藏南拆离系活动与淡色花岗岩就位——以希夏邦马峰地区为例  

South Tibetan Detachment System activity and leucogranite emplacement: Insights from the Shisha Pangma regions

作　　者：褚杨[1,2] 郭宜琳 刘谭杰 刘小驰 胡方泱[2,3] 雷宜阳 林伟 CHU Yang;GUO YiLin;LIU TanJie;LIU XiaoChi;HU FangYang;LEI YiYang;LIN Wei(State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;Key Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China)

机构地区：[1]岩石圈演化国家重点实验室,中国科学院地质与地球物理研究所,北京100029 [2]中国科学院大学地球与行星科学学院,北京100049 [3]矿产资源研究院重点实验室,中国科学院地质与地球物理研究所,北京100029

出　　处：《岩石学报》2024年第5期1461-1474,共14页Acta Petrologica Sinica

基　　金：中国科学院战略性先导科技专项(XDA0430101);国家自然科学基金项目(92355301);重点研发计划(2021YFB2301301);中国科学院地质与地球物理研究所重点部署项目(IGGCAS-202204)联合资助.

摘　　要：藏南拆离系是世界上最大的拆离断层系统,也是喜马拉雅造山带的重要构造边界,对喜马拉雅造山过程起着重要的控制作用。在拆离断层内部和断层下盘的高喜马拉雅单元,出露了大量的同构造淡色花岗岩;近期研究工作发现,这些淡色花岗岩具有良好的稀有金属成矿潜力,因此,研究藏南拆离系的活动历史和淡色花岗岩的就位过程,对理解拆离断层变形和演化过程、熔体-断层相互作用和成矿有着重要的启示意义。针对该问题,本文选择喜马拉雅造山带中段希夏邦马峰附近的两条经典剖面——吉隆和聂拉木,开展系统的构造地质学研究,就藏南拆离系的演化过程和淡色花岗岩的同构造迁移-就位机制进行初步探讨。研究表明,吉隆地区的拆离断层厚度数十米到上百米,影响范围小,下盘吉隆岩体和高喜马拉雅的向北拆离变形较弱;聂拉木拆离断层为藏南拆离系深部构造层次,拆离断层厚度达数千米,强烈的构造变形导致肉切村群和高喜马拉雅顶部发生强烈的糜棱岩化,韧性剪切后的淡色花岗岩以平行拆离断层的岩席或岩脉产出;由此,我们认为吉隆和聂拉木的拆离断层分别代表了藏南拆离系的不同构造层次,受控于后期不均一的构造隆升剥露过程,进而可以解释两个地区不同的构造特征。综合前人的研究工作,我们提出藏南拆离系内部拆离断层活动存在逐渐向上迁移现象,而淡色花岗岩的侵位对该过程有着重要的促进作用。早期藏南拆离系的主拆离断层层次较深,控制了淡色花岗岩的顺层迁移和就位;而晚期熔体向更浅层次的运移,也促使藏南拆离系的主拆离断层也向上部迁移。The South Tibetan Detachment System(STDS)is the largest detachment fault zone in the world.As the key tectonic boundary fault,it also plays an important role in the Himalayan orogeny.Voluminous leucogranites intruded into the detachment and its footwall-the Great Himalaya Unit.Recent studies reveal high potential of rare-metal mineralization.Therefore,the tectonic history of the STDS and the emplacement of leucogranites are key to understanding the detachment deformation and evolution,and melts-fault interaction.To answer this question,this paper focuses on two regions near the Shisha Pangma,Gyirong and Nyalam,and discusses the evolution of the STDS and the mechanism of syn-tectonic migration-emplacement of leucogranites.Our work reveals a relatively thin detachment in Gyirong,which is tens to hundreds of meters thick,and has a narrow deformation zone.The top-to-the N normal-sense shearing has an insignificant effect on the Gyirong pluton and the Greater Himalaya Unit.In contrast,the detachment in Nyalam is kilometers-thick and mylonitized the Rouqiecun Group and the Great Himalaya Unit,causing highly deformed granitic sheets parallel to the detachment.We infer that the detachments of Gyirong and Nyalam represent different structural levels of the STDS,which can better explain the difference of deformation patterns.Their exhumation results from uneven tectonic denudation.By summarizing previous studies,we propose a new tectonic model in which the detachment migrates upwards assisted by the emplacement of leucogranites.During this tectonic-magmatic process,the early-formed,deep detachment controls the migration and emplacement of leucogranites.When the late leucogranites intrude and migrate to the high tectonic level,the main detachment plane also migrates upwards,leading to multiple detachment fault planes in the STDS.

关 键 词：藏南拆离系 淡色花岗岩 喜马拉雅 构造变形 岩浆侵位 断层迁移 

分 类 号：P542.3[天文地球—构造地质学] P588.121[天文地球—地质学]