Palaeomagnetic Studies on a Quaternary Volcanic Region in Japan

Abstract

Palaeomagnetic studies have been conducted of the volcanic rocks in the North-Izu and Hakone volcanic region, Japan, where complete succession of lavas has been determined by one of us (H. K.). By sampling 4-7 oriented rock specimens at each of 57 sites, the period from the very beginning of the Pleistocene to Holocene has been covered. The maximum time interval between two consecutive samples may probably be not more than several tens of thousand years except that between two samples of middle to younger Pleistocene when the volcanic activity did not occur within the region concerned. Care was taken not to use the rock samples of which natural remanent magnetization may have suffered from any significant disturbances, geolgically, chemically, magnetically or otherwise. Selection of proper samples was performed according to the criteria for the stability of remanent magnetization proposed by us previously (Journ. Geomag. Geoelec., 6, No. 4, 1955). The major findings obtained through the present study are: 1) During the whole Quaternary age, the geomagnetic centred dipole has been fluctuating around an axis of which north pole wandered from 72°N, 86°E to 81°N, 32°W. 2) The direction of polarization of the centred dipole was reversed at a time in the earliest Quaternary, namely during the middle period of the formation of the Usami volcano.