The Late Jurassic oblique collisional orogen of SW Japan: New structural data and synthesis

Abstract. The structural configuration of SW Japan mainly reflects a late Jurassic-early Cretaceous orogeny. The region is divided into an inner belt and an outer belt, on the Japan sea and Pacific ocean sides respectively, by a strike-slip fault, the Median Tectonic Line (MTL). Both consist of a series of stacked nappes. The inner belt is divided into a Jurassic olistostrome known as the Tanba zone and a hinterland area comprising continental Triassic-Jurassic sediments. The Tanba zone is sliced into two units: a lower one with late Jurassic matrix and Triassic-early Jurassic radiolarite olistoliths, tectonically overthrust by an upper unit comprising an olistostrome with middle Jurassic matrix and blocks which include late Paleozoic limestone, basic lava, and radiolarite. The Tanba zone is overthrust by a Paleozoic nappe complex derived from the hinterland. The basal sole of the nappe corresponds to a peculiar unit called the ultra-Tanba zone. In the Chugoku area, the hinterland is divided into an upper nappe: the Oga nappe, formed by Permo