Using amphibole phenocrysts to track vapor transfer during magma crystallization and transport: An example from Mount St. Helens,Washington |
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| Authors: | MC Rowe AJR Kent CR Thornber |
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| Institution: | 1. Department of Geological Sciences, Oregon State University, Corvallis, OR 97330, United States;2. Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78730, United States;3. U.S. Geological Survey, Cascades Volcano Observatory, Vancouver WA 98683, United States |
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| Abstract: | In order to evaluate and further constrain models for volatile movement and vapor enrichment of magma stored at shallow levels, amphibole phenocrysts from 2004–2005 Mount St. Helens dacite were analyzed for major and selected trace elements (Li, Cu, Zn, Mn, and REE) and Li isotopes. Several recent studies have examined fluid-mobile trace element abundances in phencryst phases and melt inclusions as a means of tracking volatile movement within subvolcanic magmatic systems, and high Li contents in plagioclase phenocrysts from 1980 and 2004 Mount St. Helens dacites have been interpreted as evidence that shallow magma was fluxed by a Li-bearing vapor phase prior to eruption. |
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| Keywords: | amphibole copper diffusion lithium Mount St Helens |
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