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Jan Tullis - One of the best experts on this subject based on the ideXlab platform.
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Effect of aqueous and carbonic fluids on the Dislocation Creep strength of quartz
Journal of Geophysical Research, 2009Co-Authors: Linda J. Chernak, Greg Hirth, Jane Selverstone, Jan TullisAbstract:[1] Dislocation Creep experiments conducted on quartzite indicate that the presence of CO2 can cause strengthening or weakening depending on the oxygen fugacity of the deformation environment. Under oxidizing conditions (ferrosilite-hematite-quartz), the presence of CO2 reduces the water fugacity and results in strengthening of the quartz. Under moderately reducing conditions (∼Ni-NiO), CO2 reacts with H2 from the sample assembly to form graphite; the water produced by this reaction causes weakening. Under extremely reducing conditions (quartz-fayalite-iron), CO2 is reduced to methane, a reaction that consumes original water, thereby increasing the strength of quartz. Our results show that increasing at constant confining pressure, by changing fluid composition, has a similar effect as increasing by increasing confining pressure. The exponent suggested by our data for the Dislocation Creep flow law is 0.375 to 1 (assuming a stress exponent of 3 to 4), which is on the low side of previously reported values. Differences in deformation behavior over small length scales may thus be related to local differences in the that effectively change the in the presence of CO2.
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effect of water on the Dislocation Creep microstructure and flow stress of quartz and implications for the recrystallized grain size piezometer
Journal of Geophysical Research, 2006Co-Authors: Michael Stipp, Jan Tullis, Harald BehrensAbstract:Deformation experiments on Black Hills quartzite with three different initial water contents (as-is, water-added, and vacuum-dried) were carried out in the Dislocation Creep regime in order to evaluate the effect of water on the recrystallized grain size/flow stress piezometer. Samples were deformed in axial compression at temperatures of 750°–1100°C, strain rates between 2 × 10−7 s−1 and 2 × 10−4 s−1 and strains up to 46% using a molten salt assembly in a Griggs apparatus. An increase of the initial water content at otherwise constant deformation conditions caused a decrease in flow stress, an effect known as hydrolytic weakening. The total water content of the starting material was analyzed by Karl Fischer titration (KFT) and Fourier transform infrared (IR) spectroscopy, and quenched samples were analyzed microstructurally and by IR. Changes in the dynamic recrystallization microstructure correlate with changes in flow stress, but there is no independent effect of temperature, strain rate or water content. IR absorption spectra of the deformed spectra indicate that different water contents were maintained in the three sample sets throughout the experiments. However, the amounts of water measured within the vacuum-dried (∼260 ± 40 ppm H2O), the as-is (∼340 ± 50 ppm H2O), and the water-added (∼430 ± 110 ppm H2O) samples are significantly smaller than the initial content of the quartzite (∼640 ± 50 ppm H2O). Water from the inclusions in the starting material adds to the free fluid phase along the grain boundaries, which probably controls the water fugacity and the flow strength, but this water is largely lost during IR sample preparation. Vacuum-dried as well as water-added samples have the same recrystallized grain size/flow stress relationship as the piezometer determined for as-is samples. No independent effect of water on the piezometric relationship has been detected.
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Effects of chemical environment on Dislocation Creep of quartzite
Journal of Geophysical Research: Solid Earth, 1996Co-Authors: Alice D. Post, Jan Tullis, Richard A. YundAbstract:The water-related chemical parameter that affects Dislocation Creep in quartzite has been determined from variations in sample strength and microstructure with chemical environment in buffered deformation and hydrostatic annealing experiments. Samples were weld-sealed in double capsules;, , and were buffered using solid oxygen buffers, AgCl or CO2. Black Hills quartzite was deformed at 900°C and 1.5 × 10−5s−1. Two samples were deformed at ∼1700 MPa confining pressure at constant and , with and varying over 8 and 15 orders of magnitude, respectively. Both samples deformed by climb-accommodated Dislocation Creep with flow stresses of 300 MPa. Two additional samples were deformed at ∼700 MPa at constant lower than for the 1700-MPa samples, with varying over 2 orders of magnitude. Both samples faulted with a peak strength of ∼800 MPa. These four experiments suggest no dependence of Dislocation Creep strength on , or ; instead, a strong dependence of strength on is inferred. Previously deformed samples of Heavitree quartzite were hydrostatically annealed for 4 days at 800°C and 1200 or 500 MPa confining pressure, varying and over 2.5 and 1 order of magnitude, respectively. The microstructures of these samples show increased rates of Dislocation climb and grain boundary migration with increasing but no dependence on . These buffered experiments indicate that Dislocation Creep is affected by alone and suggest that the exponent for the term in the power law Creep flow law is >2.
