Untitled research work

The fission track dating has been carried out on zircon separated from six specimens of the Hyugami Lava which outcrops in Oita Prefecture. The results are as follows: HW-20 Two-pyroxene hornblende andesite Kameishi-yama 33°1l′30″N, 131°03′45″E 0.42±0.09 Ma HW-3 Altered hornblende andesite (borecore) Noya 33°14′28″N, 131°16′21″E 1, 56±0.41 Ma HW-5 Altered hornblende andesite (borecore) Noya 33°14′03″N, 131°15′42″E 1.80±0.29 Ma HW-7 Biotite-bearing hornblende andesite Yoko-yama 33°15′28″N, 131°14′03″E 1.78±0.32 Ma HW-12 Biotite-bearing hornblende andesite Karuto-yama 33°15′51″N, 131°17′26″E 2.2110.29 Ma HW-19 Two-pyroxene hornblende andesite Hyugami 33°10′26″N, 131°46′59″E 2.85±0.49 Ma Considering both these fission track ages and the results of modal analysis of the rocks, HW-20 may belong to the middle Pleistocene Bungo Volcanic Rocks, and HW-3, HW-5 and HW-7 to the early Pleistocene Hohi Volcanic Rocks. However, HW-12 and HW-19 erupted in the Pliocene and come under none of known volcanic groups in central Kyushu.