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Journal of Applied Sciences

Year: 2009 | Volume: 9 | Issue: 5 | Page No.: 874-882
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Authors

Z. Tahmasbi

M. Khalili

A. Ahmadi-Khalaji

Keywords

Research Article

Thermobarometry of the Astaneh Pluton and its Related Subvolcanic Rocks (Sanandaj-Sirjan Zone, Western Iran)

Z. Tahmasbi, M. Khalili and A. Ahmadi-Khalaji
The Astaneh area belongs to the Sanandaj-Sirjan Zone (SSZ) in Western Iran. The igneous rocks in this area consist of tonalite, granodiorite, monzogranite and subvolcanic rocks (rhyodacites). The mineral chemistry and microprobe analysis of mineral assemblages in these rocks indicate that the magma in this area has a metaluminous to slightly peraluminous composition, related to calc-alkaline, arc-type magmas and displays features typical of I-type granitoids. Also, the average of minimum pressure is estimated at 1.37 kbars in tonalites whereas the maximum pressure is 6.58 kbars in pargasite in dacitic enclaves. The maximum temperature is 767 °C in pargasitic amphibole crystallized in dacitic enclave whereas the minimum temperature is 650 °C in tonalite. All analyzed samples have log fO2 in the range between -13 (in dacitic enclave) to -18.3 (in tonalite ) and -15 (in tonalitic enclave), respectively, which show this magma crystallized in high fO2. The presence of phenocrysts of plagioclase (An = 80-90) together with plagioclase (An = 35-40), pargasitic amphibole in dacitic enclave and oscillatory zoned plagioclase in rhyodacites might be accounted for by a magma mixing model in the subvolcanics of Astaneh.
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