Application of chromite composition as a petrological indicator for determination of the Dehsheikh ultramafic complex origin (south of Kerman Province, Iran)

Chromite is one of the important mineral in all lithologies of the Dehsheikh ultramafic complex (South of Baft, Kerman Province) with different shapes and abundances. In the Dehsheikh harzburgites, this mineral present with two distinct generations. The first generation is refractory with variable Cr# values (between 46.2 to 60%) and contains low Al2O3 content (between 21 to 44.4 wt%). The second generation, as interstitial phase, is more Cr depleted and enriched in Al2O3 than the first one. Chemical composition of chromites from the Dehsheikh lherzolites is more similar to the second-type chromites of the Dehsheikh harzburgites. In the Dehsheikh irregular dunites, there are different shapes of chromites. The first group is chemically similar to those of the Dehsheikh chromitites, while the composition of second group is close to the harzburgitic refractory chromites. Cr-spinel in the Dehsheikh chromitties is characterized by high Cr# values (between 69 to 79) and in genetic diagram shows boninitic affinity. In TiO2 vs. Al2 O3 wt% discrimination diagram, the Dehsheikh chromites plot in suprasubduction zone field. Olivine-spinel geothermometry calculations on the Dehsheikh peridotites indicate subsolidus equilibrium temperatures (930 to 1080°C) for these rocks, while oxygen fugacity estimations yield values varing from +1.53 for the Dehsheikh lherzolites to +3.94 for irregular dunites. These values can be found in suprasubduction zone settings. In general, a suprasubduction zone with aqueous fluids derived from subducted oceanic slab is responsible for the formation of the Dehsheikh depleted peridotites and associated chromitites.