Petrologic characteristics of the newest stage in Azuma volcano group, Northeast Japan
|International Journal of Eruptive History and Informatics||Volume 1,2013|
|Corresponding Author:||Masao Ban|
|Corresponding Author's Affiliation:||Yamagata University|
|Department of Earth and Environmental Science|
|Faculty of Science|
Masao Ban; Ruriko Matsui; Naotoshi Iwata; Takahiro Yamamoto; Akihiko Fujinawa; Kazuo Nakashima
Petrologic characteristics, Petrography, Whole rock chemistry, Calc-alkaline mixed rocks, Magma evolution, Azuma volcano , Northeast Japan
Basic petrologic properties of the eruptive products of the newest stage of Azuma volcano group were examined. These are calc-alkaline andesite?dacite, possessing petrographic evidence of magma mixing events. The linear whole rock trends indicate the mixing events were between mafic and felsic end-members. Goshikidake (ca. 6.5 to 6 ka) and Oana (AD 1331) units show higher than Kofuji (ca. 6 to 5 ka) and Issaikyo (ca. 5 to 4 ka) units in mafic part of the MgO, MnO, Ni, and Cr diagrams, while the trends converge in the felsic part. During the newest stage the dacitic (64-65 wt% SiO2) magma reservoir have been stored at shallow crustal level. At the beginning (Goshikidake unit) and the recent (Oana unit) of the newest stage the least differentiated mafic magmas infused into the reservoir which resulted in the eruptions. Whereas, in the middle term (Kofuji and Issaikyo units), the mafic magma would differentiate to some extent before the infusion.
Teruki Oikawa (AIST, Tsukuba, Japan)
M.B. summarizing this article, manuscript writing, sample collection, petrological analyses, description of data; R.M. sample collection, petrological analyses, description of data; T.Y. sample collection, geological interpretation; K.N. mineralogical analyses; N.I. and A. F. geochemical and petrological interpretation.
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