Edge-driven convection

• Published in: Earth and planetary science letters Vol. 160; no. 3; pp. 289 - 296
• Main Authors: King, Scott D, Anderson, Don L
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.08.1998
• Subjects: convection; flood basalts; mantle; mantle plumes; convection; mantle; mantle plumes; flood basalts
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/S0012-821X(98)00089-2

We consider a series of simple calculations with a step-function change in thickness of the lithosphere and imposed, far-field boundary conditions to illustrate the influence of the lithosphere on mantle flow. We consider the effect of aspect ratio and far-field boundary conditions on the small-scale flow driven by a discontinuity in the thickness of the lithosphere. In an isothermal mantle, with no other outside influences, the basic small-scale flow aligns with the lithosphere such that there is a downwelling at the lithospheric discontinuity (edge-driven flow); however, the pattern of the small-scale flow is strongly dependent on the large-scale thermal structure of a much broader area of the upper mantle. Long-wavelength temperature anomalies in the upper mantle can overwhelm edge-driven flow on a short timescale; however, convective motions work to homogenize these anomalies on the order of 100 million years while cratonic roots can remain stable for longer time periods. A systematic study of the effect of the boundary conditions and aspect ratio of the domain shows that small-scale, and large-scale flows are driven by the lithosphere. Edge-driven flow produces velocities on the order of 20 mm/yr. This is comparable to calculations by others and we can expect an increase in this rate as the mantle viscosity is decreased.