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A flow law for Dislocation Creep of quartz aggregates determined with the molten salt cell
Tectonophysics, 1995Co-Authors: Gayle C. Gleason, Jan TullisAbstract:We have used the molten salt cell to conduct an experimental study on the rheology of a natural quartzite containing ∼ 0.15 wt. % water. Co-axial deformation experiments were conducted at constant piston displacement rates, approximating constant strain rates at low strain. The strengths of our natural quartzite measured in the molten salt cell are approximately half those measured at the same conditions in solid media because, unlike solid confining media, molten salt does not contribute to the strength of the sample; it reduces the friction on the moving piston, and it allows clear identification of the ‘hit’ point. We have limited the experimental conditions to those required for Dislocation Creep, and have used only steady-state flow stresses measured during climb-accommodated Dislocation Creep to calculate the flow law parameters. Two flow laws were determined, one for samples containing minor amounts of melt (1–2%) and one for melt-free samples. In both cases, the power law stress exponent, n, is 4.0 ± 0.9, which is greater than that previously reported in flow laws for Dislocation Creep of quartz aggregates determined in solid media. The activation energy, Q, is 137 ± 34 kJ mol−1 for samples with melt and 223 ± 56 kJ mol−1 for those without, within the range of previously determined values for quartz aggregates containing ∼ 0.1 wt.% water. The pre-exponential term, A, is 1.1 × 10 (−4 ± 2) MPa−ns−1 for samples without melt and 1.8 × 10(−8 ± 2) MPa−ns−1 for those with melt. The lower strengths measured in the molten salt cell indicate that previous piezometer relations for quartz experimentally determined in solid media are not correct. Extrapolation of the flow law for melt-free aggregates to natural strain rates predicts higher strengths than most previous quartz flow laws. However, accurate extrapolation requires determining the dependence of flow stress on fH2O and / or aH+.
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Dislocation Creep regimes in quartz aggregates
Journal of Structural Geology, 1992Co-Authors: Greg Hirth, Jan TullisAbstract:Using optical and TEM microscopy we have determined that three regimes of Dislocation Creep occur in experimentally deformed quartz aggregates, depending on the relative rates of grain boundary migration, Dislocation climb and Dislocation production. Within each regime a distinctive microstructure is produced due primarily to the operation of different mechanisms of dynamic recrystallization. At lower temperatures and faster strain rates the rate of Dislocation production is too great for diffusion-controlled Dislocation climb to be an effective recovery mechanism. In this regime recovery is accommodated by strain-induced grain boundary migration recrystallization. With an increase in temperature or decrease in strain rate, the rate of Dislocation climb becomes sufficiently rapid to accommodate recovery. In this regime dynamic recrystallization occurs by progressive subgrain rotation. With a further increase in temperature or decrease in strain rate Dislocation climb remains sufficiently rapid to accommodate recovery. However, in this regime grain boundary migration is rapid, thus recrystallization occurs by both grain boundary migration and progressive subgrain rotation. The identification of the three regimes of Dislocation Creep may have important implications for the determination of flow law parameters and the calibration of recrystallized grain size piezometers. In addition, the identification of a particular Dislocation Creep regime could be useful in helping to constrain the conditions at which a given natural deformation has occurred. © 1992.
David L Kohlstedt - One of the best experts on this subject based on the ideXlab platform.
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Evolution of the rheological and microstructural properties of olivine aggregates during Dislocation Creep under hydrous conditions
Journal of Geophysical Research: Solid Earth, 2016Co-Authors: Miki Tasaka, Mark E. Zimmerman, David L KohlstedtAbstract:Since hydrogen plays an important role in dynamic processes in Earth's mantle, we conducted torsion experiments to shear strains of 0.6 to 5.0 on Fe-bearing olivine aggregates [(Mg0.5Fe0.5)2SiO4: Fo50] under hydrous conditions at T = 1200 °C and P = 300 MPa. We deformed samples to high enough strains that a steady-state microstructure was achieved, which allowed us to investigate the evolution of both the rheological and microstructural properties. The stress exponent of n ≈ 5.0 and the grain size exponent of p ≈ 0 determined by fitting the strain rate, stress, and grain size data indicate that our samples deformed by Dislocation Creep. Fourier transform infrared (FTIR) spectroscopy measurements on embedded olivine single crystals demonstrated that our samples were saturated with hydrogen during the deformation experiments. The lattice preferred orientation (LPO) of olivine changes as a function of strain due to competition among three slip systems: (010)[100], (100)[001], and (001)[100]. Observed strain weakening can be attributed to geometrical softening associated with development of LPO, which reduces the stress by ~1/3 from its peak value in constant strain rate experiments. The geometrical softening coefficient determined in this study is an important constraint for modeling and understanding dynamical processes in upper mantle under hydrous conditions.
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Low oxygen fugacity dependency for the deformation of partially molten lherzolite
Tectonophysics, 2012Co-Authors: Yongfeng Wang, Junfeng Zhang, David L KohlstedtAbstract:Abstract We present the results of an experimental investigation of the influence of oxygen fugacity on the deformation of a partially molten spinel lherzolite using a 0.1 MPa gas-media Creep rig under temperatures of 1160–1190 °C, stresses of 4–74 MPa and well-controlled oxygen fugacities of 10− 7 to 10− 11 MPa. The partially molten spinel lherzolite was deformed by a Dislocation-mediated Creep process such as Dislocation Creep or Dislocation-accommodated grain boundary sliding (DGBS) (n = 3.5 ± 0.3) as well as in the diffusion Creep regime (n = 1.2 ± 0.2). The average oxygen fugacity exponent of lherzolite is 0.04 ± 0.02, which is significantly smaller than the values measured for olivine single crystals (0.10–0.36) and dunite rocks (0.20) deformed by Dislocation Creep. We attribute the low oxygen fugacity exponent of partially molten lherzolite samples either to the operation of grain boundary sliding, if DGBS dominates the deformation, or to the presence of pyroxenes whose deformation has a weak or no dependency on oxygen fugacity, if Dislocation Creep dominates the deformation. In the latter case, the oxygen fugacity exponent decreases rapidly with decreasing volume fraction of olivine. The low oxygen fugacity exponent for our partially molten lherzolite samples implies that Dislocation Creep or DGBS of mantle peridotite will most likely be insensitive to variations of oxygen fugacity in the upper mantle.
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dependence of Dislocation Creep of dunite on oxygen fugacity implications for viscosity variations in earth s mantle
Journal of Geophysical Research, 2011Co-Authors: J W Keefner, S J Mackwell, David L Kohlstedt, Florian HeidelbachAbstract:[1] Significant variations in flow behavior are known to exist both vertically and laterally in Earth's upper mantle. The sources of such variation may be thermal, compositional, or reflect differences in the chemical activity of components, such as oxygen, silica, and water. We report on the effects of oxygen fugacity on Dislocation Creep of dunite, with a view to understanding potential strength heterogeneity in the mantle. Although room pressure experiments on single crystals of olivine have shown a clear dependence of Creep rate on oxygen fugacity, no prior deformation study of polycrystalline olivine-rich rocks has demonstrated such a dependency under high-pressure conditions. In this study we performed a series of dry Creep experiments on a natural dunite under carefully controlled thermochemical conditions, including oxygen fugacity. The samples, cored from coarse-grained Aheim dunite with a grain size of ∼0.9 mm, were deformed under triaxial compression at oxygen fugacities fixed by either the iron/wustite or the nickel/nickel oxide solid state buffers, temperatures between 1150° and 1277°C, and differential stresses up to 300 MPa. The results of a global fit to all experimental data indicate a power law dependence of Creep rate on oxygen fugacity, with an oxygen fugacity exponent of m = 0.20 ± 0.01, n = 3.6 ± 0.1, A = 102.6±0.3 s−1 MPa−3.6 Pa−0.2, and an activation energy for Creep of 449 ± 7 kJ/mol. This activation energy is significantly less than the commonly used value of 535 kJ/mol because the earlier experiments made no corrections for the effects of oxygen fugacity. When applied to planetary interiors, an increase in oxygen fugacity by a factor of ∼103.5, from the iron/wustite to the fayalite-magnetite-quartz buffers, will result in a factor of ∼5 decrease in viscosity.
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Dislocation Creep accommodated by grain boundary sliding in dunite
Journal of Earth Science, 2010Co-Authors: Z. C. Wang, Yong Hong Zhao, David L KohlstedtAbstract: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 m2·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 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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Grain boundary sliding in compressed olivine aggregates.
Acta Petrologica Sinica, 2009Co-Authors: Yong Hong Zhao, Zhong Yan Wang, David L KohlstedtAbstract: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 samples synthesized from powdered San Carlos olivine. Triaxial compressive Creep tests were conducted under a temperature of 1473 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 of 10~(-4) to 10~(-6) s~(-1). With increasing differential stress, a transition from diffusion Creep to Dislocation Creep regime in which motion on the easy slip system is accommodated by grain boundary sliding ( GBS) occurs at ～50 MPa for samples with a grain size of 15μm. This grain size sensitive Creep regime is characterized by a stress exponent of 3.2±0.1, and a grain size exponent of 1.8±0.2. Comparison of our flow law for Dislocation Creep accommodated by grain boundary sliding with those for diffusion Creep and Dislocation Creep in which motion of Dislocations on the hard slip system is accommodated by Dislocation activity on the easy slip system reveals that the present flow law is important for flow of rocks with grain sizes of 100μm at differential stresses 20 MPa. Hence, GBS-accommodated Dislocation Creep is likely to be the dominant deformation mechanism in deep-rooted, highly localized shear zones in the lithospheric upper mantle.
Jun-ichi Fukuda - One of the best experts on this subject based on the ideXlab platform.
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theoretical derivation of flow laws for quartz Dislocation Creep comparisons with experimental Creep data and extrapolation to natural conditions using water fugacity corrections
Journal of Geophysical Research, 2017Co-Authors: Jun-ichi Fukuda, Ichiko ShimizuAbstract:We theoretically derived flow laws for quartz Dislocation Creep using climb-controlled Dislocation Creep models and compared them with available laboratory data for quartz plastic deformation. We assumed volume diffusion of oxygen-bearing species along different crystallographic axes (//c, ⊥R, and ⊥c) of α-quartz and β-quartz, and pipe diffusion of H 2 O, to be the elementary processes of Dislocation climb. The relationships between differential stress (σ) and strain rate (_ e) are written as _ e∝σ 3 D v and _ e∝σ 5 D p for cases controlled by volume and pipe diffusion, respectively, where D v and D p are coefficients of diffusion for volume and pipe diffusion. In previous experimental work, there were up to ~1.5 orders of magnitude difference in the water fugacity values in experiments that used either gas-pressure-medium or solid-pressure-medium deformation apparatus. Therefore, in both the theories and flow laws, we included water fugacity effects as modified preexponential factors and water fugacity terms. Previous experimental data were obtained mainly in the β-quartz field and are highly consistent with the volume-diffusion-controlled Dislocation Creep models of β-quartz involving the water fugacity term. The theory also predicts significant effects for the transition of α-β quartz under crustal conditions. Under experimental pressure and temperature conditions, the flow stress of pipe-diffusion-controlled Dislocation Creep is higher than that for volume-diffusion-controlled Creep. Extrapolation of the flow laws to natural conditions indicates that the contributions of pipe diffusion may dominate over volume diffusion under low-temperature conditions of the middle crust around the brittle-plastic transition zone.
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Theoretical derivation of flow laws for quartz Dislocation Creep: Comparisons with experimental Creep data and extrapolation to natural conditions using water fugacity corrections
Journal of Geophysical Research : Solid Earth, 2017Co-Authors: Jun-ichi Fukuda, Ichiko ShimizuAbstract:We theoretically derived flow laws for quartz Dislocation Creep using climb-controlled Dislocation Creep models and compared them with available laboratory data for quartz plastic deformation. We assumed volume diffusion of oxygen-bearing species along different crystallographic axes (//c, ⊥R, and ⊥c) of α-quartz and β-quartz, and pipe diffusion of H 2 O, to be the elementary processes of Dislocation climb. The relationships between differential stress (σ) and strain rate (_ ε) are written as _ ε∝σ 3 D v and _ ε∝σ 5 D p for cases controlled by volume and pipe diffusion, respectively, where D v and D p are coefficients of diffusion for volume and pipe diffusion. In previous experimental work, there were up to ~1.5 orders of magnitude difference in the water fugacity values in experiments that used either gas-pressure-medium or solid-pressure-medium deformation apparatus. Therefore, in both the theories and flow laws, we included water fugacity effects as modified preexponential factors and water fugacity terms. Previous experimental data were obtained mainly in the β-quartz field and are highly consistent with the volume-diffusion-controlled Dislocation Creep models of β-quartz involving the water fugacity term. The theory also predicts significant effects for the transition of α-β quartz under crustal conditions. Under experimental pressure and temperature conditions, the flow stress of pipe-diffusion-controlled Dislocation Creep is higher than that for volume-diffusion-controlled Creep. Extrapolation of the flow laws to natural conditions indicates that the contributions of pipe diffusion may dominate over volume diffusion under low-temperature conditions of the middle crust around the brittle-plastic transition zone.
S J Mackwell - One of the best experts on this subject based on the ideXlab platform.
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dependence of Dislocation Creep of dunite on oxygen fugacity implications for viscosity variations in earth s mantle
Journal of Geophysical Research, 2011Co-Authors: J W Keefner, S J Mackwell, David L Kohlstedt, Florian HeidelbachAbstract:[1] Significant variations in flow behavior are known to exist both vertically and laterally in Earth's upper mantle. The sources of such variation may be thermal, compositional, or reflect differences in the chemical activity of components, such as oxygen, silica, and water. We report on the effects of oxygen fugacity on Dislocation Creep of dunite, with a view to understanding potential strength heterogeneity in the mantle. Although room pressure experiments on single crystals of olivine have shown a clear dependence of Creep rate on oxygen fugacity, no prior deformation study of polycrystalline olivine-rich rocks has demonstrated such a dependency under high-pressure conditions. In this study we performed a series of dry Creep experiments on a natural dunite under carefully controlled thermochemical conditions, including oxygen fugacity. The samples, cored from coarse-grained Aheim dunite with a grain size of ∼0.9 mm, were deformed under triaxial compression at oxygen fugacities fixed by either the iron/wustite or the nickel/nickel oxide solid state buffers, temperatures between 1150° and 1277°C, and differential stresses up to 300 MPa. The results of a global fit to all experimental data indicate a power law dependence of Creep rate on oxygen fugacity, with an oxygen fugacity exponent of m = 0.20 ± 0.01, n = 3.6 ± 0.1, A = 102.6±0.3 s−1 MPa−3.6 Pa−0.2, and an activation energy for Creep of 449 ± 7 kJ/mol. This activation energy is significantly less than the commonly used value of 535 kJ/mol because the earlier experiments made no corrections for the effects of oxygen fugacity. When applied to planetary interiors, an increase in oxygen fugacity by a factor of ∼103.5, from the iron/wustite to the fayalite-magnetite-quartz buffers, will result in a factor of ∼5 decrease in viscosity.
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Large-strain deformation and strain partitioning in polyphase rocks: Dislocation Creep of olivine magnesiowüstite aggregates
Tectonophysics, 2006Co-Authors: Misha Bystricky, Florian Heidelbach, S J MackwellAbstract:Aggregates composed of olivine and magnesiowüstite have been deformed to large strains at high pressure and temperature to investigate stress and strain partitioning, phase segregation and possible localization of deformation in a polyphase material. Samples with 20 vol.% of natural olivine and 80 vol.% of (Mg0.7Fe0.3)O were synthesized and deformed in a gas-medium torsion apparatus at temperatures of 1127 °C and 1250 °C, a confining pressure of 300 MPa and constant angular displacement rates equivalent to constant shear strain rates of 1 3.3 × 10? 4 s? 1. The samples deformed homogeneously to total shear strains of up to ? ? 15. During constant strain rate measurements the flow stress remained approximately stable at 1250 °C while it progressively decreased after the initial yield stress at the lower temperature. Mechanical data, microstructures and textures indicate that both phases were deforming in the Dislocation Creep regime. The weaker component, magnesiowüstite, controlled the rheological behavior of the bulk material and accommodated most of the strain. Deformation and dynamic recrystallization lead to grain refinement and to textures that were not previously observed in pure magnesiowüstite and may have developed due to the presence of the second phase. At 1127 °C, olivine grains behaved as semi-rigid inclusions rotating in a viscous matrix. At 1250 °C, some olivine grains remained largely undeformed while deformation and recrystallization of other grains oriented for a-slip on (010) resulted in a weak foliation and a texture typical for pure dry olivine aggregates. Both a-slip and c-slip on (010) were activated in olivine even though the nominal stresses were up to 2 orders of magnitude lower than those needed to activate these slip systems in pure olivine at the same conditions.
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Large-strain deformation and strain partitioning in polyphase rocks: Dislocation Creep of olivine–magnesiowüstite aggregates
Tectonophysics, 2006Co-Authors: Misha Bystricky, Florian Heidelbach, S J MackwellAbstract:Aggregates composed of olivine and magnesiowustite have been deformed to large strains at high pressure and temperature to investigate stress and strain partitioning, phase segregation and possible localization of deformation in a polyphase material. Samples with 20 vol.% of natural olivine and 80 vol.% of (Mg0.7Fe0.3)O were synthesized and deformed in a gas-medium torsion apparatus at temperatures of 1127 °C and 1250 °C, a confining pressure of 300 MPa and constant angular displacement rates equivalent to constant shear strain rates of 1 3.3 × 10? 4 s? 1. The samples deformed homogeneously to total shear strains of up to ? ? 15. During constant strain rate measurements the flow stress remained approximately stable at 1250 °C while it progressively decreased after the initial yield stress at the lower temperature. Mechanical data, microstructures and textures indicate that both phases were deforming in the Dislocation Creep regime. The weaker component, magnesiowustite, controlled the rheological behavior of the bulk material and accommodated most of the strain. Deformation and dynamic recrystallization lead to grain refinement and to textures that were not previously observed in pure magnesiowustite and may have developed due to the presence of the second phase. At 1127 °C, olivine grains behaved as semi-rigid inclusions rotating in a viscous matrix. At 1250 °C, some olivine grains remained largely undeformed while deformation and recrystallization of other grains oriented for a-slip on (010) resulted in a weak foliation and a texture typical for pure dry olivine aggregates. Both a-slip and c-slip on (010) were activated in olivine even though the nominal stresses were up to 2 orders of magnitude lower than those needed to activate these slip systems in pure olivine at the same conditions.
