A Palaeomagnetic Pole from Late Cretaceous Marine Magnetic Anomalies in the Pacific

Abstract

A method for finding palaeomagnetic poles based on the skewness of marine magnetic anomalies is applied to anomalies 27-32 on the Pacific plate. Palaeomagnetic poles based on the observed skewness of these anomalies are found to be inconsistent with other palaeomagnetic data. The skewnesses of anomalies 27-32 on opposite sides of the Pacific-Antarctic Ridge are compared: a 12° to 28° skewness discrepancy is found across the ridge crest. By assuming that there is a systematic discrepancy of 12° to 14° in the skewness of anomalies 27-32, the inconsistencies in the pole positions and in the skewness of anomalies across the ridge crest are eliminated. The systematic skewness discrepancy is called ‘anomalous skewness’. Anomalous skewness can be explained either by modifying the assumed structure of the magnetic source layer or the assumed behaviour of the palaeomagnetic field. After a systematic correction of 14° is made to the observed data, a unique palaeomagnetic pole is found for the North and South-west Pacific. This pole indicates about 20° of northward motion in the last 70 My, and suggests that there has been little or no motion between the two areas since the Late Cretaceous.