Effect of Trap Magmatism on the Geochemistry of Gases in the North-Western Regions of the Siberian Platform

Results of the studies into the effect of trap magmatism on the geochemistry of gases (free and dissolved in water) and their zoning within the boundaries of north-western regions of the Siberian Platform are reported. The maximal paleotemperatures at the moment of trap intrusion reached 650 �C at the contact for the major productive horizons: Silurian (Devilish), Ordovician (Baikit), and Cambrian (Deltulino-Tanachinsky, Abakunsky, and Moktakonsky). Hydrocarbon gases in the free and water-dissolved phases were subjected to degradation in the most active form. For instance, carbon dioxide dominates, with its content more than 90 vol. % and methane content up to 5 vol. % in intrusion-affected zone at a distance up to 100 m, while at a distance of 250 m CO2 concentration decreases to 30 vol. %, and CH4 concentration increases to 60-70 vol. %. No significant effect of the thickness of intrusion on gas composition was revealed.