中部九州のいわゆる日向神溶岩のフィッション・トテック年代
1983 年 78 巻 2 号 p. 65-69
詳細
1983 年 78 巻 2 号 p. 65-69
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.
