[SVC43-P05] Phreatomagmatic explosion history and petrographical characteristics of Izu-Oshima at southeast
Keywords:phreatomagmatic eruption, essential material, accessory material, basement, matrix, breccia
We report stratigraphic and petrographic study of the volcanic products of southeastern of Izu-Oshima volcano, especially around northeastern part of Habuminato and southwestern part of Habuminato.
Northeastern part of Habuminato
L3 lava, L2 lava, Kotoshi tuff, Ooyanokubo pyroclastic surge deposits, L1 lava, Kakihara tuff, Sand and Scoria in ascending order.
Kotoshi tuff contain accessory rock fragments of Ryuo-zaki lava (Pl: 3.3 vol.%, Mg#=44). Kakihara tuff is characterized by containing accretionary lapilli. Rock fragments are Fudeshima volcanic rocks in origin (Pl: 19.6-39.1 vol. %, SiO2=49.45-50.03 wt.%).
Southwestern part of Habuminato
Shimobara lava (the Old Oshima Group), Silt, Scoria, Habu breccia (N3), Scoria & ash, and Imasaki breccia (Y4) in ascending order.
Habu breccia contain accessory rock fragments of Ryuo-zaki lava (Pl: 1.0-10.8 vol.%, Mg#=44) and Fudeshima volcanic rocks (Pl: 23.2-28.0 vol.%, SiO2=50.8-51.7). Imasaki breccia contain not only accessory rock fragments of Shimobara lava (Pl:0.2-9.3 vol.%, Mg#=39) but essential rock fragments of Y4 stage lava (Pl:0.3-0.9 vol.%, Mg#=40).