Impact of metamorphic transformations on the rheology of rocks – METROLOGY

Any mineral association (in an alloy, a battery, or a rock) out of its equilibrium field tends to react to regain stability. The changes in strength, volume and latent heat associated with such a transformation can have a significant impact on the material properties and its mechanical behaviour (i.e. its rheology). In geosciences, only recent studies highlighted the major role of transformations (metamorphic or hydrothermal) on the dynamics of the lithosphere on the short (seismicity) and long term (geodynamics). However, quantifying reaction-induced changes impact on force and energy balance still remains a challenge and requires an adequate modelling tool. The majority of current thermo-mechanical models do not allow to properly consider the transformation processes because they are based on two strong assumptions: (1) they incorporate density changes using the Boussinesq approximation, which denies the feedbacks associated with volume change on the mechanics by ignoring the compressibility of rocks and (2) phase changes are almost never used for determining transient strengths.
The goal of the METROLOGY project is therefore to develop a new generation of thermo-mechanical models that allow to properly incorporate metamorphic reactions (volume changes, rheological changes and latent heat).
These models will be constrained by laboratory experiments performed in a Griggs-type apparatus, which is a powerful tool to study reactive systems under specific selected conditions. The two key reactions in Earth Sciences on which this project will focus are the quartz-coesite reaction and the serpentinization of a peridotite. With this new numerical tool, it will then be possible to elucidate the feedbacks between metamorphic reactions and thermomechanical processes, and to quantify and isolate the mechanisms that really have an impact on the rheology of the rocks during transformation.