Study of micro-inclusions in chromian spinel : concordant and discordant chromitite from Wadi Hilti, northern Oman ophiolite

Abstract

Micro-inclusions in chromian spinel of concordant and discordant chromitites from the northern Oman ophiolite (Wadi Hilti) were examined to understand the origin(s) of chromitites. There are two kinds of micro-inclusions; (1)Needle-like exsolution lamellae mainly consist of diopside and enstatite, and (2)globular inclusions composed of enstatite, pargasite and Na-phlogopite. The latter inclusions are contained in both chromitites, but the former inclusions are contained only in the concordant chromitites. Spinels of UHP chromitites from Luobusa ophiolite (Tibet) are completely free from globular inclusions. The globular inclusions mainly composed of pargasite indicate shallow origins, and the exsolution lamellae suggest subsolidus exsolution of silicate components from spinel during cooling of the concordant chromitite. On the other hand, the UHP chromitite is obviously distinct in origin from the Hilti chromitites from Oman.