A comparison of trace element concentrations in chromite from komatiites, picrites, and layered intrusions: implications for the formation of massive chromite layers

By examining the minor and trace element contents of chromites from three intrusions—the Bushveld Complex (South Africa), Stillwater (USA), Great Dyke (Zimbabwe)—and comparing these chromite compositions with those magmas which they could have formed (komatiites picrites) we conclude that ( i) variations in Ti, V, Sc, Ga across stratigraphy individual layers do not support model magma mixing leading to chromite-only crystallization, ii) lowest levels intrusions crystallized komatiite liquids were contaminated continental crust, iii) highest Cr# incompatible a liquid closest komatiite, iv) all chromites, except Dunite Succession equilibrated also had pyroxene, v) show narrower range composition than vi) Chromites western limb contain much higher V other chromites. This requires either, oxygen fugacity fO 2 ) was lower or V-rich magma. We favor where silicate minerals cotectic proportions (?2:98). The chromite, silicates, transporting are emplaced into chamber. During emplacement separated due viscous particle flow form massive layer overlain by silicates.