Oligocene/Miocene Rotational Block-Movement and Paleostress Field of Japan

抄録

On the basis of compilation of paleomagnetic direction data, the mid-Cenozoic geography and tectonic stress field of the northeastern and southwestern Japan were restudied. Variations in paleomagnetic directions among the three tectonic provinces (northern, central and western Japan) cannot adequately be explained only by the abrupt 15Ma rotation of the two halves of Honshu arc, but can be satisfied by the preceded tectonism associated with initial spreading of the Japan Basin. The major new points are: (1) counterclockwise rotation of northeastern Japan had already occurred continuously during 32-23Ma, probably followed by another counterclockwise rotation associated with the opening of the Yamato Basin around 15Ma. (2) It is until the start of 15Ma clockwise rotation of western Japan that the three paleomagnetic provinces belonged to an extensional stress field on the elongated Honshu arc along a subduction zone of the Pacific plate. (3) The later local rotation might be probable in Northeastern Honshu during 15Ma to 7Ma concerning the development of intra-arc basin.