Areas of interest:
Geochronology mainly based on fission track methods, and other radiometric systems, including Rb/Sr. Fission tracks are lattice damage produced through the spontaneous decay of Uranium 238. In particular, I am interested in the tectonics of SW Japan, including transition and migration of igneous activity, cooling histories of plutons, uplift history of metamorphic belts, and thermal evaluation of fault systems.
(1) Dating of igneous rocks in the San-In district
This study aims to determine radiometric ages of the many types of granitic rocks and associated volcanic rocks which crop out in the San-in district of SW Japan. Analysis is focused on Cretaceous to Miocene igneous rocks. This work is directed at clearly characterizing and distinguishing differing stages of igneous activity, and the spatial migration of igneous activity within each stage, prior to opening of the Japan Sea. As part of this study, cooling histories of zoned plutons and formation of cauldrons are also being examined, and analytical techniques further refined.
(2) Cooling and uplift history of metamorphic belt and mountain ranges
This study is being carried out mainly in the Sambagawa metamorphic belt (SW Japan), the Himalaya (Nepal) and in the Andes Mountains (Colombia). The main focus of the work is the uplift history of crustal material in relation to formation of complex tectonic blocks and thrust systems in major subduction complexes and collision zones.
- Himeno O., Ohira H., Zhaojun Liu, Xue Jin and Watanabe K. 2001. Provenance ages of Cretaceous strata in the Songliao Basin, Northeast China inferred from fission track data. International Geology Review, 43, 945-952.
- Kojima T., Okada M. Ohira H. and Komuro H. 2001. Paleomagnetism and fission-track ages of Oki-Dogo Island in Southwest Japan. Earth, Planet and Space, 53, 45-54.
- Ishihara T., Ohira H. and Tateishi M. 2000. Fission track ages of the Oriwatari Formation in the Shinjo Basin, Yamagata Prefecture, NE Japan. J. Geol Soc. Japan., 106, 905-908. (in Japanese with English abstract)
- Yuhara M., Ohira H., Owada M., Kamei A. and Kagami H. 1999. Geochronological study of the Habu Granodiorite in eastern Yamaguchi Prefecture, SW Japan. Mem. Geol. Soc. Japan., 53, 323-331. (in Japanese with English abstract)
- Nomura M. and Ohira H. 1998. Fission track ages of Miocene tuffs in Tomioka Group, Gunma Prefecture, NE Japan. Annual Reports of Gunma Prefecture Museum., 2, 35-42. (in Japanese with English abstract)
- Ohira H., Isono Y., Sakakibara Y. and Yoshimura T. 1997. Fission track fading in apatite from the shin-Yahiko-1 well and its implication. Jour. Japanese Association for Petroleum Technology, 62, 544-553. (in Japanese with English abstract)