Dextral transpression in Late Cretaceous continental collision, Sanandaj–Sirjan Zone, western Iran

Abstract

The Sanandaj–Sirjan Zone of western Iran is a metamorphic belt (greenschist–amphibolite) that was uplifted during Late Cretaceous continental collision between the Afro-Arabian continent and the Iranian microcontinent. In the June area, 300 km southwest of Tehran, the Late Palaeozoic–Mesozoic succession was affected by two major episodes of deformation. The first deformation formed tight folds and axial plane schistosity. These are strongly overprinted by second deformation structures that formed during Late Cretaceous continental collision under dextral transpression. The convergence has a low obliquity and has significant deformation partitioning into two domains. (1) A widespread schist and marble domain with intensely folded and foliated rocks that are cut by thrusts and have an overall south-southwest vergence. (2) A domain with wide zones of mylonitic granite, amphibolite and less common calcite mylonite that are affected by a foliation with the same orientation as in rocks of the schist and marble domain. Rocks of this domain also contain an intense sub-horizontal stretching lineation and abundant shear-sense criteria indicating dextral shear. This contrasts with many zones of transpression where strike-slip shearing is taken up along discrete faults. A syn- D 2 pluton (the Galeh–Doz pluton) has a major S-shaped bend within it, imparted during the dextral transpression.