| Pressure dissolution is a mass transfer process involving dissolution at grain contacts, transport through a fluid phase and reprecipitation in pores. It has a wide and varied effect on rocks through compaction and complex interactions with other deformation mechanisms. Both its pervasive and localized modes are the subject of this dissertation.; The first chapter provides basic constraints on stylolite formation in some limestones, indicating that they are fractal over four orders of magnitude. The fractal dimension and power are constant throughout the stylolite surface and not orientation dependent. The grain size does not register in the analyses, implying that stylolite-generating processes operate similarly below and above the grain size. The geometry of stylolites may depend on the bulk mechanical properties of the host rock more than previously thought.; The second and third chapters present pressure solution experiments of halite indenters loaded against flat silicate plates, and observed in-situ with a confocal microscope. The deformation of the indenters occurs in two stages, the first characterized by contact area reduction and slow convergence rates, and the second by fluctuations in contact area and fast convergence rates. The transition between the two stages occurs at the maximum contact stress, which shortly precedes the maximum convergence rate. Confocal images indicate that the indenter dissolves coaxially during the first stage, producing a decreasing static contact and smooth surfaces. During the second stage, dissolution is highly asymmetric, and the surfaces of the indenter roughen. These observations reflect a system evolving from a far from equilibrium state to a steady state, and controlled by the interaction between strain-energy driven undercutting dissolution and plastic flow. Undercutting dissolution reduces the area of the contact, and preferentially removes regions with high dislocation density, while plastic flow increases the contact area by mobilizing dislocations that strain harden the indenter. The feedback between these two mechanisms drives the system towards a dynamic steady state. During the second stage the contact region is unstable, evolving from a flat, smooth and cone-shaped object into an asymmetric and fractured mesa-like structure, incised by a dynamic network of steep channels. |
