ГЕОДИНАМИЧЕСКАЯ СТРУКТУРА ТЕЧЕНИЙ В ВЕРХНЕЙ И НИЖНЕЙ МАНТИИ И ТЕПЛООБМЕН МЕЖДУ НИМИ

Abstract

The object of the study is a two-layer geodynamic model of the Earth's mantle, including the upper and lower mantle. The subject of the study is the direction of flow at the top and bottom of the lower mantle. It is determined under the known geodynamic structure in the upper mantle, the known direction of the flow at its roof and in the presence of a lifting flow in the mid-ocean ridge area. The aim of the study is to reveal the character of interaction between the upper and lower mantle large-scale free flowing cells. At the upper-lower mantle boundary, two types of interaction of upper- and lower-mantle flows are possible: either unidirectional flows - cocurrent flow, or oppositely directed - counterflow. Horizontal large-scale currents at the 670 km boundary are a consequence of the horizontal temperature gradient under conditions of free convection. Heat transfer from the flow interface occurs under conditions of free convection, and the intensity of heat transfer at this boundary is determined by the vertical temperature gradient. The analysis of heat transfer in upper-mantle and lower-mantle flows at the 670 km boundary with cocurrent flow and counterflow is presented. The decrease in the average flow temperature for the lower mantle thermal boundary layer near the 670 km boundary with a counterflow at this boundary is estimated. The density and temperature differences in the mantle under the continent and the ocean, providing an excess of the surface level of the continent above the level of the ocean floor, equal to 7 km, are presented. Comparison of the estimated characteristic temperature difference with data on heat flows in the mantle under the ocean and the continent leads to the conclusion that there is a cocurrent flow of upper mantle and lower mantle flows at the 670 km boundary. The influence of the cocurrent flow at the 670 km boundary on the structure of large-scale mantle flows is analyzed. For two different situations of interaction of upper mantle flows under the ocean with the mantle under the continent, large-scale flows in the upper and lower mantle are presented