JCJC - Jeunes chercheuses & jeunes chercheurs

Dislocations under Pressure – DiUP

Submission summary

This project is focused on the study of dislocations in deep Earth minerals. Dislocations are at the core of plastic behavior in crystals, development of lattice preferred orientations and anisotropy in deformed polycrystals. Until now, no technique could be used to study them directly in high pressure minerals. Here, we will apply both numerical models and new experimental techniques based on peak profile analysis to directly characterize the properties of dislocations in deep Earth minerals. Understanding the plastic behaviour of deep Earth materials is critical as it is one of the main parameters in geodynamical models. Moreover, plastic flow of materials, and particularly plastic flow involving dislocations, transforms the mantle and inner core into an elastically anisotropic medium. This anisotropy can be observed using seismological techniques. It is our main probe to investigate directly the movements of matter in the solid part of the deep Earth. From a mineral physics point of view, mechanical properties are complex and inherently multi-scale. At the atomistic level, plasticity involves the mobility and interaction of defects. At the mesoscale, the single crystal, the deformation process is controlled by the various interactions of gliding dislocations. At the macroscopic scale, the polycrystal, deformation can be evaluated through the grain boundary interactions and empirical constitutive laws for single grain plasticity. Studies of dislocations in upper mantle minerals have seen tremendous progress with the use of deformation apparatus and imagery techniques such as electron microscopy. However, there are limitations and, in particular, those analytical tools can not be used to study dislocations in deep Earth minerals that can not be quenched and prepared for microscopy. The new experimental technique we want to use is based on contrast factors obtained from peak profile analysis in microdiffraction. It can used for a direct characterization of dislocations using x-ray diffraction. However, the use of this technique remains confidential and it has not been applied to in-situ analysis. We plan to extend the use of this method to high pressure diamond anvil cell in-situ experiments and study the evolution of dislocations properties and densities with deformation in various deep Earth materials such as siliate perovskite, post-perovskite, magnesiowustite, stishovite, and hcp-iron. From a theoretical point of view, we will derive information on defect mobility with an atomistic description of the dislocation core using either ab-intio modelisation or empirical potential simulations. Plasticity at the mesoscale will be simulated with the help of dislocations dynamics simulations, while the aggregates behaviour will be treated with more standard finite element or visco-plastic self-consistent simulation. With this project, we plan to offer a new and complete method to describe an model dislocations and anisotropy in deep Earth minerals. Those results are crucial to study the development of seismic anisotropy in the deeper layers of the Earth.

Project coordination

Sébastien MERKEL (Organisme de recherche)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

Help of the ANR 200,000 euros
Beginning and duration of the scientific project: - 48 Months

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