Signs of the Record of Geomagnetic Reversal in Permian–Triassic Trap Intrusions of the Ergalakhsky Complex, Norilsk Region

Abstract

In the sections of two Permian–Triassic trap intrusions of the Ergalakhsky complex, Norilsk region, we revealed the alternation of the intervals of normal and reversed polarity. The near-contact zones of the intrusions are magnetized reversely, whereas magnetization in the central zones has the normal polarity. We present the arguments showing that this change in the polarity along the intrusions section is not the result of postmagmatic remagnetization or self-reversal of remanence but marks the reversal of the geomagnetic field that occurred during the emplacement of the intrusive bodies. As the Ergalakhsky intrusions represent the oldest intrusive trap complex in the Norilsk region, a highly accurate determination of their age is vitally important for the time correlation of the initial stage of magmatic activity. The paleomagnetic data show that the studied sills intruded directly at the Permian–Triassic boundary, at the very end of the Ivakinsky stage. According to the existing estimates for the durations of the reversals, the cooling of the intrusions could last a few thousand years. In the future, the studied sills of the Ergalakhsky complex can be used as a unique object for studying the structure of the geomagnetic field during the reversals and for reconstructing the thermal history under the cooling of intrusions, as well as a reference for estimating the total duration of trap magmatism.