Modeling of Dissolution‐Induced Permeability Evolution of a Granite Fracture Under Crustal Conditions

Abstract

AbstractThis work focuses on the interaction between pressure solution creep and contact area expansion under hydrothermal conditions and proposes an innovative process‐based approach for describing contact area expansion by fracture closure. The formulation is established in the physical context of pressure solution creep and represents the dynamic process of enhanced mineral dissolution over grain contacts, which moves toward equilibrium as a result of decrease of mineral solubility by pressure drop. Then, a theoretical maximum of the contact area ratio Rc,max is obtained from the formulation whose existence demonstrates that pressure solution is with an energy threshold for activation rather than spontaneously taking place under any circumstances. Based upon the formulation, a 1‐D reactive transport model is developed and applied to investigate dissolution‐induced permeability evolution of a granite fracture under crustal conditions. The applicability of the developed model to a polymineralic system is examined against the experimental measurements reported in Yasuhara et al. (2011, https://doi.org/10.1016/j.apgeochem.2011.07.005). This investigation reconfirms the significance of pressure solution creep in fracture permeability evolution under low and moderate temperatures and provides a justified interpretation for the unusual experimental observation that fracture permeability reduction does not necessarily lead to apparent increases of effluent element concentrations. The surface topography of fracture channels markedly affects hydraulic feedback on chemical compaction in terms of both magnitude and rate of change. Temperature elevation contributes to accelerating the progression of pressure solution creep.