Paleomagnetism of the Shimokura Dike Swarm in Northeast Japan

Abstract

A dike swarm is the subterranean volcanism of more than several tens of intrusions. The subaerial volcanism of a single volcano generally persists its activity for 104-105 years (e.g., Kuno, 1976). A dike swarm is also considered to be formed in the same time interval as that of the subaerial one (Nakamura, 1977). Such time interval is considered to be sufficient to average out the geomagnetic secular variation (Heki, 1983). Dike rocks are volcanic ones so that they have thermo-remanent magnetization which can yield reliable paleomagnetic data and that we can date them by some radiometric method. Furthermore, we find that dike swarms have occurred at many places throughout geological time. Dike swarms can be, therefore, used as a good tool to study paleomagnetism in spite of the uncertainty of the time sequence of individual intrusions. © 1985, Society of Geomagnetism and Earth, Planetary and Space Sciences. All rights reserved.