三江北段保梭色花岗岩锆石U-Pb定年、地球化学及地质意义  

The zircon U-Pb dating and geochemistry of the Baosuose Granite in the Northern Sanjiang Orogenic Belt and their geological significances

作　　者：陶志华 李渊 马忠贤 蔡成龙 裴有生 张彬 TAO Zhihua;LI Yuan;MA Zhongxian;CAI Chenglong;PEI Yousheng;ZHANG Bin(Second Geological Exploration Institute of Qinghai Nonferrous Geological Bureau,Xining Qinghai 810000,China;Qinghai Bureau of Environmental Geology Exploration,Xining Qinghai 810000,China)

机构地区：[1]青海省有色第二地质勘查院,青海西宁810000 [2]青海省环境地质勘查局,青海西宁810000

出　　处：《矿物学报》2024年第6期782-801,共20页Acta Mineralogica Sinica

基　　金：柴达木周缘成矿带地质矿产调查评价(编号:基[2013]03-128-027)。

摘　　要：三江复合造山带造山过程具有长期性、多期性特点。本文从保梭色花岗岩体锆石U-Pb同位素、锆石微量元素和岩石地球化学特征出发,初步探讨了该岩体的形成背景及其在三江碰撞造山过程中的意义。利用LA-ICP-MS锆石U-Pb定年获得的两件锆石的U-Pb同位素年龄分别为(49.61±0.74)、(48.48±0.59)Ma。进一步进行岩石地球化学和锆石微量元素分析研究发现:岩浆源区残余斜长石较少,残留相中以角闪石为主,并出现了石榴石,锆石饱和温度计估计岩浆起源温度应>800°C,岩浆应起源于高温高压状态的下地壳基性火成岩部分熔融;在岩浆演化过程中,发生了围岩混染作用和斜长石、角闪石的分离结晶作用。综合分析认为,保梭色岩体属于深熔的高钾钙碱性I型花岗岩,形成于后碰撞环境,U-Pb同位素年龄为本区碰撞造山提供了时限约束,即大约50 Ma,印度-欧亚大陆碰撞造山虽然还未结束,但岩体所处的金沙江地区已进入后碰撞伸展造山阶段。The orogenic process of the Sanjiang compound orogenic belt is characterized with the long-term and multi-period.Based on the U-Pb isotopes and trace elements of zircons and petrogeochemical characteristics of the Baosuose granite,in this paper,we have preliminarily discussed the formation background of the granite and its significance in the Sanjiang collisional orogenic process.The U-Pb isotopic ages of two zircon samples in the granite by using the LA-ICP-MS U-Pb dating method are(49.61±0.74)Ma and(48.48±0.59)Ma,respectively.Further research on petrogeochemistry and trace elements of zircons shows that there is relatively low content of residual plagioclase in the magma source whose residual phase consisting of major amphibole and minor garnet.By using the zircon saturation thermometer,it is estimated that the magma original temperature should be>800°C.It is believed that the magma should be originated from the partial melting of basic igneous rocks in the lower crust under high temperature and high pressure.In the evolution process of magma,the wallrock assimilation-contamination and the fractional crystallization of plagioclase and amphibole occurred in the magma.Based on the comprehensive analysis,it is believed that the Baosuose granite belongs to the anatexis high potassium calc-alkaline I-type granite,which was formed in the post-collision environment.The U-Pb isotopic ages provide time limit for the collisional orogeny in this area.These mean that at about 50 Ma,although the Indo-Eurasian collisional orogeny had not ended yet,the Jinsha River area where the granite is located was in the post-collision extensional orogenic setting.

关 键 词：三江造山带 后碰撞 高钾钙碱性 Ⅰ型花岗岩 

分 类 号：P595[天文地球—地球化学]