Abstract
Three fission-track ages of the volcanic ashes in the Plio-Pleistocene Tokai Group, were obtained by grain-by-grain method.
1) Ichinohara Volcanic Ash at Kono-minamidani..............2.8±0.2MY.
2) Ichinohara Volcanic Ash at the River Tashida................2.9±0.2MY.
3) Rokkoku Volcanic Ash at Rokkoku..........................1.4±0.2MY.
These ages were compared with the paleomagnetic time scale and the result of NRM measurement on the Tokai Group in Fig. 3. All the data are concordant with each other.
According to these results, it is sure that the grain-by-grain method of the fission-track age determination is the best technic in the case using the zircon crystals in the volcanic ash layer.
