Spinel mineralogy evidence to determine the origin of Abgarm ultramafic complex (South of Kerman province)

Abstract

Abgarm ultramafic complex in the south of Kerman province is a part of Esfandagheh - Haji Abad ophiolite which is located in the northern edge of Zagros thrust. The complex contains harzburgites, lherzolites, dunites, and chromitites. Harzburgite is the main lithology of Abgarm peridotites and dunites containing lens-shaped chromites are arranged in irregular layers between them. Some evidence such as recrystallization of grain boundaries, curved shapes boundaries, and exsolution lamellae of clinopyroxenes in orthopyroxenes in the harzburgites and lherzolite show that the peridotites of this studied complex, passed the high-temperature deformation in the upper mantle and then they have emplaced in the crust. Petrography and mineral chemistry evidences show that there are two groups of chrome spinel in Abgarm complex. The first group is the disseminated chrome spinels in the peridotites and the other group is the chrome spinels in dunites and chromitites. Chemical analysis of spinels in studied rocks shows that in these crystals maximum amounts of Cr# belong to those that exist in the dunites and chromitites (60.76 – 63.81) and the minimum is for those in the lherzolites (11 – 13.50). Chemical composition of chrome spinels from the harzburgites and lherzolites are similar to those exist in Alpine peridotites with about 5 to 15% partial melting and probably they are formed in a back-arc basin environment while the dunites and chromitites of the complex can be caused by the reaction of the basaltic melts of the back-arc basin with peridotites.