Metal‐silicate segregation in deforming dunitic rocks

Hustoft, J. W.; Kohlstedt, D. L.

doi:10.1029/2005gc001048

Cited by 53 publications

(41 citation statements)

References 39 publications

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“…Oxygen fugacity during hot-pressing and deformation was fixed within the olivine stability field by oxidation of the Ni capsule. A schematic drawing of the piston arrangement is shown by Hustoft and Kohlstedt (2006), and details of the deformation assembly are given by Mei and Kohlstedt (2000b) and Zimmerman and Kohlstedt (2004).…”

Section: Creep Experimentsmentioning

confidence: 99%

Dislocation creep accommodated by grain boundary sliding in dunite

2010

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To investigate the role of grain boundary sliding during dislocation creep of dunite, a series of deformation experiments were carried out under anhydrous conditions on fine-grained (~15 μm) samples synthesized from powdered San Carlos olivine and powdered San Carlos olivine+1.5 vol.% MORB. Triaxial compressive creep tests were conducted at a temperature of 1 473 K and confining pressures of 200 and 400 MPa using a high-resolution, gas-medium deformation apparatus. Each sample was deformed at several levels of differential stress between 100 and 250 MPa to yield strain rates in the range of 10 -6 to 10 -4 s -1 . Under these conditions, the dominant creep mechanism involves the motion of dislocations, largely on the easy slip system (010)[100], accommodated by grain boundary sliding (gbs). This grain size-sensitive creep regime is characterized by a stress exponent of n=3.4±0.2 and a grain size exponent of p=2.0±0.2. The activation volume for this gbs-accommodated dislocation creep regime is V*=(26±3)×10 -6 m 2 ·mol -1 . Comparison of our flow law for gbs-accommodated dislocation creep with those for diffusion creep and for dislocation creep reveals that the present flow law is important for the flow of mantle rocks with grain sizes of <100 μm at differential stresses >20 MPa. Hence, gbs-accommodated dislocation creep is likely to be an important deformation mechanism in deep-rooted, highly localized shear zones in the lithospheric upper mantle.

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Section: Creep Experimentsmentioning

confidence: 99%

Dislocation creep accommodated by grain boundary sliding in dunite

2010

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“…Although the general spherical shape of the liq- uid pockets and the smoothly curved grain boundaries indicate a locally equilibrated microstructure, the static sulphide liquid distribution does not represent a true textural equilibrium, as the lowest energy would be attained by complete removal of the sulphide liquid from the system (e.g. Jurewicz and Watson, 1985). The distribution rather reflects the particular starting mixture, a low liquid pocket mobility, and the annealing time.…”

Section: Static Experimentsmentioning

confidence: 99%

“…Grain-scale percolation of an interconnected Fe-S liquid through a solid silicate matrix has long been suggested to be an important mechanism of planetary differentiation (Bruhn et al, 2000;Yoshino et al, 2003;Hustoft and Kohlstedt, 2006;Terasaki et al, 2008). This differentiation mechanism has recently gained credibility due to the study of Kruijer et al (2014) that showed that the time of differentiation of iron meteorites correlates with the sulphur content in the iron.…”

Section: Differentiation After Crossing the Sulphide Solidusmentioning

confidence: 99%

“…Deformation-induced interconnection in olivine/peridotite-metallic liquid aggregates has been investigated in several experimental studies as a candidate for lowering this percentage of stranded liquid (Bruhn et al, 2000;Hustoft and Kohlstedt, 2006;Groebner and Kohlstedt, 2006;Rushmer et al, 2005;Walte et al, 2011). All studies have agreed that deformation has the potential to mobilize Fe-S liquids and lower the percentage of stranded liquid with estimations ranging from 1 vol.% (Groebner and Kohlstedt, 2006) to 2-3 vol.% (Walte et al, 2011) as long as the differential stress or strain rate is sufficient to overcome the capillary forces of the liquid (Groebner and Kohlstedt, 2006;Walte et al, 2011).…”

