Mineralogical and petrogenetic characteristics of the peridotites and associated podiform chromitites from Abgarm ultramafic complex (south-eastern Iran)

Abgarm ultramafic complex is a part of the Esfandagheh-Hajiabad coloured melange belt located in the south east of the Iranian segment of Alpine-Himalayan orogenic belt. The complex has faulted contacts with flysch-type sediments of the upper cretaceous ophiolite melange complex. Although Harzburgite is the dominant lithotype, dunites and lherzolites occur in lesser extents, where some dunites contain massive chromitite pods or bands. The chemistry of minerals of harzburgite samples reflects the depleted nature of these rocks and indicates that the Abgarm mantle peridotites experienced a melt extraction of less than 30%. Geothermo-barometric estimates indicate that the Abgarm harzburgites initially equilibrated at temperatures between 809-923 °C and then they re-equilibrated at 613-725 °C, in a range of pressures of 1.1 and 2.3 GPa. Moreover, fO2 calculation for these rocks gives a redox state (∆log=0.1-0.7 log-bar units) above the fayalite-magnetite-quartz buffer. Tectonomagmatic discrimination diagrams based on mineral compositions depict that Abgarm harzburgites and lherzolites evolved as abyssal peridotites, which shows a tendency towards SSZ peridotites and also reflects that they probably were formed in a back-arc basin environment. Dunites and chromitites of the complex can be produced by the reaction of the back-arc basin basaltic melts with the mantle peridotites.