西藏洛巴堆矽卡岩型铁多金属矿床石榴子石和锆石U-Pb测年及地质意义  

Garnet/zircon U-Pb dating and geological significance of Luobadui skarn iron polymetallic deposit in Tibet

作　　者：次仁拉姆 李金祥 岳雅慧[1] 谢静[1] 张利云[1,3] 丁林[1,2,3] Cirenlamu;LI JinXiang;YUE YaHui;XIE Jing;ZHANG LiYun;DING Lin(Key Laboratory of Continental Collision and Plateau Uplift,Institute of Tibetan Plateau Research,Chinese Academy of Sciences,Beijing 100101,China;University of Chinese Academy of Sciences,Beijing 100049,China;CAS Center for Excellence in Tibetan Plateau Earth Sciences,Beijing 100101,China)

机构地区：[1]中国科学院青藏高原研究所大陆碰撞与高原隆升重点实验室,北京100101 [2]中国科学院大学,北京100049 [3]中国科学院青藏高原地球科学卓越创新中心,北京100101

出　　处：《矿床地质》2021年第1期82-98,共17页Mineral Deposits

基　　金：国家重点研发计划(编号:2016YFC0600303);第二次青藏高原综合科学考察(编号:2019QZKK0708);国家自然科学基金(编号:41672091)项目联合资助。

摘　　要：石榴子石是矽卡岩型矿床中最常见的蚀变矿物之一,因此,对石榴子石进行年代学研究能够准确限定矽卡岩型矿床的成矿时代。青藏高原冈底斯成矿带中部发育众多矽卡岩型多金属矿床,由于缺乏精确的成矿年代学数据,制约着对这些矿床成因和动力学背景的深入认识。因此,文章以该成矿带具有代表性的洛巴堆矽卡岩型铁多金属矿床为研究对象,通过对赋矿矽卡岩中石榴子石和花岗闪长岩中锆石分别进行LA-ICP-MS U-Pb测年,以期能够准确限定该矿床的成矿时代。背散射图像和电子探针分析显示,洛巴堆矽卡岩矿床中石榴子石普遍发育环带结构特征,端员组成上以钙铝-钙铁榴石为主,w(U)为0.4×10^(-6)~28.1×10^(-6),LA-ICP-MS U-Pb测年数据显示石榴子石形成时代为(62.7±2.3)Ma(n=94)。同时,与矽卡岩密切接触的花岗闪长岩的锆石U-Pb年龄为(62.6±0.8)Ma(n=30),与石榴子石形成时代一致。这一结果说明,洛巴堆矽卡岩型铁多金属矿床形成于古新世,与同期的花岗闪长岩具有密切的成因联系。结合区域65~50 Ma时的印度-欧亚大陆碰撞事件,该测年结果显示了洛巴堆矽卡岩型铁多金属矿床形成于印度-欧亚大陆初始碰撞的构造背景。此外,通过本次研究显示,相对于云母等Ar-Ar测年,石榴子石U-Pb测年体系受青藏高原剥蚀隆升作用的影响较小,能够更好的约束成矿时代,具有广泛的应用前景。Garnet is one of the most common alteration minerals in the skarn deposit,and hence garnet geochronology can accurately define the ore-forming age of the skarn deposit.Many skarn-type polymetallic deposits are developed in the central part of the Gangdese metallogenic belt,Tibet.However,the lack of accurate mineralization chronologic data severely restricts deep understanding of the genesis and geodynamic setting of these deposits.Therefore,in this paper,the authors chose the representative Luobadui skarn iron polymetallic deposit in this metallogenic belt as the research object to conduct investigation.Through LA-ICP-MS U-Pb dating of garnet in ore-bearing skarn and granodiorite,the authors expect that U-Pb dating could accurately define the mineralization age of the deposit.Backscattering and electron microprobe analysis shows that the garnet in the Luobadui skarn deposit has generally developed zoning structure,and the end member composition is dominated by grossular-andradite,which has the U values from 0.4×10^(-6) to 28.1×10^(-6).The garnet LA-ICP-MS U-Pb dating data show that the age of garnet formation is(62.7±2.3)Ma(n=94).Meanwhile,the zircon U-Pb age of the granodiorite in close contact with skarn is(62.6±0.8)Ma(n=30),which is consistent with the formation age of the garnet.This result indicates that the Luobadui deposit was formed in the Paleocene and had a close genetic relationship with synchronous granodiorite.Combined with the 65~50 Ma India-Eurasia collision event,the dating results show that the Luobadui skarn iron polymetallic deposit was formed in the India-Eurasia initial collision setting.In addition,this study shows that the garnet U-Pb dating system is less affected by the erosion and uplift of the Tibet Plateau compared with the result of Ar-Ar dating method.The garnet U-Pb dating can accurately define mineralization age of the skarn-type deposit and has an extensive application prospect.

关 键 词：地球化学 石榴子石 LA-ICP-MS U-Pb定年 洛巴堆矽卡岩型矿床 冈底斯成矿带 青藏高原 

分 类 号：P618.31[天文地球—矿床学]