Geology and petrology of Akita-Yakeyama Volcano; 2, Evolutional history of magma composition

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Authors:Ohba, Tsukasa
Author Affiliations:Primary:
Tohoku University, Institute of Mineralogy, Petrology and Economic Geology, Sendai, Japan
Volume Title:Ganko Journal of Mineralogy, Petrology and Economic Geology
Source:Ganko = Journal of Mineralogy, Petrology and Economic Geology, 88(1), p.1-19. Publisher: Nippon Ganseki Kobutsu Kosho Gakkai, c/o: Tohoku Daigaku Rigakubu, Sendai, Japan. ISSN: 0914-9783
Publication Date:1993
Note:In Japanese with English summary. 15 refs.; charts, 9 tables
Summary:Magmatic evolution of Akita-yakeyama volcano, NE Honshu, Japan, is discussed in relation to volcanostratigraphy on the basis of major, trace elements, and Sr isotopic data of whole-rock and mineral chemistry. Eruption of lava flows and pyroclastic falls mainly of enstatite-augite andesite with subordinate olivine bearing enstatite-augite andesite, formed the main body. After a repose period, fine ash fall of enstatite-augite andesite and lithic-rich pyroclastic falls of enstatite-augite-olivine andesite were ejected from a central vent. No evidence of magma mixing is observed in the olivine-free andesite, but olivine-bearing andesite has mineralogical and chemical evidence of magma mixing, e.g. disequilibrium phenocryst assemblage, reverse zoning in pyroxene, and dusty plagioclase. Flank eruptions followed with the ejection of lithic-rich pyroclastic falls, lava flows and pumice falls of quartz-bearing olivine-enstatite-augite andesite, quartz- bearing augite-enstatite andesite, and augite-enstatite dacite. Of these andesites, quartz-bearing andesites have high 87Sr/86Sr, suggesting crustal assimilation. At the end of this event, lava domes of augite-enstatite dacite and olivine bearing augite-enstatite dacite, both of which show no evidence of magma mixing or crustal assimilation, formed in the central crater. The variation trends of Zr, Rb and Y ranging from augite andesite of the main body to the augite-enstatite dacitite of the domes cannot be explained in terms of fractional crystallization, and a difference in degree of partial melting of the source materials is required. [K.O.]
Subjects:Andesites; Augite; Chain silicates; Chemical composition; Clinopyroxene; Dacites; Fractional crystallization; Geochemistry; Hypersthene; Igneous rocks; Lava flows; Magmas; Orthopyroxene; Partial melting; Petrology; Pyroclastics; Pyroxene group; Silicates; Trace elements; Volcanic rocks; Akita Japan; Asia; Far East; Honshu; Japan; Yake-Dake
Abstract Numbers:94M/3710
Record ID:1995019754
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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