Asymmetry of geomagnetic polarity: Equatorial dipole, Pangaea, and the Earth’s core

Abstract

The paper presents the results of analyzing the set of dual-polarity paleomagnetic results the Global Paleomagnetic Database (GPMDB). The dataset was expanded by the results from the Paleomagnetic Data Catalogue for the USSR and with new data published after 2005. Some results were rejected to avoid the influence of overprints of ancient and recent magnetization. Overall, 59 dual-polarity results for the lithospheric plates of Baltica, Laurentia, and Siberia with their immediate framing were selected for the analysis in the interval of ages 207–359 Ma. The new data confirmed the model of the paleomagnetic field, according to which the field contains a long-lived component corresponding to the equatorial dipole which is responsible for the non-antipodal paleomagnetic directions in the zones of normal and reverse polarity in sedimentary and volcanic rock sequences. Retaining its value of 5–8% of the central axial dipole, the equatorial dipole changed its polarity a few times during the interval 359–207 Ma. The northern poles of the dipole formed two antipodal groups on the Earth’s surface, which lie within or near the subduction zones on the periphery of the Pangaea Supercontinent. Such localization of the equatorial dipole is suggested to be related to the ascending branches of the mantle convection and to the topography of both boundaries of the outer Earth’s core.