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[SCG62-04] Coupled effect of grain-size evolution and phase mixing: A two phase model for the ductile deformation of rocks.
Keywords:Ductile deformation, Numerical model, Earth crust, Phases mixing
To address this question, we built a model for ductile rocks deformation based on the two-phase damage theory of Bercovici & Ricard 2012. We aim to investigate the role of grain-size reduction but also phase mixing on strain localization. Instead of considering a Zener-pining effect on damage evolution, we propose to take into account the effect of the grain-boundary sliding (GBS)-induced nucleation mechanism which is better supported by experimental or natural observations (Precigout et al 2016).
This continuum theory allows to represent a two mineral phases aggregate with explicit log-normal grain-size distribution as a reasonable approximation for polymineralic rocks. Quantifying microscopic variables using a statistical approach may allow for calibration at small (experimental) scale. We use the interface density as a measure of mixture quality, and propose that its evolution is controlled by the dominant deformation mechanism. Based on the microscopic set of equations derived from these hypothesis, we compute grain-size dependent viscosity fields for a 2D creep flow model using anorthite/pyroxene gabbroic composition. The influence of initial parameters such as grain-size variability, phase proportions and strain-rate field on the occurrence and importance of strain-localization is then discussed.
Bercovici D, Ricard Y (2012) Mechanisms for the generation of plate tectonics by two phase grain damage and pinning. Physics of the Earth and Planetary Interiors 202-203:27–55
Precigout J, Stunitz H (2016) Evidence of phase nucleation during olivine diffusion creep: A new perspective for mantle strain localisation. Earth and Planetary Science Letters 405:94-105