摘要
Based on the textural and crystallographic study of four chromitite sites in the Oman ophiolite, we show that chromite crystallized in situ at Moho transition zone, where exposed as podiform chromitite deposits. Crystallization operated either by crystal fractionation in a mini-magma chamber(Tuf dyke), or more commonly by meltrock reaction of a hydrated Cr-rich melt and enclosing dunite. Oxidizing conditions at Moho level triggered the crystallization of chromite at the expense of the corroded olivine network. High-temperature mantle flow(1100-1200 ℃), recorded in the joined reacting olivine aggregates, constrains the timing of chromitite formation. Models of genesis of chromitite deposits must account for a hydrous component initiating partial melting of refractory peridotite, and the revealed occurrence of ultra-high-pressure cratonic phases included in some chromite crystals of some ophiolitic chromitites.
