Mantle Convection Triggered by Mechanical Heating during Core Formation: A 2-D Study

Details Mantle Convection Triggered by Mechanical Heating during Core Formation: A 2-D Study Mantle Convection Triggered by Mechanical Heating during Core Formation: A 2-D Study

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.u43c..02y&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #U43C-02

Physics

Geophysics

3200 Mathematical Geophysics (0500, 4400, 7833), 8121 Dynamics: Convection Currents, And Mantle Plumes

Scientific paper

We have carried out 2D numerical experiments of thermal-chemical convection for planetary core formation in a cylindrical gravity field by using a combination of finite-differences with Lagrangian marker-in-cell technique on a fully staggered Cartesian grid mapped onto a cylindrical boundary. We employed a free- surface boundary condition and compressible continuity equation within a Lagrangian formulation , thus accounting for pressure-temperature-related volume changes during the rapid time-dependent gravitational redistribution process during core-formation. We tested various cases with initial Rayleigh number for the mantle ranging from one million to ten million and standard chemical/thermal buoyancy ratio for the core/mantle density contrast ranging from 200 to 0, representing the purely thermal end member. At the high chemical to thermal buoyancy ratio of 200 corresponding to the density contrast between the iron core and the primitive silicate mantle the gravitational redistribution process lasts for less then 1 Myr (depending on the effective viscosity) been fully dominated by shear heating and thermal advection. In this case internal gravitational redistribution processes result in planetary shape-changing revealing significant transient aspherical deviations from the original perfectly round geometry. Most of the enormous amount of heat is produced during this very short time span associated with the core-formation and is then chaotically distributed throughout both the core and the mantle. Viscous heating is generated much more for thermal-chemical convection than for pure thermal convection.The magnitude of thermal perturbations can reach several thousand degrees, which cataclysmically raises the effective Rayleigh number for the planetary mantle to a very large number and possibly resulting in the formation of a magma ocean with the molten mantle rocks rising from the deep planetary interior.

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