Spinel as the most stable crystalogeraphic phases against serpentinaziation in peridotites of Baft ophiolite mélange in Kerman province

Baft coloured mélange with approximate area 617 km2, is located along Baft and Shahr-e-Babak major faults in south of Kerman province. Field and microscopic studies on peridotites, chromitites and related dunites in this area indicate that they are formed in mantle environment. Because peridotites in this mélange have been deeply altered (serpentinized), primary minerals such as olivine and pyroxene have been changed into secondary minerals, spinels are only resistant primary minerals against alteration in these rocks that has been survived in completely serpentinized rocks. In this study, chemical compositions of spinel's unaltered cores have been used for the petrogenesis and tectonic setting of the studied peridotites and chromitites. Based on evidences, the studied lithologies can be divided into two groups. The first group is peridotites include harzburgite, dunite and lherzolite that belong to Alpian type peridotites and the harzburgites, probably resulted from 15-20 percent partial melting of a fertile lhrzolitic mantle. Second groups are chromitites for which a magmatic genesis could be assumed. The studied chromitites are podiform and their parental magma is boninite. The chromites with average Cr2O3=62.8% and Cr#=0.83 are classified as Cr-rich chromitites or as the first grade type chromites in the world. Cr# and Mg# values indicate that the studied chromitites have been crystallized from boninite magmas, probably in suprasubduction zone setting in a back arc environment.