喜马拉雅东部库曲淡色花岗岩的成因及其稀有金属成矿意义:来自年代学、地球化学及Nd-Hf同位素的证据  

Geochronology,geochemistry and Nd-Hf isotopic compositions of the Kuqu leucogranite in the eastern Himalaya:Implications for the tectonic setting and rare metal mineralization

作　　者：刘朵 杨成业[1] 李玉彬 央宗 张金树[1] 张根[1] 李若铭 Liu Duo;Yang Chengye;Li Yubin;Yang Zong;Zhang Jinshu;Zhang Gen;Li Ruoming(College of Engineering,Tibet University,Lhasa 850000;Tibet Institute of Geological Survey,Lhasa 850000)

机构地区：[1]西藏大学工学院,拉萨850000 [2]西藏自治区地质调查院,拉萨850000

出　　处：《地质科学》2024年第5期1326-1341,共16页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：西藏自治区重点研发计划项目(编号:XZ202201ZY0020G);2023年中央支持地方高校改革发展资金(第二批)——新工科规划背景下川藏铁路廊带重大工程问题及能源规划建设研究项目(编号:00061146);西藏自治区重大专项(编号:XZ202201ZD0004G);第二次青藏高原综合科学考察研究项目(编号:2019QZKK0806)资助。

摘　　要：喜马拉雅淡色花岗岩是研究印度—亚洲大陆碰撞造山过程的极佳对象。本文对喜马拉雅东缘库曲淡色花岗岩开展了详细的年代学、地球化学及原位Sr-Nd同位素研究。锆石及独居石的LA-ICP-MS U-Pb定年结果表明库曲岩体形成于~25 Ma,具有较高的SiO2(73.32%~74.53%)、Al2O3(14.72%~15.25%)含量以及A/CNK(1.14~1.23)和Rb/Sr比值(2.38~15.4),与典型的高分异花岗岩一致。它们富集大离子亲石元素(如Rb、K、Pb),亏损高场强元素(如Nb、Zr、Ti),呈现右倾的稀土配分模式和较为明显的负Eu异常,均具有较低的ε_(Nd)(t)(-13.4~-11.7)和ε_(Hf)(t)(-10.4~-7.86)值,与高喜马拉雅结晶序列一致。我们认为库曲淡色花岗岩是由高喜马拉雅古老变质基底部分熔融产生的熔体,经高度分异演化形成的,形成于藏南拆离系活动造成的伸展环境。淡色花岗岩及相关伟晶岩较高的稀有金属含量显示出喜马拉雅淡色花岗岩具有一定的稀有金属成矿潜力。The Himalayan leucogranite is an excellent target for understanding orogenic process of the India-Asia collision.An integrated geochronological,geochemical and in situ Nd-Hf isotopic data are presented for the Kuqu leucogranite in the eastern Himalaya,Tibet.LA-ICP-MS U-Pb dating of zircon and monazite show that they were emplaced at~25 Ma.These leucogranites have high SiO2 and Al2O3 contents of 73.32%to 74.53%and 14.72%to 15.25%,respectively.They are characterized by high aluminum saturation index of 1.14~1.23 and Rb/Sr ratios of 2.38~15.4,representative of highly fractionated granite.These leucogranites are enriched in large ion lithophile elements(e.g.,Rb,K and Pb),and depleted in high field strength elements(e.g.,Nb,Zr and Ti).They display lowε_(Nd)(t)(-13.4 to-11.7)andε_(Hf()t)(-10.4 to-7.86),consistent with isotopic characteristics of the higher Himalayan sequence.Their petrogenesis can be considered as highly fractionated melt derived from ancient basement from the higher Himalayan sequence in regional extension due to the activity of the South Tibetan detachment system.The significantly high lithium and beryllium content of the leucogranites and related pegmatites suggest that the Himalayan leucogranites have huge potential for the rare metal mineralization.

关 键 词：淡色花岗岩 岩石成因 稀有金属 喜马拉雅 

分 类 号：P588.12+1[天文地球—岩石学] P597[天文地球—地质学]