HR: 14:55h
AN: T33F-05    [Abstracts]
TI: Is Core-Formation Enhanced by Deformation? Olivine-FeS Melt Experiments With the Deformation-DIA
AU: * Walte, N P
EM: nico.walte@uni-bayreuth.de
AF: Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth, 95440 Germany
AU: Frost, D J
EM: dan.frost@uni-bayreuth.de
AF: Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth, 95440 Germany
AU: Rubie, D C
EM: dave.rubie@uni-bayreuth.de
AF: Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth, 95440 Germany
AB: Contrary to most common silicate melt phases, a high dihedral angle (>60°) between metallic melt and silicate minerals leads to an early breakdown of the grain-scale melt network before complete melt extraction by porous flow can be achieved. This inefficient segregation from a solid matrix provides important support for the magma ocean model of core formation, which allows molten metal droplets to segregate from silicate melt by gravitational settling. However, some authors have demonstrated that deformation can dynamically enhance melt connectivity so that extensive melting of the silicate proto-earth may not have been necessary. In this study, deformation experiments with FeS melt in a matrix of synthetic olivine (Fo90) were performed to investigate a potentially enhanced dynamic melt segregation as a function of strain rate and melt fraction. The experiments were performed with a deformation-DIA, a cubic multi-anvil device, at a confining pressure of 3 GPa and at a temperature of 1400°C using a wide range of melt fractions (1-15 vol. %) and strain rates (10-2-10-6 s-1). The samples were quenched rapidly to preserve the dynamic melt geometry. Our results show that despite local wetting of grain boundaries, especially during high strain rate experiments, no interconnected melt networks were present at melt fractions below ~3 vol. %. Thus, melt migration by continuous porous flow should be inhibited. However, deformation has a significant effect on melt distribution. Compared to statically annealed samples, the amount of melt in large melt pockets (> 200 mm2) decreases, while the amount of melt in smaller pockets increases, i.e. deformation disperses melt more evenly throughout the grain matrix. At the same time, the overall melt fraction decreases to an apparently stable value of ~1.5 vol. %. Segregated melt can often be observed at the side of the capsule. Although no continuous melt pathways were observed in the low melt-fraction experiments, individual melt patches must have still been mobilized during deformation. Thus, although deformation can aid melt segregation to a certain extent, a decrease of melt-fraction below ~1.5 vol.% did not occur in our experiments so that deformation could not have been the sole mechanism for an efficient core formation.
DE: 3600 MINERALOGY AND PETROLOGY
DE: 8030 Microstructures
DE: 8045 Role of fluids
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8125 Evolution of the Earth (0325)
SC: Tectonophysics [T]
MN: Fall Meeting 2005