Metamorphic Evolution of Garnet Amphibolite from the Yaganbuyang Area in the South Altyn Orogen,West China:Insights from Phase Equilibria Modeling and Geochronology

作     者：Xin Li Liang Liu Xiaoying Liao Yongsheng Gai Tuo Ma Guojian Geng Tong Li Xin Li;Liang Liu;Xiaoying Liao;Yongsheng Gai;Tuo Ma;Guojian Geng;Tong Li

作者机构：State Key Laboratory of Continental DynamicsDepartment of GeologyNorthwest UniversityXi'an 710069China 

出 版 物：《Journal of Earth Science》 (地球科学学刊（英文版）)

年 卷 期：2023年第34卷第3期

页      面：640-657页

核心收录：

学科分类：0709[理学-地质学] 070901[理学-矿物学、岩石学、矿床学] 07[理学] 

基　　金：supported by the National Natural Science Foundation of China(Nos.42030307,41972054,41430209,41672187,41902051) the MOST Special Fund from the State Key Laboratory of Continental Dynamics,Xi’an,China 

主　　题：South Altyn Orogen garnet amphibolite phase equilibria modeling zircon U-Pb dating geochronology 

摘      要：Garnet amphibolite is one of the common metabasic rocks exposed in collisional orogenic belt,the metamorphic evolution of which is associated closely with orogenic *** Yaganbuyang garnet amphibolites occur as blocks hosted by massive granitic gneiss,and consist mainly of hornblende,garnet,clinopyroxene,plagioclase,biotite,quartz with minor rutile/ilmenite and phengitic *** garnet amphibolites were interpreted to have experienced decompression-dominated evolution that can be divided into three generations(M1,M2,M3),based on the petrographic observations and phase equilibria modeling calculated by *** assemblage of the first generation(M1)is inferred to possibly be dominated by garnet+omphacite+rutile+phengite+quartz,which is modeled to be roughly stable at P25 kbar and T800℃.The second generation(M2)is characterized by the local symplectites of clinopyroxene+plagioclase produced from omphacite,indicating a near-isothermal decompression from~23.8 kbar/875℃to~10 kbar/852℃.The third generation(M3)is marked by the kelyphitic rims of plagioclase+hornblende around garnet and of hornblende+ilmenite around clinopyroxene,involving the late-stage retrogression from~9.8 kbar/848℃to~5.8 kbar/645℃.Zircon U-Pb dating yielded one group metamorphic age of c.500 Ma that is interpreted to represent the timing of the peak eclogite-facies metamorphism.A combination of petrography observation,phase modeling results and geochronology data suggests that the Yaganbuyang garnet amphibolites have once undergone eclogite-facies metamorphism by continental subduction rather than crustal ***,the Yaganbuyang area is an eastward extension part of the South Altyn HP-UHP metamorphic belt.