Physics
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmmr12a..08d&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #MR12A-08
Physics
5480 Volcanism (6063, 8148, 8450), 6219 Io, 8121 Dynamics: Convection Currents, And Mantle Plumes, 8125 Evolution Of The Earth (0325), 8148 Planetary Volcanism (5480, 8450)
Scientific paper
The mantle of young terrestrial planets is partially molten and mixed by turbulent convection. Once lavas are extracted from the mantle, they cool down at the surface by heat radiation as a black body. It has been suggested that magma extraction and advective heat transfer at the surface could efficiently cool down the mantle. In this study, we propose a numerical model to test such hypothesis. We used a two phase-flow model of convection in a 2-D Cartesian box with an homogeneous internal heating. Solid rocks are driven by convection and they melt when their temperature exceeds the depth dependent solidus. Then, the magmas migrate through the porous residual to the surface following Darcy's law. We use a top boundary permeable to the magma. Magmas flow across the top boundary with their own temperature. To compensate for the localized extraction of magma, a uniform downgoing flux of solid rocks is imposed. We find that the advective heat transfer across the top permeable boundary is much more efficient than the diffusive heat transfer across a top impermeable boundary to cool down the mantle. Such behavior was observed in a previous study using a simple one phase model of convection with a permeable top boundary. Due to the magma extraction the mantle temperature cools down until melting stops. Then, the top boundary layer becomes impermeable and the mantle warms up, until a new magmatic episode occurs. In this study, we show that the timescale of mantle cooling due to the magmas extraction is very short. This suggests that young terrestrial planets could not conserve a magma ocean for a long time and that the Earth could have been sufficiently cold in its primitive history to allow the presence of liquid water at its surface. We show that successive cycles of fast mantle cooling due to magma extraction and slow mantle heating due to radioactive decay can take place. This suggests that the mantle of young terrestrial planets can undergo successive major events of melting.
Dubuffet Fabien
Ricard Yanick
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