No abstract

The tempo of Large Igneous Province emplacement is crucial to determining the environmental consequences of magmatism on the Earth. Based on detailed flow-by-flow paleomagnetic data from the most representative Permian-Triassic Siberian Traps lava stratigraphy of the northern Siberian platform, we present new constraints on the rate and duration of the volcanic activity in the Norilsk and Maymecha-Kotuy regions. Our data indicate that volcanic activity there occurred during a limited number of short volcanic pulses, each consisting of multiple individual eruptions, and that the total duration of discrete eruption pulses did not exceed~10,000 years (hiatuses are not included). Our study confirms the occurrence of a thick interval in the lower part of the Norilsk lava sections, which contains a record of geomagnetic reversal and excursion. Based on combined evidence from paleomagnetic secular variation and typical timescales for such reversals, we conclude that the~1-km-thick lava stratigraphy, corresponding tõ 20,000 km 3 of basalt, of the Kharaelakh, Norilsk, and Imangda troughs was formed during a brief, but voluminous, eruptive period of several thousand years or less. Our data further suggest that the ore-bearing Norilsk-type intrusions are coeval or nearly coeval with the boundary between the Morongovsky and Mokulaevsky formations. We calculated a new Siberian Permian-Triassic paleomagnetic pole Norilsk-Maymecha-Kotuy (NMK): PLat = 52.9°, PLong = 147.1°, A95 = 4.3°, K = 23.2, and N = 49 lava flows. It is shown that geomagnetic field variations circa 252 Ma were similar to those observed in the latest Cenozoic.

We present detailed paleomagnetic data from the Permian-Triassic Cu-Ni-Pt–bearing intrusions of the Norilsk region (northwestern Siberian platform). Based on the analysis of geomagnetic secular variations recorded in the intrusions, we correlate the Norilsk ore-bearing intrusions with the Siberian Traps volcanic sequences in the region. The similarity of paleomagnetic directions of the ore-bearing intrusions to those of the Morongovsky and Mokulaevsky volcanic formations suggests that the emplacement of these lavas and intrusions occurred during the same stage of the magmatic activity. Furthermore, some weakly mineralized intrusions and barren nondifferentiated sills demonstrate paleomagnetic directions close to those of the ore-bearing intrusions. This implies that ore-bearing, weakly mineralized, and barren intrusions were emplaced during the same stage of magmatic activity. On the other hand, the paleomagnetic directions of different ore-bearing intrusions (Norilsk 1, Talnakh, and Kharaelakh), while close, are statistically different. Thus, the formation of these three intrusions and their satellites corresponds to discrete magmatic events within the same stage of magmatic activity. Based on the paleomagnetic data, the emplacement duration of individual intrusions can be estimated as <10 k.y. Our correlation scheme is consistent with some genetic models for the ore-bearing intrusions. The analysis of geomagnetic secular variations can be used as an independent tool for the investigation of other Cu-Ni and platinum group element-bearing magmatic complexes.