Palaeomagnetic analyses of the Leaf Rapids area in Manitoba

Abstract

Conventional methods of analyses of palaeomagnetic data, leave a lot to be desired. Fisher statistics, by far the most popular technique, is a method that was developed long before computers were widely available. Understandably, it is not specifically a computer application. Furthermore, the necessary selective procedures used to identify "valid" palaeomagnetic samples, introduce a subjective form of analysis. In order to answer to these shortcomings in current analysis, two digital computer methods were developed. In one method, Gaussian distributions representing the probability of a position corresponding to the true value were fitted to measurements made at each cleaning field strength. The most probable orientation was taken from the location of the highest amplitude. In the second method, the same measurements were summed using vector addition. The final vector sum was assumed to the most probable orientation. Rock core samples used in this study were obtained from the Leaf Rapids area and are of mid-proterozoic age (1800-1900Ma). These samples were analyzed in the laboratory and the results were used to test the above methods. The equipment used was a Schonstedt model DSM-1 spinner magnetometer, while magnetic cleaning was done by using an alternating frequency demagnetizer. The rock samples were collected during a reconnaissance survey carried out in 1974. The methods used in this study offers a better interpretation of the results than fisher statistics would allow.