琉球列島産新生代酸性貫入岩類のフィッション・トラック年代

抄録

The fission track ages of zircon have been measured in nine acidic intrusive rocks from the Ryukyu Islands by the arranged fix-area population method and the external-surface external-detecter grain-by-grain method. The ages are as follows: Kuchinoerabujima xenolith (granodiorite), 15.0±1.2Ma; Okinoerabujima granodiorite, 32.9±2.7 Ma; Okinawajima tonalite, 30.0±4.7Ma; Okinawajima quartzporphyry, 15.7±1.3Ma, 15.3±1.5Ma, and 15.8±1.7Ma; Ishigakijima Omoto granite, 28.7±0.9Ma, 29.9±0.9Ma and 29.9±1.1Ma. These fission track ages indicate that the acidic intrusive rocks were emplaced in late Oligocene and early to middle Miocene times.