Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p11a1576l&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P11A-1576
Physics
[1060] Geochemistry / Planetary Geochemistry, [1507] Geomagnetism And Paleomagnetism / Core Processes, [5430] Planetary Sciences: Solid Surface Planets / Interiors, [5455] Planetary Sciences: Solid Surface Planets / Origin And Evolution
Scientific paper
Recent evidence indicates that much of the Earth mass was accreted through collisions between already differentiated planetary objects. Previous studies have shown that, during the final stages of Earth accretion, the amount of energy released through shock heating after each impact was sufficient to melt the projectile and a substantial part of the growing proto-Earth. The liquid core of the projectile, denser than the surrounding liquid silicates, tends to segregate at the base of the magma ocean. Partial or complete fragmentation of the projectile core is expected as a consequence of shear and buoyancy instabilities during this migration, allowing some chemical re-equilibration between silicates and metal. Understanding the physical mechanisms during metal-silicate differentiation in a low-viscosity magma ocean would help to interpret the geochemical observations including the measured tungsten isotopic ratios and siderophile element abundances. Here we present results from laboratory experiments on the fragmentation of immiscible fluids with density ratios comparable to the metal-silicate system. During metal-silicate segregation in a magma ocean, buoyancy and inertia forces dominate over surface tension and viscous forces, with Weber, Reynolds and Bond numbers of order 1014. Such extreme conditions cannot be achieved in experiments, but highly turbulent regimes can be reached. In a first series of experiments, a finite volume of a denser fluid is released at the top of a tank filled with a lighter fluid. We find that fragmentation starts with the destabilization of a vortex ring formed directly after the discharge and we explore the parameter space by varying the volume and density of the released fluid. In a second series of experiments we study fragmentation of quasi-stationary, immiscible buoyant jets which allow to reach more turbulent conditions. We depict the successive destabilization steps at the interface between the two immiscible fluids and study the evolution of the jet breakup length as a function of the governing parameters including the Reynolds number, the Weber number and the density ratio.
Deguen Renaud
Landeau Maylis
Olson Peter
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