Preliminary results on variability evaluations of non-dipole zonal terms for distinctive geomagnetic reversal frequency intervals along the Phanerozoic

Abstract:

In this work we investigate, in wide paleolatitudinal coverage, the variability of the non-dipole zonal terms over two groups of distinctive geomagnetic reversal frequency (fr) intervals within the Phanerozoic: (1) $\sim$460-480 Ma Ordovician Reversed Superchron, $\sim$262-318 Ma Permo-Carboniferous Reversed Superchron, and the $\sim$84-125 Ma Cretaceous Normal Superchron; (2) the last 5 Ma, Jurassic ($\sim$145-200 Ma) and the Illawarra Hyperzone of Mixed Polarity ($\sim$228.7-266.7 Ma). For both groups, estimates of deviation of the geocentric axial dipole (GAD) model by means of calculations of non-dipole anomaly ΔI, as well as the dipole ($g^1_0$), quadrupole ($g^2_0$), and octupole ($g^3_0$) zonal terms (which allowed to access the weighted contribution of the quadrupolar (G2 = $g^2_0$/$g^1_0$) and octupolar (G3 = $g^3_0$/$g^1_0$) spherical harmonics) were provided by selections of igneous-based, high-quality paleomagnetic databases. Our preliminary results indicated patterns of G2 and G3 fluctuations which are clearly dependent of the geomagnetic reversal frequency, with major contribution of G2(G3) in periods of low(high) geomagnetic reversal frequency – hence providing new clues on the variability of the non-dipolar fields for geomagnetic reversal frequency changes along geological times.