西藏冈底斯带查隆花岗岩地球化学特征、锆石U-Pb年龄及其成矿意义

Geochemical characteristics, zircon U-Pb age and metallogenic significance of Chalong granites in the Gangdise Belt of Tibet

查隆花岗岩位于中冈底斯带火山岩浆弧,主要岩性为黑云花岗闪长岩、花岗闪长岩,其中中细粒花岗闪长岩锆石^(206)Pb/^(238)U年龄为89.88±0.55Ma(95%置信度,n=24,MSWD=0.43),中粒黑云花岗闪长岩锆石^(206)Pb/^(238)U年龄为86.6±1.0Ma(95%置信度,n=30,MSWD=0.64)。岩石化学特征表明,查隆花岗岩为高钾钙碱性的偏铝质I型花岗岩,稀土元素配分曲线呈右倾型,岩浆经过一定程度的分异;微量元素Ti、Nb、P相对亏损。该岩体为雅鲁藏布江洋壳单向俯冲作用的结果,形成于火山弧环境,为具有壳幔混合特征的中酸性岩浆的产物。与该岩体密切相关的查隆磁铁矿成因类型为矽卡岩型-热液叠加改造型,与区域上发现的矿床有极其相似的成矿地质背景。

The Chalong granite is located in volcanic magma arc of the Mid-Gangdise belt.The granite petrologically consists of biotite granodiorite and granodiorite;the zircon U-Pb age of fine-grained granodiorite is 89.88 ± 0.55Ma(95% conf.,n=24,MSWD=0.43)and that of medium-grained biotite granodiorite is 86.6 ± 1.0Ma(95% conf.,n=30,MSWD=0.64).Their petrochemical characteristics indicate that they are high-K calc alkaline peraluminous"I"type granite.The REE distribution curves are right-inclines,and the magma experienced differentiation to some extent.The trace elements Ti,Nb and P are relatively deficient.The intrusive rock resulted from the unidirectional subduction of the Yarlung Zangbo River crust,was formed in the volcanic arc environment,and was the product of intermediate acid magma with crust mantle mixing Characteristics.The genetic type of Chalong magnetite mineral deposit closely related to the intrusive rock is skarn hydrothermal superimposition type.Chalong magnetite mineral deposit has a similar metallogenic geological background to the discovered deposits in the area.