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

Abstract

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