The fluid regime of crystallization of water-saturated granitic and pegmatitic magmas: a physicochemical analysis |
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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. Tomsk State University, pr. Lenina 36, Tomsk, 634050, Russia;1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China;2. Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China;3. Institute of Geophysics and Geomatics, China University of Geosciences, Wuhan 430074, China;4. Department of Earth and Space Science and Engineering, York University, Toronto M3J 1P3, Canada;5. Department of Geography, York University, Toronto M3J 1P3, Canada;1. State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences and Resources, China University of Geosciences (Beijing), Beijing 100083, China;2. Centre for Geoscience Computing, School of Earth Sciences, The University of Queensland, Brisbane, QLD 4072, Australia;1. Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria;2. Department of Geology, Faculty of Science, Minia University, El-Minia, 61519, Egypt;3. Institute of Mineralogy and Petrology, Karl-Franzens University, Graz, Austria |
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| Abstract: | Miarolitic granite pegmatites are a unique natural object that makes it possible to study magmatic processes that lead to the formation of ore-forming media and systems. This paper summarizes modern views on phase transformations in aqueous silicate systems at parameters close to those of the transition from magmatic to hydrothermal crystallization. Comparison of phase diagrams and the results of study of pegmatite-forming media permits making conclusions about the crystallization of the water-saturated magmas of miarolitic granite pegmatites. The fluid regime of aqueous granite systems of simple composition, not enriched in fluxing components, is determined mainly by magma degassing or the supply of volatiles with flows of transmagmatic fluids. These processes cause the separation of essentially carbon dioxide or essentially hydrous fluid. During the evolution of such magmas, crystallization from silicate melt is separated in PT-space and, possibly, in time from the crystallization from aqueous or mixed carbon dioxide-aqueous super- and subcritical solutions. The evolution of chambers of water-saturated granitic and pegmatitic magma enriched in F, B, and alkali metals presupposes the formation of a heterogeneous mineral-forming medium in which crystallization occurs in the magmatic melt at high-temperature stages; as temperature decreases, crystallization can proceed in hydrous fluid, hydrosilicate, and/or hydrosaline liquids simultaneously. Hydrothermal crystallization can also take place in a heterogeneous medium consisting of aqueous solutions of different salinities and vapor or vapor-carbon dioxide gas mixture. The relationship between different fluid regimes during the evolution of volatile-saturated granitic and pegmatitic magmas determines the variety of postmagmatic rocks accompanying granite massifs. |
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