Quartz dissolution at mica-quartz interfaces due to surface potential effects

Abstract

Time-dependent compaction creep processes play an important role in compaction behaviour of clastic sediments in subsiding basin settings. We performed dissolution experiments on quartz grains in contact with either quartz (similar surface contact) or in contact with mica (dissimilar surface contact) under different amounts of applied normal stress over the grain contacts, to investigate the effect a dissimilar surface has on the dissolution velocity under in-situ stresses. We qualitatively compared dissolution under different stresses and with varying concentrations of dissolved Calcium (Ca2+ cations). The surfaces of these grains were imaged using an atomic force microscope (AFM) to visualize the dissolution features (e.g. etch pits) and measure the depth of these features to approximate dissolution rates. The experiments were inconclusive in showing quantitative results for the dissolution rates, but showed qualitative results on the grain contacts in the form of dissolution features after the month long duration of the experiment that were not present on the grain contacts before the experiments started. The theoretical model contains both the effects from grain contact stress and the effect of dissimilar mineral surfaces on dissolution velocities. The dissolution velocity increases both with the difference in surface potential between the surfaces and an increased stress across the grain boundary. The lower the effective surface potential of the dissimilar surface in contact with the quartz grain is, the higher the dissolution velocity will be. Resulting in a factor ~2 increase in dissolution velocity for a quartz-mica contact compared to a quartz-quartz contact.