Petrology and geochemistry of three Early Holocene eruptions from Makushin Volcano, Alaska
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RESEARCH ARTICLE
Petrology and geochemistry of three Early Holocene eruptions from Makushin Volcano, Alaska J. F. Larsen 1
&
Janet Schaefer 2 & J. W. Vallance 3 & O. K. Neill 4
Received: 3 February 2020 / Accepted: 2 October 2020 # International Association of Volcanology & Chemistry of the Earth's Interior 2020
Abstract Makushin stratovolcano, Alaska, produced three, highly explosive, andesitic eruptions between ~ 9292 and 6215 yBP. Those eruptions are informally named the CFE (“crater-forming eruption”), Nateekin, and Driftwood Pumice, and they deposited significant tephra fallout in the present-day port of Dutch Harbor and City of Unalaska area. The focus of this study is to examine the geochemistry and petrology of those eruptions to better understand Makushin volcano hazards, andesite petrogenesis and eruption triggering by mafic recharge processes. The CFE, Nateekin, and Driftwood Pumice samples range from basaltic andesite to dacite but are predominantly andesitic (SiO2 = 55.6 to 63.5 wt%). The CFE deposits are slightly compositionally stratified, with the top CFE samples slightly more mafic (55 to 60 wt% SiO2) than the basal deposits (58 to 60 wt% SiO2). Disequilibrium mineral compositions and textures in the CFE, Nateekin, and Driftwood Pumice samples, combined with two pyroxene thermometry and An-rich plagioclase microlites (An80) found only in the top of the CFE deposits, provide evidence for repetitive mafic recharge triggering those eruptions, consistent with prior studies. We compare the Makushin geochemical data with data from select satellite vents and cones in the Makushin Volcanic Field (MVF) from prior studies, to examine possible genetic relationships. The geochemical data and Rhyolite-MELTS models run at crustal storage conditions (2 kbar, fO2 = Ni-NiO, and 1.5 and 3.5 wt% H2O) indicate that no single parental magma supplies the MVF satellite cones and Makushin volcano. Instead, two component mixing models better fit the MVF geochemical array. Our Makushin results compare well with models of predominantly andesitic volcanoes that require mafic recharge to mobilize the andesites and trigger eruptions. Keywords Makushin . Magma mixing . Andesite . Aleutians . Alaska
Introduction Editorial responsibility: A.V. Ivanov Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00445-020-01412-5) contains supplementary material, which is available to authorized users. * J. F. Larsen [email protected] 1
Geophysical Institute, Department of Geosciences, Alaska Volcano Observatory, University of Alaska, Fairbanks, Fairbanks, AK 99775, USA
2
Alaska Volcano Observatory, State of Alaska Division of Geological and Geophysical Surveys, Fairbanks, AK 99709, USA
3
Cascades Volcano Observatory, U.S. Geological Survey, Vancouver, WA 98683, USA
4
Robert B. Mitchell Electron Microbeam Analysis Laboratory, School of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109, USA
Makushin volcano is an 1800-m-high, Pleistocene to historically act
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