Deformation of olivine at mantle pressure using the D-DIA (original) (raw)
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Stress measurements of deforming olivine at high pressure
Physics of the Earth and Planetary Interiors, 2004
Rheological properties of mantle minerals are critical for understanding the dynamics of the Earth's deep interior. Due to limitations in experimental technique, previous quantitative studies of the rheological properties of mantle minerals are limited to either low pressure or low temperature. The present understanding of mantle flow is mostly inferred from the extrapolation of relatively low-pressure data to mantle high-pressure conditions. However, the effect of pressure (represented by activation volume) on the rheological properties of olivine is still controversial. Therefore, deformation experiments, carried out at mantle pressures, are necessary to understand and model mantle flow. Here we report an experimental study of plastic deformation of San Carlos olivine (Mg, Fe) 2 SiO 4 under upper mantle conditions. Macroscopic differential stress and strain rates have been measured in situ in a large-volume high-pressure apparatus using newly developed techniques. The differential stress at high temperature and high pressure that we measured is significantly lower than that estimated by many currently accepted olivine flow laws. We document the first in situ experimental differential stress results in a multi-anvil press. Our results give direct evidence for a relatively small activation volume (less than 10 −5 m 3 mol −1). This shows that the effect of pressure on dislocation creep is small.
Experimental deformation of olivine single crystals at mantle pressures and temperatures
2009
Deformation experiments were carried out in a Deformation-DIA high-pressure apparatus (D-DIA) on oriented San CarlosB B B olivine single crystals, at pressure (P) ranging from 3.5 to 8.5 GPa, temperature (T) from 1373 to 1673 K, and in poor water condition. Oxygen fugacity (fOB 2 B) was maintained within the olivine stability field and contact with enstatite powder ensured an orthopyroxene activity aB opx B = 1. Two compression directions were tested, promoting either [100] slip alone or [001] slip alone in (010) crystallographic plane, here called respectively a-slip and c-slip. Constant applied stress (σ) and specimen strain rates (ε) were monitored in situ using timeresolved x-ray synchrotron diffraction and radiography, respectively. Transmission electron microscopy (TEM) investigation of run products revealed that dislocation creep was responsible for sample deformation. Comparison of the obtained high-P deformation data with the data obtained at room-P by Bai et al. (1991)-on identical materials deformed at comparable T-σ-fOB 2 B-aB opx B conditions-allowed quantifying the P effect on a-slip and c-slip rheological laws. A slip transition with increasing pressure, from dominant a-slip to dominant c-slip, is documented. a-slip appears sensitive to pressure, which translates into the high activation volume VB a B * = 12 ± 4 cmP 3 P/mol in the corresponding rheological law, while pressure has little effect on c-slip with VB c B * = 3 ± 4 cmP 3 P/mol. These results may explain the discrepancy between olivine low-P and high-P deformation data which has been debated in the literature for more than a decade.
Plastic deformation of minerals at high pressure
Mineral behaviour at extreme conditions, 2005
Mechanical properties of real materials are controlled by crystal defects such as point defects, dislocations, stacking faults and grain boundaries. Taken individually, these defects can be described at the fundamental level through their atomic and electronic structures, which can be found by solving the Schrödinger equation. First-principles calculations and molecular dynamics are used to address such problems. At the scale of a grain, the mechanical properties are often the result of the collective behaviour of these defects in response to the loading conditions. Newly developed three-dimensional dislocation dyna-EMU Notes in Mineralogy, Vol. 7 (2005), Chapter 16, 389-415 the model, at the expense of predictive accuracy. There are many atomic-scale methods available to study point and planar defects in mantle minerals (for examples of studies of defects in forsterite see but here we concentrate on the study of dislocations. Most applications of these techniques for dislocation modelling have been concerned with simple metallic systems and semiconductors. Minerals usually represent a more complicated case because of their large unit cells, low symmetries and complex crystal chemistries. This complexity makes the atomistic approach even more relevant, as such fundamental issues as plastic shear anisotropy (which is responsible for crystal preferred orientations), dislocation mobilities and Peierls stresses need to be addressed at this scale.
Journal of Synchrotron Radiation, 2009
Dramatic technical progress seen over the past decade now allows the plastic properties of materials to be investigated under extreme pressure and temperature conditions. Coupling of high-pressure apparatuses with synchrotron radiation significantly improves the quantification of differential stress and specimen textures from X-ray diffraction data, as well as specimen strains and strain rates by radiography. This contribution briefly reviews the recent developments in the field and describes state-of-the-art extreme-pressure deformation devices and analytical techniques available today. The focus here is on apparatuses promoting deformation at pressures largely in excess of 3 GPa, namely the diamond anvil cell, the deformation-DIA apparatus and the rotational Drickamer apparatus, as well as on the methods used to carry out controlled deformation experiments while quantifying X-ray data in terms of materials rheological parameters. It is shown that these new techniques open the new field of in situ investigation of materials rheology at extreme conditions, which already finds multiple fundamental applications in the understanding of the dynamics of Earth-like planet interior.
