Determining palaeomagnetic poles and anomalous skewness from marine magnetic anomaly skewness data from a single plate

SUMMARY We present a method for simultaneously determining palaeomagnetic poles and anomalous skewness from the observed skewness of marine magnetic anomalies from a single plate. Skewness is esimated by visual comparison of phase-shifted observed anomaly profiles with an ideal zero-phase synthetic anomaly calculated for sea-floor formed and observed in a vertical magnetic field. We assume that each crossing of the same anomaly or anomalies is anomalously skewed by an identical amount. This assumption is supported by the great reduction in squared error (i.e., x') obtained by adding just this one adjustable parameter. Our inversion procedure determines the palaeomagnetic pole and anomalous skewness that give a maximum likelihood best fit in a least-squares sense to the observed effective remanent inclinations, which are inferred by simple calculation from the observed phase shift. Our method determines 95 per cent confidence limits both from a constant-chisquare boundary and by linear propagation of errors and also estimates the information distribution of the data. The anomalous skewness values we determine agree with values estimated from comparison of anomalies across a spreading centre. These encouraging results suggest that further skewness studies may permit variations in anomalous skewness with age to be quantified, provide constraints for models that describe the processes affecting the magnetic source layer during its creation and evolution, and permit oceanic plate apparent polar wander paths to be determined with a fine age resolution.