Deformation-aided segregation of Fe-S liquid from olivine under deep Earth conditions: Implications for core formation in the early solar system

Berg, Madeleine; Bromiley, Geoffrey; Butler, Ian B.; Frost, Mungo; Bradley, Robert L.; Carr, James L.; Godec, Yann Le; Montési, Laurent G. J.; Zhu, Wenlu; Miller, Kevin J.; Perrillat, Jean-Philippe; Mariani, Elisabetta; Tatham, Daniel J.; Redfern, Simon A. T.

doi:10.1016/j.pepi.2017.01.004

Cited by 12 publications

(31 citation statements)

References 41 publications

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“…This allowed to trace the stress dominated vs. surface tension dominated boundary experimentally for the olivine -FeS melt, olivine -Au melt (Walte et al 2011), and the olivine -FeS + basalt melt system (Cerantola et al 2015). While olivine -FeS deformation experiments by Todd et al (2016) supported the results of Walte et al (2011), a later study by Berg et al (2017) was not able to reach the surface tension dominated regime under similar experimental conditions. The reason for this discrepancy is currently unclear.…”

Section: Introductionmentioning

confidence: 91%

The effect of dynamic recrystallisation on the rheology and microstructures of partially molten rocks

Llorens

Gomez‐Rivas

Ganzhorn

et al. 2019

Journal of Structural Geology

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The present study is based on a series of two-dimensional simple shear numerical simulations of two-phase non-linear viscous materials used to investigate the mechanical behaviour of two-phase aggregates representing partially molten rocks. These simulations couple viscoplastic deformation with dynamic recrystallisation (DRX). The aim of these simulations is to investigate the competition between deformation and recrystallisation, and how they affect the mechanical behaviour and resulting microstructures of the deforming material. We systematically vary the melt to solid rock ratio, the dihedral angle of melt and the ratio of DRX vs. deformation. The results show that the amount of DRX and the dihedral angle have a first-order impact on the bulk rheology and the melt distribution in the aggregate. The numerical results allow defining two regimes, depending on the relative contribution deformation and DRX: (1) a deformation-dominated regime at high strain rates (i.e., with a low ratio of recrystallisation vs. viscoplastic deformation) and (2) a recrystallisationdominated regime at low strain rates (i.e., with a high ratio of recrystallisation vs. viscoplastic deformation). The first case results in systems bearing large connected melt pockets whose viscous flow controls the deformation of the aggregate, while disconnected smaller melt pockets develop in models where dynamic recrystallisation dominates. The results of this study allow us to better understand the development of connected melt pockets, which may focus melt flow. The distribution of the melt phase plays a key role in the formation of larger scale melt-enriched shear bands, which in turn has a direct influence on large-scale convective mantle flow.

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Section: Introductionmentioning

confidence: 91%

The effect of dynamic recrystallisation on the rheology and microstructures of partially molten rocks

Llorens

Gomez‐Rivas

Ganzhorn

et al. 2019

Journal of Structural Geology

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“…However, importantly, the image thresholding technique used by Todd et al (2016) was based partly on expected melt contents of radiographic images; as such, at the resolution available, finer melt networks were not resolved, and permeability may have been significantly underestimated. Furthermore, they did not observed melt textures previously described in olivine-FeS high pressure deformation experiments (Walte et al, 2011;Berg et al, 2017), suggesting that deformationaided melt segregation was not simulated in the experiments.…”

Section: Introductionmentioning

confidence: 70%

“…Numerous studies have highlighted the key role of shear deformation in mobilizing Fe-S rich melts that would otherwise be trapped within solid silicate matrices (Bruhn et al, 2000;Rushmer et al, 2005;Groebner and Kohstedt, 2006;Hustoft and Kohlstedt, 2006;Rushmer and Petford, 2011). Although Walte et al (2011) argued that this mechanism of deformation-aided melt segregation does not operate at lower strain rates, the recent study of Berg et al (2017) demonstrated the efficiency of this mechanism over a wide-range of experimental strain rates under high PT. Shi et al (2013) demonstrated that extreme pressure also plays a fundamental role in modifying textures in equilibrated Fe-S liquid-silicate systems, implying that percolative flow would have occurred in the lower mantles of the early Earth and Venus.…”