Section: Differentiation After Crossing the Sulphide Solidusmentioning

confidence: 99%

“…In order to understand whether the increasing liquid-pocket sizes observed in all two-liquid experiments (except at the fastest strain rates) initiate a run-away accumulation process, the underlying liquid accumulation and dispersion processes have to be considered. In general, liquid accumulation is energetically favorable in solid-liquid systems with a dihedral angle larger than ∼70 • (note that this threshold is larger than the full interconnectivity angle of 60 • , see Jurewicz and Watson, 1985). This tendency of the isolated liquid pockets to grow relies on slow diffusive processes (Ostwald ripening) or on coalescence when they come into contact with each other during grain growth or deformation.…”

Section: Liquid Accumulation Vs Liquid Dispersionmentioning

confidence: 99%

See 2 more Smart Citations

Deformation of a crystalline olivine aggregate containing two immiscible liquids: Implications for early core–mantle differentiation

Cerantola

Walte

Rubie

2015

Earth and Planetary Science Letters

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Deformation-assisted segregation of metallic and sulphidic liquid from a solid peridotitic matrix is a process that may contribute to the early differentiation of small planetesimals into a metallic core and a silicate mantle. Here we present results of an experimental study using a simplified system consisting of a polycrystalline Fo 90 -olivine matrix containing a small percentage of iron sulphide and a synthetic primitive MORB melt, in order to investigate whether the silicate melt enhances the interconnection and segregation of FeS liquid under deformation conditions at varying strain rates. The experiments have been performed at 2 GPa, 1450 • C and strain rates between 1 × 10 −3 s −1 to 1 × 10 −5 s −1 . Our resultsshow that the presence of silicate melt actually hinders the migration and segregation of sulphide liquid by reducing its interconnectivity. At low to moderate strain rates the sulphide liquid pockets preserved a roundish shape, showing the liquid behavior is governed mainly by surface tension rather than by differential stress. Even at the highest strain rates, insignificant FeS segregation and interconnection were observed. On the other hand the basaltic melt was very mobile during deformation, accommodating part of the strain, which led to its segregation from the matrix at high bulk strains leaving the sulphide liquid stranded in the olivine matrix. Hence, we conclude that deformation-induced percolation of sulphide liquid does not contribute to the formation of planetary cores after the silicate solidus is overstepped. A possible early deformation enhanced core-mantle differentiation after overstepping the Fe-S solidus is not possible between the initial formation of silicate melt and the formation of a widespread magma ocean.

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Development of anisotropic contiguity in deforming partially molten aggregates: 1. Theory and fast multipole boundary elements method

Drombosky

Hier‐Majumder

2015

JGR Solid Earth

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The microstructure of partially molten rocks strongly influences the macroscopic physical properties. Contiguity, a geometric parameter, is a tensorial quantity that describes the area fraction of intergranular contact in a partially molten aggregate. It is also a key parameter that controls the effective elastic strength of the grain network. As the shape of the grains evolves during deformation, so does the contiguity of each grain. In this article, we present the first set of numerical simulations of evolution of grain‐scale contiguity of an aggregate during matrix deformation using a fast multipole boundary elements method‐based model. We simulate a pure shear deformation of an aggregate of 1200 grains up to a shortening of 0.47 and a simple shear deformation of 900 grains up to a shear strain of 0.75, for solid‐melt viscosity ratios of 1 and 50. Our results demonstrate that the initially isotropic contiguity tensor becomes strongly anisotropic during deformation. We also observe that the differential shortening, the normalized difference between the major and minor axes of grains, is inversely related to the ratio between the principal components of the contiguity tensor. In pure shear, the principal components of the contiguity tensor remain parallel to the irrotational principal axes of the applied strain. In simple shear, however, the principal components of the contiguity tensor rotate continually during the course of deformation in this study. In the companion article we present the seismic anisotropy resulting from the anisotropic contiguity and the implications for the Earth's lithosphere‐asthenosphere boundary.

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Metal‐silicate segregation in deforming dunitic rocks

Cited by 53 publications

References 39 publications

Dislocation creep accommodated by grain boundary sliding in dunite

Dislocation creep accommodated by grain boundary sliding in dunite

Deformation of a crystalline olivine aggregate containing two immiscible liquids: Implications for early core–mantle differentiation

Development of anisotropic contiguity in deforming partially molten aggregates: 1. Theory and fast multipole boundary elements method

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