Miocene intra‐arc bending at an arc‐arc collision zone, central Japan

Abstract Recent paleomagnetic studies are reviewed in an effort to clarify the relationship between the intra‐arc deformation of central Japan and the collision tectonics of the Izu‐Bonin Arc. The cusp structure of the pre‐Neogene terranes of central Japan, called the Kanto Syntaxis, suggests a collisional origin with the Izu‐Bonin Arc. The paleomagnetic results and newly obtained radiometric ages of the Kanto Mountains revealed the Miocene rotational history of the east wing of the Kanto Syntaxis. More than 90° clockwise rotation of the Kanto Mountains took place after deposition of the Miocene Chichibu Basin (planktonic foraminiferal zone of N.8: 16.6–15.2 Ma). After synthesizing the paleomagnetic data of the Japanese Islands and collision tectonics of central Japan, it appears that approximately a half rotation (40–50°) probably occurred at ca 15 Ma in association with the rapid rotation of Southwest Japan. The remainder (50‐40°) continued until 6 Ma, resulting in the sharp bent structure of the pre‐Neogene accretionary complexes (Kanto Syntaxis). The latter rotation seems to have been caused by the collision of the Izu‐Bonin Arc on the northwestward migrating Philippine Sea Plate.