Numerical modeling of the effects of major components in the melt on the chrome-spinel stability and a possible solution of the origin chromitites problem

Abstract

Using a new model of the spinel-melt equilibrium SPINMELT-2.0, the effect of variations of fo-, fa-, en-, fs-, di-, an- and ab-components in high-Mg basaltic melts on the topology of the spinel liquidus was quantified. It has been established that enrichment of the melt in pyroxene components leads to an increase, and with plagioclase components, to a decrease in the solubility of chromite. This effect can be important during gravitational compaction of cumulates, accompanied by the extraction of intercumulus melt and its infiltration upward. In this case, one can expect a sequential re-equilibration of the infiltrating melt with cumulative piles of different composition. This suggests the possibility of transfer and new concentration of chrome-spinel at the postcumulus stage of solidification of layered intrusions. The nature of the concentration consists in the extraction of chrome-spinel into the melt enriched in pyroxene components, followed by its discharge during the reaction of this melt with a feldspar-rich matrix of proto-anorthosite layers. The realism of the proposed mechanism is evidenced by the well-known spatial association of chromite layers with anorthosites (intrusion of Ram island, Bushveld complex).