Kinematic evidence for cordierite porphyroblast growth in a contact aureole during progressive deformation; Shah-Kuh granitoid, NE Lut Block, Iran

The Shah-Kuh granitoid has intruded in the Triassic–Jurassic, pelitic and psammitic low-grade metamorphic rocks of the NE Lut Block, in Central Iran. Cordierite porphyroblasts are common in the southern pelitic sediments, but are rare in the northern psammitic rocks, in the contact aureole. Deformation fabrics in the contact aureole are well-preserved within the cordierite porphyroblasts. The relation of the cordierite porphyroblasts and deformation fabrics indicate that the time of growth has started and is synchronous with the first deformation phase and ends after the second deformation stage. The porphyroblasts are also generated in syn-intrusion ductile shear zones existing in the contact aureole and continue inside the Shah-Kuh granitoid. Shear zones in the contact aureole contain deformed cordierite porphyroblasts, with microstructures indicating clear shear sense. Structural analysis of various metamorphic rocks in the contact aureole of the Shah-kuh granitoid indicates a first stage, which is tight to the isoclinal folds, with well-developed axial-plane foliation, and a second stage of crenulation cleavage. Sequential growth of cordierite porphyroblasts preserved fabric from various stages of a progressive deformation in the granite contact aureole. It is concluded that the Shah-Kuh granitoid has intrusions synchronous with progressive deformation, cordierite porphyroblasts growth, and shear zone development in the contact aureole of the granitoid.