The thermodynamics of deformed metamorphic rocks: A review

► Generalised Thermodynamics unifies processes operating during deformation and metamorphism. ► The unifying principle is: dissipative processes are coupled by the second law of thermodynamics. ► Deformation-metamorphic processes are described by reaction diffusion deformation equations. ► Structures form to minimise the (non-convex) Helmholtz energy and are critical phenomena. ► Localised folds are the norm in deformed rocks and also form to minimise the Helmholtz energy.