The Mid-Paleozoic and Mid-Triassic Pulses of Trap Magmatism in the East of the Siberian Platform: Evidence from the First ⁴⁰Ar/³⁹Ar Isotope Dating of Dolerite Sills

The paper presents the results from the first ⁴⁰Ar/³⁹Ar isotope dating of eleven mafic sills recovered by deep boreholes in the eastern Siberian Platform. Most of the dates are assigned to the Devonian magmatic stage (357–379 Ma). The two previously established pulses of dike magmatism in the Yakutsk-Vilyui large igneous province also fall within this range. The ages of 397.6 ± 4.3 and 406.2 ± 5.6 Ma obtained in this study imply one more pulse of magmatism at the Emsian-Eifelian boundary. The chemical composition of the dolerites corresponds to that of the derivatives of garnet peridotite. Estimates of the depth of the melting center suggest its location both inside the mantle lithosphere and at the lithosphere-asthenosphere boundary. The Mid-Triassic age (232.6 ± 7.4 Ma) of the sill recovered by the Morkoka borehole implies the manifestation here of the second pulse of trap magmatism related to the Siberian plume.