南部阿武隈山地花崗岩類の角閃石K-Ar年代
1983 年 78 巻 10 号 p. 405-410
詳細
1983 年 78 巻 10 号 p. 405-410
K-Ar age determinations were carried out on 19 homblendes and 4 biotites from 9 granitic masses and two metamorphic rocks in the southern Abukuma Plateau, Northeast Japan. Hornblende ages for granitic rocks range from 96.4 to 119 Ma and are apparently not correlated with area or mass. Biotites show a limited age range of 96.1-97.8 Ma. The variation in hornblende age is attributed to the difference in cooling rate of granitic rocks. Hornblende ages for the Gosaisho and Tamadare metamorphic rocks are 115 and 103 Ma, respectively, and nearly equal to those for the adjacent granites.
No old ages were found on hornblendes from the Ishikawa, Miyamoto and Samegawa masses, which constitute the older type granites and gave Rb-Sr whole-rock ages of about 400 Ma. This may impose a severe constraint on the thermal history of the older type granites.
