On the geothermodynamic mechanism of formation of hydrocarbon deposits in the Cenozoic subduction zone of the Amur Lithospheric Plate

Abstract

The purpose of the paper is to focus on the geothermodynamic mechanism of formation of hydrocarbon deposits formed in the zones of Cenozoic lithospheric subduction of the Amur Plate, as well as on the tectonic-magmatic mechanism of their migration to the upper structural floors of the folded system. In the future, this leads to the removal of hydrocarbons by hydrothermal solutions into folded formations of the island-arc type and the formation of hydrothermal oil and gas deposits. The research methods work under the assumption of non-Newtonian mantle rheology. As a result, for the non-Newtonian mantle rheology case the 2D dissipation-driven thermal convection in the mantle wedge above the Amur Lithospheric Plate subducting under the Okhotsk Sea Lithospheric Plate to the east of the Sakhalin Island is modeled numerically. The effects of the 410 km and 660 km phase transitions are taken into account in the model. It was also shown that, within the framework of the constructed model, the localization, latitudinal extent and magnitude of the heat flow in the zone of anomalous mantle heat flow extended parallel to the Sakhalin Island correspond to the subduction velocity of ~ 8–10 mm per year at the observed subduction angle (~36°) occurring in the east direction and the water content in the mantle wedge ~1 weight %. At such a subduction velocity, one convective cell with a single 2D convective flow ascending to the zone of the maximum mantle heat flux of ~130 mW · m^-2 and observed in the Okhotsk Sea basin is excited in the mantle wedge. In conclusion, it may be said that the comparison of the model scales and locations of convective flows in the mantle wedge for the cases of continental and oceanic types of the Okhotsk Sea Lithospheric Plate serves as the evidence in favor of the former (continental) type of Okhotsk Sea Lithospheric Plate. Upwelling mantle wedge convective flow is indicated to be able to provide the mantle wedge hydrocarbons transport to the daylight surface.