Clinopyroxene mineral chemistry of Peshtasar basalts, sedimentary basin of Moghan (NW Iran)

With the east–west exposure trend, Peshtasar basalts are in the sedimentary basin of Moghan (Talesh structural zone), in the northwest of Iran.The Peshtasar complex lithologically includes basalt, andesitic basalt or basaltic andesite, megaporphyric andesite, leucite tephrite and volcanic breccia. The main constituent minerals are plagioclase, clinopyroxene, and iddingsitized olivine in basalts and plagioclase megacryst, clinopyroxene, and leucite in tephrite. The results of the microprobe analyses of clinopyroxene reveal the diopside composition. Clinopyroxenes of Peshtasar basalts have igneous nature originated from alkaline and continental magmatic serries. The results of termobarometry studies indicate the crystallization range from 800 -1200 degrees centigrade and crystallization pressure less than 5 kb. There was no water in composition of the parent magma of these rocks. The titanium contents of clinopyroxenes were low, indicating the presence of titano-magnetite (opaque minerals) in the rock. The ferric iron values in clinopyroxenes represents a high oxygen fugacity of magma.