Spatial extent of intermediate-time scale vertical tectonic motions across the eastern Zagros, Iran

English Abstract:

The Zagros fold belt of Iran marks the present southern front of the broad Arabia-Eurasia collision zone. GPS and seismicity show the Zagros absorbs an important part of the overall convergence. Our study area covers south-eastern Zagros, where the continental collision (the Zagros) switches to the oceanic subduction (the Makran wedge). We have mapped deformed fluvial terraces along the Kol River using kinematic GPS and high-resolution imagery in order to unravel the spatial extent of vertical displacements and to analyze active deformation and its implications for seismicity. The Kol River intersects a few active folds and faults, as well as Mountain Front Fault (MFF) and High Zagros Fault (HZF). The long profile of the river shows two different spatial extent of vertical incision, 1) short-wavelength incision (d_s), controlled by structural reactivation of pre-existing structures and lateral folds propagation (plunge panel growth), and 2) long-wavelength incision (d_n) toward the entire course of the river (toward the HZF). We attribute both distribution patterns of vertical incision to reflect differential rock uplift along the river. The d_s and d_n are respectively consistent and inconsistent with the GPS strain distribution and the seismicity pattern. We suggest a young scenario of geologic strain accommodation over the active ramp of the MFF. On the other side, we estimate limited slip for the HZF, consistence with the current hypothesis about uplift propagation across the Zagros belt and through time toward the foreland. Cosmogenic nuclide exposure ages of the Kol River strath terraces (in process) improve understanding of recent crustal deformation rates and its variations through time and space across and eastern Zagros. Such information helps to provides more reliable estimates of seismic hazard for the Zagros, amongst the world's most seismically active mountain ranges.