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-P18] Foaming temperature and textural classification of vesicular substance by heating experiments of obsidians

*Keiji Wada1, Shunya Tsurumaki1, Ryo Ikeyauchi1, Kyohei Sano2, Eiichi Sato3 (1.Earth Science Laboratory, Hokkaido University of Education at Asahikawa, 2.Shirataki-Geopark Promotion Department, Engaru town, 3.Institute for Promotion of Higher Education, Kobe University)

Keywords:obsidian, perlite, heating experiment, foaming temperature, volcanic glass

Obsidian includes H2O component in the glass. The H2O component is vesiculated when heated at a high temperature, and their foams surrounded by dense obsidian glass expand to porous material, referred to as “perlite”. We have carried out heating experiments with an electric furnace for 11 obsidian samples from each different locality to determine the foaming temperature (Tf) and perlite-formation temperature (Tp) of their obsidians. The results are as follows; Akaigawa obsidian Tf=780℃; Tp=830℃, Okushiri obsidian Tf=790℃; Tp=850℃, Kozushima obsidian Tf=890℃; Tp=950℃, Shirataki obsidian (IK outcrop) Tf=900℃; Tp=1030℃, Tokachi-Mitsumata obsidian Tf=930℃; Tp=1060℃, Oketo obsidian (Tokoroyama) Tf=990℃; Tp=1100℃, Oketo obsidian (Kita-Tokoroyama) Tf=1010℃; Tp=1090℃, Shirataki obsidian (Tokachi-Ishizawa outcrop) Tf=1030℃; Tp=1160℃, Shirataki obsidian (Kyukasawa outcrop) Tf=1060℃; Tp=1150℃, Shirataki obsidian (Nishi atelier) Tf=1070℃; Tp=1190℃, Shirataki obsidian (Ajisainotaki outcrop) Tf=1070℃; Tp=1190℃.
Perlite texture was classified into three types (type-A, -B and -C) based on the diameter, morphology and number density of vesicles. Type-A has discrete spherical forms with about 1 mm in diameter, which belongs to Tf>990℃, Tp>1060℃ group. Type-B, Tf=900-930℃, Tp=1030-1060℃ group, has distorted spherical forms with 1.5 to 5.0 mm in diameter. Type C is characterized by high number density and small size of vesicles (< 0.5 mm) connecting with each other, belonging to low Tf (<890℃) and Tp (<950℃) group.
The texture of perlite made by obsidian heat experiment is different from that of natural vesicle substance such as pumice and vesiculated obsidian. Lower number density of vesicles in the experimental product perlite is due to low H2O content in quenched obsidian after degassing of H2O in obsidian magma. The difference in vesicle morphology between the spherical form of perlite and reticulated irregular-shaped vesicle of natural vesicle substance is related to the difference in the static or dynamic condition of formation environment.