【摘要】 金水口堇青石花岗岩是迄今在青藏高原东北缘发现的唯一的一个强过铝质花岗岩岩体,含堇青石、石榴子石和黑云母等镁铁质矿物,属于镁铁质过铝质花岗岩.但目前对该岩体的成因机制及其对基底源区的构造属性和构造演化意义尚缺乏深入研究.为此,本文以详细的地质学和岩相学研究为基础,综合开展了元素和Nd-Sr-Pb同位素地球化学研究.金水口堇青石花岗岩的A/CNK=1.12～2.05,K2O/Na2O=0.44～2.99,富Rb、Th、U,贫Sr、Ba,Rb/Sr=0.42～1.23,Nb/Ta=11.88～15.30,显示明显的负Eu异常(δEu=0.41～1.01,平均0.62),全岩ISr值=0.7114～0.7503,εNd(t)=-9.30～-13.32.这表明,该岩体的岩浆是由地壳上部含黑云母的变质杂砂岩部分熔融而成,高的熔融温度但较浅的熔融深度表明存在额外热源,暗示加里东热构造事件晚期在柴南缘发生过俯冲板片拆沉、软流圈地幔上隆、基性岩浆上侵和底侵等深部过程.金水口堇青石花岗岩的二阶段亏损地幔Nd模式年龄为1.9～2.2Ga,初始铅同位素比值206Pb/204Pb为18.181～18.389、207Pb/204Pb为15.582～15.632、208Pb/204Pb为37.914～38.243,表明柴达木地块基底可能具有扬子陆块的构造属性.更多还原

【Abstract】 The Jinshuikou cordierite granite (JCG) is the only strong peraluminous granite pluton discovered so far on northwestern margin of the Tibetan plateau. This cordierite granite contains mafic minerals of cordierite, garnet and biotite, characterizing mafic peraluminous granite. However, more comprehensive investigations of its genetic mechanism and implications for affinity and tectonic evolution of the basement of the Qaidam block is needed. This paper studies systematically on major and trace elements and Nd-Sr-Pb isotopic geochemistry of the JCG following the geology and petrographical observation. The JCG pluton shows A/CNK=1.12-2.05, K2O/Na2O=0.44-2.99, Rb/Sr=0.42-1.23, Nb/Ta=11.88-15.30, and is enriched in Rb, Th and U, but depleted in Sr and Ba, significant negative Eu anomalies (δEu=0.41-1.01, average at 0.62), ISr=0.711 4-0.750 3 and εNd(t)=-9.30 to -13.32. These data suggest that magma for the JCG was derived from partial melting of biotite-bearing metagreywacke in the upper continental crust, and that the melting conditions featuring high temperature but shallow depth level suggest existence of an extra heat source, implying that deep processes of subducted plate delamination, asthenospheric mantle upwelling, mafic magma intrusion and underplating might occurred at southern margin of the Qaidam block in the late caledonian. The JCG pluton has Nd model age (TDM2) of 1.9-2.2 Ga and initial Pb isotope ratios 206Pb/204Pb of 18.181-18.389, 207Pb/204Pb values of 15.582-15.632 and 208Pb/204Pb values of 37.914-38.243, suggesting that the basement of the Qaidam block is geochemically akin to that of the Yangtze block.更多还原