HR: 09:45h
AN: T21A-08    [PDF]
TI: Compositional Effects of Trace Element Partitioning Between Mg-Silicate Perovskite and Silicate Melt
AU: * Liebske, C
EM: christian.liebske@uni-bayreuth.de
AF: Universitaet Bayreuth, Bayerisches Geoinstitut, Bayreuth, 95440 Germany
AU: Corgne, A
EM: Alexandre.Corgne@bristol.ac.uk
AF: University of Bristol, Department of Earth Science, Bristol, BS8 1RJ United Kingdom
AU: Frost, D J
EM: dan.frost@uni-bayreuth.de
AF: Universitaet Bayreuth, Bayerisches Geoinstitut, Bayreuth, 95440 Germany
AU: Rubie, D C
EM: david.rubie@uni-bayreuth.de
AF: Universitaet Bayreuth, Bayerisches Geoinstitut, Bayreuth, 95440 Germany
AU: Wood, B J
EM: B.J.Wood@bristol.ac.uk
AF: University of Bristol, Department of Earth Science, Bristol, BS8 1RJ United Kingdom
AB: Models for the accretion of the Earth propose the existence of a deep magma ocean that may have extended to depths corresponding to the present day lower mantle. Crystallization and fractionation of such a deep magma ocean could lead to chemical differentiation and stratification within the Earth. While it seems that the upper part of Earth's mantle has been rehomogenized by subsequent mantle convection it is possible that chemical layering may have survived in the lower mantle causing a chemical and geophysical signature. In this study we present new experimental data on trace element partitioning between Mg-silicate perovskite (Mg-pv) with various compositions and coexisting silicate melt. High pressure melting experiments have been performed in Re and graphite containers in a multi-anvil apparatus between 25-27 GPa and temperatures up to 2573 K. Starting materials were synthetic pyrolite compositions with varying aluminum contents and a CI chondrite model composition, both doped with a selection of trace elements at the 100-500 ppm concentration level. Trace elements in crystals and quenched melt were analyzed by secondary ion mass spectroscopy. Mg-pv is found to have an affinity for four-valent high field strength elements (Ti, Zr, Hf) with a tendency for higher mineral-melt partition coefficients ($D^{Mgpv/melt}$) with increasing Al content of the solid phase. Large ion lithophile elements (LILE) and rare earth elements (REE's) are found to be incompatible in Mg-pv except for Lu for which the $D^{Mgpv/melt}$ value also increases with increasing Al content. We consider possible effects on the crystal chemistry of Mg-silicate perovskite as a function of major element concentration and discuss the question to what extend perovskite fractionation into a hidden reservoir in the deep mantle could have occurred without disturbing chondritic element ratios preserved in the residual upper mantle
DE: 1025 Composition of the mantle
DE: 1065 Trace elements (3670)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting