Eruption sequence and magmatic plumbing system of the 12 ka eruption at Nantai Volcano, Japan

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doi: 10.2465/gkk.33.197
Authors:Ishizaki, Yasuo; Kureyama, Masakazu
Author Affiliations:Primary:
Toyama University, Department of Earth Sciences, Toyama, Japan
Volume Title:Ganseki Kobutsu Kagaku Japanese Magazine of Mineralogical and Petrological Sciences
Source:Ganseki Kobutsu Kagaku = Japanese Magazine of Mineralogical and Petrological Sciences, 33(5), p.197-207. Publisher: The Mineralogical Society of Japan and The Japanese Association of Mineralogists, Petrologists and Economic Geologists, Tokyo, Japan. ISSN: 1345-630X
Publication Date:2004
Note:In Japanese with English summary. 19 refs.; illus., incl. 1 table, sketch map
Summary:The 12 ka eruption of Nantai Volcano, central Honshu, Japan, produced a succession of pyroclastic deposits followed by the emplacement of a lava flow. The 12 ka eruption began with phreatic eruptions, forming a fine ash deposit (unit A). Explosive magmatic eruption followed forming a scoria-fall (unit B) and partially welded scoria-flow deposits (unit C). The scoria eruption was followed by a pumice eruption producing a pumice-fall deposit (unit D) and a consecutive voluminous pumice-flow deposit (unit E). The 12 ka eruption finished with the extrusion of a heterogeneous dacite-andesite mingled lava flow (unit F). The early scoriae are phenocryst-poor (∼3-15 vol.%) tholeiitic dacite and andesite with an anhydrous phenocryst assemblage (plagioclase + orthopyroxene + clinopyroxene + Fe-Ti oxides ± olivine), whereas unit D-F eruptives are porphyritic calc-alkaline dacite and andesite with a hydrous phenocryst assemblage (plagioclase + hornblende + quartz + orthopyroxene + clinopyroxene + Fe-Ti oxides ± olivine). This suggests that two magma types, firstly tholeiitic and secondly calc-alkaline, fed the 12 ka eruption. Although major and trace elements are broadly similar in all dacites erupted between unit D and F, there are considerably differences in phenocryst contents: unit-D and unit-E dacites have lower crystal contents (∼17 vol.%) whereas unit-F lava has higher crystal contents (∼50 vol.%). The unit D-E dacite (pumice) and the unit-F dacite (lava) may have been derived from different parts of a magma chamber, perhaps from inner melt-rich and marginal mushy parts, respectively.
Subjects:Cenozoic; Chemical composition; Dacites; Eruptions; Igneous rocks; Magma transport; Magmas; Major elements; Mineral assemblages; Petrography; Phenocrysts; Phreatomagmatism; Pleistocene; Pyroclastics; Quaternary; Scoria; Tholeiitic composition; Trace elements; Upper Pleistocene; Volcanic ash; Volcanic rocks; Whole rock; Asia; Far East; Honshu; Japan; Nantai
Coordinates:N364400 N364400 E1393600 E1393600
Abstract Numbers:06M/1834
Record ID:2005045616
Copyright Information:GeoRef, Copyright 2020 American Geosciences Institute.
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