Известия Томского политехнического университета: Инжиниринг георесурсов (Sep 2017)
Rheological and geothermal features of the Okhotsk sea plume
Abstract
The relevance of the research is caused by the need to reveal the tectonic nature of the Sea of Okhotsk and the deep structure of a tectonosphere in the transitional zone «continent-ocean» because the oil-gas forecasting in this region is connected with these issues. The aim of the work is to research the space distributions of formalized and mutually independent gravity and geothermic parameters to receive an evidence of the plume structure in the Okhotsk Sea tectonosphere. The method used in the study: theconstruction of 3D gravity and geothermic models of the tectonosphere. Results. The author has described the features of linear rift-nature and concentrically zonal (above plume) distributions of geophysical parameters with the help of the gravity and thermometric models. This indicates the existence of two types of deep tectonic structures and corresponding two geodynamic processes in the Sea of Okhotsk Area. In the result of analysis of space distributions of temperature and gravity parameter, which reflects rheological properties of geological media the author determined the setting and the space sizes of the Okhotsk Sea plume head. The central part of the plume is arranged to the Academy Science underwater rise. A roof of the plume with the diameter of 800-850 km is downthrown above a mantle trunk. In the roof of thermal astenosphere with the temperature of 1200 °C the viscos medium areas were revealed. Probably they correspond to magmatic chambers beneath the Deryugina Basin, South Okhotsk and Tatar rifts. The second level of magmatic chambers under the same structures as well as under volcanic belts (the Okhotsk-Chukotka, East-Kamchatka and East-Sikhote-Alin) was determined into the lower crust layer at a depth of 20-30 km and in subcrustal layer. In the stretch-structures the astenosphere raises toward the Earth's surface up to a depth of 30-60 km. Received models prove a spreading of the astenosphere beneath the lithosphere bottom. The lower lithosphere of the Okhotsk Sea Area is broken off by two regional stretch-zones: Deryugina and South-Okhotsk, which are superimposed on the plume or which preceded it.
