Mineral Chemistry and Tectonic Setting of Peridotites of the Garmab Ophiolitic Sequence, NE Kamyaran

Kamyaran ophiolite sequence as a part of the Kermanshah ophiolite-radiolarite belt is located in the northeast of Kamyaran, northwest Iran. No complete ophiolitic sequence is seen in this area and only a peridotite part including harzburgite, lherzolite and serpentinite is observed. The sequence is cut by some gabbroic dykes. According to the microprobe analytical data, olivine in the studied rocks displays forsterite (Fo) contents of 90.11 to 92.5. Their clinopyroxenes are diopside and augite. Orthopyroxenes in the mentioned rocks are compositionally enstatite with Mg# ranging from 0.91 to 0.92. The studied pyroxenes are rich in chromium, with 0.80-01.39 wt% chromium oxide. High contents of chromium in clinopyroxenes and orthopyroxenes are consistent with the degree of partial melting and the depleted nature of these rocks. The studied Cr-spinels are Al rich in composition and their average Cr# and Mg# are 0.37 and 0.69, respectively. From the mineral chemistry of harzburgites and lherzolites, it is inferred that the studied rocks are similar to the abyssal peridotites belonging to residual peridotites remained after extraction of mid-ocean ridge basalt (MORB) in a back arc basin setting.