The Zagros core: Deformation of the continental lithospheric mantle

Abstract

[1] The Zagros of Iran form one of the youngest collisional orogenic belts on Earth. At shallow depths, shortening across the Zagros is accommodated by folding in the sediments, high-angle thrust faulting in the basement and thickening of the lower crust, but how shortening is accommodated by the lithospheric mantle has been uncertain largely because the upper mantle seismic structure has been poorly known. We map the lateral variations in upper mantle shear wave speed beneath this region using a large, multimode surface wave data set. The upper mantle is slow for most of the Middle East, but a high shear wave speed lid extending to $225 km depth exists beneath the Zagros. We use a T(V s , z) relation to convert the shear wave speed profiles to temperature profiles and fit these with geotherms to identify the base of the lithosphere. The upper mantle temperatures from the seismic model are consistent with temperatures derived from geochemical modeling. The lithosphere is less than $120 km thick over the region except for a thick lithospheric root beneath the Zagros, implying that shortening in the mantle is accommodated by lithospheric thickening. The composition of the volcanic rocks from above the area of the thickened lithosphere has depleted magma source regions with densities $60 kg m À3 less than the MORB source. Elsewhere in the Middle East the volcanic source regions have compositions and densities similar to that of MORB. The shortening across the Zagros is accommodated by lithospheric thickening but the cool thickened lithosphere has been stabilized from delamination by depletion.Components: 6600 words, 8 figures.

Petrogenesis of mafic collision zone magmatism: The Armenian sector of the Turkish–Iranian Plateau

“…1) may be a realistic model for magmatism in NW Iran and parts of Eastern Anatolia during the Middle-Late Miocene (~15-10 Ma) (e.g. Pang et al, 2013), but it does not obviously apply to regions overlying the~100-225 km thick lithosphere of the Zagros Mountains (Priestley et al, 2012), or to parts of the plateau hundreds of km from the suture (Fig. 1).…”

Flexural bending of the Zagros foreland basin

“…Additional loads, potentially correlated with topography, could be due to inhomogeneities of crustal density, possibly due to the thermal structure of the range and metamorphic reactions associated with underthrusting and exhumation of Arabian crust. It could also account for the possible effect of the lithospheric core imaged by Priestley et al (2012) . N i is the number of data belonging to the ith data set, and δ 2 i is the variance associated with the measurements of the ith data set.…”

“…From surface wave tomography, Priestley et al (2012) imaged a thickened lithosphere that coincides clearly with the high topography and the thickened crust of the Zagros (Paul et al 2010;Manaman et al 2011;Fig. 2).…”

“…However, it has been suggested that the equivalent elastic thickness, T e , derived from gravity data using such a spectral method could be overestimated in areas of low topography and that an admittance technique would be more reliable. It also avoids the possible bias introduced in case of correlated (Priestley et al 2012). Colour shading shows Moho depth obtained by combining results from regional body-wave seismological investigations by Grad et al (2009), Manaman et al (2011 and Mechie et al (2013).…”

Small-volume melts of lithospheric mantle during continental collision: Late Cenozoic lavas of Mahabad, NW Iran

“…The breakdown of hydrous phases was one of the many possibilities considered, and 17 ultimately dismissed, by Pearce et al (1990) The significance is uncertain, but we note that the Mahabad magmatism also occurs 14 above a region with a pronounced lithospheric thickness gradient (Priestley et al, 2012 early models such as those of Defant and Drummond (1990) and Peacock et al (1994).…”