Constraining Earth's Upper-Mantle Plasticity

Paul Raterron, UMET (CNRS 8702), Université Lille 1, France

Upper-mantle dynamics is not well understood because:
i) pressure (P) reaches 14 GPa in the upper mantle and until recent years deformation experiments were limited to low P<3 GPa.
ii) Recent high-P reports show an unexpected effect of P on olivine rheology.
iii) Data refinement and extrapolation to natural (low) stress requires an approach coupling experimental data with aggregate mean-field homogenization modeling.

In order to better constrain Earth’s mantle plasticity, a series of experiments have been carried out on single crystals in the Deformation-DIA apparatus (D-DIA) at the X17B2 beamline (NSLS), at mantle pressure and temperature (typically up to 12 GPa and 1400°C, respectively). Oriented single crystals allow activating specific dislocation slip systems during deformation, which activities can then be isolated and quantified. A dislocation slip transition with increasing P has been observed - from a dominant [100] dislocation slip to a dominant [001] slip (Raterron et al., 2009). This transition, which occurs in experiments at 7-8 GPa and may occur in nature at lower P, may be responsible for the seismic velocity anisotropy attenuation observed in the Earth’s mantle from 200-km depth. This study opens the way to a thorough understanding of mantle plasticity, and more generally of aggregate plasticity, taking into account all available information on crystal plasticity integrated at all scales in a global modeling (Figure).

This research was partially supported by COMPRES, EAR 10-43050

Castelnau, O., Cordier, P., Lebensohn, R. A., Merkel, S., Raterron, P. (2010) Microstructures and rheology of the Earth upper mantle inferred from a multiscale approach, Comptes  Rendus de l’Accadémie des Sciences (Physique), 11, 304-315.

Raterron, P., Amiguet, E., Chen, J., Li, L., Cordier, P. (2009) Experimental deformation of olivine single crystals at mantle pressures and temperatures, Physics of the Earth and Planetary Interiors, 172, 74-83.

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