THE CHARACTERISTICS OF THREE DIFFERENT SUBDUCTION ZONES IN IRANIAN PLATEAU

Iranian plateau is a tectonically young complex region resulting from collision of Arabian Plate with Eurasia. Existence of three different subduction zones within different geographical parts provides different tectonic and geodynamic characteristics with the plateau. In this study, we use surface wave tomography based on Partitioned Waveform Inversion (PWI) method to image S-velocity structure of upper mantle and Moho depth variations across the Iranian plateau. Of nearly 3000 waveforms originally chosen for analysis, we have fitted 974 waveforms from 47 events and 39 stations which result in 11688 linear constraints on the upper-mantle S-velocity structure and Moho depth for the studied area.

Our S-velocity images show that there is a clear evidence for subducting of Arabian plate beneath central Iran across the Zagros collisional zone in south-west Iran. The oceanic crust of South Caspian Basin is being westward underthrusting under Talesh and Alborz mountains in northern part of Iran. Active subduction still occurs to the southeast of Iran where the oceanic part of Arabian plate is being subducted beneath Makran coast. The slab in western Makran is subducting with a low dip angle of about 7°, increasing to about 55°, where it bends into the asthenosphere beneath volcanic arc.

The resulted Moho map shows significant crustal thickening beneath the SSZ in Zagros region (with maximum depth of 65 km) and also indicates deep root under the quaternary volcanoes which is not observed in CRUST2. Beneath the South Caspian Basin, the crust has a broad arch-like structure, with the crust thinning more rapidly under its western boundary than eastern boundary. According to our results, the transition from thick continental crust of Arabian plate (in Zagros region) to thin oceanic crust of Oman Sea (in Makran region) is marked with clear indication coinciding with Minab Fault.