Gas flows in the Sea of Okhotsk as a result of active Cretaceous-Cenozoic tectonomagmatic activity in the Sea of Okhotsk region
The paper presents a model of geological evolution of the Sea of Okhotsk which is based on the studies made of the radioisotope age, mineral and isotope-geochemical composition of the Late Mesozoic-Cenozoic volcanic rocks. A probable interaction between volcanic processes in the Sea of Okhotsk and gas geochemical manifestations of the gas flows with anomalous concentrations of methane, gas hydrate and formation of different geological structures of the rock basement and sedimentary deposits of the Sea of Okhotsk with the fault zones, pork marks, landslides and episodes of earthquakes is duscussed. As a result of the studies made, the nature of each volcanic stage has been determined. These are the Late Cretaceous continental-marginal belt stage (alkali-calcic), the Eocene transform-marginal (adakite) stage, and the Pliocene-Pleistocene island arc stage in the southern part of the Sea of the Okhotsk region. Sources of magma generation have been recognized, namely, the lithosphere subcontinental, asthenosphere oceanic, and plume-oceanic (OIB). The change in the geodynamic regimes was traced from the Late Cretaceous subduction regime to the Maastrichtian-Danian transform-marginal which continued as far as Pliocene and was completed by the resumption of the Pliocene - Pleistocene subduction of the Pacific Plate under the Eurasian continent.It included the processes of destruction of the subduction plate, lithosphere and asthenosphere diapirism, and lower mantle plume upwelling. In the periods of geodynamic, seismo-tectonic and volcanic activity together with the raising of different volcanic substrates from the upper and lower mantle gas migrated along the fault zones from depth to the surface. The gas contained CO2, CH4, H2, He, N2, O2 and superheated steam. Gas played an important dynamic and physico-chemical role in the development of the Sea of Okhotsk. At the present stage, gas flows from the depths to the surface manifest themselves like gas bubble from the bottom sediments into water and some part of the gas penetrates to atmosphere. In the areas with gas fluxes, fields including anomalous concentrations of hydrocarbon, gas-hydrate, carbon-dioxide gas, carbon, and helium result in the formation of gas hydrate and associations of authigenic minerals and various geochemical elements.