ABSTRACT The Middle Miocene Takaiwa Rhyolite dike swarm in central Shikoku, southwest Japan, provides a key opportunity to evaluate whether arc‐parallel dikes record the regional stress field in a crustal domain with a pervasive ENE–WSW structural grain. We measured 37 intrusive contacts and found that 36 dikes sharply crosscut schistosity, folds, and tectonic lines of the Sanbagawa Metamorphic Complex, demonstrating that their orientations were not governed by host‐rock anisotropy. Using full three‐dimensional dike‐wall orientations and a mixed Bingham paleostress inversion, we obtained a single transtensional stress state with an NNW–SSE‐trending σ₃ axis. Although this σ₃ direction is consistent with previous reconstructions for the Setouchi region, the Takaiwa stress regime differs from the extensional regimes documented at other Setouchi localities. The inferred transtensional configuration may reflect either depth‐dependent modification of the Setouchi stress field or proximity to the compressional forearc domain. These results show that the ENE–WSW‐striking Takaiwa dikes reliably record the regional Middle Miocene stress field, resolving long‐standing concerns that arc‐parallel dike trends in southwest Japan might simply reflect structural inheritance. The study highlights the importance of integrating outcrop‐scale observations with three‐dimensional orientation analyses when reconstructing paleostress fields in structurally anisotropic regions.
Haji et al. (Thu,) studied this question.