Texture Characterization of a Porphyroblastic Pyrope

Two pyrope megablasts have been extracted from the very-high-pressure Brossasco-Isasca Unit in the Southern Dora-Maira massif (Italy). They underwent a complex polyphasic metamorphism that should have caused a recrystallization or a deformation structure. Since pyrope is optically isotropic, it is impossible to evaluate the deformation using a petrologic microscope. For this reason the X-ray texture characterization was carried out. After a first indexing based on the crystal morphology, sections of the sample were cut parallel to (100) and (110) and were analyzed by XRD. The analysis of the pole figures obtained confirms the morphological characterization, thus excluding the pseudomorphic recrystallization of the pyrope. In spite of the complex metamorphic genesis and possible deformation, the degree of internal misfit is very low. For each section the texture analysis was carried out on different areas, a few centimeters apart, obtaining the same pole figures. The subgrain structure was analyzed from the measured pole broadening using a perfect crystal to determine the instrumental width.