American Geophysical Union Become an AGU Member
Subscribe to AGU Journals		 AGU Home AGU Publications

Read Full Article (file size: 1947720 bytes)    Cited by

GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, VOL. 5, Q01L01, doi:10.1029/2003GC000583, 2004

Steady plumes in viscously stratified, vigorously convecting, three-dimensional numerical mantle convection models with mobile plates

Julian P. Lowman

School of Earth Sciences, University of Leeds, Leeds, West Yorkshire, LS2 9JT, UK


Scott D. King

Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, IN 47907-1397, USA


Carl W. Gable

Hydrology, Geochemistry and Geology (EES-6), Los Alamos National Laboratory, Los Alamos, NM MS T003, 87545, USA


Abstract

We present results from three-dimensional (3-D) Cartesian geometry computations featuring vigorous (high Rayleigh number) mantle convection in a system incorporating stiff tectonic plates with dynamically determined, time-dependent velocities. We track plume-related hot spot motion while calculating associated synthetic hot spot tracks, allowing us to estimate plume migration rates relative to plate motion rates. Plate-like surface motion is achieved explicitly by specifying both the plate geometry and rigidity; however, plate velocities evolve dynamically in response to the buoyancy distribution within the convecting system, including buoyancy within the plate itself. We find that convection is characterized by downwelling sheets and varying numbers of 3-D upwelling structures when the lower mantle to upper mantle viscosity ratio is varied from 9 to 90. As the lower mantle viscosity is increased relative to the upper mantle viscosity, the upwellings in the calculations evolve into vigorous (active) plumes characterized by long, narrow, thermal conduits with broad, disk-like heads. The total number, shape, and persistence of the plumes are affected by the specified viscosity stratification in the calculations. Our findings indicate that hot spots associated with mantle plumes drift by smaller distances in comparable amounts of time when the lower mantle viscosity is increased relative to the upper mantle viscosity. In cases with a high lower mantle to upper mantle viscosity ratio, the depth of the flow aligned with plate motion is diminished and the plate-scale return flow is integrated into a deep, unorganized, sluggish layer. As a result, plume conduit morphology in the lower mantle of such calculations is less influenced by plate motion than in calculations with a small difference between upper mantle and lower mantle viscosity. For lower mantle viscosities 30 times and 90 times greater than the upper mantle viscosity, the lower mantle velocity field is dominated locally by active plumes anchored in the lower thermal boundary layer of the convecting system and plume migration rates are typically only about 10% of the overriding plate velocity. In such cases, we also find that plume-related hot spots persist for periods that we estimate to be between 0.55 and 1.1 plume-transit times.

Received 30 May 2003; accepted 29 October 2003; published 13 January 2004.

Index Terms: 8121 Tectonophysics: Dynamics, convection currents and mantle plumes; 8120 Tectonophysics: Dynamics of lithosphere and mantle—general; 8162 Tectonophysics: Rheology—mantle.

Read Full Article (file size: 1947720 bytes)    Cited by

Citation: Lowman, J. P., S. D. King, and C. W. Gable (2004), Steady plumes in viscously stratified, vigorously convecting, three-dimensional numerical mantle convection models with mobile plates, Geochem. Geophys. Geosyst., 5, Q01L01, doi:10.1029/2003GC000583.