U-Pb detrital zircon dating of pelitic schists and quartzite from the Kurosegawa Tectonic Zone, Southwest Japan

要旨

The Kurosegawa Tectonic Zone, which is one of the least geochronologically understood areas of the Japanese Islands, contains several rock types of contrasting ages in a serpentinite mélange. This paper presents the U-Pb ages of detrital zircons in pelitic schists and quartzite from the Kurosegawa Tectonic Zone, where high-pressure/low-temperature metamorphic rock (e.g., blueschist) is one of the main constituents. We analyzed a variety of samples including glaucophane-bearing pelitic schist from the Itsuki area in Kyushu and the Toba area on the Kii Peninsula, and quartzite from the Anan area in eastern Shikoku. The U-Pb age distributions reflect similar characteristics for all three areas, indicating significant peaks at 450-500 Ma and ∼ 600 Ma, with additional scattered ages of 800-1800 Ma, and ages older than 2000 Ma. These results suggest that the provenance of the protolith of these high-pressure/low-temperature metamorphic rocks from the Kurosegawa Tectonic Zone would be the same between Kyushu and the Kii Peninsula through the Shikoku area. The distributions of detrital zircon ages in the Kurosegawa Tectonic Zone are similar to those from Permian-Triassic collision-related metamorphic rocks of the Ogcheon Metamorphic Belt and Gyeonggi Massif in South Korea, and from Devonian sedimentary rocks in the South China Craton.

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