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Chromite is a key magmatic mineral frequently used as petrogenetic indicatorof physico-chemical conditions of mafic magma crystallization. In this work,magnesiochromite and chromite solubility in a natural basalt and an iron-freehaplobasalt was investigated at 1440{\deg}C and atmospheric pressure undercontrolled CO-CO2 gas mixtures corresponding to the range two log units belowto two log units above the fayalite-magnetite-quartz buffer. The source ofchromium was either natural chromite or synthetic Cr2O3, the latter reactingwith the basaltic liquids to form a magnesiochromite. The highestconcentrations of Cr in haplobasaltic melts are found in equilibrium withmagnesiochromite, depending on redox conditions. In detail, at low fO2, liquidshave high Cr contents, but the variation of log [Cr, ppm] is not a linearfunction of log fO2. Using our new data and data from the literature a modelfor Cr concentrations at chromite/magnesiochromite saturation in silicate meltshas been developed based upon a thermodynamic formalism. Our model may be usedto assess the effect of melt composition on chromite and magnesiochromitesolubility in silicate melts during peridotite melting and assimilation. Atmoderate and high oxygen fugacities, concentration levels of Cr at chromitesaturation are higher for ultramafic than for felsic rocks. Our data imply thatassimilation of magnesiochromite-bearing serpentinite lithosphere could resultin high Cr contents in mafic melts, triggering massive crystallization ofchromite, especially upon the system hydridization, cooling, oxidation andmagma degassing. Our model may be applied for quantitative prediction ofchromite crystallization and formation of the terrestrial mantle-crusttransition zones and mantle represented by chromitites and dunites.

New model of chromite and magnesiochromite solubility in silicate melts