FROM LOW-TEMPERATURE TO HIGH-TEMPERATURE CONDITIONS: ARE OUR INSIGHTS INTO MINERAL REACTION KINETICS TRANSFERABLE?

During metamorphism and hydrothermal alteration of rocks, mineral reactions in the presence of water occur via dissolution-transport-precipitation mechanisms. Since the 1980's many experimental studies support for this concept. However, direct observations of reacting systems were difficult or impossible since such experiments need to be conducted in autoclaves at elevated temperatures and pressures. At the same time, our theoretical concepts of reaction kinetics at elevated pressure and temperature conditions were embryonic. Therefore, our ability to interpret experimental results was hampered, and our knowledge of metamorphic reaction kinetics remained patchy. More recently, the interest in these questions has been rejuvenated. By revisiting the mechanistic concept, e.g., Putnis (2004) has highlighted the importance of coupled mineral dissolution-precipitation kinetics for important metamorphic systems. However, the experimental challenge to observe the reacting systems directly and quantitatively remains largely unsolved.

In this situation, it becomes an interesting question whether experimental results obtained at lower pressures and temperatures can be transferred to systems reacting at elevated P-T conditions? At temperatures ranging from 10 – 200 C, our recent studies of mineral dissolution and growth kinetics employ a combination of direct observational techniques, for example atomic force microscopy (AFM) and vertical scanning interferometry (VSI), and computer simulations. This research has led to a theoretical model that emphasizes the need to fully incorporate the three-dimensional crystal lattice into a fundamental kinetic model of crystal dissolution (and growth). Such a model can be derived from a stochastic approach that uses parameterized Monte Carlo techniques. Model predictions can then be tested by combining experimental data and field observations. Our discussion will emphasize that such a combination of theoretical, experimental and observational tools applied at a large range of lengths and time scales may be able to shed light on important problems of modern metamorphic petrology.