Tectonic setting and formation of the Setouchi volcanic rocks in the western Seto Inland Sea, Japan

The Setouchi volcanic rocks include high-Mg andesites (HMAs) and garnet-bearing dacite–rhyolite, are sporadically distributed along the Median Tectonic Line, Japan. New U–Pb zircon ages geological geochemical data presented for those in Western region (W-Setouchi). Previous studies referred to altered andesite W-Setouchi as “pre-Setouchi rocks.” However, on basis of new age (14.4 Ma ± 0.3 Ma) characteristics, we redefine it Jikamuro Formation, part rocks. Incompatible elements more enriched Formation than HMAs. characteristic element compositions may be explained by mixing compositionally different magmas, including subducted sediment melts, plus a contribution from crustal contamination. A stress-inversion technique with Bingham distribution method was applied orientations felsic mafic dikes within rocks, indicates paleo-stress conditions during period volcanism W-Setouchi. analysis reveals NNW-extensional stresses strike-slip stress. We infer that former represents extensional main latter stress transition most recent (after 12 Ma).