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 LutBlock, in Central Iran. Cordierite porphyroblasts are common in the southern pelitic sediments, but are rare in the northern psammiticrocks, in the contact aureole. Deformation fabrics in the contact aureole are well-preserved within the cordierite porphyroblasts. Therelation of the cordierite porphyroblasts and deformation fabrics indicate that the time of growth has started and is synchronous withthe first deformation phase and ends after the second deformation stage. The porphyroblasts are also generated in syn-intrusion ductileshear zones existing in the contact aureole and continue inside the Shah-Kuh granitoid. Shear zones in the contact aureole containdeformed cordierite porphyroblasts, with microstructures indicating clear shear sense. Structural analysis of various metamorphic rocksin the contact aureole of the Shah-kuh granitoid indicates a first stage, which is tight to the isoclinal folds, with well-developed axialplanefoliation, and a second stage of crenulation cleavage. Sequential growth of cordierite porphyroblasts preserved fabric fromvarious stages of a progressive deformation in the granite contact aureole. It is concluded that the Shah-Kuh granitoid has intrusionssynchronous with progressive deformation, cordierite porphyroblasts growth, and shear zone development in the contact aureole of thegranitoid.