Exhumation processes of the high-P metamorphic rocks constrained by integrated radiogenic ages of zircon in the clasts of the Miocene conglomerates

对四国和关东中新世和始新世砾岩的出露和碎屑中的片岩样品，用多种放射成因定年方法（多硅白云母K-Ar法、锆石裂变径迹法和锆石U-Pb法）研究了高压型变质岩（三宝川变质岩）的折返过程。我们的结果如下：（1）除四国岛万岛带的始新统砾岩外，较老（始新统）砾岩中碎屑的折返年龄大于中新统砾岩，甚至大于现今出露的片岩。(2)三坝川变质岩的原岩时代为晚白垩世早期，因此与四万十带的增生杂岩有关。(3)三坝川变质作用的折返持续时间估计约为6000万年，比之前估计的要长。

Exhumation processes of high pressure type metamorphic rocks (Sanbagawa metamorphics) was examined using various radiogenic dating method (phengite K-Ar, zircon fission-track and zircon U-Pb) for the schist samples from exposures and from the clasts of Miocene and Eocene conglomerates in Shikoku and Kanto. Our results are as follows; (1) The exhumation age of the clasts in the older (Eocene) conglomerate is older than those in the Miocene conglomerate and even than schists from current exposures, except the case of Eocene conglomerate in the Shimanto Belt in Shikoku. (2) Protolith of the Sanbagawa metamorphics dated is early Late Cretaceous, therefore is correlative with the accretionary complex of the Shimanto belt. (3) Duration time of the exhumation of the Sanbagawa metamorphics is estimated about 60 m.y., longer than previously estimated.