Mechanisms of reaction-enhanced deformability in minerals and rocks

Abstract

In naturally deformed rocks, two or more mechanisms probably operated in conjunction to enhance deformability. During dehydration reactions, for example, it is possible that mechanisms operating simultaneously include: 1) diffusion-accomodated grain- boundary sliding of fine-grained reaction products; 2) cataclastic flow due to an elevated pore-fluid pressure; 3) enhancement of grain-boundary diffusion rates due to the presence of water produced by dehydration, and 4) transformation plasticity. In natural examples in which high strain rates developed under conditions of enhanced deformability, the small grain size of the reaction products appears to be an important factor. In such cases, the dominant mechanism may be diffusion creep, possibly with a large contribution from grain-boundary sliding.