Progressive deformation and annealing of quartz inclusion in porphyroblastic feldspar during synmetamorphic non-coaxial deformation

Abstract

A single crystalline inclusion in a single crystalline porphyroblast of metamorphic tectonites is deformed to an ellipsoid. The rate of shape change of ellipsoidal inclusion is controlled by the rounding process driven by reduction of the interfacial free energy and the deformation process of the ellipsoidal inclusion caused by deformation of host porphyroblast during synmetamorphic progressive deformation. In this paper, the model for shape change of inclusion mineral during contemporaneous deformation and annealing is proposed in the two dimensional case. It is concluded that the critical grain size of spherical inclusion is possibly defined in a function of strain rate in this model. The application to the Sambagawa and Ryoke metamorphic rocks clarifies that the strain rate of the former is much higher than that of the latter by two orders of magnitude.