Paleomagnetism of trap intrusions, East Siberia: Implications to flood basalt emplacement and the Permo-Triassic crisis of biosphere

- New paleomagnetic results on Siberian trap intrusions are obtained.
- Paleomagnetic data from six 35 to 200 km long profiles are very tightly grouped.
- We assume that all intrusions in each area have been emplaced for <3 millenniums.
- Brief magmatic pulses affect our views on the causes of the end-Permian mass extinction.

Despite decades of concentrated studies, large igneous provinces (LIPs) are still among the most enigmatic phenomena of the Earth evolution. Among the myriad questions facing researchers, the duration of eruptive magmatic activity and its distribution through time are probably the most mysterious ones. Although the accuracy of modern dating techniques offers relatively high resolution, it is impossible to discriminate whether magmatic activity was more or less uniform or concentrated in few powerful outbursts. Consequently, many “trap-related” questions, from their origin to possible impact on the biosphere, still cannot be answered. Some of the above questions can be addressed with paleomagnetic data as have been effectively done in the case of the end-Cretaceous Deccan traps. The Siberian traps are one of the largest LIPs in the Phanerozoic and are thought, by some, to be the triggering event for the end-Permian mass extinction. We conducted a paleomagnetic study of trap intrusions along two long profiles in the eastern part of the province and found that most site-mean directions are grouped several times tighter than is common for the data on thick lava series and dyke swarms; similar over-grouping is found in other parts of the Siberian trap province too. We argue that this phenomenon is the most likely related to nearly simultaneous emplacement of trap intrusions over areas of several ten to few hundred kilometers in dimension for few millenniums or even faster. Moreover, such brief events account for all, or nearly all, magmatism in each area; how such events correlate over the entire Siberian LIP, however, remains an open question. Still, our data together with paleomagnetic results on thick lava series in Siberia strongly indicate that magmatic activity consisted of a number of brief pulses. In comparison to the other LIPs, the Siberian one is underlain by the thickest succession of carbonates, evaporites and coal-bearing clastics that are capable of producing huge amount of green-house and poisonous gases. We hypothesize that these very fast injections of magma into thick underlying sediments and the unique geological setting of the Siberian LIP are the major reasons for the Permo-Triassic mass extinction being the strongest in Earth history.

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