Neogene tectonic stress fields of northeast Honshu Arc and implications for plate boundary conditions

Abstract

More than 3300 metalliferous veins were analyzed to reconstruct the Neogene tectonic stress field of the northeast Honshu Arc using basic fracture mechanics. The veins are grouped into a dominant NE system and subordinate E-W, N-S and NW systems. The NE system is associated with assemblages of conjugate strike-slip faults and extension joints or normal faults which were formed during a period from 15 to 5 Ma. The fractures suggest that σ 1 or σ 2 was oriented ENE and σ 3 was oriented NNW. σ 3 is thought to have been tensional, because no veins are associated with thrust faults. This stress orientation is neither perpendicular nor parallel to the axis of the Japan Trench where the Pacific plate was moving west-northwest and was subducted under the northeast Honshu Arc. The inconsistency between the stress orientation and the plate kinematics can be explained by the dynamic effects related to other plate boundaries surrounding the northeast Honshu Arc, namely compression on the Hokkaido Axial Zone and the Itoigawa-Shizuoka Tectonic Line. In addition, the triple junction of the Japan Trench, Izu-Bonnin Trench and the Sagami Trough was probably located 300–400 km northeast from its present position and the subduction zone of Nankai Trough-Sagami Trough is assumed to have been a tensional plate boundary. The reconstructed stress field is consistent with transtensional backarc rifting at about 15 Ma.