Chromite in the mantle section of the Oman ophiolite: A new genetic model

This paper reviews the compositional data (major elements, platinum group element [PGE] concentrations, Os- and O-isotopes) for chromites from the mantle section of the Oman ophiolite. Chromites in chromitite from the Oman ophiolite lie on a compositional spectrum between high-Cr#, boninite-like and low-Cr#, mid-oceanic ridge basalt-like end-members. The high-Cr# end-member is low in Ti, has a fractionated PGE pattern and is enriched in iridium group-platinum group elements (IPGE). The low-Cr# end-member has higher Ti and an unfractionated PGE pattern. The compositional variation in the chromitites reflects their crystallization from a range of different melt compositions. It is proposed that this wide variation in melt compositions was produced by the process of a melt-rock reaction, whereby a basaltic melt has reacted with harzburgitic mantle to yield successively more Cr-rich melts. In contrast to previous models, this approach does not require a change in the tectonic environment to explain the different chromite types.