Lithospheric mantle heterogeneities beneath the Zagros Mountains and the Iranian Plateau: A petrological-geophysical study

© The Authors 2014. Published by Oxford University Press on behalf of the Royal Astronomical Society. We apply a combined geophysical-petrological methodology in order to study the thermal, compositional, density and seismological structure of the crust and upper mantle along two transects across the Arabia-Eurasia collision region. Results on the crustal thickness show minimum values beneath the Arabia Platform and Central Iran (42-43 km), and maximum values beneath the Sanandaj Sirjan zone (SSZ; 55-63 km), in agreement with seismic data. Major discrepancies in Moho depth from those derived from seismic data are locally found in the SSZ (central Zagros) and Alborz Mountains where more moderate crustal thicknesses are modelled. Results on the lithosphere thickness indicate that the Arabian lithosphere is ~220 km thick along both profiles, whereas Eurasian lithosphere is up to ~90 km thinner, especially belowtheCentral Iran and AlborzMountains. The lithosphere-asthenosphere boundary (LAB) shows different geometries between the two transects. In the northern profile (northern Zagros), the LAB rises sharply below the SSZ in a narrow region of ~90 km, whereas in the southern profile (central Zagros), rising occurs in wider region, from the Zagros fold-and-thrust belt (ZFTB) to the SSZ. The best fit of seismic velocities (Vp, Vs) and densities requires lateral changes in the lithospheric mantle composition. Our results are compatible with Proterozoic peridotitic mantle compositions beneath the Arabian Platform, Mesopotamian Foreland Basin and the accreted terrains of Eurasia Plate, and with a more depleted Phanerozoic harzburgitictype mantle composition below the ZFTB and imbricated zone.This study is a contribution of the Group of Dynamics of the Lithosphere (GDL) within the framework of the following projects: ATIZA (CGL2009–09662-BTE), TopoMed/ GASAM (CGL2008–03474-E/BTE/07-TOPO-EUROPE-FP-006), TopoIberia-Consolider Ingenio 2010 (CSD2006–00041), TECLA (CGL2011–26670) and DARIUS Programme and its sponsors.Peer Reviewe

Neotectonic Deformation in Central Eurasia: A Geodynamic Model Approach

Central Eurasia hosts wide orogenic belts of collision between India and Arabia with Eurasia, with diffuse or localized deformation occurring up to hundreds of kilometers from the primary plate boundaries. Although numerous studies have investigated the neotectonic deformation in central Eurasia, most of them have focused on limited segments of the orogenic systems. Here we explore the neotectonic deformation of all of central Eurasia, including both collision zones and the links between them. We use a thin-spherical sheet approach in which lithosphere strength is calculated from lithosphere structure and its thermal regime. We investigate the contributions of variations in lithospheric structure, rheology, boundary conditions, and fault friction coefficients on the predicted velocity and stress fields. Results (deformation pattern, surface velocities, tectonic stresses, and slip rates on faults) are constrained by independent observations of tectonic regime, GPS, and stress data. Our model predictions reproduce the counterclockwise rotation of Arabia and Iran, the westward escape of Anatolia, and the eastward extrusion of the northern Tibetan Plateau. To simulate the observed extensional faults in the Tibetan Plateau, a weaker lithosphere is required, provided by a change in the rheological parameters. The southward movement of the SE Tibetan Plateau can be explained by the combined effects of the Sumatra trench retreat, a thinner lithospheric mantle, and strik-slip faults in the region. This study offers a comprehensive model for regions with little or no data coverage, like the Arabia-India intercollision zone, where the surface velocity is northward showing no deflection related to Arabia and India indentations. ©2017. American Geophysical Union.Funding was granted by the Spanish Government through the project MITE (CGL2014-59516-P) and ALPIMED (PIECSIC-201530E082).Peer reviewe