Petrology and thremochronological study for youngest exposed pluton of the World

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Thermochronological paleomagnetic and geological studies have been carried out on the Quaternary Takidani Granodiorite and the Late Pliocene Kurobegawa Granite in order to elucidate their cooling history and the mechanism for emplacement. Major results are as follows.1. Paleomagnetic directions for both the Takidani Granodiorite and the Kurobegawa Granite could not determine for unstability of remanent magnetization of them.2. Roof volcanic rocks of the above granitic pluton show reversed polarities of remanent magnetization with east-shifted directions as the result of eastward tilting of eastern-half area of the Hida Mountain Range.3. Both the granitic pluton show strongly mylonitized texture along the N-S tending reverse faults at their western contact.4. Systematic bottomward younging of biotite K-Ar ages (1.4 Ma to 1.0 Ma) for the Takidani Granodairite can be explained by the slower start in cooling at deeper level of the pluton. Such a cooling history may be affected by the eastward tilting and uplifting of the eastern-half area of the Hida Mountain Range. Mylonitic displacement took place during the cooling process of the Takidani Pluton about 1.0 Ma.