Journal of Synchrotron Radiation, 2009
Dramatic technical progress seen over the past decade now allows the plastic properties of materials to be investigated under extreme pressure and temperature conditions. Coupling of high-pressure apparatuses with synchrotron radiation significantly improves the quantification of differential stress and specimen textures from X-ray diffraction data, as well as specimen strains and strain rates by radiography. This contribution briefly reviews the recent developments in the field and describes state-of-the-art extreme-pressure deformation devices and analytical techniques available today. The focus here is on apparatuses promoting deformation at pressures largely in excess of 3 GPa, namely the diamond anvil cell, the deformation-DIA apparatus and the rotational Drickamer apparatus, as well as on the methods used to carry out controlled deformation experiments while quantifying X-ray data in terms of materials rheological parameters. It is shown that these new techniques open the new field of in situ investigation of materials rheology at extreme conditions, which already finds multiple fundamental applications in the understanding of the dynamics of Earth-like planet interior.
Viscoplasticity of polycrystalline olivine experimentally deformed at high pressure and 900°C
Tectonophysics, 2014
We have performed tri-axial compression experiments on olivine aggregates at 900°C and at a confining pressure of 300 MPa in a high-resolution gas-medium mechanical testing apparatus. Deformation at two different constant strain rates (1.1 × 10 −5 s −1 and 3.4 × 10 −4 s −1 ) yields continuous hardening, reaching maximal differential stresses of 930 and 1076 MPa, respectively, before sample failure at ca. 10% strain. The deformed samples were characterized by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Crystallographic preferred orientations (CPO) are weak but reveal an alignment of the [010] axes around the compression direction and some concentration of [001] and [100] axes normal to it. TEM observations confirm plastic deformation by dislocation glide, with both [001] and [100] Burgers vectors. Electron tomography, performed for the first time on deformed fined-grained olivine, shows that [001] dislocations glide extensively on {110} and {130} planes, in complement to the and glide planes often reported at high temperatures.
Physics of the Earth and Planetary Interiors, 2008
Large-strain plastic deformation experiments of wadsleyite and olivine were conducted using a rotational Drickamer apparatus (RDA) up to pressure and temperature conditions corresponding to the Earth's mantle transition zone. Sintered ring-shaped (Mg,Fe) 2 SiO 4 wadsleyite and olivine samples were deformed at P ∼ 16 GPa and T = 1600 and 1800 K, and P ∼ 11 GPa and T = 1800 K, respectively, with equivalent strain rate ofε E ∼ 6 × 10 −5 s −1. In situ observations of deforming samples were carried out using the synchrotron radiation facility at Brookhaven National Laboratory, NSLS, X17B2. Stress was measured by X-ray diffraction at six different angles with respect to the compression axis. The stress estimated by X-ray diffraction was in good agreement with the stress estimated from dislocation density (for olivine). Strain was determined using X-ray radiographs of a strain marker (Re or Mo foil). Deformation of samples with a RDA involves both uniaxial compression and simple shear. A new formulation is developed to analyze both components to determine the rheological properties of a sample. Stress-strain curves show strain-hardening up to the equivalent strain of ε E ∼ 0.2 followed by the quasi-steady state deformation. Wadsleyite is found to be stronger than olivine compared at similar conditions and the creep strength of olivine at P ∼ 11 GPa is much higher than those at lower pressures.
Activities of olivine slip systems in the upper mantle
Physics of the Earth and Planetary Interiors, 2012
We investigated the effect of pressure (P) on olivine [1 0 0](0 0 1) and [0 0 1](1 0 0) dislocation slip systems by carrying out deformation experiments in the Deformation-DIA apparatus (D-DIA) on single crystals of Mg 2 SiO 4 forsterite (Fo100) and San Carlos (SC) olivine (Fo89), at P ranging from 5.7 to 9.7 GPa, temperature T = 1473 and 1673 K, differential stress r in the range 140-1500 MPa, and in water-poor conditions. Specimens were deformed in axisymmetry compression along the so-called [1 0 1] c crystallographic direction, which promotes the dual slip of [1 0 0] dislocations in (0 0 1) plane and [0 0 1] dislocations in (1 0 0) plane. Constant r and specimen strain rates (_ e) were monitored in situ by synchrotron X-ray diffraction and radiography, respectively. Comparison of the obtained high-P rheological data with room-P data, previously reported by Darot and Gueguen (1981) for Fo100 and Bai et al. (1991) for SC olivine, allowed quantifying the activation volume V Ã in classical creep power laws. We obtain V Ã = 9.1 ± 1.6 cm 3 /mol for Fo100. For SC olivine, we obtain V Ã = 10.7 ± 5.0 cm 3 /mol taking into account the oxygenfugacity uncertainty during the high-P runs. These results, combined with previous reports, provide complete sets of parameters for quantifying the activities of olivine dislocation slip systems. Extrapolation of the rheological laws obtained for SC olivine crystals to conditions representative of natural deformations show that [1 0 0](0 1 0) slip largely dominates deformation in the shallow upper mantle. At depths greater than 65kmalonga20−Maoceanicgeothermor65 km along a 20-Ma oceanic geotherm or 65kmalonga20−Maoceanicgeothermor155 km along a continental geotherm, the dual activity of [1 0 0](0 0 1) and [0 0 1](1 0 0) slips becomes comparable to that of [1 0 0](0 1 0) slip. At depths greater than $240 km, [0 0 1](0 1 0) slip becomes dominant over all other investigated slip systems. Such changes in olivine dislocation-slips relative activity provide a straightforward explanation for the seismic anisotropy contrast and attenuation with depth observed in the Earth's upper mantle.