Geographical distribution of transitional VGPs: Evidence for non-zonal equatorial symmetry during the Matuyama-Brunhes geomagnetic reversal

Abstract

Paleomagnetic records of the Matuyama-Brunhes polarity reversal obtained recently from the northern, equatorial and southern latitudes of the Atlantic sector display a distinct symmetry with respect to the Equator. The virtual geomagnetic pole (VGP) paths from the mid-latitude sites in the northern and southern hemispheres (DSDP Site 609 and Core V16-58) are nearly coincident, tracking northward through the Americas. The VGP path from the equatorial site (ODP Site 664) tracks northward through eastern Asia, nearly antipodal to the other two paths. Modeling results indicate that superimposing an h 1 3 geometry onto a reversing axial dipole explains the sense of equatorial symmetry exhibited by these three records. These results are consistent with the bulk of the data available from other records of this polarity transition, suggesting that the transitional VGPs during this reversal tend to fall along two distinct longitudinal bands. The grouping of transitional VGPs suggests that there is a strong geographical control over the reversal process. An apparent correlation between the longitudinal bands of transitional VGPs and the location of the major flux concentrations in the radial component of the historical geomagnetic field at the core-mantle boundary [1] suggests that the processes which cause these flux concentrations may have influenced the geometry of the Matuyama-Brunhes transitional field.