Physicochemical conditions of crystallization of dunites of the Nizhnii Tagil Pt-bearing massif (Middle Urals) |
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| Institution: | 1. V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia;2. Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia;3. Institute of Geology, Ufa Science Center, Russian Academy of Sciences, ul. Karla Marksa 16/2, Ufa, 450000, Russia;4. Yu.A. Kosygin Institute of Tectonics and Geophysics, Far Eastern Branch of the Russian Academy of Sciences, ul. Kim-Yu-Chena 65, Khabarovsk, 680000, Russia;5. ARC Centre of Excellence in Ore Deposits (CODES COE), University of Tasmania, Private Bag 79, Hobart, Tasmania 7001, Australia;1. Department of Geology, Faculty of Science, Kafrelsheikh University, El-Geish Street, 33516 Kafrelsheikh, Egypt;2. Department of Earth Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa 920-1192, Japan;3. Research and Development Center for Ocean Drilling Science, JAMSTEC, Yokosuka 237-0061, Japan;1. Dipartimento di Scienze della Terra e del Mare, Università di Palermo, Via Archirafi 22, 90123 Palermo, Italy;2. Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Palermo, Via U. La Malfa 153, 90146 Palermo, Italy;3. Université d''Orléans, ISTO, UMR 7327, 45071, Orléans, France;4. CNRS/INSU, ISTO, UMR 7327, 45071 Orléans, France;5. BRGM, ISTO, UMR 7327, BP 36009, 45060 Orléans, France;1. Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, China;2. Institut für Geologische Wissenschaften, Freie Universität Berlin, Malteserstr. 74–100, 12449 Berlin, Germany;3. College of Earth Science, University of Chinese Academy of Sciences, Beijing 100049, China;4. GeoZentrum Nordbayern, Universität Erlangen–Nürnberg, Schlossgarten 5a, D-91054 Erlangen, Germany |
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| Abstract: | Studies of primary multiphase silicate inclusions in accessory Cr-spinels from the fine-grained dunites of the Nizhnii Tagil Pt-bearing massif reveal their similarity to melt inclusions trapped by chromite during its growth. The analyzed Cr-spinels with multiphase silicate inclusions differ in composition from ore chromites of the same massif and from chromites (with melt inclusions) from ultramafic oceanic complexes but are similar to Cr-spinels in dunites from Pt-bearing alkaline ultramafic massifs (Konder and Inagli). According to petro- and geochemical data on heated multiphase silicate inclusions, the studied Cr-spinels crystallized with the participation of subalkalic picrobasaltic melts similar to the magmas of the Konder Pt-bearing massif and having almost the same chemical composition as tylaites. The differences between the compositions of olivines formed within the multiphase silicate inclusions and of the rock-forming minerals show that the studied Cr-spinels formed from an intercumulus liquid melt in the olivine crystal interstices during the cumulate crystallization of most of the Nizhnii Tagil massif dunites in the intrusive chamber. Numerical modeling based on the compositions of heated multiphase silicate inclusions in accessory Cr-spinels demonstrates that olivines and Cr-spinels from the studied dunites crystallized at 1430 to 1310 °C and then olivine formation continued to 1280 °C during the evolution of melts. |
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