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

Abstract

[1] 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.Citation: Hoffman, K. A., and N. Mochizuki (2012), Evidence of a partitioned dynamo reversal process from paleomagnetic recordings in

Paleomagnetic direction and paleointensity variations during the Matuyama–Brunhes polarity transition from a marine succession in the Chiba composite section of the Boso Peninsula, central Japan

“…These rebound-like VGP swings contain clustering features in South Asia or the equatorial western Pacific and in North America. The VGP clustering in North America is likely to be consistent with that observed in marine sediment cores from the North Atlantic Ocean 983B (Channell and Kleiven 2000) and the Indian Ocean V16-58 (Clement and Kent 1991) as well as in the Tahitian lavas (Hoffman and Mochizuki 2012).…”

Millennial‐Scale Instability in the Geomagnetic Field Prior to the Matuyama‐Brunhes Reversal

“…Our stratigraphy suggests that the most probable sequence of VGP latitudes prior to 773 ka, arranged from oldest to youngest, is R-N-T-N-T-R-N-T-N ( Figure 5). This sequence differs from that suggested by Hoffman and Mochizuki (2012), who proposed that the precursor phase (780-800 ka) contains paleomagnetic orientations pointing toward Australia, which then flip closer to the final reversal, orientating toward NE North America. Instead, our sequence suggests that the orientation flips between nonaxial dipole locations frequently during the 33 kyr prior to the Bruhnes chron.…”

Rare palaeomagnetic evidence of long-term mantle control of the geodynamo and possible role of the NAD field in the reversal process

“…How then the morphology of fluid flow at depth containing axial dipole flux adjusts to changing thermally-induced energetic conditions may determine the degree of interaction with shallow core flux. Therefore, if the NAD-field is in some manner the product of flux manipulation in the shallow core by the lowermost mantle, and as suggested by Hoffman & Mochizuki (2012), reverses polarity at a different time from that of the axial dipole, then it follows that times of strong interaction between shallow core flux and deeper-sourced AD-flux may be the initial stage of an attempt by the dynamo to reverse polarity.…”