Paleomagnetic results from permian greenstones in central Japan and their geologic significance

Abstract

A systematic paleomagnetic study has been made of Permian greenstones and associated sediments from the inner belt of central Japan. The greenstones are generally metamorphosed into the zeolite facies to greenschist facies grade. The intensity of the natural remanent magnetization of the greenstones decreases with increase of metamorphic grade toward the greenschist facies. Metamorphism as low or lower than the greenschist facies grade does not create chemical remanent magnetization in the greenstones. Reliable magnetic directions were obtained from the greenstones and associated sediments occurring in the lowest grade metamorphic zones after thermal demagnetization and alternating field demagnetization. After correction of the magnetic directions with respect to the folding axes and bedding planes, the Permian magnetic inclination in Japan was deduced yielding the suggestion that Japan was situated in an equatorial region in the late Paleozoic period, perhaps as part of a missing continent, Pacifica. Since then, the Far East microplate including Japan migrated toward the north, and collided with the Asian mainland in the late Mesozoic.