Stratigraphy and eruption age of the volcanic rocks in the west of Miyanoharu area, Kumamoto Prefecture. Age and distribution of the volcanic activity of central-north Kyushu, Japan.

Abstract

The detailed stratigraphic survey, K-Ar age determinations and NRM measurements of the volcanic rocks in the W of Miyanoharu area revealed the volcanic history as follows. Hornblende andesite lava with plagioclase megacryst (Yoshinomoto lava) erupted during 2.8- 2.5 Ma (Gauss normal epoch), accompanied by small amount of pyroclastic materials. After this eruption, Kamitarumizu hypersthene-augite andesite lava (1.7-1.3 Ma; reversed), Yabakei pyroclastic flow (0.99 Ma; Jaramillo normal event), Yamakogawa biotite rhyolite lava (0.9 Ma; reversed) and Daikanbo hypersthene-augite andesite lava (0.8 Ma; normal) erupted successively prior to the Aso-1 pyroclastic flow (0.3-0.4 Ma). Both the K-Ar ages and NRM data are consistent with the stratigraphic sequence which suggests that the activity of andesite and rhyolite is intercalated with each other during the Pleistocene in the studied area.-from English summary