Evidence of a partitioned dynamo reversal process from paleomagnetic recordings in Tahitian lavas

Abstract

Lavas erupted at the Society hotspot during the Matuyama-Brunhes (M-B) polarity reversal record transitional field behavior containing two tight paleodirectional groups that when averaged are antipodal at the 95% confidence level, and thus correlate to antipodal clustered virtual geomagnetic poles (VGPs). The occurrence of these observations-data obtained from two published records of the M-B transition from distinct sections of a succession of flows on Tahiti-is associated with a time when the strength of the axial dipole was significantly reduced. One of the clusters was recorded by lavas that were not erupted in succession, suggesting that significant time had passed during this volcanic activity. Time spent during the formation of the antipodal cluster is unknown, although it resides in the same location as VGP clusters associated with four other transitional events obtained from Society hotspot lavas. Calculated VGPs at the Society hotspot for both "polarities" of the averaged historic field-less the axial dipole term-are found in the cluster locations. These findings offer strong evidence for a two-tiered dynamo process in which nearly the entire axial dipole component undergoes both demise and regeneration quasi-independently from that of the remainder of the field, the pattern of which is tied to long-held physical conditions of the lower-most mantle. Copyright 2012 by the American Geophysical Union.