Textural patterns at porphyroblast margins and their use in determining the time relations of deformation and crystallization

Summary Textural patterns characteristic of supposed pre-, post- and to a lesser extent syn-tectonic porphyroblasts are reviewed. Difficulties of interpretation arise where anSi(internal schistosity) is absent, andSe(external schistosity) behaviour adjacent to porphyroblast margins is the only available criterion; examples may be found showing truncation ofSeby pre-Seporphyroblasts. Truncation and/or deflection textures are not by themselves sufficient criteria for determining the time relations of particular phases of deformation and crystallization.