Geodynamics of rapid voluminous felsic magmatism through time |
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| Authors: | MJ Pankhurst BF Schaefer PG Betts |
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| Institution: | 1. Earth and Environmental Division, Los Alamos National Laboratory, P.O. Box 1663, M.S. J535, Los Alamos, NM 87545, United States;2. Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal H3A 0E8, Canada;3. School of Earth, Atmosphere and Environment, Monash University, 9 Rainforest Walk, VIC 3800, Australia;1. Key Laboratory of Orogen and Crust Evolution, Peking University, Beijing 100871, China;2. State Key Laboratory for Mineral Deposits Research, Nanjing University, Nanjing, 210093, China;3. Centre for Exploration Targeting, University of Western Australia, 35, Stirling Highway, Crawley, WA 6009, Australia;4. Xinjiang Research Center for Mineral Resources, Chinese Academy of Sciences, Urumqi 830011, China;1. Faculty of Earth Resources, China University of Geosciences (Wuhan), Wuhan 430074, China;2. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China;1. Institute for Geology, TU Bergakademie Freiberg, Bernhard-von-Cotta-Straße 2, 09599 Freiberg, Germany;2. Museum für Naturkunde, Leibniz Institute for Research on Evolution and Biodiversity, Invalidenstraße 43, 10115 Berlin, Germany;3. Geological Museum, Korea Institute of Geoscience and Mineral Resources, 34132 Daejeon, Republic of Korea;4. Institute for Mineralogy, TU Bergakademie Freiberg, Brennhausgasse 14, 09596 Freiberg, Germany;5. Geological Survey of Saxony, Halsbrücker Straße 31a, 09599 Freiberg, Germany |
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| Abstract: | Two end member geodynamic settings produce the observed examples of rapid voluminous felsic (rhyolitic) magmatism through time. The first is driven by mantle plume head arrival underneath a continent and has operated in an identifiable and regular manner since at least 2.45 Ga. This style produces high temperature (≤ 1100 °C), low aspect ratio rheoignimbrites and lavas that exhibit high SiO2/Al2O3 ratios, high K2O/Na2O ratios, and where available data exists, high Ga/Al2O3 ratios (> 1.5) with high F (in thousands of parts per million) and low water content. F concentration is significant as it depolymerizes the silicate melt, influencing the magmas' physical behavior during development and emplacement. These rhyolites are erupted as part of rapidly emplaced (10–15 Myr) mafic LIPs and are formed primarily by efficient assimilation-fractional crystallization processes from a mafic mantle parent. The second is driven by lithospheric extension during continental rifting or back arc evolution and is exclusive to the Phanerozoic. SLIPs (silicic large igneous provinces) develop over periods < 40 Myr and manifest in elongate zones of magmatism that extend up to 2500 km, contrasting with the mafic LIP style. Some of the voluminous felsic magmas within SLIPs appear to have a very similar geochemistry and petrogenesis to that of the rhyolites within mafic LIPs. Other voluminous felsic magmas within SLIPs are sourced from hydrous lower crust, and contrast with those sourced from the mantle. They exhibit lower temperatures (< 900 °C), explosive ignimbrites with lower SiO2/Al2O3 ratios, and lower K2O/Na2O ratios. Rapid voluminous felsic magmatism represents both extreme examples of continental growth since the Archean, and also dramatic periods of crustal recycling and maturation during the Phanerozoic. |
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