Natural Remanent Magnetization of Tertiary Plutonic Rocks affected by Tectonic Movement of Land Mass in Central Japan

Abstract

About 100 samples were collected from 12 outcrops of Tertiary plutonic rocks in 5 localities distributed over the central part of Honshu, Japan, and their natural remanent magnetization (n.r.m.) were measured. The results of the measurements were classified into three groups: (1) the n.r.m. parallel to the present dipole field, (2) the n.r.m. along the direction of N 20°E and (3) the n.r.m. along the direction of N 31°W.The central part of Honshu had been subjected to tectonic activities in Tertiary age and the intrusions of plutonic rocks were associated with these activities. Some of these intrusion seems to have been affected by the tectonic movements and moved in different ways after the solidification. The sites, from where the rock samples were collected, are located over 5 different intrusions and the difference of the directions of the n.r.m. mentioned above can be explained by the relative movement of these intrusions.