Fluid-rock interaction in retrograde granulites of the Southern Marginal Zone,Limpopo high grade terrain,South Africa

作     者：Jan Marten Huizenga Dirk van Reenen Jacques L.R.Touret 

作者机构：Unit of Environmental Sciences and ManagementNorth-West UniversityPrivate Bag X60012520South Africa Economic Geology Research Institute(EGRU)School of Earth and Environmental SciencesJames Cook UniversityTownsvilleQLD 4811Australia Department of GeologyUniversity of JohannesburgJohannesburgSouth Africa Institut de Mineralogie.de Physique des Materiauxet de Cosmochimie(IMPMC) Sorbonne Universites UPMC Univ Paris 06UMR CNRS 7590 Museum National d'Histoire Naturelle.IRD UMR 206.4 Place Jussieu.F-75005 

出 版 物：《Geoscience Frontiers》 (地学前缘（英文版）)

年 卷 期：2014年第5卷第5期

页      面：673-682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：DDvR would like to thank the NRF(Grant No. IFR1202190048) the University of Johannesburg for financial support 

主　　题：GranuliteFluidLimpopoRetrogradeSouthern Marginal Zone 

摘      要：Fluid infiltration into retrograde granulites of the Southern Marginal Zone （Limpopo high grade terrain） is exemplified by hydration reactions, shear zone hosted metasomatism, and lode gold mineralisation. Hydration reactions include the breakdown of cordierite and orthopyroxene to gedrite ＋ kyanite, and anthophyllite, respectively. Metamorphic petrology, fluid inclusions, and field data indicate that a low H2O-activity carbon-saturated CO2-rich and a saline aqueous fluid infiltrated the Southern Marginal Zone during exhumation. The formation of anthophyllite after orthopyroxene established a regional retrograde anthophyllite-in isograd and occurred at P-Tconditions of -6 kbar and 610 ℃, which fixes the minimum mole fraction of H20 in the CO2-rich fluid phase at ~ 0.1. The maximum H20 mole fraction is fixed by the lower temperature limit （~800 ℃） for partial melting at -0.3. C-O-H fluid calculations show that the CO2-rich fluid had an oxygen fugacity that was 0.6 log10 units higher than that of the fayalite-magnetite- quartz buffer and that the CO2/（CO2＋CH4） mole ratio of this fluid was 1. The presence of dominantly relatively low density CO2-rich fluid inclusions in the hydrated granulites indicates that the fluid pressure was less than the lithostatic pressure. This can be explained by strike slip faulting and/or an increase of the rock permeability caused by hydration reactions.