Dark bands in the submarine nankai accretionary prism - Comparisons with miocene-pliocene onshore examples from Boso Peninsula

Abstract

Unique planar structures made of thin, dark bands in host siltstones were described at microscopic scale in samples collected from the Tenryu Canyon in the eastern Nankai accretionary prism. Their mechanisms of formation and tectonic relationships were compared with similar onshore examples from the unmetamorphosed Miocene-Pliocene Miura-Boso accretionary prism. Four modes of occurrences that had been identified previously in onshore rocks were recognized in the submarine rock samples. The dark bands were formed at different stages. Two formed during sedimentation and subsequent burial (i.e., gravity origin), and the other two formed during accretion (i.e., tectonic origin).