Evolution of the virtual dipole moment through the Paleoarchean-Phanerozoic

Abstract

In the context of the dipole model of the earth’s magnetic field, the data from the international bank of digital information on the distribution of the virtual dipole moment (VDM) values in time, combined with the data obtained by subsequent investigations (7082 values in total), served as the basis for reconstructing its behavior through the Paleoarchean-Phanerozoic. The VDM behavior is characterized by a positive linear trend in the interval of 4.1 × 1022 Am2 (3.5 Ga ago) to 5.5 × 1022 Am2 (now). This background linear growth of the field strength is complicated by irregularly distributed VDM variations ranging in the amplitude from 1.7 × 1022 to 3.7 × 1022 Am2 with the wavelength varying from 220 to 920 Ma. The average wavelength of such fluctuations is estimated to be 570 Ma, which is approximately equal by duration to the Wilson geological cycles. The interval of 0.84–1.3 Ga is first established to be characterized by the relatively calm VDM region of 4.7–4.9 × 1022 Am2. The first defined deep minimum described by 10 data points with the extremum of 2.3 × 1022 Am2 (2.15 Ga ago) corresponds to the terminal phase in the formation of the earth’s core geometry and initiation of the formation of the modern dipole field.