A Study of the Palaeomagnetism of the Pilansberg Dykes

• Published in: Geophysical Journal International
• Main Author: Gough, D. I.
• Format: Text
• Language: English
• Published: Oxford University Press 1956
• Subjects: Articles; North Magnetic Pole
• Online Access: http://gsmnras.oxfordjournals.org/cgi/content/short/7/4/196; https://doi.org/10.1111/j.1365-246X.1956.tb05564.x

A detailed study has been made of the remanent magnetization of five Pilansberg dykes, by means of measurements on oriented specimens of the rocks. Outcrops of the dykes prove to have suffered magnetic disturbance of their original thermo-remanent magnetization. Specimens from depths of a few thousand feet, taken in Witwatersrand gold mines, show highly consistent magnetisation of the basic parts of the dykes over considerable distances between sampling sites. The mean directions given by the five dykes agree well, and the mean direction from the five dykes gives a North-seeking magnetic pole with inclination +69°.3 and azimuth N 24° 0 E. Assuming thermo-remanent magnetisation by a geocentric dipole field, this places a North magnetic pole in latitude 7½° N, longitude 42½° E at the time of intrusion of the dykes. The age of the dykes is uncertain, but is probably about 300 to 400 million years. Some of the specimens have been subjected to alternating magnetic fields in order to test the stability of their magnetisations. The basic specimens are found to be highly stable, being only slightly affected by fields of 100 to 300 oersteds. The possible implications of the results are discussed, in terms of hypotheses of polar wandering and continental drift.