Time-Space of the evolution of the Hida metamorphic rocks based on CHIME age

根据锆石、独居石、晶质铀矿和钍石的U-Th-Pb化学年龄（CHIME年龄），研究了希达变质带演化的时间和空间。这项研究是希达变质岩岩石学研究的延伸（Sohma等，1995），其中确定了各种岩石类型的母女关系（相对年龄关系）。主要结论如下：1碰撞变质带中U-Th-Pb矿物的CHIME年龄主要受热液作用控制，而不是矿物的闭合温度; 2侏罗系船津花岗岩类中绝大多数具有石炭纪-二叠纪锆石年龄，并具有240 Ma左右的希达变质年龄的独居石和晶质铀矿。它们是变质岩，并将被称为希达变花岗岩类。3 Unazuki变质带不是一个单独的变质带，而是作为希达变质带的一部分发展起来的，因为Unazuki变质岩与希达变花岗岩类共生。4希达变质带是一个多变质造山带，5希达变质作用始于270 Ma左右的俯冲带花岗质岩浆活动，经历了热峰期和热液期，240 Ma晶质铀矿结晶，并持续到变质带的抬升和冷却，如角闪石和黑云母的K-Ar年龄所示。

The time and space of the evolution of the Hida metamorphic belt were studied on the basis of U-Th-Pb chemical age (CHIME age) of zircon, monazite, uraninite and thorite. This study is an extention of the petrological studies of the Hida metamorphic rocks (Sohma et al., 1995), in which mother-daughter relationships (relative age relationship) of various rock types were determined. The followings are the major conclusions of this study.1 CHIME age of U-Th-Pb minerals of a collision type metamorphic belt were controled by hydrothermal reactions rather than closure temperature of the minerals.2 The majority of the so called Jurassic Funatsu granitoids show Carboniferous to Permian zircon ages in origin, and possess monazite and uraninite of the Hida metamorphic age of 240Ma. They are metamorphic rocks, and will be called the Hida metagranitoids.3 The Unazuki metamorphic belt is not a separate one, but has been developed as a part of the Hida metamorphic belt, because of the association of the Unazuki metamorphic rocks and the Hida metagranitoids.4 The Hida metamorphic belt is a polymetamorphic orogen, but its lithology were finally formed at about 270Ma.5 The Hida metamorphism started with subduction zone granitic magmatism at about 270Ma, showed a thermal peak followed by a hydrothermal event in which uraninite of 240Ma age crystallized, and continued to the uplift and cooling of the metamorphic belt as indicated by K-Ar ages of hornblende and biotite.