Seminar of Mathieu Soret

Deep crustal shear zones, fundamental to the dynamics of terrestrial plate tectonics, exhibit complex processes of initiation and evolution that are yet to be comprehensively quantified across both long and short temporal scales. Conventionally, thermo–mechanical models posit that crustal rock behaviour is dominated by a few monomineralic aggregates undergoing processes like intracrystalline plastic deformation by dislocation creep. However, high-pressure and temperature conditions in crustal rocks render minerals extremely strong mechanical properties, challenging strain localization theories. Drawing on groundbreaking deformation experiments performed at eclogite-facies, our research reveals that strain is efficiently localized through dissolution–precipitation creep, operating at notably lower stresses than dislocation creep. Strain accommodation and mass transfer are further accelerated by dynamic permeability resulting from grain boundary movements, fracturing and densification reactions, facilitating dilatancy and enhancing fluid flow within reacting shear zones. Our results illuminate the interconnected thermo–hydro–mechanical–chemical processes underpinning crustal shear zone development, regardless of the mineral aggregate plastic strength. We advocate that the inception and progression of subduction plate interfaces beyond the seismogenic zone are predominantly steered by local transient changes of rheology, rooted in the chemical disequilibrium and fluid concentration of the slab materials, including sediments and mafic to ultramafic compositions.