Provenance of trench-fill deposits of the Jurassic Chichibu accretionary complex, Southwest Japan

Abstract

This study constrains the provenance of the trench-fill turbidite sandstones of the Jurassic accretionary complex (Chichibu accretionary complex) in Southwest Japan using detrital zircon U–Pb ages data. Zircons from all sites (six sites) yielded mainly Precambrian and Permian–Jurassic ages. The Precambrian zircons were derived from the North China Block, whereas the Permian–Jurassic zircons were derived from igneous rocks in and around the Korean Peninsula. The percentage of Precambrian zircons ranged from 39.9% to 52.9% (average 45.5%) of the total, and that of the Permian–Jurassic zircons ranged from 46.5% to 57.6 (average 52.6%). Thus, during the Jurassic, an equal number of zircons was continuously supplied from in and around the Korean Peninsula and the North China Block into a trench on the eastern margin of the Asian continent. The percentage of Permian and Triassic zircons gradually decreased over time, whereas the percentage of Jurassic zircons gradually increased. These changes likely reflected the igneous activity in and around the Korean Peninsula during the Jurassic. These results indicate that the turbidite sandstones of the Jurassic accretionary complex in Southwest Japan comprise detritus from not only the North China Block but also the igneous activity in and around the Korean Peninsula. Therefore, the Jurassic accretionary complex in Southwest Japan was likely formed near the North China Block.