5:15 PM - 6:30 PM
[SGL37-P04] New U-Pb ages of the Nakanogawa Group in southern Hidaka Belt, northern Japan
Keywords:U-Pb dating, LA-ICP-MS, Nakanogawa Group, Hidaka Belt, Hidaka metamorphic zone, Early Eocene
We have taken two samples of turbidite sandstone and two samples of acidic tuff from the top and bottom horizon. After separating euhedral zircon grains, we tried to measure U-Pb age by using the LA-ICP-MS method. As a result, the distribution of the following three ages revealed.
(1) 66~53Ma as young ages group (euhedral zircon of high Th/U ratio from igneous rocks)
(2) 73.9, 156, and 334Ma as intermediate group
(3) 2621, 1800Ma as rework zircon group (purple zircon)
In conclusion, the depositional age of turbidite facies of Nakanokawa group may be considered ca. 53Ma (Early Eocene) because the youngest euhedral zircon grains are contained in these four samples in common.
Nanayama, F., 1992. Stratigraphy and facies of the Paleocene Nakanogawa Group in the southern part of central Hokkaido, Japan. Jour. Geol. Soc. Japan, 98, 1041-1059.
Nanayama, F. and Ganzawa, Y., 1997. Sedimentary stratigraphy, environment and age of the northern unit of Nakanogawa Group in the Hidaka belt, central Hokkaido, Japan. Mem. Geol. Soc. Japan, no. 47, 279-293.