Thermodynamics of continental deformation

Abstract

Plate tectonics theory postulates the existence of rigid mobile plates. However, what defines and controls their internal deformation, particularly within continents, is not yet fully understood. Using data-driven thermomechanical modelling of the Alpine Himalayan Collision Zone, we hypothesize that deviations from an equilibrium between mantle dynamics, plate-boundary forces, and thermochemical configuration of the lithosphere controls continental deformation. We quantify such balance between the internal energy of the plate and tectonic forces in terms of a critical crustal thickness, that match the global average of present-day continental crust. It follows that thicker intraplate domains than the critical crust (orogens) must undergo weakening due to their increased internal energy, and, in doing so, they dissipate the acquired energy within a diffused zone of deformation, unlike the localized deformation seen along plate boundaries. This evolution is controlled by a dissipative thermodynamic feedback loop between thermal and mechanical relaxation of the driving energy in the orogenic lithosphere. Exponentially growing energy states, leading to runaway extension are efficiently dampened by enhanced dissipation from radioactive heat sources. This ultimately drives orogens with their thickened radiogenic crust towards a final equilibrium state. Our results suggest a genetic link between the thermochemical state of crust and the tectonic evolution of silicate Earth-like planets.