Deformation process and kinematics of mélange in the Early Cretaceous accretionary complex of the Mino‐Tamba Belt, eastern southwest Japan

Abstract

The Kanayama unit of the Mesozoic Mino‐Tamba accretionary complex in eastern southwest Japan is a thick mélange unit composed mainly of abundant muddy matrix and variously sized clasts of chert, hemipelagic siliceous mudstone, and sandstone. Two episodes of deformation formed the mélange fabrics: the first involved fragmentation of sandstone layers in response to mud injections; the second involved layer‐parallel, noncoaxial shear that resulted in the mixing of pelagic to terrigenous clasts and the formation of S‐C‐like asymmetric fabrics with scaly foliation. The S‐C fabrics exhibit a predominantly sinistral shear sense in plan view. After fold and tilt corrections, the restored slip motion inferred from the S‐C fabrics indicates a bulk top‐to‐the‐south shear. Combining the unit's terminal fossil age and radiometric age with a regional plate reconstruction model, these data suggest that the Kanayama mélange formed along a décollement during oblique subduction of the Izanagi plate in the Early Cretaceous.