Tertiary Tectonic Movement of Central Japan Inferred from Paleomagnetic Studies

抄録

Paleomagnetic studies of the Tertiary volcanic rocks were carried out in the four regions of the Noto Peninsula, the Sado Island, Niigata Prefecture and Fukushima Prefecture located on both sides of the Itoigawa-Shizuoka tectonic line in central Japan.
Rocks older than 16 Ma show a clear contrast in their declinations between the sides of the line. The paleomagnetic mean declination for the Noto region shows no significant deflection while those of the Sado and Fukushima regions are deflected westerly by 17° to 27°.
Moreover, as for the mean declinations for the period younger than 14Ma, there is a slight difference recognized between the data obtained from Niigata and Fukushima regions. It is concluded that the rotational tectonisms were still continuing until the late Miocene time in the eastern part of central Japan, and that central Japan was not a single tectonic block but has divided into several local sub-blocks.