High-temperature retrogression of granulite-facies marbles from the Reynolds Range Group, Central Australia: Phase equilibria, isotopic resetting and fluid fluxes

Reynolds Range Group rocks underwent granulite-facies metamorphism (M₂) at ∼1·6 Ga (∼5 kbar, 750-800°C) and were subsequently retrogressed in narrow strike-parallel zones at 1·59-1·57 Ga. Within these zones, metacarbonates that initially equilibrated at Xco₂>0·8 during M₂ were mineralogically reset by the infiltration of water-rich fluids (Xco₂≤0·02-0·3) at 650-700°C and 3-4 kbar. δ¹⁸O(Carb) values of the retrogressed metacarbonates were variably reset during fluid infiltration, with the lowest values (10-13‰) suggesting that the fluids that caused retrogression were exsolved from segregated partial melts, themselves derived from the underlying granulite-facies metapelites. Mineralogical and isotopic resetting were locally accompanied by silica metasomatism. The mineralogically reset marbles record time-integrated fluid fluxes of typically ∼10¹-10² m³/m² and metasomatic rocks record time-integrated fluid fluxes as high as ∼10³-10⁴ m³/ m². For upward flow of high-temperature fluids through the marbles over a distance of ∼200 m in ∼18 Ma, the observed mineralogical and isotopic resetting, and metasomatism require intrinsic permeabilities between ∼10^-22 and 10^-19 m² that vary across strike on a centimetre to metre scale, indicating that fluid flow was strongly channelled.