Presentation Information
[T13-O-11]The Kurosegawa belt (Japan) as a part of pre-Jurassic Nipponides orogen in East Asia: geotectonic significance of Triassic accretionary complex in Choshi
*Yukio ISOZAKI1, Yukiyasu TSUTSUMI2, Naoya IWAMOTO3, Shuro UEDA3 (1. Dept. Earth Sci. & Astron. Univ. Tokyo, 2. Department of Science, National Museum of Nature and Science, 3. Choshi Geopark Promotion Council Office, Choshi-City Board of Education)
Keywords:
Kurosegawa belt,SW Japan,accretionary complex,orogenic belt,detrital zircon,U-Pb age
The Kurosegawa belt in SW Japan composed of pre-Jurassic subduction-related orogenic products occurs for more than 1000 km from Kyushu to Kanto. Thpresent U-Pb dating of detrital zircons for an undated pre-Cretaceous sandstone (the Atagoyama unit) at Choshi on the east end of Kanto detected the abundant occurrence of Early to Middle Triassic grains with the youngest one with ca. 237 Ma (around the Middle-Late Triassic boundary). The newly recognized Triassic sandstone is correlated with those in the Permo-Triassic accretionary complex of the Kurosegawa belt in SW Japan. This new information revised the location of easternmost Kurosegawa belt at Choshi, ca. 150 km further to the east from the previous recognition. In further northeast, potential candidates for the extension of the Kurosegawa belt include the Paleozoic arc granitoids, blueschists, fore-arc strata, and ophiolite in the South Kitakami and Nedamo belts, and also some Paleozoic remnants (protoliths of Cretaceous schists and some roof pendants) within the Cretaceous granitoids in the Abukuma belt. All these pre-Jurassic orogenic rocks in NE Japan, as well as those in the Sergeevka belt in southern Primorye (Far East Russia), probably have formed a ca. 3000 km-long orogen Nipponides through Paleozoic-Triassic subduction-accretion processes along the Panthalassan margin of the Greater South China block, which was composed of South China, East China Sea, Japan, and Khanka-Jiamusi-Bureya.