Paleomagnetism of the Great Dyke of the Kola Peninsula (2.68 Ga): New Evidence of Ultra-Low Paleointensity of the Earth’s Magnetic Field in the Late Archean

Giant mafic dykes are the key markers of the Earth’s evolution in the Precambrian and have been the subject of extensive research. This article presents the results of the paleomagnetic, rock-magnetic, and paleointensity B_anc studies of the Great Dyke of the Kola Peninsula (2.68 Ga). The mean paleomagnetic  direction of the characteristic magnetization component and the paleomagnetic pole of the Murmansk craton were calculated using the data from 5 sites (n = 41 samples): D = 117.6°, I = 77.1°, K = 40.9, α₉₅ = 12.1°, slat = 69.265°, slong = 34.35447°, plat = 51.5°, plong = 70.7°, dp/dm = 21.1°/22.6°, and paleolat = 65°. The rocks under study were thoroughly examined for their thermomagnetic properties, revealing that the main carriers of remanent magnetization are single-domain or small pseudo–single-domain (group A) or multidomain (group B) magnetite. The paleointensity values B_anc = (6.16 ± 0.92) μT were obtained for 12 samples from group A by the Thellier–Coe method. The corresponding mean virtual dipole moment VDM_2.68Ga = (0.85 ± 0.13)×10²² Am² was determined. These new findings align with previous results on the Archean and Proterozoic objects, indicating that the Earth’s magnetic field was remarkably weak in the Late Archean.

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