Implication for the two-stage layer-parallel faults in the context of the Izu forearc collision zone: examples from the Miura accretionary prism, Central Japan

摘要

The southern tip of the Miura Peninsula, central Japan, exposes nice outcrops of forearc sediment accreted to another forearc, which occurred during a series of Izu are collision with the Honshu are. Neogene deep marine volcaniclastic sedimentary sequences, the Misaki Formation, show many types of faulting and folding associated with layer-parallel faults besides many imbricate thrusts of the main deformation stage. The layer-parallel faults are divided into two stages, one is related to northwestward gravity-driven slump deposits, the other is southeastward thrust faulting, and the both are associated with many layer duplications with liquefaction of sediments. The slumping is commonly developed in the upper part of the sequence in the surface of the down-going slab before accretion, whereas the thrusting is dominant in the lower part within the toe of the accretionary prism, probably along the decollement zones in the prism. Thus, the Misaki Formation represents a good example of deformation just before and after shallow forearc accretion in the are-collision zone. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 31]