Abstract

In order to model the role of gypsum in crustal deformation and in trapping hydrocarbons, a quantitative, mechanism‐based understanding of the deformation and compaction behaviour of gypsum is needed. Previous laboratory experiments indicate that intergranular pressure solution is an important deformation mechanism in gypsum and may be controlled by the kinetics of gypsum precipitation. To examine this further, the growth kinetics of gypsum were investigated using seed crystals and super‐saturated aqueous solutions prepared from natural gypsum powders. The results showed both nucleation and growth dominated behaviour. Results relating purely to seed (over)growth showed that at low driving forces (<1 kJ/mole) precipitation follows a second order growth law, while at larger driving forces the order is 3–4. The growth rates are 1 to 2 orders of magnitude slower than those reported in studies on pure systems. However, pressure‐solution creep rates, predicted by coupling the present growth data with a microphysical model for pressure solution, are 1 to 2 orders of magnitude too fast to be consistent with experimentally obtained creep rates. On the other hand, the predicted and measured creep rates show an almost identical dependence on applied stress and grain size, supporting the hypothesis that pressure‐solution creep in gypsum is controlled by the kinetics of precipitation.

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