Can a Newtonian viscous-matrix model be applied to microboudinage of columnar grains in quartzose tectonites?

A Newtonian viscous rheology was assumed for the matrix around the microboudins of columnar mineral grains in metamorphic tectonites, and a new expression was derived for predicting the proportion of boudinaged grains as a function of the aspect ratio of the columnar grains and the magnitude of far-field differential stress. The predicted proportion was compared with the measured proportions of tourmaline, piemontite and sodic amphibole in seven samples from various orogenic belts. The comparison revealed that the predictions were remarkably different from the measured values. This suggests that the viscous-matrix model cannot be applied to the stress state of the matrix during microboudinage.