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| Experimental and petrological constraints on local-scale interaction of biotite-amphibole gneiss with H2O-CO2-（K, Na）Cl fluids at middle-crustal conditions： Example from the Limpopo Complex, South Africa | |
| 作者姓名： | Oleg G. Safonov Elizaveta I. Kovaleva Svetlana A. Kosova H.M. Rajesh Georgy A. Belyanin Maria A. Golunova Dirk D. Van Reenen |
| 作者单位： | [1]Institute of Experimental Mineralogy RAS, Chernogolovka, Moscow Region 142432, Russia [2]Department of Petrology, Moscow State University, Moscow 119899, Russia [3]Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park 2006, Johannesburg, South Africa [4]Labor fur Geoehronologie, Department fftr Lithosphfirenforschung, Universitiit Wien, Althanstrasse 14, A-1090 Vienna, Austria |
| 摘 要： | 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-CO-2-（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）Cl 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 arc in good agreement with the petrological data on the dehydration zones within the Sand River orthoeneisses. |
| 关 键 词： | Charnockite Fluid-rock interaction CO2-rich fluids NaCl-KCl brines Partial melting Experimental petrology |
| 收稿时间： | 13 February 2012 |
http://www.sciencedirect.com/science/article/pii/S1674987112000862 |
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| Oleg G. Safonov,Elizaveta I. Kovaleva,Svetlana A. Kosova,H.M. Rajesh,Georgy A. Belyanin,Maria A. Golunova,Dirk D. Van Reenen.http://www.sciencedirect.com/science/article/pii/S1674987112000862[J].Geoscience Frontiers,2012,3(6):829-841. | |
| Authors: | , Oleg GSafonov , Elizaveta IKovaleva , Svetlana AKosova , HMRajesh , Georgy ABelyanin , Maria AGolunova , Dirk DVan Reenen |
| Institution: | 1. Institute of Experimental Mineralogy RAS, Chernogolovka, Moscow Region 142432, Russia ;Department of Petrology, Moscow State University, Moscow 119899, Russia ;Department of Geology, University of Johannesburg, P.O.Box 524, Auckland Park 2006, Johannesburg, South Africa 2. Labor für Geochronologie, Department für Lithosph(a)renforschung, Universit(a)t Wien, Althanstrasse 14, A-1090 Vienna, Austria 3. Institute of Experimental Mineralogy RAS, Chernogolovka, Moscow Region 142432, Russia 4. Department of Geology, University of Johannesburg, P.O.Box 524, Auckland Park 2006, Johannesburg, South Africa |
| Abstract: | 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 °C and 5.5–6.2 kbar, partial melting, and later exsolution of residual brine and H2O-CO2 fluids during melt crystallization at 650–700 °C. 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 °C and 5.5 kbar. It follows that the interaction of biotite-amphibole gneiss with H2O-CO2-(K, Na)Cl fluids is accompanied by partial melting at 750–800 °C. Orthopyroxene-bearing assemblages are characteristic for temperature 800 °C 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 orthogneisses. |
| Keywords: | Charnockite Fluid-rock interaction CO2-rich fluids NaCl-KCl brines Partial melting Experimental petrology |
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