Palaeomagnetic Study on a Granitic Rock Mass with Normal and Reverse Natural Remanent Magnetization

Abstract

The author collected intrusive rocks in Nose district in Kinki Province and measured their natural remanent magnetization. Results of measurements of rocks collected from one rock body are as follows: the natural remanent magnetization of the intrusive rocks collected at the contact zone with country rocks was normal, while that of the intrusive rocks collected at places a little far from the contact zone was reverse. The directions of remanent magnetization were neither typical normal nor reverse. The normal direction deviated easterly relative to the present field direction, and the reverse one westerly.A fact that the rocks from a single mass possess both the normal and reverse magnetization can be explained, considering that the rock mass had been formed at the times when a transition of the geomagnetic field occurred, and the intermediate direction of magnetization seems to indicate the transition of the dipole of the geomagnetic field. The pole positions obtained from the intermediate direction of natural remanent magnetization lie in the same zone as those obtained from the Mio-Pliocene rocks in southwestern Japan.