ALBERT

Description: The study of mantle lithosphere plays a key role to reveal predominant tectonic setting process of a region. The current geological and tectonic setting of Iran is due to the ongoing continental–continental collision of the Arabian and Eurasian plates. We applied a combined P and S receiver function analysis to the teleseismic data of nine permanent broadband seismic stations of the International Institute of Earthquake Engineering and Seismology located in different tectonic zones of Iranian plateau. More than 4 years of data were used to estimate the thickness of the crust and mantle lithosphere. According to our results, the crust is 50 km thick beneath the Zagros fold and thrust belt (ZFTB). We found the maximum Moho depth of approximately 70 km under the Sanandaj-Sirjan zone (SSZ) indicating the overthrusting of the crust of Central Iran onto the Zagros crust along the main Zagros thrust (MZT). Below the northeasternmost part of the Urumieh–Dokhtar Magmatic Arc (UDMA) and Central Iran, the Moho becomes shallower and lies at 40 km depth. Towards northeast, beneath the Alborz zone, the crust is 55 km thick. Based on S receiver functions, we provided new insights into the thickness of the Arabian and Eurasian lithospheres. The location of the boundary between these plates was estimated to be beneath the SSZ, which is slightly shifted northeastward relative to the surficial expression of the MZT. Furthermore, the Arabian plate is characterized by the relatively thick lithosphere of about 130 km beneath the ZFTB reaching 150 km beneath the SSZ, where the thickest crust was also observed. This may imply that the shortening across the Zagros is accommodated by lithospheric thickening. In contrast, UDMA and Central Iran are recognized by the thin lithosphere of about 80– 85 km. This thin lithosphere may be associated with the asthenospheric upwelling caused by either lithospheric delamination or Neo-Tethys slab detachment beneath the Zagros collision zone.

Description: The Alborz Mountains build the northern part of the Alpine–Himalayan orogen in western Asia. They are located south of the Caspian Sea and form an east–west range across the north of Iran. This region is one of the most active tectonic areas, as it undergoes extensive crustal deformation and shortening. In the present work, we used data from 11 permanent stations of the Tehran Telemetry Seismic Network to estimate the thickness of the crust and mantle lithosphere beneath the Central Alborz region by P- and S-receiver function methods. Results of both P and S receiver functions revealed a relatively large crustal thickness beneath this region (∼51–54 km), which can be associated with the shortening process related to the orogenic belt. No remarkable crustal thickening has been detected below the high topography of Central Alborz. A thick crust (∼67.5 km) is observed locally in the region beneath the Damavand volcano, which is possibly related to the magmatic addition at the base of the crust beneath the volcanic region. The S receiver functions exhibit the existence of a seismic discontinuity in the upper mantle at a depth of ∼90 km, which we interpreted as the base of the lithosphere. The missing crustal root and the relatively thin lithosphere beneath the Alborz may imply that sublithospheric mantle could be responsible for and support the elevation of the Alborz.

Description: The Iranian Plateau is characterized by diverse tectonic domains, including the continental collisions (e.g. the Zagros and Alborz Mountains) and oceanic plate subduction (e.g. Makransubduction zone). To derive a detailed image of the crust–mantle (Moho) and lithosphere–asthenosphere (LAB) boundaries in some tectonically units of the Iranian Plateau, we used a large number of S receiver functions obtained from teleseismic events recorded at 68 national permanent stations (19 broadband and 49 short period stations). The S receiver functions clearly imaged the base of the crust and lithosphere and their variations within the different tectonic zones of the Iranian Plateau. Our new seismic images show a significant variation of the lithospheric thickness in the different geological features. The most complex structure was detected beneath the Zagros Mountains where the Arabian Plate is believed to underthrust beneath centralIran. We found the thickest crust under the Sanandaj-Sirjan metamorphic zone (SSZ)which proposes the overthrusting of the crust of central Iran into the Zagros crust along the main Zagros thrust (MZT), in agreement with the results of Paul et al., (2010). Furthermore, our results clearly show a shallow LAB at about 80-90 km depth beneath the Alborz, the central domain (CD) and central Iranian micro plate (CIMP) zones. Based on our results, the Arabian LAB, beneath the Zagros fold and thrust belt (ZFTB), SSZ and the Urumieh-Dokhtar magmatic assemblage (UDMA) is 200 km and may contain a dipping structure at depths ranging from 100 beneath the ZFTBto 150 km beneath the SSZ and the UDMA. This dipping structure interpreted as the presence of remnants of the fossil Neo-Tethys subduction. The location of the boundary between the Arabian and central Iranian lithospheres is beneath the UDMA, which is shifted northeastward relative to the surficial expression of the MZT.

Description: Geographic location of Iran plateau between Arabia and Eurasia plates caused the Iranian plate to be in a high pressure condition. Configuration and tectonic structures procedure in this region is affected by motions of these plates. With respect to this fact that the Iran plateau is in a high pressure situation, it is expected that the main construction of contractions and faults in this region to be reverse or thrust. Kope Dagh region has the same configurations and tectonic structures process. So, this region considered as an active tectonic region. Thus, the study of its crust is essential to locate the future earthquakes. The depth of Moho is an important parameter to characterize the overall structure of a crust and can often be related to geology and tectonic evolution of the region. In this study, we use the teleseismic receiver function technique to determine the crustal thickness and Vp/Vs ratios for 6 stations in Kope Dagh region. The teleseismic receiver function represents the structural response near a recording station to the incoming teleseismic P wave. The first-order information about the crustal structure under a station can be derived from the radial receiver function which is dominated by P-to-S converted energy from a series of velocity discontinuities in the crust and upper mantle. Because of the large velocity contrast at the crust-mantle boundary, the Moho P-to-S conversion is often the largest signal following the direct P. In this work, the teleseismic waves, which had been registered by the 6 stations of the Ghuchan and Mashhad seismic networks have been processed using the P receiver function method to calculate the Moho depth beneath the Kope Dagh region. We used the available short period data. Our results showed a Moho depth of approximately 45 km on average, which varies between 41 and 49 km. These results confirmed the previous results obtained from other studies in this region. We calculated also P and S receiver functions for a single broadband station and compared our results with those obtained from short period stations in Kope Dagh.