Large charnockite massifs occur in the high-grade Southern Granulite Terrain （SGT） and Eastern Ghats Belt （EGB） crustal provinces of Peninsular India. Available geochronological data indicate that the magmatism is...Large charnockite massifs occur in the high-grade Southern Granulite Terrain （SGT） and Eastern Ghats Belt （EGB） crustal provinces of Peninsular India. Available geochronological data indicate that the magmatism is episodic, associated with distinct orogenic cycles in the different crustal domains. The geochemical data also indicate a change in composition from trondhjemitic at - 3.0-2.9 Ga to domi- nantly tonalitic at - 2.6-2.5 Ga to tonalitic-granodiorite-granitic at - 2.0--1.9 Ga to dominantly tonalitic at 1.7--1.6 Ga to quartz monzonitic or tonalitic at - 1.0-0.9 Ga to granodiorite-granitic at - 0.8-0.7 Ga. The trondhjemitic and tonalitic end members are metaluminous, magnesian and calcic to calc-alkalic, characteristic of magnesian group charnockites. The granodioritic to granitic end members are metalumi- nous to slightly peraluminous, ferroan and calc-alkalic to alkali-calcic, characteristic of ferroan group charnockites. The quartz monzonitic end members are metaluminous to peraluminous, magnesian to ferro- an and calcic to calc-alkalic, neither characteristic of the magnesian group nor of the ferroan group of char- nockites. Based on the occurrence and difference in composition of the charnockite massifs, it is suggested that the charnockite magmatism registers the crustal growth of the Indian plate on its southern （SGT） and eastern （EGB） sides, along active continental margins by accretion of arcs.展开更多
Reaction textures and fluid inclusions in the -2.0 Ga pyroxene-bearing dehydration zones within the Sand River biotite-hornblende orthogneisses （Central Zone of the Limpopo Complex） suggest that the formation of the...Reaction textures and fluid inclusions in the -2.0 Ga pyroxene-bearing dehydration zones within the Sand River biotite-hornblende orthogneisses （Central Zone of the Limpopo Complex） suggest that the formation of these zones is a result of close interplay between dehydration process along ductile shear zones triggered by H2O-CO2-salt fluids at 750--800 ℃ and 5.5--6.2 kbar, partial melting, and later exsolution of residual brine and H2O-CO2 fluids during melt crystallization at 650--700 ℃. These processes caused local variations of water and alkali activity in the fluids, resulting in various mineral assemblages within the dehydration zone. The petrological observations are substantiated by experiments on the interaction of the Sand River gneiss with the H2O-CO2-（K, Na）Cl fluids at 750 and 800 ℃ and 5.5 kbar. It follows that the interaction of biotite-amphibole gneiss with H2O-CO2-（K, Na）CI fluids is accompanied by partial melting at 750--800 ℃. Orthopyroxene-bearing assemblages are characteristic for temperature 800 ℃ and are stable in equilibrium with fluids with low salt concentrations, while salt-rich fluids produce clinopyroxene-bearing assemblages. These observations are in good agreement with the petrological data on the dehydration zones within the Sand River olthogneisses.展开更多
1. Introduction The continental crust, covering nearly a third of the Earth＇s surface, is dominantly made up of granites and granodiorites （Rudnick and Gao, 2003）. Although the vast majority of these granitoids are...1. Introduction The continental crust, covering nearly a third of the Earth＇s surface, is dominantly made up of granites and granodiorites （Rudnick and Gao, 2003）. Although the vast majority of these granitoids are amphibole- and/or biotite-bearing, orthopyroxene-bearing granitoids form a minor but important component of the lower continental crust in many high-grade terrains （e.g., Bohlender et al., 1992; Kilpatrick and Ellis, 1992; Sheraton et al., 1992; Berger et al., 1995; Zhou et al.,展开更多
文摘Large charnockite massifs occur in the high-grade Southern Granulite Terrain （SGT） and Eastern Ghats Belt （EGB） crustal provinces of Peninsular India. Available geochronological data indicate that the magmatism is episodic, associated with distinct orogenic cycles in the different crustal domains. The geochemical data also indicate a change in composition from trondhjemitic at - 3.0-2.9 Ga to domi- nantly tonalitic at - 2.6-2.5 Ga to tonalitic-granodiorite-granitic at - 2.0--1.9 Ga to dominantly tonalitic at 1.7--1.6 Ga to quartz monzonitic or tonalitic at - 1.0-0.9 Ga to granodiorite-granitic at - 0.8-0.7 Ga. The trondhjemitic and tonalitic end members are metaluminous, magnesian and calcic to calc-alkalic, characteristic of magnesian group charnockites. The granodioritic to granitic end members are metalumi- nous to slightly peraluminous, ferroan and calc-alkalic to alkali-calcic, characteristic of ferroan group charnockites. The quartz monzonitic end members are metaluminous to peraluminous, magnesian to ferro- an and calcic to calc-alkalic, neither characteristic of the magnesian group nor of the ferroan group of char- nockites. Based on the occurrence and difference in composition of the charnockite massifs, it is suggested that the charnockite magmatism registers the crustal growth of the Indian plate on its southern （SGT） and eastern （EGB） sides, along active continental margins by accretion of arcs.
基金supported by Russian Foundation for Basic Research(project 10-05-00040 to OGS)Russian President Grants for Young Scientists(MD-222.2012.5 to OGS)+1 种基金grant from the National Science Foundation of South Africa(GUN:20531 92 to DDvR)University of Johannesburg as a part of the Russian South African scientific collaboration
文摘Reaction textures and fluid inclusions in the -2.0 Ga pyroxene-bearing dehydration zones within the Sand River biotite-hornblende orthogneisses （Central Zone of the Limpopo Complex） suggest that the formation of these zones is a result of close interplay between dehydration process along ductile shear zones triggered by H2O-CO2-salt fluids at 750--800 ℃ and 5.5--6.2 kbar, partial melting, and later exsolution of residual brine and H2O-CO2 fluids during melt crystallization at 650--700 ℃. These processes caused local variations of water and alkali activity in the fluids, resulting in various mineral assemblages within the dehydration zone. The petrological observations are substantiated by experiments on the interaction of the Sand River gneiss with the H2O-CO2-（K, Na）Cl fluids at 750 and 800 ℃ and 5.5 kbar. It follows that the interaction of biotite-amphibole gneiss with H2O-CO2-（K, Na）CI fluids is accompanied by partial melting at 750--800 ℃. Orthopyroxene-bearing assemblages are characteristic for temperature 800 ℃ and are stable in equilibrium with fluids with low salt concentrations, while salt-rich fluids produce clinopyroxene-bearing assemblages. These observations are in good agreement with the petrological data on the dehydration zones within the Sand River olthogneisses.
文摘1. Introduction The continental crust, covering nearly a third of the Earth＇s surface, is dominantly made up of granites and granodiorites （Rudnick and Gao, 2003）. Although the vast majority of these granitoids are amphibole- and/or biotite-bearing, orthopyroxene-bearing granitoids form a minor but important component of the lower continental crust in many high-grade terrains （e.g., Bohlender et al., 1992; Kilpatrick and Ellis, 1992; Sheraton et al., 1992; Berger et al., 1995; Zhou et al.,
