西藏羌塘中部猫耳山石榴角闪岩的岩石学、地球化学及年代学研究  

Petrology,geochemistry and geochronology of Maoershan garnet amphibolite from central Qiangtang,Tibet

作　　者：李超[1,2,3] 王根厚 赵中宝[1,3] 杨锋[2] 李典 闻俊豪[6] 王仕林 李海兵 LI Chao;WANG GenHou;ZHAO ZhongBao;YANG Feng;LI Dian;WEN JunHao;WANG ShiLin;LI HaiBing(Key Laboratory of Continental Tectonics and Dynamics of Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;China National Institute of Standardization,Beijing 100191,China;Jiangsu Donghai Continental Deep Hole Crustal Activity National Observation and Research Station,Lianyungang 222300,China;School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China;College of Earth Sciences,Chengdu University of Technology,Chengdu 610059,China;Administrative and Protection Bureau of China Precambrian Provincial Geological Nature Reserve,Kunming 650600,China;Exploration and Production Research Institute,Sinopec Northwest Oil Field Company,Urumqi 830011,China)

机构地区：[1]中国地质科学院地质研究所,自然资源部大陆动力学重点实验室,北京100037 [2]中国标准化研究院,北京100191 [3]江苏东海大陆深孔地壳活动国家野外观测研究站,连云港222300 [4]中国地质大学地球科学与资源学院,北京100083 [5]成都理工大学地球科学学院,成都610059 [6]中国前寒武系省级地质自然保护区管护局,昆明650600 [7]中国石油化工股份有限公司西北油田分公司勘探开发研究院,乌鲁木齐830011

出　　处：《岩石学报》2023年第12期3661-3684,共24页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(42202257);第二次青藏高原综合科学考察研究项目(2019QZKK0901);南方海洋科学与工程广东省实验室(广州)人才团队引进重大专项(GML2019ZD0201);中国地质调查局项目(DD20221630、121201103000150004);自然资源部深地动力学重点实验室项目(J2201)联合资助.

摘　　要：青藏高原腹地羌塘地体中部猫耳山增生杂岩内保留有早古生代变质记录,对研究冈瓦纳大陆北缘的早古生代构造格架和演化具有重要意义。猫耳山石榴角闪岩呈透镜状产出于斜长角闪岩内,主要由石榴石、角闪石、单斜辉石、斜长石、白云母、黝帘石、绿泥石、榍石和钛铁矿组成。石榴角闪岩的全岩地球化学分析表明其具有俯冲带上(SSZ型)蛇绿岩特征,与区域内寒武-奥陶纪蛇绿岩残片一致。根据岩相学、矿物化学、相平衡模拟以及锆石定年结果,得出石榴角闪岩的成因及变质过程如下:(1)石榴角闪岩原岩为~477Ma的特提斯洋蛇绿岩残片;(2)在394~383Ma发生麻粒岩相变质过程,峰期变质温压条件为~900℃、~1.55GPa,矿物组合为石榴石+角闪石+透辉石;(3)早期的折返导致其降温降压至~800℃、~1.0GPa,矿物组合为石榴石+角闪石+透辉石+斜长石;(4)进一步的角闪岩相退变质发生于358~348Ma,矿物组合为角闪石+斜长石+透辉石+钛铁矿,在石榴石周围和港湾处形成斜长石+角闪石的后成合晶结构。石榴角闪岩的P-T-t演化轨迹结合区域蛇绿岩和岩浆岩记录,指示早古生代特提斯洋壳俯冲、泥盆纪特提斯洋弧后扩张和石炭纪特提斯洋内岛弧增生的过程。Early Paleozoic metamorphic records were preserved in the Maoershan accretionary complex in the central Qiangtang in the hinterland of the Qinghai-Tibetan Plateau,which is of great significance for studying the Early Paleozoic tectonic evolution of the northern margin of the Gondwana.The Maoershan garnet amphibolite occurs as lenticular inside the amphibolite,and it is mainly composed of garnet,hornblende,diopside,plagioclase,muscovite,zoisite,chlorite,sphene and ilmenite.The whole-rock geochemical analysis of the garnet amphibolite shows that it has the characteristics of ophiolite in the subduction zone(SSZ type),which is consistent with the Cambrian-Ordovician ophiolite remnants in the region.According to petrography,mineral chemistry,phase equilibrium simulation and zircon dating results,the genesis and metamorphic process of the garnet amphibolite are revealed as follows:(1)The protolith of the garnet amphibolite was ophiolite remnant formed in the Tethys Ocean at~477Ma;(2)The granulite facies metamorphism occurred in 394~383Ma,with the peak metamorphism P-T conditions of~900℃and~1.55GPa and the mineral assemblage of garnet+amphibole+diopside;(3)Early exhumation lead to the decrease of P-T to~800℃and~1.0GPa,with the mineral assemblage of garnet+amphibole+diopside+plagioclase;(4)The further amphibolite facies retrograde metamorphism occurred at 358~348Ma,with the mineral assemblage of amphibole+plagioclase+diopside+ilmenite,while the plagioclase+amphibole worm-like symplectite remains at the harbor of the coarse-grained garnet.Combined with regional ophiolite and magmatic records,the P-T-t evolution process of garnet amphibolite indicates the Early Paleozoic subduction of the Tethys Ocean,the Devonian back-arc expansion,and the Carboniferous accretion of the island arc.

关 键 词：青藏高原羌塘地体 猫耳山增生杂岩 石榴角闪岩 P-T-T轨迹 古特提斯洋 

分 类 号：P588.34[天文地球—岩石学] P597.3[天文地球—地质学]