Mechanisms of rock weakening in continental crust: the effects of chemical interactions between phases – WEAKSTROCK

Earth surface dynamics is governed by the relative displacement of the tectonic plates. Deformation is mainly localized at plate boundaries, in zones of strain localization called shear zones, mechanically weaker than plate interiors -although generally composed of the same material. The goal of WEAKSTROCK is to unravel the processes of mechanical weakening in shear zones of the continental crust. In these shear zones, phyllosilicates as micas are systematically observed but the rheology of mica-bearing systems is largely unconstrained. Classical mechanical models describe the rheological behaviour of two-phase assemblages by averaging the rheology of pure mineral phases. However, our recent deformation experiments on quartz-mica (phlogopite) assemblages show that the behaviour of the two-phase assemblage is far more complex and weakening is controlled by unexpected, additional deformation processes activated through the chemical interactions between minerals. Starting from quartz-mica assemblages used as simplified analogues of continental crustal rocks, WEAKSTROCK aims to revise rheology for crustal rocks from a view where weakening and deformation processes are dominated by plasticity to a view where they are dominated by chemical interactions among solid phases and solids and fluids at grain boundaries.