摘要
青山堡岩体位于阿拉善弧型构造南缘之龙首山隆起中段,紧邻芨岭岩体,是龙首山-祁连山铀矿成矿带的重要组成部分。为了理清岩体源区性质和演化过程,还原大地构造动力学背景,对青山堡岩体进行系统的地质地球化学研究。常量元素地球化学分析显示,青山堡岩体属于富硅富钾的钙碱性花岗岩类;稀土元素方面,细晶花岗岩呈现出平缓的配分曲线、强烈的Eu谷特征(δEu=0.05),而其余花岗岩类样品均呈现出明显的配分曲线右倾趋势,Eu谷程度较小(δEu=0.43~0.89);微量元素方面,各岩体样品基本均富集Th,U,Nb,Zr,Hf等高场强元素和La,Nd,Y,Lu等稀土元素,亏损大离子亲石元素Ba,Sr,P和高场强元素Ti等,而细晶花岗岩具有极低的Sr值(9.4)和非常高的Yb值(9.34);青山堡岩体中粗粒钾长花岗岩的锆石U-Pb年龄为441.6±4.2 Ma(MSWD=1.4,n=14),细晶花岗岩的锆石U-Pb年龄为430.1±5.6 Ma(MSWD=1.8,n=11),与阿拉善地块的碰撞运动时间(加里东晚期)相一致;全岩Sr-Nd同位素分析显示青山堡岩体具有较低的初始(87Sr/86Sr)i比值(0.663767~0.707767)和较低的εNd(t)负值(-0.1^-7.4),其应起源于古元古代龙首山群古老基底地壳物质的重熔,但也有部分地幔物质的贡献。综合分析认为,青山堡岩体除细晶花岗岩外均形成于阿拉善地块与北祁连岛弧的碰撞造山运动,为I型花岗岩;而细晶花岗岩应是碰撞造山作用期后伸展运动的产物,属于A型花岗岩。
The Qingshanbao pluton in the center of Longshou mountain of the southern margin of Alxa arc structure is an important part of uranium ore belt in Longshou-Qilian Mountains.Systematic geologic and geochemical studies of Qingshanbao rock body were carried out in order to unravel the source types of rock body,establish its evolutionary process and restore its tectonic dynamic conditions.Major elements analysis of the Qingshanbao rock body indicates that it belongs to high silicon and potassium Ca-alkaline series.Rare earth element analysis shows that the fine-grained granite has strong negative Eu anomalies(δEu=0.05) with flat REE distribution curves. However,the rest granitoid samples has moderately negative Eu anomalies(δEu=0.43-0.89) with steep right-dipping REE distribution curves.The trace elements in the rock are characterized by enrichment in high field strength elements such as Th,U,Nb,Zr,Hf and REE such as La,Nd,Y and Lu,and depletion in large-ion lithophile elements such as Ba,Sr,P and high field strength elements such as Ti.The fine-grained granite has extremely low Sr(9.4) and very high Yb(9.34). Medium-coarse grained K-feldspar granite in Qingshanbao pluton has a zircon U-Pb age of 441.6±4.2 Ma(MSWD=1.4,n=14),and the zircon U-Pb age of the fine grained granite is 430.1±5.6 Ma(MSWD=1.8,n=11),consistent with collision time(late Caledonian) of Alxa block.Analysis of whole-rock Sr-Nd isotopes shows that the Qingshanbao pluton has lower initial ratio((87Sr/86Sr)i=0.663 767-0.707 767) and lower εNd(t)(-0.1 to-7.4),indicating that the rock is likely to be originated from remelting of crustal material of Palaeoproterozoic Longshoushan Group basement,mixed with partial mantle material.It is considered that the Qingshanbao rock body belongs to I-type granites,while the fine-grained granite belongs to A-type granites, which was formed in extension stage after collision orogenesis.
作者
刘文恒
潘家永
刘晓东
王凯兴
王刚
薛培
Liu Wenheng;Pan Jiayong;Liu Xiaodong;Wang Kaixing;Wang Gang;Xue Pei(State Key Laboratory of Nuclear Resources and Environment,East China University of Technology,Nanchang,Jiangxi 330030;Key Laboratory for Digital Land and Resources of Jiangxi Province,East China University of Technology,Nanchang,Jiangxi 330030;Jiujiang University,Jujiang,Jiangxi 332000,China;School of Earth Sciences,East China University of Technology,Nanchang,Jiangxi 330030,China;Research Institute NO.203 of Nuclear Industry,Xianyang,Shanxi 712000,China;Wanbao mining LTD.,Beijing 100053,China)
出处
《矿物岩石》
CAS
CSCD
北大核心
2019年第4期26-40,共15页
Mineralogy and Petrology
基金
东华理工大学核资源与环境重点实验室开放基金项目(NRE1613)
东华理工大学博士科研基金项目(DHBK201409)地质资源经济与管理研究中心开放基金项目(17JC02)
江西省数字国土重点实验室开放基金项目(DLLJ201708)
