A SELF-CONSISTENT 2D MODEL OF MANTLE CONVECTION WITH A FLOATING CONTINENT

Abstract

The mantle is modeled by a viscous fluid filling a horizontally elongated 2D region with an aspect ratio of 10:1. A model with Ra = 10 6 is constructed on a 200 <img src="latex008.gif" alt="times"> 80 mesh. Developed nonsteady-state thermal convection including narrow downwellings and upwellings sets in, with mantle flow velocities ranging from 1 to 10 cm/yr. Then, at a certain moment, a continent floating on the mantle is introduced into the model. The continent is modeled by a thin long plate of a thickness of 0.03 and a length of 2.0 relative units with respect to the mantle thickness, which corresponds to dimensional values of 90 and 6000 km, respectively. To demonstrate mantle heating beneath continent, the latter is positioned at the coldest place of the mantle where downgoing flows dominate at the moment chosen. The evolution of the mantle-continent system is found from numerical solution of equations governing the momentum, mass, and heat transfer in viscous fluid and rigid continent. The problem is rigorously formulated, a self-consistent method is given for the solution of coupled integrodifferential equations, and a technique of their numerical implementation is described. The continent remains virtually immobile during a long time (about 500 Ma), but the mantle flow pattern dramatically changes, which results in suppression of cold mantle downwellings under the continent and their gradual replacement by hot upwellings. Afterwards the viscous drag of mantle flows begins to move the continent at a variable velocity averaging about 1 cm/yr. The mantle flow pattern and continent velocity constantly changes under the action of mechanical coupling and thermal interaction between the mantle and moving continent. After a time of about 1.5<img src="latex008.gif" alt="times"> 109, when the continent has traveled over a distance of about 15000 km, it arrives at a place where several cold mantle downwellings concentrate. Then the continent velocity sharply decreases, and the continent continues its motion in either primary or opposite direction, depending on the general mantle flow pattern. The results of the numerical experiment can be used for the analysis of mechanism responsible for the motion of Eurasia-type continents, origination and ascent of plumes, and geodynamic processes in the subcontinental mantle., when the continent has traveled over a distance of about 15000 km, it arrives at a place where several cold mantle downwellings concentrate. Then the continent velocity sharply decreases, and the continent continues its motion in either primary or opposite direction, depending on the general mantle flow pattern. The results of the numerical experiment can be used for the analysis of mechanism responsible for the motion of Eurasia-type continents, origination and ascent of plumes, and geodynamic processes in the subcontinental mantle.