Kinematics of the Sirjan mylonite nappe, Zagros Orogenic Belt: Insights from strain and vorticity analyses

Abstract

The Sirjan mylonite nappe is part of the HP–LT Sanandaj–Sirjan Metamorphic Belt (Zagros Orogenic Belt, Iran). This nappe was emplaced in a transpressional regime during oblique convergence between the Afro–Arabian Continent and Central Iranian Microcontinent. In order to investigate the type of flow, fabrics from deformed quartz and K-feldspar porphyroclasts were analyzed. Quantitative finite strain (RXZ = 1.9–3.8) and mean kinematic vorticity number (Wm = 0.60–0.85) analyses revealed that both the strain ratio and the simple shear component of deformation increase towards SE along a 2 km long NW–SE-oriented transect. Analysis of quartz and K-feldspar textures suggests shearing at c. 400–650 °C. We also conclude that deformation in the Sirjan mylonite nappe began with nearly pure shear flow but became a more simple-shear flow in character as strain accelerated.