Kimio Hirooka

Paleomagnetic studies combined with fission-track datings on the western arc of Sulawesi, east Indonesia

Abstract Paleomagnetic studies in conjunction with fission-track dating on the western arc of Sulawesi yield important evidence bearing on the tectonic history of the area. During the Paleogene to Early Miocene time interval the paleomagnetic pole for southwestern Sulawesi was situated at 36.5°E 44.8°N. This pole position is significantly different from that in the time interval Middle Miocene to Recent, which is consistent with the north pole of the axial geocentric dipole. This fact suggests that subsequent to the Paleogene to Early Miocene period, possibly 19–13 m.y. B.P., a major tectonic event occurred which caused about 40 degrees of anticlockwise rotation of the area. It is suggested by the present work that the postulated collision followed by welding of eastern Sulawesi with western Sulawesi during the Pliocene (Katili, 1978) may be the tectonic event mentioned above. In addition, our data does not support the hypothesis that western Sulawesi has been derived from the dispersal of Gondwanaland.

Paleomagnetic evidence of the rotation of central Japan and the paleoposition of Japan

Abstract Paleomagnetic studies of the Daishoji, the Echigo-Yuzawa and the Kataimogawa areas revealed complex intrablock tectonic rotations in the Central Honshu block which is sandwiched in between the Southwest and Northeast Honshu blocks. Paleogeographic maps of 16, 15 and 14 Ma are reconstructed by using paleomagnetic declinations obtained so far in Japan.