Constraining transformation weakening in plagioclase-pyroxene mixtures

International audienceMafic rocks are a key constituent of the oceanic and lower continental crust. Strain localisation and fabric development in these rocks is controlled by the active deformation mechanisms. From studies of natural rocks it has been established that strain localisation and weakening in mafic rocks is directly related to fluid availability and resultant mineral reactions. Understanding the interplay between reactions, fluid availability, and deformation aids in quantifying the stresses and rates of deformation processes. We have conducted an experimental investigation to constrain the weakening mechanisms in gabbro. Shear experiments were performed in a Griggs-type apparatus at 800-900°C, and 1.2-1.5 GPa with a shear strain rate of 10 ⁵s 1. The starting material consists of mixed powders with