Anomalous magnetizations in 3.4 b.y. old Barberton Mountain Land samples

The ratio of natural remanence (NRM) to saturation remanence is exceedingly high for a number of basaltic to ultramafic samples from the 3.4 billion year old Barberton Mountain Land greenstone belt, South Africa. Although conventional paleointensity methods indicate paleofields of several oersteds, demagnetization curves plotted on logarithmic scale clearly show the NRM in these samples to be unlike thermal remanence. It is probable that the observed NRM is a chemical remanence related to the greenschist metamorphic event, and that the intense magnetizations are the result of internally generated, rather than external fields.