西藏洛扎地区中新世基性岩的发现及其对淡色花岗岩成岩成矿的意义  

The discovery of Miocene basic rocks and its significance for the petrogenesis and mineralization of leucogranites in Luozha area,Xizang

作　　者：付建刚 李光明 郭伟康 董随亮 张海 李应栩 张林奎 焦彦杰 FU JianGang;LI GuangMing;GUO WeiKang;DONG SuiLiang;ZHANG Hai;LI YingXu;ZHANG LinKui;JIAO YanJie(Department of Mineral Geology,Chengdu Center,China Geological Survey(Geosciences Innovation Center of Southwest China),Chengdu 610218,China)

机构地区：[1]中国地质调查局成都地质调查中心(西南地质科技创新中心)矿产地质室,成都610218

出　　处：《岩石学报》2025年第3期820-836,共17页Acta Petrologica Sinica

基　　金：第二次青藏高原综合科学考察(2019QZKK0806);国家重点研发计划项目(2021YFC2901903、2023YFC2908400、2024YFC2909300、2024YFC2910102);国家自然科学基金项目(91955208);中国地质调查局项目(DD20242104)联合资助.

摘　　要：喜马拉雅成矿带东段的洛扎地区出露大量的晚侏罗世-早白垩世基性岩脉,而中新世的基性岩鲜有报道。本文选取出露于洛扎地区拉隆和恰隆穹窿滑脱系中的变基性岩,对其进行岩石学、角闪石Ar-Ar定年和全岩地球化学等综合研究。结果表明,拉隆穹窿的2个变基性岩样品的角闪石Ar-Ar坪年龄分别为18.02±0.53Ma和18.89±0.72Ma,表明其形成于中新世。变基性岩的主量元素中,SiO_(2)含量为48.23%~50.32%,Al_(2)O_(3)含量为12.14%~15.48%,MgO含量为4.94%~6.72%,K_(2)O含量为0.20%~0.79%,表明其属于低钾拉斑系列岩石。微量元素呈现出Nb、Ta、Ti负异常,具有E-MORB特征,表明变基性岩起源于岩石圈地幔,并在形成和就位过程中受到了地壳物质混染。变基性岩和淡色花岗岩具有很好的时空关系,不仅在形成时代方面基本一致,而且均产出于穹窿滑脱系中(对应于藏南拆离系)。此外,二者均经历了强烈的构造变形,在藏南拆离系(STDS)强烈活动过程中,这些镁铁质和花岗质岩浆沿着STDS构造通道经过了长距离迁移并在穹窿位置就位。中新世变基性岩一方面为喜马拉雅带淡色花岗岩的形成提供深部地幔物质参与和热能量,另一方面提供了稀有金属大规模成矿和高度富集所需的热能量。There are many Late Jurassic-Early Cretaceous basic dikes in the Luozha area in the eastern part of the Himalayan metallogenic belt,while the Miocene basic rocks are rarely reported.In this paper,a comprehensive study of petrology,amphibole Ar-Ar dating and whole rock geochemistry has been carried out on the metamorphic basic rocks exposed at the detachment systems in the Lalong Dome and Qialong Dome in Luozha area.The results show that the amphibole Ar-Ar plateau ages of two samples of the metamorphic basic rocks are 18.02±0.53 Ma and 18.89±0.72 Ma,indicating that it was formed in the Miocene.The major elements of the metamorphic rocks are SiO_(2)=48.23%~50.32%,Al_(2)O_(3)=12.14%~15.48%,MgO=4.94%~6.72%and K_(2)O=0.20%~0.79%,indicating they belong to the low potassium tholeiitic series rocks.The trace elements of the analyzed samples show negative anomalies of Nb,Ta and Ti,with the characteristics of E-MORB,indicating that the metabasic rocks were originated from the lithospheric mantle and contaminated by crustal materials during their formation and emplacement.The metamorphic basic rocks and the leucogranites in this area have a good spatio-temporal relationship,not only in terms of formation age which is basically the same,but also in terms of tectonic emplacement environment which were produced in the detachment system(corresponding to the southern Tibet detachment system).As a result,both of them have undergone strong tectonic deformations during the intense activity of the Southern Tibet Detachment System(STDS).These mafic and granitic magmas migrate a long distance along the tectonic channels of the STDS and take up positions in the dome.On the one hand,the Miocene basic rocks provide deep mantle material participation and thermal energy for the formation of leucogranites in the Himalayan belt,and on the other hand,they provide thermal energy required for large-scale mineralization and high enrichment of rare metals.

关 键 词：中新世基性岩 角闪石 AR-AR定年 岩石成因 喜马拉雅成矿带 

分 类 号：P588.145[天文地球—岩石学] P597.3[天文地球—地质学]