THE INFLUENCE OF PLUMES, WHICH HAVE NOT REACHED THE SURFACE AND CREATE SURFACE UPLIFTS
Authors:   Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk, Kirdyashkin A. , Kirdyashkin A. ,   Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk
Published: December 2022

The thermochemical plume originates at the core-mantle boundary in an area of increased concentration of light components that lower the melting point. The object of the study is mantle thermochemical plumes that have not reached the surface and create surface uplifts due to superlithostatic pressure on the plume roofs. The objectives of the study are to present the structure of the plume channel that has not reached the surface, the mechanism of daytime surface uplifts formation and to determine the influence of the plume roof depth and the influence of the plume group on the structure of daytime surface uplift above them. Research methodology and methods are to study the influence of mantle thermochemical plumes formed at the core-mantle boundary on the height and structures of surface rises, the method of geodynamic modeling is used: the motion in the high-viscosity massif above the plume roof, occurring under superlithostatic pressure is analyzed. Based on geological and geophysical data, a geodynamic model of surface rises is created which satisfies the three laws of conservation: energy, matter and momentum. The plume conduit is a melt in the mantle massif. Based on the available experimental modeling data, the cellular structure of the plume conduit is presented. Depending on the location depth of the roof of the plume that has not reached the surface, the thermal power on the plume base, plume diameter, and the superlithostatic pressure on the plume roof are determined. Movement in the high-viscosity block above the plume roof occurs under the influence of superlithostatic pressure. To determine the velocity field in the block above the plume roof, the solution obtained for the sphere moving in a highly viscous liquid with a constant velocity is used. When the day surface rises, the driving force due to the superlithostatic pressure decreases. When the superlithostatic pressure at the plume roof is equal to the pressure caused by elevation, the movement in the block above the plume stops. The maximum elevation height hmax = 4.5 ... 6 km was found. Elevation profiles were found for different values of the location depth of the plume roof X. The dependence of the horizontal size of the main part of the elevation y1 on the location depth of the plume roof is found. Elevation profiles were obtained for a group of five plumes, the roofs of which are at a depth of 30 km and the distance between the plume axes is y = 150 km. The elevation profiles were obtained for a group of three plumes for y = 400 km as well. At y > y1, the height of the main ridge has a saw-toothed character. Ridges whose axes are perpendicular to the axis of the main ridge are formed during the formation of uplift. The number of such ridges is equal to the number of plumes responsible for the formation of uplift. The uplift formed by a group of plumes at X = 30 km refers to the uplift of the Caucasus type, at X = 100 km refers to the uplift of the Tibet type