Cordierite-bearing granulites from Ihosy,southern Madagascar:Petrology,geochronology and regional correlation of suture zones in Madagascar and India  

作　　者：Li Tang Meng Pan Toshiaki Tsunogae Yusuke Takamura Yukiyasu Tsutsumi N.O.T.Rakotonandrasana 

机构地区：[1]School of Earth Sciences and Resources,China University of Geosciences Beijing,29 Xueyuan Road,Beijing,100083,China [2]Graduate School of Life and Environmental Sciences,University of Tsukuba,Ibaraki,305-8572,Japan [3]Department of Geology,University of Johannesburg,Auckland Park,2006,South Africa [4]Department of Geology and Paleontology,National Museum of Nature and Science,Ibaraki,305-0005,Japan [5]Yokohama National University,Yokohama,240-8501,Japan

出　　处：《Geoscience Frontiers》2019年第6期2007-2019,共13页地学前缘（英文版）

基　　金：Partial funding for this project was produced by a Grant-in-Aid for Scientific Research(B) from Japan Society for the Promotion of Science(JSPS) to Tsunogae(Nos.22403017,26302009 and 18H01300)

摘　　要：Madagascar,a major fragment of Gondwana,is mainly composed of Precambrian basenent rocks formed by Mesoarchean to Neoproterozoic tectono-thernial events and recording a Pan-African metamorphic overprint.The Ranotsara Shear Zone in southern Madagascar has been correlated with shear zones in southern India and eastern Africa in the reconstruction of the Gondwana supercontinent.Here we present detailed petrology,mineral chemistry,metamorphic P-T constraints using phase equilibrium modelling and zircon U-Pb geochronological data on high-grade metamorphic rocks from Ihosy within the Ranotsara Shear Zone.Garnet-cordierite gneiss from Ihosy experienced two stages of metamorphism.The peak mineral assemblage is interpreted as garnet+sillimanite+cordierite+quartz+plagioclase+Kfeldspar+magnetite+spinel+ilmenite,which is overprinted by a retrograde mineral assemblage of biotite+garnet+cordierite+quartz+plagioclase+K-feldspar+magnetite+spinel+ilmenite.Phase equilibria nodelling in the system Na2 O-CaO-K2 O-FeO-MgO-Al2 O3-SiO2-H2 O-TiO2-Fe2 O3(NCKFMASHTO)indicates peak metamorphic conditions of 850-960℃ and 6.9-77 kbar,and retrograde P-Tconditions of<740℃ and<4.8 kbar,that define a clockwise P-T path.Near-concordant ages of detrital zircon grains in the garnet-cordierite gneiss dominantly exhibit ages between 2030 Ma and 1784 Ma,indicating dominantly Paleoproterozoic sources.The lower intercept age of 514±33 Ma probably indicates the timing of high-grade metamorphism,which coincides with the assembly of the Gondwana supercontinent.The comparable rock types,zircon ages and metamorphic P-T paths between the Ranotsara Shear Zone and the Achankovil Suture Zone in southern India support an interpretation that the Ranotsara Shear Zone is a continuation of the Achankovil Suture Zone.Madagascar,a major fragment of Gondwana,is mainly composed of Precambrian basenent rocks formed by Mesoarchean to Neoproterozoic tectono-thernial events and recording a Pan-African metamorphic overprint.The Ranotsara Shear Zone in southern Madagascar has been correlated with shear zones in southern India and eastern Africa in the reconstruction of the Gondwana supercontinent.Here we present detailed petrology,mineral chemistry,metamorphic P-T constraints using phase equilibrium modelling and zircon U-Pb geochronological data on high-grade metamorphic rocks from Ihosy within the Ranotsara Shear Zone.Garnet-cordierite gneiss from Ihosy experienced two stages of metamorphism.The peak mineral assemblage is interpreted as garnet+sillimanite+cordierite+quartz+plagioclase+Kfeldspar+magnetite+spinel+ilmenite,which is overprinted by a retrograde mineral assemblage of biotite+garnet+cordierite+quartz+plagioclase+K-feldspar+magnetite+spinel+ilmenite.Phase equilibria nodelling in the system Na2 O-CaO-K2 O-FeO-MgO-Al2 O3-SiO2-H2 O-TiO2-Fe2 O3（NCKFMASHTO） indicates peak metamorphic conditions of 850-960 C and 6.9-77 kbar,and retrograde P-Tconditions of <740 C and <4.8 kbar,that define a clockwise P-T path.Near-concordant ages of detrital zircon grains in the garnet-cordierite gneiss dominantly exhibit ages between 2030 Ma and 1784 Ma,indicating dominantly Paleoproterozoic sources.The lower intercept age of 514±33 Ma probably indicates the timing of high-grade metamorphism,which coincides with the assembly of the Gondwana supercontinent.The comparable rock types,zircon ages and metamorphic P-T paths between the Ranotsara Shear Zone and the Achankovil Suture Zone in southern India support an interpretation that the Ranotsara Shear Zone is a continuation of the Achankovil Suture Zone.

关 键 词：PSEUDOSECTION modelling Cordierite-bearing granulite Detrital zircon GEOCHRONOLOGY Madagascar Gondwana SUPERCONTINENT 

分 类 号：P58[天文地球—岩石学]