On a possibility of geomagnetic reversal recording in dolerite sills of Norilsk region: results of mathematical modeling

Abstract

The possibility of reconstructing the geological chronicle by identifying the peculiarities in the variations of the Earth’s magnetic field associated with the reversals is one of the fundamental applications of paleomagnetism. The most detailed records of reversal events whose duration is, on average, one to ten thousand years have been recognized from the results of studying flood basalts of the large igneous provinces. At the same time, recent publications report the facts that are interpreted as a record of a geomagnetic reversal in the intrusion bodies. Inter alia, these data have been obtained for the relatively thin Ergalakh dolerite sills in the Norilsk region of the Siberian trap province which are supposed to have recorded the «Ivakinsky-Syverminsky» reversal corresponding to the Permian–Triassic boundary. The interpretation is based on the hypothesis of slow cooling of the intrusion during which its apical parts are magnetized during the Ivakinsky epoch of reversed polarity whereas the central parts acquire magnetization after the reversal during the Syverminsky time corresponding to normal polarity. In this paper, we consider the results of mathematical modeling to discuss the validity of these assumptions and the potential eligibility of subvolcanic intrusions as a source of information for studying geomagnetic reversals. It is shown that the duration of their cooling including the interval of the most probable magnetization is a few orders of magnitude shorter than the duration of the reversal transitions, whereas the presence of the components with normal and reversed polarity is most likely to be due to the effect of self-reversal.