HR: 16:00h
AN: MR14A-01 INVITED [Abstracts]
TI: Grain-Boundary Enrichment of Iron in MgSiO3 Perovskite.
AU: * Dobson, D P
EM: d.dobson@ucl.ac.uk
AF: University College London, Gower Street, London, WC1E 6BT
United Kingdom
AU: Alfredson, M
EM: m.alfredson@ucl.ac.uk
AF: University College London, Gower Street, London, WC1E 6BT
United Kingdom
AU: Brodholt, J P
EM: j.brodholt@ucl.ac.uk
AF: University College London, Gower Street, London, WC1E 6BT
United Kingdom
AU: Holzapfel, C
EM: c.holzapfel@mx.uni-saarland.de
AF: Bayerisches Geoinstitut, Universitaet Bayreuth, Bayreuth, D-95440
Germany
AU: Holzapfel, C
EM: c.holzapfel@mx.uni-saarland.de
AF: Universitaet de Saarlandes, Postfach 15 11 50, Saarbrucken, D-66041
Germany
AB:
We present an experimental and theoretical study of grain-boundary partitioning of Fe in magnesium silicate perovskite. The
sample studied here (annealed at 24 GPa and 1950 K) shows significant enrichments of Fe at grain-boundaries. The molecular
dynamics simulations of (Mg,Fe)SiO3 perovskite show enrichments of iron on perovskite grain boundaries. The grain
boundary/lattice partitioning coefficient in the simulations is KGB ~2, consistent with the experimental results.
Simulations of the elastic strength of iron-free and iron-bearing grain boundaries suggest that iron will weaken grain
boundaries to shear. However, chemical enrichment at grain boundaries requires longer diffusive scales for equilibrium
grain-boundary migration, reducing grain-boundary mobility. This complex elastic-diffusive behaviour of iron-bearing grain
boundaries can cause significant modification of the anelasticity of silicate perovskite. In addition, partitioning of iron
onto grain boundaries will result in increased scattering of light and, consequently, a reduced radiative component of the
thermal conductivity. The fact that iron, which is relatively compatible in the perovskite structure, should show
significant grain-boundary enrichment suggests that many less compatible, and trace, elements should also be susceptible to
grain-boundary enrichment in silicate perovskite.
DE: 3904 Defects
DE: 3909 Elasticity and anelasticity
DE: 3924 High-pressure behavior
DE: 3947 Surfaces and interfaces
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005