Flotation and remelting of plagioclase in the Kalka Intrusion,central Australia: Petrological implications for anorthosite genesis

Flotation of early-formed plagioclase in the layered gabbroic Kalka Intrusion of central Australia was accompanied by gravitational settling of co-crystallizing pyroxenes. Remelting of the rising plagioclase upset the normal gravitational crystal-extractive processes which control classic basaltic fractionation trends. Together with high pressures of crystallization which cause orthopyroxene rather than olivine to be the first phase to precipitate, this may help to explain the eventual production of at least 800 m of plagioclase cumulates (anorthosites) as late-stage products of fractionation in Kalka. Addition or removal of melts at various stages of fractionation are further processes affecting the differentiation trends of layered intrusions. Variations in the occurrence of such processes may explain many of the differences between anorthosite suites throughout the world.