Seismic Anisotropy and Its Geodynamic Implications in Iran, the Easternmost Part of the Tethyan Belt

Amir Sadeghi-Bagherabadi, Lucia Margheriti, Abdelkrim Aoudia, Farhad Sobouti
2018 Tectonics  
In this study, we use the results of seismic anisotropy as inferred from shear wave splitting analyses of SKS phases to propose a geodynamical model of the Arabia-Eurasia collision zone. A detailed analysis of the 202 non-null splitting and 196 null splitting measurements obtained from a dense temporary network are utilized to investigate the possibility of lateral and vertical variations in the anisotropic parameters and the hypothesis of a dipping anisotropic layer. A 2-D geodynamical model
more » ... the western part of the collision zone is constructed. The preferred 2-D model suggests that the belt-parallel orientation of fast axes in the western Zagros originates from a lithospheric transpressional deformation. The plate motionparallel pattern in central Iran and western Alborz coincides with the decrease in the lithospheric thickness. Thus, we believe this trend has its origin in the asthenosphere. A combination of the keel effect of the thickened Zagros lithosphere, the asthenospheric edge-driven convection flow and the lithospheric deformation in the shear zones can cause the NW-SE-oriented splitting pattern reported in some parts of central Iran. The asthenospheric flow beneath the thinner lithosphere to the south of the Bitlis suture in northern Iraq is likely the causative mechanism for our observed plate motion-parallel splittings there. The variation of the convergence obliquity along the Alborz and Zagros inferred from analysis of geodetic data implies that a change in the pattern of lithospheric deformation and the consequent anisotropy is expected. The subduction of the Paleo-Tethys and the Neo-Tethys ocean basins under Eurasia and the subsequent collision of Arabia with Eurasia over a very long geological time span have resulted in the formation of a geodynamic assemblage in the Iran region composed of the Zagros, Alborz and Kopet Dagh fold-and-thrust belts, the Sanandaj-Sirjan Zone (SSZ) and the Urmieh Dhokhtar Magmatic Arc (UDMA), and the central and eastern Iran microcontinental blocks (Figure 1) . The Zagros collision started in the Oligocene. It first affected the SSZ and progressively moved south to the High Zagros during the Miocene, and since the Pliocene it has reached its peak in the fold-and-thrust belt (Agard et al., 2011; Alavi, 1994; Mouthereau et al., 2012) . The SSZ and UDMA Neo-Tethyan volcanic arc structures developed during the Mesozoic and the Cenozoic, respectively, as the dynamics of the subduction zone changed during the course of time (Agard et al., 2011) . The Arabia-Eurasia collision zone is a natural laboratory for the study of the geodynamics of the continental collision and lithospheric/asthenospheric deformation during the early stages of mountain building.
doi:10.1029/2018tc005209 fatcat:aidcd2ouorgipcypzgclwngcqi