Japan Geoscience Union Meeting 2016

Presentation information


Symbol S (Solid Earth Sciences) » S-VC Volcanology

[S-VC48] Volcanic and igneous activities, and these long-term forecasting

Sun. May 22, 2016 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall HALL6)

Convener:*Teruki Oikawa(Institute of Earthquake and Volcano Geology, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology), Takeshi Hasegawa(Department of Earth Sciences, College of Science, Ibaraki University), Daisuke MIURA(Geosphere Sciences, Civil Engineering Research Laboratory, Central Research Institute of Electric Power Industry), Yoshihiro Ishizuka(Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology), Nobuo Geshi(Geological Survey of Japan, The National Institute of Advanced Industrial Science and Technology)

5:15 PM - 6:30 PM

[SVC48-P10] The formation process of lava domes in Sambe volcano

*Ippei Asano1 (1.Graduate School of Science, Kobe University)

Keywords:Sambe volcano, dacite, bulk-rock composition

Sambe volcano is an active volcano laying astride the volcanic front of the SW Japan arc. The latest eruption of this volcano was ca. 3800 ybp and may formed the present volcanic topography showing lava domes with four peaks (Mt. Osambe, Mt. Mesambe, Mt. Kosambe, Mt. Magosambe). The formation process of these topographically isolated four domes has been controversial. In order to access this problem, rocks from these peaks have been analyzed petrographically, which provide the following results:
(1) Rocks from Osanbe and Mesanbe are poorer in quartz phenocrysts than those from Magosanbe and Kosanbe,
(2) Al2O3, CaO, and Na2O contents decrease with increasing SiO2 for all rocks from four peaks, which may correspond the change in the amount of plagioclase phenocrysts,
(3) Rocks can be divided into 2 groups, the Osambe-Mesambe and the Kosambe- Magosambe groups, based on the difference in K2O, Sr, Zr and Nb concentrations,
(4) Osambe and Mesambe rocks can be identified by the SiO2 and the plagioclase phenocryst contents,
(5) High-T oxidation is recognized even for rocks that form the valley between peaks, showing the original distribution of these rocks at the kava surface.
These lines of evidence may lead to the conclusion that the four domes formed independently rather than that a large lava dome has been reshaped into four peaks by subsequent eruption and/or erosion.