Petrogenetic evolution and tectonic environment of the harzburgites from Ab-Bid ultramafic complex (East of Hadji-Abad, Hormozgan province)

Ab-Bid ultramafic complex in the north of Hormozgan province is a part of Hadji-Abad-Esphandagheh ophiolitic belt. Harzburgite forms more than 90 volume percent of the complex and lherzolite, dunite, pyroxenite and chromitite are the other lithologies. The harzburgites occur as massive non-layered outcrops with oriented minerals. Textures such as orientation and elongation of crystals, recrystallization, clinopyroxene exsolution lamellae in orthopyroxenes and different generations of minerals in these rocks show that they have been formed in the upper mantle and then emplaced in the crust. Mineral chemistry data indicate that the Ab-Bid harzburgites formed in an environment similar to those considered for MORB peridotites and they have experienced about 15 % partial melting. Then, they affected by mantle metasomatism and were enriched in incompatible elements. Olivine-spinel thermometry in these harzburgites shows equilibrium temperatures of 1000-1200 ºC and suggests that they have been equilibrated in spinel peridotite field. Chemical evidence and tectonic setting of the studied harzburgites show that these rocks are similar to the abyssal peridotites and probably formed in a back arc basin environment. Ab-Bid harzburgites probably were part of mantle wedge over the Neotethys subducted slab in a back arc basin environment.