Mineral chemistry of a Cenozoic igneous complex,the Urumieh–Dokhtar magmatic belt,Iran: Petrological implications for the plutonic rocks |
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| Authors: | Maryam Honarmand Nematollah Rashidnejad Omran Franz Neubauer Ghasem Nabatian Mohammad Hashem Emami Manfred Bernroider Jamshid Ahmadian Mohammad Ebrahimi Xiaoming Liu |
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| Institution: | 1. Department of Earth Sciences, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan, Iran;2. Department of Geology, Faculty of Basic Sciences, Tarbiat Modares University, Tehran, Iran;3. Department of Geography and Geology, University of Salzburg, Salzburg, Austria;4. Department of Geology, Faculty of Science, University of Zanjan, Zanjan, Iran;5. Research Institute for Earth Sciences, Geological Survey of Iran, Tehran, Iran;6. Department of Geology, Payame Noor University, Iran;7. State Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an, China |
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| Abstract: | The Niyasar plutonic complex, one of the Cenozoic magmatic assemblages in the Urumieh‐Dokhtar magmatic belt, was the subject of detailed petrographic and mineralogical investigations. The Niyasar magmatic complex is composed of Eocene to Oligocene mafic rocks and Miocene granitoids. Eleven samples, representing the major rock units in the Niyasar magmatic complex and contact aureole were chosen for mineral chemical studies and for estimation of the pressure, temperature, and oxygen fugacity conditions of mineral crystallization during emplacement of various magmatic bodies. The analyzed samples are composed of varying proportions of quartz, plagioclase, K‐feldspar, hornblende, biotite, titanite, magnetite, apatite, zircon, garnet, and clinopyroxene. Application of the Al‐in‐hornblende barometer indicates pressures of around 0.2 to 0.4 kbar for the Eocene–Oligocene mafic bodies and around 0.5 to 1.7 kbar for the Miocene granitoids. Hornblende‐plagioclase thermometry yields relatively low temperatures (661–780 °C), which probably reflect late stage re‐equilibration of these minerals. The assemblage titanite–magnetite–quartz as well as hornblende composition were used to constrain the oxygen fugacity and H2O content during the crystallization of the parent magmas in the Miocene plutons. The results show that the Miocene granitoids crystallized from magmas with relatively high oxygen fugacity and high H2O content (~5 wt% H2O). The Miocene granitoids show similar range of oxygen fugacity, H2O contents and mineral chemical compositions, which indicate a common source for their magmas. Although the crystallization pressures of the Miocene plutons discriminate various categories of plutonic bodies emplaced at depths of about 5.7–6.5 km (Marfioun pluton), about 4.2 km (Ghalhar pluton) and 1.9–2.3 km (Poudalg pluton), they were later uplifted to the same level by vertical displacement of faults. The emplacement depths of the Niyasar plutons suggest that the central part of the Urumieh‐Dokhtar magmatic belt has experienced an uplift rate of ca. 0.25–0.4 mm/yr from the Miocene onwards. |
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| Keywords: | calc‐alkaline plutons geobarometry geothermometry Iran mineral chemistry oxygen fugacity uplift rate Urumieh– Dokhtar magmatic belt 鉱 物 組 成 地 質 温 度 計 地 質 圧 力 計 酸 素 分 圧 上 昇 速 度 カ ル ク ― ア ル カ リ 深 成 岩 体 Urumieh‐Dokhtar火 成 岩 帯 イ ラ ン |
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