Pressure solution creep has been re

Pressure solution creep has been recognized as a rock deformation mechanism in the geologic literature since its introduction by Henry B.Sorby in the 1860’s [38]. Despite knowledge of the major steps characterizing pressure solution creep and observations of this mechanism in geologic studies, details of it thermodynamics and kinetics are not yet fully understood and have been intensively debated for over a century by geologists, and largely ignored in the field of material science [39]. A detailed discussion of the contending explanations of pressure solution creep is beyond the scope of this paper, but interested readers should refer to a recent comprehensive historical review of the process by Gratier et al. [25] (specifically, section 3.4.). In CSP, the pressure solution creep mechanism occurs due to the application of uniaxial pressure upon a solid in the presence of a fluid in an open system. The process is thus governed by the non-equilibrium thermodynamics of locally-controlled solid-fluid interface-coupled dissolution precipitation mechanisms within confined spaces; but also by the thermodynamics of non-hydrostatically stressed solids, as defined by the Gibbs-Kamb theory [40]. Shimizu showed that hydrostatic pressure does not affect the entire process of dissolution-mass transport-precipitation, therefore excluding it from possible causes of pressure solution creep [39]. The driving force of pressure solution creep is thus not “pressure” [41], but rather the stress gradients in the solids, manifested by the difference in chemical potentials across solid-fluid boundaries [39]. The application of the afore mentioned non-equilibrium thermodynamic principles applied to open systems remains a largely open question, so the extension of such principles in the search of a fundamental understanding of CSP is similarly unresolved. There are also experimental challenges to fundamentally investigate CSP as there is a lack of in situ characterization techniques that can operate under the applied processing conditions. For example, it is only recently that localized solid-fluid interface-coupled dissolution-precipitation reactions have been monitored in situ using atomic force microscopy (AFM) [42,43]. To extend such techniques to CSP, instruments would need to be developed to allow for such measurements under a load with an evaporating solvent.