Scientific Quarterly Journal of Geosciences

Scientific Quarterly Journal of Geosciences

Magma evolution and physicochemical conditions of the Ghohroud granitoid complex on mineral chemistry and thermobarometric data

Document Type : Original Research Paper

Authors
1 Department of Petrology, Faculty of Basic Sciences, Tarbiat Modares University, Tehran, Iran
2 Department of Geology, Payame Noor University, Tehran, Iran
10.22071/gsj.2026.533389.2209
Abstract
The Ghohroud granitoid complex, located southwest of Kashan in the central part of the Urumieh–Dokhtar Magmatic Arc (UDMA), mainly consists of granodiorite–tonalite rocks hosting mafic microgranular enclaves (MMEs) with compositions ranging from gabbrodiorite to tonalite. The main mineral assemblage includes amphibole, biotite, plagioclase, and alkali feldspar. Mineral chemistry indicates that plagioclase is andesine, amphiboles are Mg-rich hornblende, and biotites are also magnesium-rich. Amphiboles show relatively high Fe³/(Fe³ + Fe²) ratios, while magmatic ones are characterized by low total Al and Fe/(Fe + Mg) ratios, suggesting crystallization under moderately oxidizing conditions. Oxygen fugacity (ƒO), calculated relative to the nickelnickel oxide (NNO) buffer, ranges from 1012 to 1014 bar (ΔNNO +1.23) in tonalitic samples, and from 1014 to 1016 bar (ΔNNO +0.34) in granodioritic rocks and their associated enclaves. Thermobarometric calculations based on calcic amphiboles yield maximum pressures of about 4.39 kbar at 800 °C for tonalites, and around 3.89 kbar at 750 °C for granodiorites and their enclaves, corresponding to amphibole crystallization depths around ~12-16 km. Primary biotites in the Ghohroud granitoids crystallized slightly later, at 690–784 °C (average ~712 °C).
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Volume 36, Issue 2 - Serial Number 140
Summer 2026, Vol. 36, Issue 2, Serial No. 140
Spring 2026
Pages 67-84