HR: 0800h
AN: MR31B-0375 [Abstracts]
TI: Percolation experiments of FeS melts in partially molten peridotites
AU: * Bagdassarov, N S
EM: nickbagd@geophysik.uni-frankfurt.de
AF: Institut für Geowissenschaften, Universität Frankfurt am Main, Altenhöferallee 1,
Frankfurt a. Main, D-60438, Germany
AU: Solferino, G
EM: solferino@erdw.ethz.ch
AF: Institute for Mineralogy und Petrology,
Department Erdwissenschaften, ETH Zürich, Clausiusstrasse 25, Zürich, CH-8092, Switzerland
AU: Schmidt, M
EM: max.schmidt@erdw.ethz.ch
AF: Institute for Mineralogy und Petrology,
Department Erdwissenschaften, ETH Zürich, Clausiusstrasse 25, Zürich, CH-8092, Switzerland
AB:
The series of percolation experiments have been done on partially molten fertile garnet peridotite xenolith by
using the centrifuging piston-cylinder press. Powders with 100-200 μm and 20-30 μm grain size were
mixed with 5-30 vol% Fe-FeS eutectic composition. The deformed high-T garnet peridotite with Mg# ~ 0.90
is composed from 60 vol% Ol, 15 vol% Opx, 6 vol% Cpx and 19 vol% Gar. The centrifuge experiments revealed
a negligible percolation of Fe70S30 melts through the partially molten peridotite matrix. At 1150° C
and 4.5 vol% of FeS the separation is 0.7 vol%/mm. Only at 1260° C and starting with 5 vol% of
Fe70S30 the vertical gradient achieved 1-2 vol%/mm, and in samples wiith initial 15 vol% FeS the
vertical separation achieved 2-2.5 vol%/mm after 10 h of centrifuging at 500 g. At 1280° C and 25 vol% of
melting the initial 30 vol% of FeS have been removed during 0.5 h at 600 g. The partial melting of peridotite
contributes in the increase of Fe70S30 droplet size, in agreement with Yoshino and Watson (2005)
and in the increase of the effective velocity of FeS percolation. The permeabilities of partially molten peridotite
with FeS using the viscosity of melt 0.1 Pa s are ~ 10-16 \div 10-17 m2, which is one order of
magnitude lower than estimations (Roberts et al., 2007) from static experiments. The slow percolation of FeS
in the absence of high degree of partial melting of silicates ( <15 vol%) preclude the scenario of the metallic
core formation before the partial melting of silicate mantle in planetary bodies is started. The segregation
velocities, scaled to 1 g are 10-5 mm/h. At higher degree of partial melting (>15 vol%) the interconnected
FeS phase coagulates in large spherical clusters. At further partial melting ( ~30 vol%) the large clusters of
FeS disintegrated into smaller droplets and moved in silicate melt channels downwards whereas the silicate
melt migrates upward. The rate of FeS percolation according to this mechanism is 5× 10-3 mm/h. After
flow of a large amount of FeS melt the system of silicate melt channels remains aligned vertically and the
permeability of partially molten matrix is anisotropic. To remove the rest of FeS (the last 3-5 vol%) from the
silicate matrix is not possible even applying the large centrifugal accelerations. The grain size reduction due to
the phase transition Gar into Sp does not block the segregation of FeS, the smaller crystals are easier to shift and
to rotate under the force of the sinking FeS droplets.
DE: 3600 MINERALOGY AND PETROLOGY
DE: 3900 MINERAL PHYSICS
DE: 3909 Elasticity and anelasticity
DE: 3924 High-pressure behavior
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting