https://sam.ensam.eu:443 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Fri, 05 Jun 2026 22:23:39 GMT 2026-06-05T22:23:39Z http://hdl.handle.net/10985/7989 Multiscale modeling of upper mantle plasticity: From single-crystal rheology to multiphase aggregate deformation RATERRON, Paul; DETREZ, Fabrice; CASTELNAU, Olivier; BOLLINGER, Caroline; CORDIER, Patrick; MERKEL, Sébastien We report a first application of an improved second-order (SO) viscoplastic self-consistent model for multiphase aggregates, applied to an olivine + diopside aggregate as analogue for a dry upper mantle peridotite deformed at 10 15 s 1 shear strain rate along a 20-Ma ocean geotherm. Beside known dislocation slip systems, this SO-model version accounts for an isotropic relaxation mechanism representing ‘diffusionrelated’ creep mechanisms in olivine. Slip-system critical resolved shear stress (CRSS) are evaluated in both phases – as functions of P, T, oxygen fugacity (fO2) and strain rate – from previously reported experimental data obtained on single crystals and first-principle calculations coupled with the Peierls–Nabarro model for crystal plasticity; and the isotropic-mechanism dependence on T and P matches that of Si selfdiffusion in olivine, while its relative activity is constrained by reported data. The model reproduces well the olivine and diopside lattice preferred orientations (LPO) produced experimentally and observed in naturally deformed rocks, as well as observed sensitivities of multiphase aggregate strength to the volume fraction of the hard phase (here diopside). It shows a significant weakening of olivine LPO with increasing depth, which results from the combined effects of the P-induced [100]/[001] dislocation-slip transition and the increasing activity with T of ‘diffusion-related’ creep. This work thus provides a first quantification of the respective effects of [100]/[001] slip transition and diffusion creep on the olivine LPO weakening inducing the seismic anisotropy attenuation observed in the upper mantle. Wed, 01 Jan 2014 00:00:00 GMT http://hdl.handle.net/10985/7989 2014-01-01T00:00:00Z RATERRON, Paul DETREZ, Fabrice CASTELNAU, Olivier BOLLINGER, Caroline CORDIER, Patrick MERKEL, Sébastien We report a first application of an improved second-order (SO) viscoplastic self-consistent model for multiphase aggregates, applied to an olivine + diopside aggregate as analogue for a dry upper mantle peridotite deformed at 10 15 s 1 shear strain rate along a 20-Ma ocean geotherm. Beside known dislocation slip systems, this SO-model version accounts for an isotropic relaxation mechanism representing ‘diffusionrelated’ creep mechanisms in olivine. Slip-system critical resolved shear stress (CRSS) are evaluated in both phases – as functions of P, T, oxygen fugacity (fO2) and strain rate – from previously reported experimental data obtained on single crystals and first-principle calculations coupled with the Peierls–Nabarro model for crystal plasticity; and the isotropic-mechanism dependence on T and P matches that of Si selfdiffusion in olivine, while its relative activity is constrained by reported data. The model reproduces well the olivine and diopside lattice preferred orientations (LPO) produced experimentally and observed in naturally deformed rocks, as well as observed sensitivities of multiphase aggregate strength to the volume fraction of the hard phase (here diopside). It shows a significant weakening of olivine LPO with increasing depth, which results from the combined effects of the P-induced [100]/[001] dislocation-slip transition and the increasing activity with T of ‘diffusion-related’ creep. This work thus provides a first quantification of the respective effects of [100]/[001] slip transition and diffusion creep on the olivine LPO weakening inducing the seismic anisotropy attenuation observed in the upper mantle. http://hdl.handle.net/10985/15116 Microstructures and rheology of the Earth's upper mantle inferred from a multiscale approach CASTELNAU, Olivier; CORDIER, Patrick; LEBENSON, RA; MERKEL, SEBASTIEN; RATERRON, PAUL The strongly anisotropic rheology of olivine polycrystals, associated to their microstructure, constitutes a key feature affecting the dynamics of the Earth's upper mantle. High pressure deformation experiments carried out on olivine single crystals under synchrotron radiation, together with estimations of lattice friction based on first-principle calculations, show a transition from easy [100] to easy [001] slips as pressure and temperature (thus depth) increases. We input these data at the slip system level into the second-order extension of the self-consistent scheme to assess microstructure evolution along a typical flow pattern beneath an oceanic spreading center Fri, 01 Jan 2010 00:00:00 GMT http://hdl.handle.net/10985/15116 2010-01-01T00:00:00Z CASTELNAU, Olivier CORDIER, Patrick LEBENSON, RA MERKEL, SEBASTIEN RATERRON, PAUL The strongly anisotropic rheology of olivine polycrystals, associated to their microstructure, constitutes a key feature affecting the dynamics of the Earth's upper mantle. High pressure deformation experiments carried out on olivine single crystals under synchrotron radiation, together with estimations of lattice friction based on first-principle calculations, show a transition from easy [100] to easy [001] slips as pressure and temperature (thus depth) increases. We input these data at the slip system level into the second-order extension of the self-consistent scheme to assess microstructure evolution along a typical flow pattern beneath an oceanic spreading center http://hdl.handle.net/10985/19945 Application of electron tomography of dislocations in beam-sensitive quartz to the determination of strain components MUSSI, Alexandre; GALLET, Julien; CASTELNAU, Olivier; CORDIER, Patrick In this study we apply electron tomography of dislocations to quartz with a view to assess whether the von Mises-Taylor criterion is satisfied or violated in a deformed crystal of quartz. We propose a method to perform electron tomography with few projected images which allows extension of this technique to beam-sensitive materials such as quartz. The 3D characterization of the dislocation microstructure allows the evaluation of contributions to dislocation mobility with no ambiguity. From the geometrical characteristics of the dislocations and their Burgers vectors, we show how to identify the non-zero components of the strain tensor. We show that in the quartz grain investigated, the von-Mises-Taylor criterion is satisfied thanks to the climb of 〈c + a〉 dislocations. Fri, 01 Jan 2021 00:00:00 GMT http://hdl.handle.net/10985/19945 2021-01-01T00:00:00Z MUSSI, Alexandre GALLET, Julien CASTELNAU, Olivier CORDIER, Patrick In this study we apply electron tomography of dislocations to quartz with a view to assess whether the von Mises-Taylor criterion is satisfied or violated in a deformed crystal of quartz. We propose a method to perform electron tomography with few projected images which allows extension of this technique to beam-sensitive materials such as quartz. The 3D characterization of the dislocation microstructure allows the evaluation of contributions to dislocation mobility with no ambiguity. From the geometrical characteristics of the dislocations and their Burgers vectors, we show how to identify the non-zero components of the strain tensor. We show that in the quartz grain investigated, the von-Mises-Taylor criterion is satisfied thanks to the climb of 〈c + a〉 dislocations. http://hdl.handle.net/10985/9880 Effective viscoplastic behavior of polycrystalline aggregates lacking four independent slip systems inferred from homogenization methods; application to olivine DETREZ, Fabrice; CASTELNAU, Olivier; CORDIER, Patrick; MERKEL, Sébastien; RATERRON, Paul Polycrystalline aggregates lacking four independent systems for the glide of dislocations can deform in a purely viscoplastic regime only if additional deformation mechanisms (such as grain boundary sliding and diffusion) are activated. We introduce an implementation of the self-consistent scheme in which this additional physical mechanism, considered as a stress relaxation mechanism, is represented by a nonlinear isotropic viscoplastic potential. Several nonlinear extensions of the self-consistent scheme, including the second-order method of Ponte-Castañeda, are used to provide an estimate of the effective viscoplastic behavior of such polycrystals. The implementation of the method includes an approximation of the isotropic potential to ensure convergence of the attractive fixed-point numerical algorithm. The method is then applied to olivine polycrystals, the main constituent of the Earth's upper mantle. Due to the extreme local anisotropy of the local constitutive behavior and the subsequent intraphase stress and strain-rate field heterogeneities, the second-order method is the only extension providing qualitative and quantitative accurate results. The effective viscosity is strongly dependent on the strength of the relaxation mechanism. For olivine, a linear viscous relaxation (e.g. diffusion) could be relevant; in that case, the polycrystal stress sensitivity is reduced compared to that of dislocation glide, and the most active slip system is not necessarily the one with the smallest reference stress due to stress concentrations. This study reveals the significant importance of the strength and stress sensitivity of the additional relaxation mechanism for the rheology and lattice preferred orientation in such highly anisotropic polycrystalline aggregates. Thu, 01 Jan 2015 00:00:00 GMT http://hdl.handle.net/10985/9880 2015-01-01T00:00:00Z DETREZ, Fabrice CASTELNAU, Olivier CORDIER, Patrick MERKEL, Sébastien RATERRON, Paul Polycrystalline aggregates lacking four independent systems for the glide of dislocations can deform in a purely viscoplastic regime only if additional deformation mechanisms (such as grain boundary sliding and diffusion) are activated. We introduce an implementation of the self-consistent scheme in which this additional physical mechanism, considered as a stress relaxation mechanism, is represented by a nonlinear isotropic viscoplastic potential. Several nonlinear extensions of the self-consistent scheme, including the second-order method of Ponte-Castañeda, are used to provide an estimate of the effective viscoplastic behavior of such polycrystals. The implementation of the method includes an approximation of the isotropic potential to ensure convergence of the attractive fixed-point numerical algorithm. The method is then applied to olivine polycrystals, the main constituent of the Earth's upper mantle. Due to the extreme local anisotropy of the local constitutive behavior and the subsequent intraphase stress and strain-rate field heterogeneities, the second-order method is the only extension providing qualitative and quantitative accurate results. The effective viscosity is strongly dependent on the strength of the relaxation mechanism. For olivine, a linear viscous relaxation (e.g. diffusion) could be relevant; in that case, the polycrystal stress sensitivity is reduced compared to that of dislocation glide, and the most active slip system is not necessarily the one with the smallest reference stress due to stress concentrations. This study reveals the significant importance of the strength and stress sensitivity of the additional relaxation mechanism for the rheology and lattice preferred orientation in such highly anisotropic polycrystalline aggregates. http://hdl.handle.net/10985/25489 Evidence of Dislocation Mixed Climb in Quartz From the Main Central and Moine Thrusts: An Electron Tomography Study WEIDNER, Timmo; MUSSI, Alexandre; CASTELNAU, Olivier; KRONENBERG, Andreas; LAW, Richard; CORDIER, Patrick In this study we apply electron tomography to characterize 3D dislocation microstructures in two quartz mylonite specimens from the Moine and Main Central Thrusts, both of which accommodated displacements by dislocation creep in the presence of water. Both specimens show dislocation activity with dislocation densities of the order of 3–4 × 1012 m−2 and evidence of recovery from the presence of subgrain boundaries. ⟨a⟩ slip occurs predominantly on pyramidal and prismatic planes (⟨a⟩ basal glide is not active). [c] Glide is not significant. On the other hand, we observe a very high level of activation of ⟨c + a⟩ glide on the , , (n = 1,2) and even planes. Approximately 60% of all dislocations show evidence of climb with a predominance of mixed climb, a deformation mechanism characterized by dislocations moving in a plane intermediate between the glide and the climb planes. This atypical mode of deformation demonstrates comparable glide and climb efficiency under natural deformation conditions. It promotes dislocation glide in planes not expected for the quartz structure, probably by inhibiting lattice friction. Our quantitative characterization of the microstructure enables us to assess the strain that dislocations can generate. We show that glide systems indicated by the observed dislocations are sufficient to accommodate any arbitrary 3D strain by themselves. Although historically dislocation glide has been regarded as being primarily responsible for producing strain, activation of climb can also directly contribute to the finite strain. On the basis of this characterization, we propose a numerical modeling approach for attempting to characterize the local stress state that gave rise to the observed microstructure. Mon, 01 Jul 2024 00:00:00 GMT http://hdl.handle.net/10985/25489 2024-07-01T00:00:00Z WEIDNER, Timmo MUSSI, Alexandre CASTELNAU, Olivier KRONENBERG, Andreas LAW, Richard CORDIER, Patrick In this study we apply electron tomography to characterize 3D dislocation microstructures in two quartz mylonite specimens from the Moine and Main Central Thrusts, both of which accommodated displacements by dislocation creep in the presence of water. Both specimens show dislocation activity with dislocation densities of the order of 3–4 × 1012 m−2 and evidence of recovery from the presence of subgrain boundaries. ⟨a⟩ slip occurs predominantly on pyramidal and prismatic planes (⟨a⟩ basal glide is not active). [c] Glide is not significant. On the other hand, we observe a very high level of activation of ⟨c + a⟩ glide on the , , (n = 1,2) and even planes. Approximately 60% of all dislocations show evidence of climb with a predominance of mixed climb, a deformation mechanism characterized by dislocations moving in a plane intermediate between the glide and the climb planes. This atypical mode of deformation demonstrates comparable glide and climb efficiency under natural deformation conditions. It promotes dislocation glide in planes not expected for the quartz structure, probably by inhibiting lattice friction. Our quantitative characterization of the microstructure enables us to assess the strain that dislocations can generate. We show that glide systems indicated by the observed dislocations are sufficient to accommodate any arbitrary 3D strain by themselves. Although historically dislocation glide has been regarded as being primarily responsible for producing strain, activation of climb can also directly contribute to the finite strain. On the basis of this characterization, we propose a numerical modeling approach for attempting to characterize the local stress state that gave rise to the observed microstructure.