Early Eocene leucocratic sill/dike swarms in the Gangdese belt, southern Tibet: Tectonic implications for Indo-Asian collision  

作　　者：Xu-xuan Ma Li-E Gao Zhong-bao Zhao Xi-jie Chen Hai-bing Li 

机构地区：[1]Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China [2]Southern Marine Science and Engineering Guangdong Laboratory,Guangzhou 511458,China [3]Development and Research Center of China Geological Survey,Beijing 100037,China

出　　处：《China Geology》2021年第1期56-66,共11页中国地质（英文）

基　　金：the National Key Research and Development Project“Key scientific issues of transformative technology”(2019YFA0708601);the Key Special Project for Introduced Talents Team of the Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(GML2019ZD0201);the second Tibetan Plateau Scientific Expedition and Research Program(STEP)Grant(2019QZKK0802);the Research Grants of Chinese Academy of Geological Sciences(J2024);the Geological Survey of China(DD20190057 and DD20190060);the National Natural Science Foundation of China(41502198);the open fund of State Key Laboratory for Mineral Deposits Research at Nanjing University(2020-LAMD-K04).

摘　　要：The timing of the initial Indo-Asian collision is a subject of debate for a long time.Besides,the magmatic trace of the collisional process is also unclear.In the present study,the authors report Early Eocene leucocratic sill/dike swarms in the northern edge of the Nymo intrusive complex of the Gangdese belt,southern Tibet.The Nymo intrusive complex was emplaced at ca.50–47 Ma and surrounded by the metamorphosed Jurassic-aged Bima Formation volcano-sedimentary sequence along its northern side.At outcrops,the leucocratic sills/dikes intruded along or truncated the deformed foliations of the host Bima Formation,which has been subject to high-temperature amphibolite-facies metamorphism at ca.50–47 Ma.Detailed cathodoluminescence image analyses reveal that the zircon grains of the leucocratic sills/dikes have core-mantle textures.The cores yield the Jurassic ages comparable to the protolith ages of the Bima Formation.In contrast,the mantles of zircon grains yield weighted mean ages of ca.49–47 Ma,representing the crystallization timing of these leucocratic sills/dikes.The coeval ages for the Nymo intrusive complex,the high-temperature metamorphism,and the leucocratic sills/dikes indicate that a close relationship exists among them.The authors tentatively suggest that these leucocratic sills/dikes were generated from partial melting of the Jurassic-aged Bima Formation volcanic rocks,triggered by the high heat from the magma chamber of the Nymo intrusive complex.This Early Eocene tectono-thermal event of coeval magmatism,metamorphism and partial melting was most likely formed during the Indo-Asian collisional setting.

关 键 词：Leucocratic sill/dike swarm Early Eocene Indo-Asian collision GANGDESE Tibet China 

分 类 号：P534.53[天文地球—古生物学与地层学] P542[天文地球—地质学]