The spreading-rate dependence of anomalous skewness of pacific plate magnetic anomaly 32: Revisited

Abstract

We test the consistency of 108 estimates of skewness (a measure of asymmetry that depends on the orientation of lithospheric magnetization) of magnetic anomaly 32 from the Pacific plate with a model for spreading-rate-dependent anomalous skewness formulated for data in the Arctic, Atlantic, and Indian Oceans. In a prior study, a chron 32 (71.6-73.0 Ma) paleomagnetic pole was determined that best fit these 108 skewness estimates while simultaneously solving for a third parameter, anomalous skewness, assumed to be independent of spreading rate. An analysis of the residuals in skewness was previously used to test for any dependence on spreading rate and indicated an increase in residual skewness with increasing spreading rate, which is opposite in trend to that observed in other ocean basins. In contrast with the prior analysis of residuals, we find the data to be consistent with anomalous skewness increasing with decreasing spreading half rate less than 50 mm yr -1 . Thus, the spreading-rate dependence of anomalous skewness in the Pacific is consistent with that found in other ocean basins and with the model for spreading-rate-dependent anomalous skewness. The resulting revised paleomagnetic pole lies only 1.2° from the prior pole. The revised pole, as was the case for the original pole, shows that the Hawaiian hotspot has shifted southward relative to the spin axis by 13° since ca. 72 Ma. © 2011 Geological Society of America.