Computer Science
Scientific paper
Dec 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993e%26psl.120..387s&link_type=abstract
Earth and Planetary Science Letters (ISSN 0012-821X), vol. 120, no. 3-4, p. 387-393
Computer Science
17
Entrainment, Free Convection, Magma, Particles, Sediments, Viscous Flow, Beds (Geology), Dunes, Earth Core, Rayleigh Number, Reynolds Stress
Scientific paper
Differentiation in magma chambers, in the Earth's core and in the partially molten early Earth is a competitive process between sedimentation and re-entrainment of crystals in the presence of convection. Previous studies show that the particles suspended in convective layers eventually settle and do so almost as fast as in the absence of convection. However, the nature and magnitude of the competing entrainment has remained unclear. Here we provide a simple theory and experimental evidence showing that entrainment occurs at the crests of dunes created in the particle bed at the base of a convecting fluid. In both laminar and turbulent regimes, the dune formation and entrainment are driven by viscous stress produced by thermal plumes. At sufficiently high Rayleigh numbers the particles are probably entrained by Reynolds stresses. Entrainment in the Earth's core is hardly possible because it requires unreasonably small crystals. Entrainment of 10(exp -2) - 10(exp -1) cm diameter crystals is very likely in magma oceans. For magma chambers entrainment requires large viscosities (greater than 10(exp 6) P) and even when it occurs, the total amount of the suspended solid fraction is very small.
Olson Peter
Solomatov Viatcheslav S.
Stevenson David J.
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