The Control of Mantle Viscosity Stratification on Plume Migration Rates Versus Plate Velocities In 3D Numerical Mantle Convection Models
Abstract
The determination of the mantle's radial viscosity structure and the degree to which hotspots remain fixed are two long standing issues in global geophysics. Because plume motion is directly affected by the viscosity stratification of the mantle, the widely held view that hotspots are the surface expression of the impingement of deep rooted mantle plumes on the base of the lithosphere leads to a model in which these issues are intimately related. Moreover, the viscosity structure of the mantle affects the nature (e.g., wavelength) of the convecting system and consequently the buoyancy/dynamics of mantle plumes. To gain insight into the effect of mantle viscosity stratification on the dynamics of mantle plumes, we have studied several 3D Cartesian geometry numerical models of vigorous mantle convection that incorporate stiff tectonic plates with dynamically determined time-dependent velocities. In these models, plate geometry and rigidity is achieved by explicitly prescribing plate-like surface motion on the convecting system, however, the plate motion evolves dynamically in order to reflect the distribution of buoyancy within the convecting system. The result allows for an examination of the feedback between convection driven by thermal buoyancy and plate-like surface motion in systems with a specified plate geometry. All of the models include periodic (wrap around) boundaries. We find that convection in models including both basal and internal heating is characterized in all cases by downwelling sheets and varying numbers of 3D upwelling structures. The upwellings in these high Rayleigh number calculations typically evolve into mushroom shaped plumes by the time they reach the upper mantle. The total number, shape, and lifetime of the plumes is determined by the specified viscosity stratification of the models. We track plume motion versus plate motion in a number of models and estimate plume migration rates relative to plate motion rates as well as comparing the true plate motion with synthetic hotspot tracks determined by the intersection of the plumes with the base of the model lithosphere. Because the evolving plate motion is determined dynamically in the models, we find several examples of plates changing direction above mantle plumes and investigate how closely hotspot tracks represent plate motion in such cases. Our findings indicate that plumes frequently migrate in the opposite direction of the plate motion but that plume migration rates are on the order of mm/yr when plate velocities are on the order of cm/yr.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFM.T62A1290L
- Keywords:
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- 8120 Dynamics of lithosphere and mantle: general;
- 8121 Dynamics;
- convection currents and mantle plumes;
- 8125 Evolution of the Earth;
- 8130 Heat generation and transport;
- 8162 Rheology: mantle