家重点研发计划(2016YFC0600304);公益性行业科研专项(201511022);国家自然科学基金项目(41425010);中国地质调查局地质调查项目(12120115027101)联合资助

摘　　要：拉萨白堆复合岩体寄主为含包体的花岗闪长岩,并被一系列平行-近平行东西走向中-基性岩脉群穿插,总体形成类似"条纹码"般的构造形式。锆石U-Pb定年表明,这些基性岩脉主要形成于85~68Ma。同期中性和基性脉岩都表现出富集大离子亲石元素和LREE,亏损高场强元素,Sr同位素初始比值较低,但Nd同位素比值(εNd(t)>+3.1)和锆石Hf同位素组成(εHf(t)>+10.7)较高,都不具有Eu异常。与中性脉岩相比,基性脉岩具有(1)Mg O含量较高和较高的Mg#(>50.6);(2)较高的Cr、Ni、Co含量;(3)较富集HREE且平坦分布。但中性脉岩Y含量较低,Sr/Y比值(38~72)较高,具有高Sr-低Y的特征;这些特征表明:这些岩浆岩的源区可能为受流体交代的岩石圈地幔。中-基性脉岩之间具有岩浆演化关系,在岩浆演化过程中以角闪石的分离结晶为主。结合文献数据,这些新数据表明冈底斯岩基的在晚白垩世(85~68Ma)经历了弧上伸展构造作用,岩浆作用持续活动,可能与新特提斯洋板片的北向斜俯冲相关。A series of sub-parallel,W-E trending dikes of mafic to dioritic compositions（ the Baidui dike swarms） intruded into the Baidui granodiorite complex and collectively form a ‘bar code＇-like structure. Zircon U-Pb dating indicates these dikes formed at a time of period of 85 - 68 Ma. Irrespective of their major element compositions,they all are characterized by enrichment in LILE and LREE,depletion in HREE and HFSE,and no Eu anomalies,similarily low Sr（87Sr/86Sr（t） 〈0. 7041） but high Nd（ εNd（t）〉 ＋ 3. 1）and zircon Hf（ εHf（t） 〉＋ 10. 7） isotope compositions. As compared those in the dioritic dikes,mafic ones contain substantially higher amounts of Mg O,Cr,Ni,Co and HREE and are characterized by relatively higher Mg#（ 〉50. 6） but lower Sr/Y ratios.Interestingly,the dioritic dikes show elevated Sr/Y greater than 38 and up to 72. These features suggest that these magmas were derived from subarc fluid metasomatized lithospheric mantle and subjected to various degrees of fractional crystallization of hornblende.Together with literature data,these new data indicate that a major episode of Late Cretaceous arc magmatism along the southern Gangdese batholith and within-arc extension possibly due to northward oblique subduction of the Neo-Tethyan oceanic lithosphere.

关 键 词：冈底斯岩基 白堆复合岩体 弧岩浆作用 伸展构造 斜向俯冲 

分 类 号：P588.13[天文地球—岩石学] P597.3[天文地球—地质学]