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International audienceFluid 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 þ kyanite, andanthophyllite, respectively. Metamorphic petrology, fluid inclusions, and field data indicate that a lowH2O-activity carbon-saturated CO2-rich and a saline aqueous fluid infiltrated the Southern Marginal Zoneduring exhumation. The formation of anthophyllite after orthopyroxene established a regional retrogradeanthophyllite-in isograd and occurred at P-T conditions of w6 kbar and 610 C, which fixes the minimummole fraction of H2O in the CO2-rich fluid phase at w0.1. The maximum H2O mole fraction is fixed by thelower temperature limit (w800 C) for partial melting at w0.3. C-O-H fluid calculations show that theCO2-rich fluid had an oxygen fugacity that was 0.6 log10 units higher than that of the fayalite-magnetitequartzbuffer and that the CO2/(CO2þCH4) mole ratio of this fluid was 1. The presence of dominantlyrelatively low density CO2-rich fluid inclusions in the hydrated granulites indicates that the fluid pressurewas less than the lithostatic pressure. This can be explained by strike slip faulting and/or an increase ofthe rock permeability caused by hydration reactions

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