HR: 14:25h
AN: V43F-04    [Abstracts]
TI: Crystallization of a basal magma ocean and its geochemical consequences
AU: * Coltice, N
EM: coltice@univ-lyon1.fr
AF: Laboratoire de Sciences de la Terre, Université Lyon 1, ENS Lyon, Bat Geode, 43 Bd du 11 novembre 1918, Villeurbanne, 69100, France
AU: Labrosse, S
EM: stephane.labrosse@ens-lyon.fr
AF: Laboratoire de Sciences de la Terre, Université Lyon 1, ENS Lyon, Bat Geode, 43 Bd du 11 novembre 1918, Villeurbanne, 69100, France
AU: Hernlund, J W
EM: hernlund@gmail.com
AF: Department of Earth and Ocean Sciences, The University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4, Canada
AB: The seismological evidence of partial melt at the base of the mantle suggests that more extensive melting occured in the past when the mantle was hotter. The Fe enrichment of the melt, its high density at very high pressure together with its low viscosity preserved the basal magma ocean from entrainment by solid-state convection. It is therefore an ideal hidden and unsampled reservoir for incompatible elements, even if its size is relatively small today. The \varepsilon_¹⁴²Nd difference between Earth and chondrites, as well as the mass balance of heat producing elements are used to constrain our thermo-chemical models of the basal magma ocean evolution through time. The best fit is obtained for an initial melt layer about 800km thick crystallizng with a decay time of 1~Gy, the remaining melt today being ULVZs. The solids crystallizing at the top of the cooling melt layer have increasing Fe content with time and when they become dense enough, they start to form stable piles which are actually observed from seismic studies. They are slowly entrained within mantle plumes providing a deep mantle component which is very diluted in incompatible elements. Though, we show that this component can provide the primitive-like noble gas signature that constrasts with that of the intensively degassed ovelying mantle.
DE: 1212 Earth's interior: composition and state (7207, 7208, 8105, 8124)
DE: 8125 Evolution of the Earth (0325)
DE: 8130 Heat generation and transport
DE: 8439 Physics and chemistry of magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting