Physics
Scientific paper
Mar 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000e%26psl.176..401h&link_type=abstract
Earth and Planetary Science Letters, Volume 176, Issue 3-4, p. 401-411.
Physics
18
Scientific paper
We have studied with an aspect-ratio four box the thermal-chemical convective evolution with strongly temperature- and depth-dependent viscosity and moving heat sources within the extended-Boussinesq framework, in which both adiabatic and viscous heating are included and a depth-dependent thermal expansivity is assumed in the equation of state. Our focus is to show how this type of mantle evolution with an averaged Ra of 0(106) may develop with a linear chemical stratification and a uniformly hot mantle as an initial condition. The effects of extended-Boussinesq and depth-dependent thermal expansivity are to prevent the effective destruction of the chemical heterogeneities. Our results show that this initial condition would, after the age of the Earth, lead to a `lava lamp' mode consisting of a thick chemically stratified and intensely internally heated layer with a thickness of around a quarter of the whole mantle thickness. However, in this isolated internally convecting layer, exceedingly high temperatures greater than 4500 K would be reached in the deep mantle. Plumes can be launched from the top of this thick denser layer. This `lava lamp' stage would give way to the formation of denser hill-like structures at the core-mantle boundary. Then upwellings with deep lower mantle origins can be induced by the interaction of the downwellings with the D'' layer. Our simulations show the possibility for some long-range mass transfer interaction between these widely separated chemical hills promoted by the fast horizontal flow induced by the sinking currents along the low-viscosity zone due to temperature-dependent rheology at the core-mantle boundary.
Hansen Ulrich
Yuen Dave A.
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