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Large-strain deformation and strain partitioning in polyphase rocks: Dislocation Creep of olivine–magnesiowüstite aggregates
Tectonophysics, 2006Co-Authors: Misha Bystricky, Florian Heidelbach, S J MackwellAbstract:International audienceAggregates composed of olivine and magnesiowüstite have been deformed to large strains at high pressure and temperature to investigate stress and strain partitioning, phase segregation and possible localization of deformation in a polyphase material. Samples with 20 vol.% of natural olivine and 80 vol.% of (Mg0.7Fe0.3)O were synthesized and deformed in a gas-medium torsion apparatus at temperatures of 1127 °C and 1250 °C, a confining pressure of 300 MPa and constant angular displacement rates equivalent to constant shear strain rates of 1 3.3 × 10? 4 s? 1. The samples deformed homogeneously to total shear strains of up to ? ? 15. During constant strain rate measurements the flow stress remained approximately stable at 1250 °C while it progressively decreased after the initial yield stress at the lower temperature. Mechanical data, microstructures and textures indicate that both phases were deforming in the Dislocation Creep regime. The weaker component, magnesiowüstite, controlled the rheological behavior of the bulk material and accommodated most of the strain. Deformation and dynamic recrystallization lead to grain refinement and to textures that were not previously observed in pure magnesiowüstite and may have developed due to the presence of the second phase. At 1127 °C, olivine grains behaved as semi-rigid inclusions rotating in a viscous matrix. At 1250 °C, some olivine grains remained largely undeformed while deformation and recrystallization of other grains oriented for a-slip on (010) resulted in a weak foliation and a texture typical for pure dry olivine aggregates. Both a-slip and c-slip on (010) were activated in olivine even though the nominal stresses were up to 2 orders of magnitude lower than those needed to activate these slip systems in pure olivine at the same conditions
Patrick Cordier - One of the best experts on this subject based on the ideXlab platform.
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low steady state stresses in the cold lithospheric mantle inferred from Dislocation dynamics models of Dislocation Creep in olivine
Earth and Planetary Science Letters, 2015Co-Authors: Francesca Boioli, Patrick Cordier, Andréa Tommasi, Sylvie Demouchy, Alexandre MussiAbstract:Transmission electron microscopy observations on olivine crystals deformed at moderate (≤1273 K) temperature evidenced Dislocations interactions explaining the hardening observed in the experiments, but also recovery mechanisms by the absorption or emission of point defects. Thus we investigate the possibility that, at geological strain-rates, these recovery processes allow steady-state deformation by Dislocation Creep at low to moderate temperatures in the lithospheric mantle. We test this hypothesis using a 2.5-D Dislocation dynamics (DD) model, which combines Dislocation glide and recovery by climb. This model shows that diffusion-controlled recovery processes allow for steady-state deformation by Dislocation Creep in the lithospheric mantle at stresses <500 MPa. For stresses of 50–200 MPa, steady-state strain-rates of 10−15 s−110−15 s−1 may be attained at temperatures as low as 900 K. Fitting of the DD model produces a flow law, which represents a lower bound for the lithospheric mantle strength, since the models describe the deformation of an olivine single crystal in an easy slip orientation. Comparison of strain-rates and Moho temperatures inferred for different geodynamic environments and the predictions of this model-based flow law implies, nevertheless, that, except in incipient rifts, most of the observed deformation may be produced by stress levels ≤200 MPa, consistent with those inferred to be produced by convection. This convergence suggests that the present models, which explicitly calculate the time-dependent Dislocation dynamics, may provide a correct first order estimate of the mechanical behaviour of the lithospheric mantle, which cannot be derived directly from any existing data.
