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    Metamorphism evolution of mafic granulite from the Larsemann Hills,East Antarctica
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    Abstract:
    The Larsemann Hills are located in the central part of the Prydz tectonic belt in East Antarctica. The study of granulite metamorphism of this area is essential to understanding the tectonic nature of the Prydz belt. The petrographic study of the garnetbearing mafic granulite boulder collected from the region demonstrates that pre-peak prograde mineral assemblage( M1) consists of hb+ opx ± cpx + pl + bi + ilm ± q ± mt,and peak metamorphic assemblage( M2) comprises g + opx + cpx + hb + ilm ± mt ± q,whereas the symplectite opx + pl + bi + ilm ± mt represents a superimposed assemblage( M3) associated with a decompression event. Mineral chemistry shows that garnets and orthopyroxenes in the mafic granulite have weak compositional zonings. Through the use of THERMOCALC program,the thermodynamic modeling in the NCFMASHTO system has been undertaken for the mafic granulite.Combined with conventional thermobarometers and the average P-T estimates,P-T conditions of the different metamorphic stages are estimated as 650 ~ 750℃ /5. 5 ~ 6. 5kb( M1),850 ~ 950℃ /8 ~ 8. 5kb( M2),and 800 ~ 900℃ /5. 5 ~ 6. 5kb( M3),respectively.Its metamorphism evolution of the mafic granulite is a typical post-peak isothermal decompression( ITD) clockwise P-T path. Compared with the mafic granulites in this region,we argue that this sample may originate from basement in Larsemann Hills. Combined with available chronological data in the region,it is suggested that the peak metamorphism likely corresponds to the Greenville high-grade tectonism,whereas post-peak retrograde metamorphism may be related to the Pan-African high-grade tectonism,implying that the PanAfrican Prydz belt could be an intracontinental mobile belt.
    The Archean metamorphism in the southwestern Siberian craton was confirmed by the studies of the Kitoy and Irkutsk blocks. However, the parameters of the metamorphism process are still poorly investigated. The article presents the first results of studying the metamorphism conditions of garnet amphibolites sampled from the Kitoy sillimanite deposit. The reaction relationships of the studied minerals give grounds to distinguish two episodes of the regional metamorphism. At the end of the first episode, (Т=710–770 °С and Р=8.3–8.8 kb), the pressure reduced to 1.3–2.5 kbar at T=700 °C at the retrograde stage, and amphibole-plagioclase rims formed around garnet grains. During the second episode of metamorphism, the temperature reached 890 °С (granulite facies), and Cpx+Opx paragenesis replaced hornblende. The second episode of metamorphism is not evident in all the samples (considering the same bulk rocks composition of the rocks), which suggests its local character.
    Paragenesis
    Hornblende
    Amphibole
    Sillimanite
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    of the HGC. This decompressional process, probably initiated in The Hwacheon granulite complex (HGC), occupying the norththe kyanite stability field, reached pressures of >3–6 kbar at eastern margin of the Gyeonggi massif, consists mainly of gar660–750°C. The clockwise P–T path may reflect the exhumation netiferous leucocratic gneiss and leucogranite together with minor of a deep-seated crustal segment along discrete, ductile shear zones kyanite–garnet gneiss, aluminous gneiss, mafic granulite and garnet during the Permo-Triassic collisional orogeny prevalent in Far-East amphibolite. Mineral assemblages and reaction textures in various Asia. rock types of the HGC document five distinct metamorphic stages: pre(M1) and peak (M2) granulite-facies metamorphism; lower temperature, high (M3) and low (M4) pressure upper amphibolitefacies metamorphism; and local retrogression (M5) producing andalusite-bearing assemblages. Each metamorphic stage can be in
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