Fluid flow in metacarbonates associated with emplacement of the Bushveld Complex, South Africa

The 2.06 Ga Bushveld Complex (BC) intrudes the Transvaal Supergroup. Calcsi licate xenoliths within the mafic phase of the BC (Rustenburg Layered Suite , or RLS) preserve xenoliths with high-temperature (similar to 1200 degrees C), anhydrous mineralogies that were later metasomatised at 2059 +/- 1.1 M a (U-Pb titanite age) by hydrous, retrograde (similar to 600-700 degrees C) fluids. These fluids were in approximate O-isotopic equilibrium with host mafic rocks. In the aureole, marbles show significant (similar to 5-10 part s per thousand) but variable lowering of O-isotope values with increasing m etamorphic grade. Mineral assemblages were typically buffered to higher X-C O2 with increasing grade, except at the highest grades, where skarns and lo w-X-CO2 assemblages occur locally. These data are generally consistent with variable flow of fluid derived from devolatilisation of interlayered metap elites up-temperature towards the intrusion. Limited, low-temperature chann elling of low-O-18 fluids that had equilibrated with the RLS occurred along fault zones within the aureole. (C) 2000 Elsevier Science B.V. All rights reserved.