Abstract
The viscoplastic behavior of polycrystalline Mg$_2$SiO$_4$ wadsleyite aggregates, a major high pressure phase of the mantle transition zone of the Earth (depth range: 410 -- 520 km), is obtained by properly bridging several scale transition models. At the very fine nanometric scale corresponding to the disloca-tion core structure, the behavior of thermally activated plastic slip is modeled for strain-rates relevant for laboratory experimental conditions, at high pressure and for a wide range of temperatures, based on the Peierls-Nabarro-Galerkin model. Corresponding single slip reference resolved shear stresses and associated constitutive equations are deduced from Orowan's equation in order to describe the average viscoplastic behavior at the grain scale, for the easiest slip systems. These data have been implemented in two grain-polycrystal scale transition models, a mean-field one (the recent Fully-Optimized Second-Order Viscoplastic Self-Consistent scheme of [44]) allowing rapid evaluation of the effective viscosity of polycrystalline aggregates , and a full-field (FFT based [45] [33]) method allowing investigating stress and strain-rate localization in typical microstructures and heterogeneous activation of slip systems within grains. Calculations have been performed at pressure and temperatures relevant for in-situ conditions. Results are in very good agreement with available mechanical tests conducted at strain-rates typical for laboratory experiments.
Highlights
The flow of rocks in the Earth’s mantle controls many large-scale geodynamic processes
The dislocation resistance to shear has been computed relying on generalized stacking faults energies incorporation the strong influence of pressure on atomic bonding, combined with Peierls–Nabarro approach
The constitutive equation of a slip system involving these dislocations is obtained from the Orowan equation
Summary
The flow of rocks in the Earth’s mantle controls many large-scale geodynamic processes. The computational approach is an alternative to infer the viscoplastic behavior of mantle rocks and offers the potentiality to tackle the extremely low strain-rate conditions issue, provided all relevant and physical-based deformation mechanisms at play in the mantle are properly taken into account. This requires bridging several characteristic length scales, from sub-nanometer to sub-meter. Core structures of dislocations belonging to given slip systems can be calculated using the Peierls–Nabarro–Galerkin method [4], relying on first principle simulations of generalized stacking fault (GSF) surfaces This allows addressing accurately the effect of pressure on atomic bonding.
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call