Formation ages of elevated peneplains of the Japanese Islands-An approach from the fission-track dating.

松田等人(1997年)明确指出，钛铁矿、锆石和磷灰石的裂变径迹年龄分别提供了约300℃、240℃和110℃的冷却年龄，比日达山花岗岩的形成年龄更年轻。喜达花岗岩的磷灰石裂变径迹年龄在40~50 Ma范围内较窄，而锆石裂变径迹年龄在99~172 Ma之间较宽。他们指出，假定相当于闭合温度为110℃的磷灰石裂变径迹年龄的最新抬升和冷却年龄，在40-50 Ma之间的日达山脉是相似的。此外，他们得出的结论是，这一年龄对应于日达山隆起的准平原的形成时代。这项工作是他们为确定日本群岛隆起的准平原的形成时代而开展的工作的延伸。本文测定了花岗岩和白垩纪火山岩的磷灰石裂变径迹年龄。磷灰石裂变径迹年龄为：北上山脉82~100 Ma，阿布库马山脉46~78 Ma(主要为55~70 Ma)。后藤岛，6.08 Ma；飞田山，40-50 Ma(其轨迹长度模式为缓慢冷却)；中部地区，花岗岩和酸性火山岩，45-55 Ma；中部地区，16-30 Ma；Awaji和四国岛，28-46 Ma。每个地区的年龄都很窄。日本岛屿不同地区的降温幅度约为110℃。这表明，根据磷灰石裂变径迹年龄推断的隆起准平原的形成年龄在白垩纪以后不同地点不同。

As Matsuda et al., (1997) made clear, the titanite, zircon and apatite fission track ages whose ages provide the cooling ages down to about 300℃, 240℃ and 110℃ respectively were younger than the formation ages of the granitic rocks of the Hida mountains. For the Hida granitic rocks, the apatite fission track ages are rather narrow in range from 40 to 50 Ma, although the zircon fission track ages are wide in range from 99 to 172 Ma. They pointed out that the latest uplift and cooling age that is assumed to be equal to the apatite fission track age with closure temperature of 110℃ was similar through the Hida mountains, 40-50 Ma. Further, they concluded that the age corresponded to the formation age of the elevated peneplain in the Hida mountains. The present work is an extension of their work for detarmination of the formation age of the elevated peneplains of the Japanese Islands. For the present work, we determined the apatite fission track ages of granitic rocks and Cretaceous volcanic rocks. The apatite fission track ages are as follows ; the Kitakami mountains, 82-100 Ma ; the Abukuma mountains, 46-78 Ma (mostly 55-70 Ma) ; Mt. Goto in Niigata prefecture, 6.08 Ma ; the Hida mountains, 40-50 Ma (the pattern of their track length is of slow cooling) ; granitic and acidic volcanic rocks in Chubu district, 45-55 Ma ; Chugoku district, 16-30 Ma ; Awaji and Shikoku islands, 28-46 Ma. The age is narrow in each area. The cooling by about 110℃ differs between areas of the Japanese islands. This suggests that the formation ages of the elevated peneplain deduced from the apatite fission track dating are different from place to place after the Cretaceous time.