Thermal plumes as mixers and samplers of the mantle. Laboratory experiments
Abstract
As they bring deep mantle material to the surface, mantle plumes offer an unique opportunity to probe the planet's deep interior. But deciphering their geochemical message requires to understand quantitatively plume dynamics and sampling. For several decades, much effort has been devoted to understand plume dynamics and to provide scaling laws for plume ascent velocity or for plume growth by entrainment of ambient fluid. However, only a few of them have focused on entrainment, deformation and sampling of material, both in transient and steady state. Using a laboratory model of a thermal plume generated from a small heat source in a high Prandtl number fluid which viscosity depends strongly on temperature, we present a study of the entrainment of fluid as a function of the temperature of the source, the height, density and viscosity of the fluid and the dimensionless numbers. In order to understand the mechanism of entrainment, we designed a new experimental set-up which allow us to visualize simultaneously the temperature field, the velocity field and the displacement of passive markers without disturbing the flow. We observe that the sampled material systematically passes by the source of the plume. This study could also yield the characteristic spatial and temporal scales of heterogeneities in a mantle mixed by thermal plumes.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMDI21A1941F
- Keywords:
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- 1038 GEOCHEMISTRY / Mantle processes;
- 8120 TECTONOPHYSICS / Dynamics of lithosphere and mantle: general;
- 8121 TECTONOPHYSICS / Dynamics: convection currents;
- and mantle plumes;
- 8130 TECTONOPHYSICS / Heat generation and transport