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

Abstract

The 2.06 Ga Bushveld Complex (BC) intrudes the Transval Supergroup. Calcsilicate xenoliths within the mafic phase of the BC (Rustenburg Layered Suite, or RLS) preserve xenoliths with high-temperature (~ 1200°C), anhydrous mineralogies that were later metasomatised at 2059 ± 1.1 Ma (U-Pb titanite age) by hydrous, retrograde (~600-700°C) fluids. These fluids were in approximate O-isotopic equilibrium with host mafic rocks. In the aureole, marbles show significant (~5-10‰) but variable lowering of O-isotope values with increasing metamorphic grade. Mineral assemblages were typically buffered to higher X(CO2) with increasing grade, except at the highest grades, where skarns and low-X(CO2) assemb..