Mantle thermochemical plumes and their influence on the formation of highlands

The structure of a thermochemical plume conduit rising from the core-mantle boundary and reaching the maximal height when its rising (melting of a plume conduit) terminates is considered in this paper. The relative thermal power of plumes not reaching the surface is Ka < 1.15, and they are called plumes of low thermal power. The dependences of the rate of rising of a ball-like roof of the plume and the rate of rising of day surface above the plume on time are presented. Due to the influence of superlithostatic pressure on the plume roof, the day surface rises above the plume. The elevation of the day surface formed above the plume was calculated for various times in dependence on the horizontal coordinate. With decreasing viscosity of the lithosphere above the plume roof and depth of the plume roof, the rate of rising of the day surface increases, and the time necessary for reaching of the maximal surface elevation decreases. The maximal elevation of the highland above the plume was estimated. The surface elevations formed under the influence of two or three plumes that did not reach the surface were estimated for various times. Based on the suggested model of the formation of elevations above the plume, it is concluded that large highlands (mountain ridges and plateaus) can be formed under the influence of plume clusters that do not reach the day surface. The estimates of the rate of rising of the day surface above the plume obtained in this study are in a good agreement with the geological data on the rates of rising of Tibet and the Caucasus. The rising of a temperature front above the plume roof reaching the maximal rising height is considered. The dependences of the height and rate of rising of a temperature front above the plume roof on time were obtained. The local increase of a specific heat flux in the highland formed above the plume may show that the maximal height of rising of a surface above the plume was gained. Based on the analysis of the heat transfer, the association between the activity of plume clusters that do not reach the surface and the formation of hot fields is suggested.