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

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 similar to 220 km thick along both profiles, whereas Eurasian lithosphere is up to similar to 90 km thinner, especially below the Central Iran and Alborz Mountains. 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 similar to 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 harzburgitic-type mantle composition below the ZFTB and imbricated zone.