Stable isotope constraints on the mechanism of fluid flow during contact metamorphism around the Marulan Batholith, NSW, Australia

The Bungonia Limestone was contact metamorphosed adjacent to the Glenrock G ranodiorite at Marulan, NSW, Australia. At >60 m from the contact the limes tone is a pure calcite marble. Closer it is extensively skarned in breccia zones that represent channellways for metasomatic, magmatically-derived flu ids. The marble is typically little reset in delta(18)O (delta(18)O > 20 pa rts per thousand) even within millimetres of the skarn breccias. The patter n of metasomatism and isotope resetting around and within the skarn zones d oes not accord with models that assume the initial presence of a fluid fill ed porosity. Instead, the data suggest hydrofracture of metasomatic fluids into initially dry rocks. (C) 2000 Elsevier Science B.V. All rights reserve d.