The Permian-Triassic volcanic activity in the West Siberian basin: A buried silicic LIP coeval to the Siberian Traps

Traps of the Siberian platform and associated basaltic rifts in the West Siberian basin constitute one of the most voluminous continental Large Igneous Provinces (LIP). The contribution of silicic volcanic rocks to this vast province was underestimated. We present results of the first comprehensive study of silicic rocks from the Froly-Krasnoleninsky region (the central part of West Siberia). Permian-Triassic volcanics in this area are buried under the thick sedimentary cover (2.5–3.5 km) and are available only as drill cores. Volcanic rocks fill the Rogozhnikov-Nazym graben and other rifts.

The volcanic sequence in this area is dominated by lavas of rhyolitic-dacitic composition, which exhibit similar petrographic and geochemical characteristics in all studied districts. A complex of structural and geochemical features of silicic rocks corresponds to the tectonic setting of post-collisional rifting. Basalts are subordinate and similar to those from middle-upper parts of the Noril’sk volcanic section (the Siberian platform). Based on geochemical features, we suggest that silicic rocks are derived mainly from the partial melting of mafic lower continental crust due to the input of additional heat from the Siberian mantle plume. Late Paleozoic crust of the central part of West Siberia, saturated with mafic underplates during prior subduction events, provided favorable conditions for the generation of silicic magmas, while post-collisional rifts acted as magma-conducting zones.

Nine new U-Pb ages constrain the timing of silicic volcanic activity in West Siberia as ∼5–10 Myr at the Permian-Triassic boundary (253.69–248.21 Ma), which is nearly coeval to the main phase of the Siberian Traps emplacement. Temporal and spatial relationships, along the geochemical similarity of the silicic and mafic rocks confirm their genetic relations. In total, silicic rocks occupy about 10⁵ km² within the West Siberian basin and can be considered as a Silicic Large Igneous Province (SLIP), coeval and genetically linked to the mafic Siberian Traps LIP.