Revisiting a domain state independent method of paleointensity determination

The use of a domain-state independent method (the Wilson method) of acquiring absolute paleointensities is tested using three sets of historical lavas from Mexico, Italy and Iceland. The Wilson method works by comparing continuous thermal demagnetization curves of the original natural remanent magnetization with that of a laboratory-induced thermoremanence. By comparing the results with the known fields, a new rejection criterion is proposed that accounts for chemical alteration. The application of this criterion is shown to improve the quality of the paleointensity estimates. The Wilson paleointensity estimates are compared with paleointensity determinations made on the same suite of samples using standard Thellier-type heating. Generally, the Wilson paleointensity estimates compare favorably for samples that yielded correct Thellier-type determinations, however, at one locality the Wilson method did not yield any estimates due to severe chemical alteration, in contrast it was still possible to determine the paleointensity from the low-temperature Thellier data. To assess, the Wilson paleointensity protocol’s ability to return a correct estimate for a true multidomain system, a synthetic multidomain magnetite sample was imparted with a thermal remanent magnetization. The Wilson protocol returned the correct paleointensity within error, in contrast the Thellier-type protocol failed. As the Wilson method is significantly faster than Thellier-type methods, it is suggested that the Wilson method should be tried as a ‘first approach’ in paleointensity studies, or for samples dominated by multidomain material.