南阿尔金玉苏普阿勒克塔格花岗岩体锆石U-Pb年代学、地球化学特征及地质意义

Zircon U-Pb Geochronology, Geochemistry of the Yusupuleke Granite Pluton in South Altyn and Its Geological Implications

玉苏普阿勒克塔格岩体是南阿尔金出露面积较大的花岗岩体之一.为了查明该岩体的成因与形成的构造环境,探讨南阿尔金地区的岩浆演化过程,对该岩体进行了岩石学、地球化学及锆石U-Pb年代学方面的研究.研究结果表明玉苏普阿勒克塔格岩体主要由中粗粒似斑状黑云二长花岗岩及中细粒含斑黑云二长花岗岩组成.本次研究获得中粗粒似斑状黑云二长花岗岩的锆石U-Pb年龄为442~448 Ma,中细粒含斑黑云二长花岗岩的锆石U-Pb年龄为423~430 Ma.岩石地球化学显示,早期花岗岩具有准铝质特征(A/CNK=0.97),晚期花岗岩具有弱过铝质特征(A/CNK=1.04).两期花岗岩均属于高钾钙碱性I型花岗岩,轻稀土富集重稀土亏损,具有Eu的弱负异常.两期花岗岩都富集Rb、Th、K等元素,亏损Ba、P、Sr、Ti等元素.根据两期花岗岩的形成时代,结合区域地质背景认为玉苏普阿勒克塔格岩体形成于活动大陆边缘环境,是早古生代南阿尔金洋向北俯冲碰撞,在构造体制转换阶段幔源岩浆上涌新生地壳发生部分熔融形成.

Yusupuleke pluton is one of the largest granite plutons in the south margin of the Altyn orogenic belt.It presents petrology,geochemistry,zircon U-Pb chronology to study the genesis and the evolution of the magmatism in this paper.The pluton is mainly composed of medium-coarse grained porphyritic biotite monzonitic granites and medium-fine grained phenocystsbearing biotite monzonitic granites.The zircon U-Pb age of the former is 442-448 Ma while the latter is 423-430 Ma.The early granites belong to metaluminous series(A/CNK=0.97)and the late granites belong to weakly peraluminous series(A/CNK=1.04).Both of them show significant I-type granite characteristics with depletion in HREE,Ba,P,Sr,Ti,enrichment in LREE,Rb,Th,K,and slightly negative Eu anomaly.Combined with the geochronological data and the regional geological background,It is inferred that the Yusupuleke granites formed in an active continental margin tectonic setting related to the northward subduction of the South Altyn Ocean in Early Paleozoic.In the process of the tectonic regime transition,along with the upwelling of the mantle component,the partial melting of the juvenile crust formed the parent magma and the Yusupuleke granites crystallized after the fractionation of the magma.