Volcanic activity of the Miocene Basalts in Yatakayama Area, Kibi Plateau, Takahashi City, Okayama Prefecture, SW Japan

Takumi Nagato; Shigeyuki Suzuki; Haruo Koami; Kotaro Nakai; Toru Tachibana

Presentation information

[J] Poster

S (Solid Earth Sciences ) » S-VC Volcanology

[S-VC47] Volcanic and igneous activities, and these long-term forecasting

convener:Teruki Oikawa(GSJ, National Institute of Advanced Industrial Science and Technology ), Takeshi Hasegawa(Department of Earth Sciences, College of Science, Ibaraki University), Daisuke MIURA(Department of Physical Science, Graduate School of Science, Osaka Prefecture University), Nobuo Geshi(Geological Survey of Japan, The National Institute of Advanced Industrial Science and Technology)

[SVC47-P12] Volcanic activity of the Miocene Basalts in Yatakayama Area, Kibi Plateau, Takahashi City, Okayama Prefecture, SW Japan

*Takumi Nagato¹, Shigeyuki Suzuki¹, Haruo Koami², Kotaro Nakai¹, Toru Tachibana³ (1.Okayama University, 2.Okayama Prefectual Okayama Asahi Senior High School, 3.Soil Engineering Corporation)

Keywords:Basalt, reconstruction of volcanism, volcanic product, Miocene, field survey

Numbers of basaltic rocks are sporadically distributed in Kibi Plateau, around the border between Okayama Prefecture and Hiroshima Prefecture. These basalts are alkali basalts (Takamura,1973) and formed in late Miocene, 7.4-9.5Ma (Uto,1995). The study areas are Mt. Sushiyama, Mt. Yatakayama, Tachiarai areas which are located in western side of Okayama Prefecture. We discovered contact planes of basaltic intrusive rocks, tuff breccias and lava flow which help to understand volcanic evolution of the Miocene Basalts.

Observed basaltic dikes intruded into the Miocene Bihoku Group and tuff breccia of the Miocene Basalt. The basaltic tuff breccia is composed of lapilli (5mm to 10cm) and matrix (cement and pore). The lava has brecciated nature. Some basaltic fragments have jigsaw-fit structure.