Patterns of fluid flow in proterozoic calc-silicates: Fluid channeling and variations in fluid fluxes and intrinsic permeabilities

Calc-silicates in three Proterozoic terrains (Mt Isa, the Reynolds Range and the Grenville of Canada) record the influx of water-rich fluids through the resetting of mineral assemblages, stable-isotope rätios and major elements. In all cases time-integrated fluid fluxes are inferred to have varied by over an Order of magnitude on the millimetre to metre scale, and fluids were often channelled across strike. These results indicate that intrinsic permeabilities during metamorphism varied considerably over a small scale. It is suggested that fluid flow was within microfractures, and that the variations in intrinsic permeability reflect variable microfracture densities.