Experiments on metal-silicate plumes and core formation.
Short-lived isotope systematics, mantle siderophile abundances and the power requirements of the geodynamo favour an early and high-temperature core-formation process, in which metals concentrate and partially equilibrate with silicates in a deep magma ocean before descending to the core. We report results of laboratory experiments on liquid metal dynamics in a two-layer stratified viscous fluid, using sucrose solutions to represent the magma ocean and the crystalline, more primitive mantle and liquid gallium to represent the core-forming metals. Single gallium drop experiments and experiments on Rayleigh-Taylor instabilities with gallium layers and gallium mixtures produce metal diapirs that entrain the less viscous upper layer fluid and produce trailing plume conduits in the high-viscosity lower layer. Calculations indicate that viscous dissipation in metal-silicate plumes in the early Earth would result in a large initial core superheat. Our experiments suggest that metal-silicate mantle plumes facilitate high-pressure metal-silicate interaction and may later evolve into buoyant thermal plumes, connecting core formation to ancient hotspot activity on the Earth and possibly on other terrestrial planets.
Olson
Peter
P
Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD 21218, USA. olson@jhu.edu
Weeraratne
Dayanthie
D
D018534:Earth, Planet; D008670:Metals / Q000737:chemistry; D016083:Planets; D011312:Pressure; D017640:Silicates / Q000737:chemistry
D008670:Metals; D017640:Silicates