Seismological evidence for crustal-scale thrusting in the Zagros mountain belt (Iran)

Abstract

International audienceCrustal receiver functions computed from the records of 45 temporary seismological stations installed on a 620-km long profile across central Zagros provide the first direct evidence for crustal thickening in this mountain belt. Due to a rather short 14-km average station spacing, the migrated section computed from radial receiver functions displays the Moho depth variations across the belt with good spatial resolution. From the coast of the Persian Gulf to 25 km southwest of the Main Zagros Thrust (MZT), the Moho is almost horizontal with slight depth variations around 45 km. Crustal thickness then increases abruptly to a maximum of ~70 km beneath the Sanandaj-Sirjan metamorphic zone, between 50 and 90 km northeast of the surface exposure of the MZT. Further northeast, the Moho depth decreases to ~42 km beneath the Urumieh-Dokhtar magmatic assemblage and the southern part of the Central Iranian micro-continent. The region of thickest crust is located ~75 km to the northeast of the Bouguer anomaly low at –220 mgals. Gravity modelling shows that the measured Moho depth variations can be reconciled with gravity observations by assuming that the crust of Zagros underthrusts the crust of central Iran along the MZT considered as a crustal-scale structure. This hypothesis is compatible with shortening estimates by balanced cross-sections of the Zagros folded belt, as well as with structural and petrological studies of the metamorphic Sanandaj-Sirjan zone

Crustal structure of Northwest Zagros (Kermanshah) and Central Iran (Yazd and Isfahan) using teleseismic Ps converted phases

“…The results of PRF show that the average Moho depth in northwest of Zagros (Kermanshah region) is about 41 km which is in good agreement with the results obtained by PRF modeling (~42.5). Our results also are in accordance with those obtained from other studies in ZFTB (Paul et al, 2006(Paul et al, , 2010. Both RF method and PRF inversion revealed an average thickness of 14km sedimentary layer.…”

“…Results of PRF reveal that in UDMA, average Moho depth is about 47 km but, average Moho depth obtained by PRF modeling is about 43 km. Regarding previous studies in this region (Paul et al, 2006(Paul et al, , 2010, 43 km depth is more acceptable. In SSZ, both of methods show that average Moho depth is 51 km.…”

“…In Isfahan region, the thickest crust was observed beneath the GAR station located on SSZ. Paul et al (2006) proposed that localized thickening beneath the SSZ is resulted from the overthrusting of the crust of Central Iran on the Zagros crust along the MZRF. The thinnest crust of Isfahan region was found beneath the KLH station located in the UDMA.…”

Crustal-scale cross-sections across the NW Zagros belt: implications for the Arabian margin reconstruction

“…A more precise modelling of the Bouguer anomaly data conducted by Snyder & Barazangi (1986) shows a profile near our cross-section with crustal thickening from 40 km beneath the Mesopotamian foreland to ∼ 60 km beneath the Main Zagros Fault. More recently, Paul et al (2006Paul et al ( , 2010 published crustal transects across the Zagros Mountains based on receiver function analysis of teleseismic earthquakes to image the Moho (see location in Fig. 1).…”

Geological evolution of Central Asian Basins and the western Tien Shan Range

“…Kind et al 2002) and the Zagros-Iran (e.g. Paul et al 2006Paul et al , 2010 regions and 3D regional studies (e.g. Zor et al 2003), although less than 19% of the region has crustal thickness data coverage better than one measurement per 50 000 km 2 .…”