Genesis of the Ray-Iz chromitite, Polar Urals: Inferences to mantle conditions and recycling processes

Ophiolitic chromitites in the eastern sector of the Alpine-Himalayan and Polar Ural orogenic belts preserve evidence of formation under ultra-high-pressure (UHP), deep mantle conditions. The textural and compositional characteristics of microscopic and submicroscopic inclusions in magnesiochromite from the Ray-Iz ophiolites are considered as clues of their complex evolutionary history. Bulk-rock platinum-group-element (PGE) compositions of refractory and metallurgical chromitite ores (102–309 ppb) with generally IPGE>PPGE are consistent with supra-subduction zone (SSZ) metasomatism. The abundant unusual UHP phases (e.g., micro-diamonds, moissanite, coesite…etc.), together with clinopyroxene lamellae, and globular silicate inclusions in the Cr-spinel are seen as indications of deep mantle recycling of the mantle section of the Ray-Iz ophiolites. The calculated fO₂ values for dunite and chromitite (+1.17 to +4.16, generally above the FMQ buffer) are in line with interaction of mid-ocean ridge (MOR) or back-arc ophiolites with oxidized, Mg-rich silicic (boninitic) melts in a SSZ environment.