Palaeomagnetism of East Siberian traps and kimberlites: two new poles and palaeogeographic reconstructions at about 360 and 250 Ma

Abstract

Summary We studied basalt sills and dykes and kimberlite pipes from the eastern part of the Siberian platform. These are spread out over a few hundred kilometres and are divided into two age groups: Late Permian–Early Triassic (Mir, Aikhal and Olenyek regions) and Late Devonian–Early Carboniferous (Viluy and Markha basins, Aikhal region). The palaeomagnetic poles determined for each sill or dyke are statistically different from each other, but averaging all corresponding directions from these sills and dykes with those from kimberlites of different generations yields results with acceptable statistics. This is probably due to the averaging out of secular variation and/or changes in magnetic polarity. The resulting palaeomagnetic poles allow one to reconstruct the palaeopositions of Siberia during the two large flood basalt events at about 360 and 250 Ma. A significant rotation of the Siberian platform during the Devonian and Carboniferous is suggested. The new data are in general agreement with some earlier palaeomagnetic poles for the Late Permian–Early Triassic traps of the Tungusska basin, and significantly reduce uncertainties for previous Late Devonian–Early Carboniferous Siberian poles, which were very scattered. Together with geological and absolute age data, the palaeomagnetic data support the hypothesis that kimberlite magmatism and trap intrusions were both rapid and relatively close in time. The 360 Ma event is emerging as a magmatic event with considerable extent over the Russian and Siberian platforms, related to incipient continental break‐up and triple junction formation, possibly at or near the time of the Frasnian–Famennian mass extinction.

On the ages of flood basalt events

“…To the east and southeast, sills extend the total area of the province to at least 1.5 Mkm 2 [197]. Recently, Kravchinsky et al [101] have shown that many of the kimberlite pipes lying east of the traps actually have the same paleomagnetic direction and age and correspond to early, highly explosive phases of the volcanism. Even more recently, Reichow et al [147] have documented a subsurface extension of the traps nearly 1000 km west of the previously known limits of the province, in a drill core from the West Siberian basin.…”

“…Griffin et al [61] emphasized this problem for different kimberlite fields, especially for the K-Ar method, and in several cases in contradiction with reliable geological dating, which suggests excess of argon. Presently, the age interval cannot be constrained to better than 377-350 Ma [101], which contains the age of the Frasnian-Fammenian extinction. It is therefore hard to escape the hypothesis that these kimberlite pipes could be all that remains of a major CFB that caused the extinction.…”

“…Kravchinsky et al [101] studied basaltic sills and dykes, and kimberlite pipes from the eastern part of the Siberian platform. These are spread out over a few hundred kilometers in the Mir, Aikhal and Olenyek regions and in the Viluy and Markha basins, and Aikhal region.…”

Paleomagnetism of Silurian and Devonian volcanics from the Chingiz island arc, Kazakhstan, and its bearing on tectonic evolution of the Ural-Mongol belt

“…Нам вариант СТ2, рассчитанный без учета раннеперм ского полюса, кажется предпочтительнее. В итоге но вая кривая [Cocks, Torsvik, 2007] включает достаточно многочисленные и достаточно надежные данные по раннему палеозою, один единственный полюс для гра ницы девона и карбона [Kravchinsky et al, 2002] и пермскотриасовые полюса по сибирским траппам (табл. 4).…”

“…Палеоши рота, пересчитанная из позднесилурийского -ранне девонского результата по Туве [Bachtadse et al, 2000], так же неплохо согласуется с представленным в этой работе результатом по живетским базальтам (КU). Од нако для всего интервала с начала девона до конца перми по Сибири есть только один позднедевонский-раннекарбоновый полюс [Kravchinsky et al, 2002] и для этого интервала времени сравнение движений Си бири и других блоков остается крайне спекулятивным.…”