INFLUENCE OF INHERITED STRUCTURES AND SHALLOW VISCOUS DEFORMATION IN MORPHOLOGY AND DECOUPLING IN THE ZAGROS, IRAN

The Zagros fold belt results from the collision of the Arabian plate with the central Iran micro-continent. According to seismicity, recent GPS data and geomorphology, present-day convergence across the Zagros is concentrated in the Simply Folded Zone. The kinematic markers and long profiles helped us to image the spatial pattern of deformation In SE Zagros. The precise locations and elevations of the kinematic markers along the river were measured using GPS-RTK. Uplift of the Pleistocene surfaces along the Shour and the Kol Rivers, where the rivers cut the produced synclinal pop-ups, show evidence of superficial ductile deformation that seems commonly results in near-continuous strain and interlayer slow slip. The Anveh syncline is one of typical structure that developed above a décollement level in the anhydrite and marl rich intervals of Mishan Formation and Gachsaran evaporates. These ductile units have partially decoupled deformation within Neogene-Quaternary sediments from the underlying sedimentary units (>4 km). It suggests that have permitted the re-activation of pre-existing synclinal structures, through upward extrusion of the core of the syncline. Abrupt frontal limbs of the syncline (35±3 m) suggests at depth faulting or possibly ductile flow but within a narrow low viscosity layer in the Mishan Formation. Surface deformation and the damming of the Shour River by the up-thrown hangingwall mimics those produced by kink-like fold structure or fault propagation fold deformation in Northern flank of the syncline, above a flat-ramp system at depth (3-4 km). According to radar interferometry data interpretation, the 2005 Fin earthquake (Mw=5.9, ~8 km Centroid depth) below the synclinal structure caused a maximum of about 5.12 cm of uplift. Comparison earthquake uplift and deformed river terraces (vd_max=72 m) along the synclinal structure show ~1 km shifting between peak of elevation changes of co-seismic displacement and terrace height seems due to the decoupling process. It suggests that the role of the inherited synclinal structures and viscous deformation within the upper detachment levels play an important role to accommodate superficial aseismic forward movements with various rates of deformation.