Section: Introductionmentioning

confidence: 99%

“…They obtained high resolution 3-D X-ray tomographic images of a sample of 4.5 vol% FeS melt in polycrystalline olivine during progressive annealing at high PT and during torsional deformation. However, the method which they used provided a limited voxel size of 2 µm; previous experimental studies have demonstrated that melt networks in deforming olivine-FeS systems typically develop at the micron scale or smaller (Berg et al, 2017), and only scale to larger features at very high strain rates when extensive melt channeling develops. Todd et al (2016) determined melt migration velocities indirectly using Lattice-Boltzmann simulations, which were then used to simulate flow through meshes created from their 3-D textural datasets.…”

Section: Introductionmentioning

confidence: 99%

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Rapid Core Formation in Terrestrial Planets by Percolative Flow: In-Situ Imaging of Metallic Melt Migration Under High Pressure/Temperature Conditions

et al. 2018

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Core formation has left a lasting geochemical signature on the Earth. In order to constrain the composition of the Earth we must fully understand the processes by which newly formed Earth, and the bodies which accreted to it, differentiated. Percolation of iron-rich melt through solid silicate has been invoked as a mechanism for differentiation and core formation in terrestrial bodies in the early solar system. However, to date the contribution of percolation to core formation cannot be assessed due to the absence of data on Fe-rich melt migration velocities. Here we use a novel experimental design to investigate textural changes in an analog system, Au melt in polycrystalline h-BN, at 3 GPa, relevant to core formation in the early solar system. Using a combination of high resolution, in-situ X-ray tomography and fast 2-D radiographic imaging, we obtain the first direct data on melt migration velocities at high PT. Melt migration is highly variable and episodic, driven by variations in differential pressure during melt migration and matrix compaction. Smaller scale melt processes, representing migration of melt along pre-existing melt networks, give comparatively fast velocities of 0.6-60 µms −1. Ex-situ experiments are used to compare melt networks in analog systems to Fe-rich melt in silicates. Two competing processes for melt migration are percolation of melt along grain boundaries, and hydraulic fracturing induced by melt injection. Typically, both processes are noted in experimental and natural systems, although the relative importance of each mechanism is variable. Using a simple model for melt flow through a porous media, migration velocities determined here account for full differentiation of Earth-sized bodies within 10 1-10 3 Myr, for submicron diameter melt bands, or within a few Myr or micron-sized melt bands. This is consistent with rapid timescales inferred from geochemistry for core formation in planetesimals, implying that percolation may have had an important contribution to core differentiation in the Earth.

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“…Cerantola et al (2015) further suggested that the onset of silicate melting nullifies any effect of deformation on melt segregation and may hinter segregation of Fe-rich melt by reducing its connectivity. In contrast, Berg et al (2017) suggested that deformation aided percolation at high pressure over a very large range of strain rates.…”

Section: Melt Connectivity and Percolation Thresholdmentioning

confidence: 98%

Wetting Behavior of Iron–Carbon Melt in Silicates at Mid-Mantle Pressures With Implications for Earth’s Deep Carbon Cycle

Dong¹,

Li²,

Zhu³

2019

Front. Earth Sci.

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Metallic melt containing iron (Fe) and carbon (C) may be present at depths greater than 250 km inside the Earth. Depending on its wetting behavior, such dense melt may be trapped locally or drain into deep mantle and core. Here, we report experimental data on the wetting behavior of Fe-C melt in silicates at the conditions of Earth's mid-mantle between 10 and 23 GPa and 1600 and 1800 • C. The measured dihedral angles of Fe-C melt in olivine, ringwoodite or bridgmanite and ferropericlase matrixes are 117 ± 14 • , 120 ± 14 • , and 107 ± 16 • , respectively, well above the critical value of 60 • for complete wetting. The estimated percolation thresholds are at least 7% in volume, far exceeding the amount of metal in the mantle. Consequently, slab-derived Fe-C melt in the midmantle is expected to occur as isolated pockets and would not percolate through its silicate matrix.

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Deformation-aided segregation of Fe-S liquid from olivine under deep Earth conditions: Implications for core formation in the early solar system

Cited by 12 publications

References 41 publications

The effect of dynamic recrystallisation on the rheology and microstructures of partially molten rocks

The effect of dynamic recrystallisation on the rheology and microstructures of partially molten rocks

Rapid Core Formation in Terrestrial Planets by Percolative Flow: In-Situ Imaging of Metallic Melt Migration Under High Pressure/Temperature Conditions

Wetting Behavior of Iron–Carbon Melt in Silicates at Mid-Mantle Pressures With Implications for Earth’s Deep Carbon Cycle

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