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Low steady-state stresses in the cold lithospheric mantle inferred from Dislocation dynamics models of Dislocation Creep in olivine
Earth and Planetary Science Letters, 2015Co-Authors: Francesca Boioli, Patrick Cordier, Andréa Tommasi, Sylvie Demouchy, Alexandre MussiAbstract:Transmission electron microscopy observations on olivine crystals deformed at moderate (≤1273 K) temperature evidenced Dislocations interactions explaining the hardening observed in the experiments, but also recovery mechanisms by the absorption or emission of point defects. Thus we investigate the possibility that, at geological strain-rates, these recovery processes allow steady-state deformation by Dislocation Creep at low to moderate temperatures in the lithospheric mantle. We test this hypothesis using a 2.5-D Dislocation dynamics (DD) model, which combines Dislocation glide and recovery by climb. This model shows that diffusion-controlled recovery processes allow for steady-state deformation by Dislocation Creep in the lithospheric mantle at stresses
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Polycrystalline Olivine Rheology in Dislocation Creep: Revisiting Experimental Data to 8.1 GPa
Physics of the Earth and Planetary Interiors, 2014Co-Authors: Caroline Bollinger, Paul Raterron, Patrick Cordier, Sébastien MerkelAbstract:Abstract The rheology of polycristalline San Carlos olivine is investigated on synchrotron beamline in the Deformation-DIA (D-DIA) at pressure (P) between 3.8 and 8.1 GPa, temperature (T) within 1373–1673 K, and at steady-state strain rates ranging from 1.1 × 10−5 to 5.8 × 10−5 s−1. Transmission electron microscopy (TEM) on run products reveals microstructures characteristic of the so-called “Dislocation Creep regime”. Fourier transform infrared (FTIR) measurements reveal hydroxyl concentrations within 153–1526 ppm H/Si (Paterson’s calibration), indicating ‘wet’ conditions of deformation. Analysis of our data together with previously published ‘wet’ deformation data obtained at room and high P, assuming a stress exponent n = 3.5 in classical power law, results in a linear dependence of the activation enthalpy with P, i.e., in an activation volume of V∗ = 12.8 ± 5 cm3 mol−1. This value of V∗ is also consistent with a global dataset including ‘wet’ data and ‘dry’ published deformation data for olivine aggregates. We thus conclude that, up to 8 GPa, the effect of P on ‘dry’ and ‘wet’ olivine Dislocation Creep is consistent with V∗ = 12.8 ± 5 cm3 mol−1.
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pressure sensitivity of olivine slip systems and seismic anisotropy of earth s upper mantle
Nature, 2005Co-Authors: David Mainprice, Patrick Cordier, Andréa Tommasi, Helene Couvy, Daniel J FrostAbstract:The mineral olivine dominates the composition of the Earth's upper mantle and hence controls its mechanical behaviour and seismic anisotropy. Experiments at high temperature and moderate pressure, and extensive data on naturally deformed mantle rocks, have led to the conclusion that olivine at upper-mantle conditions deforms essentially by Dislocation Creep with dominant [100] slip. The resulting crystal preferred orientation has been used extensively to explain the strong seismic anisotropy observed down to 250 km depth1,2,3,4. The rapid decrease of anisotropy below this depth has been interpreted as marking the transition from Dislocation to diffusion Creep in the upper mantle5. But new high-pressure experiments suggest that Dislocation Creep also dominates in the lower part of the upper mantle, but with a different slip direction. Here we show that this high-pressure Dislocation Creep produces crystal preferred orientations resulting in extremely low seismic anisotropy, consistent with seismological observations below 250 km depth. These results raise new questions about the mechanical state of the lower part of the upper mantle and its coupling with layers both above and below.
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Dislocation Creep in mgsio3 perovskite at conditions of the earth s uppermost lower mantle
Nature, 2004Co-Authors: Patrick Cordier, Tamas Ungar, Lehel Zsoldos, Geza TichyAbstract:Seismic anisotropy provides an important observational constraint on flow in the Earth's deep interior. The quantitative interpretation of anisotropy, however, requires knowledge of the slip geometry of the constitutive minerals that are responsible for producing rock fabrics. The Earth's lower mantle is mostly composed of (Mg, Fe)SiO3 perovskite, but as MgSiO3 perovskite is not stable at high temperature under ambient pressure, it has not been possible to investigate its mechanical behaviour with conventional laboratory deformation experiments. To overcome this limitation, several attempts were made to infer the mechanical properties of MgSiO3 perovskite on the basis of analogue materials. But perovskites do not constitute an analogue series for plastic deformation, and therefore the direct investigation of MgSiO3 perovskite is necessary. Here we have taken advantage of recent advances in experimental high-pressure rheology to perform deformation experiments on coarse-grained MgSiO3 polycrystals under pressure and temperature conditions of the uppermost lower mantle. We show that X-ray peak broadening measurements developed in metallurgy can be adapted to low-symmetry minerals to identify the elementary deformation mechanisms activated under these conditions. We conclude that, under uppermost lower-mantle conditions, MgSiO3 perovskite deforms by Dislocation Creep and may therefore contribute to producing seismic anisotropy in rocks at such depths.