HR: 08:57h
AN: MR41A-05 [Abstracts]
TI: The First Terrestrial Pb-isotope Paradox and the Core Formation
AU: * Malavergne, V
EM: Malavergne@lpi.usra.edu
AF: Lunar and Planetary Institut, 3600 Bay Area Boulevard, Houston, TX 77058-1113
United States
AU: * Malavergne, V
EM: Malavergne@lpi.usra.edu
AF: Laboratoire des Gomatriaux, Universite de marne La Vallee.
5, boulevard Descartes
Champs-sur-Marne., Marne-La-Valle, 77454
France
AU: Tarrida, M
EM: tarrida@univ-mlv.fr
AF: Laboratoire des Gomatriaux, Universite de marne La Vallee.
5, boulevard Descartes
Champs-sur-Marne., Marne-La-Valle, 77454
France
AU: Combes, R
EM: combes@univ-mlv.fr
AF: Laboratoire des Gomatriaux, Universite de marne La Vallee.
5, boulevard Descartes
Champs-sur-Marne., Marne-La-Valle, 77454
France
AU: Bureau, H
EM: HBUREAU@DRECAM.CEA.FR
AF: Laboratoire Pierre-Se, CEA-CNRS, CE Saclay, Gif sur Yvette, 91191
France
AB:
The first terrestrial Pb-isotope paradox refers to the fact that the Pb isotope compositions of most marine sediments and
MORB plot well to the right of the area defined by meteorites in 207Pb/204Pb vs. 206Pb/204Pb space. This paradox requires at
least one reservoir formed in the early Earth's history that plots to the left of the meteorite isochron. The core is one
candidate that have been widely discussed in the past.
In order to quantify possible fractionation into the metallic core, we have done different set of multi-anvil experiments at
high pressure (up to 20 GPa) and high temperature (1900C). The partitioning of Pb between liquid metal and silicates is
investigated at different oxygen fugacity by using different metallic starting compositions. The oxygen fugacity in most
experiments has been calculated by using two independent buffers : iron/wstite (IW) and SiO2/Si, allowing to link
consistently the Fe contents in silicates, the Si contents in metal and the temperatures of the experiments. The
concentration of Pb in metal and in silicates has been measured by electron microprobe and ?PIXE. At oxygen fugacities 3 log
units below IW, we have found partition coefficients between metal and silicate melt ranging from 6 to 9 depending on the
starting composition of the metal. A first conclusion for this study is that Pb would remain siderophile even with a metal
without sulphur.
These first results heighten the importance of :(1) the hypothesis that the fisrt Pb-paradox could be the result of the Pb
incorporation into a metallic phase at the time of core formation, (2) doing more experimental work at different pressures,
temperatures and fO2 relevant to the early Earth.
DE: 8115 Core processes (1507)
DE: 7207 Core and mantle
DE: 3924 High-pressure behavior
DE: 1212 Earth's interior--composition and state (8105)
DE: 1507 Core processes (8115)
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting