Could the Norilsk Region Dolerite Sills Have Recorded Geomagnetic Field Reversals? Results of Mathematical Modeling

Аннотация

The possibility of reconstructing geologic events by identifying patterns in variations of the geomagnetic field related to reversals is one of the fundamental applications of paleomagnetism. The most detailed records of reversal events, whose duration averages 1–10 thous. years, are known from studies of flood basalts of large igneous provinces. At the same time, there have been recent publications presenting facts interpreted as records of geomagnetic reversals in intrusive bodies. Specifically, such data were obtained for relatively thin dolerite sills of the Ergalakh complex in the Norilsk region of the Siberian trap province that supposedly recorded the Permian-Triassic “Ivakin-Syvermin” reversal. This interpretation is based on the hypothesis of a slowly cooling intrusion, in which its apical parts magnetized in the Ivakin epoch of reversed polarity and the central parts—after the reversal in the Syvermin epoch of normal polarity. In this paper, using results of mathematical modeling, we discuss the validity of such assumptions and the potential attractiveness of subvolcanic intrusions for studies of geomagnetic reversals. We demonstrate that the duration of their cooling, including the most probable interval of magnetization is several orders of magnitude less than the duration of reversal transitions, and that the most probable cause of the occurrence of both polarities is the self-reversal effect.