Seismic anisotropy in the crust and upper mantle of the Central Alborz Region, Iran

Sadidkhouy, A.; Doloei, Gholam Javan; Siahkoohi, Hamid Reza

doi:10.1016/j.tecto.2008.05.001

Cited by 24 publications

(18 citation statements)

References 35 publications

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“…In the Alborz, plate motion-parallel (NE-SW) fast axes were observed by Sadeghi-Bagherabadi et al (2018) and Sadidkhouy et al (2008). The same pattern has been reported by Arvin et al (2014) in NW Iran and by Moradi et al (2015) in western Alborz.…”

Section: The Alborzsupporting

confidence: 84%

“…Yellow line is the smoothed Alborz trend estimated from free‐air gravity anomaly, and red line shows a second‐order polynomial fitted to this trend. Blue, magenta, and black markers are the splitting results of Sadeghi‐Bagherabadi et al (), Kaviani et al (), and Sadidkhouy et al (), respectively. Green bars illustrate the Pn anisotropy measurements (Lü et al, ).…”

Section: Discussionmentioning

confidence: 99%

“…By combining the results of our analysis with the current state of knowledge of the geometry and deep structure of the lithosphere and the upper mantle of Iran, we aim to develop a model that can improve our understanding of the geodynamic evolution of the Arabia-Eurasia convergence zone. Sandvol et al (2003) in eastern Turkey, Kaviani et al (2009), andSadidkhouy et al (2008) (2018). Green bars illustrate the Pn anisotropy measurements (Lü et al, 2017), and red lines mark the outcrop regions of the major volcanic and intrusive rocks.…”

Section: Supporting Informationmentioning

confidence: 99%

“…Sadeghi‐Bagherabadi et al () reported non‐null station average measurements with fast axes subparallel to the trend of the mountain range in the Zagros (NW‐SE; Figure ). In the Alborz they obtained NE‐SW directed fast axes at a sharp angle to the strike of the mountains there, in accordance with the works of Sadidkhouy et al (), Arvin et al (), and Moradi et al (). Sadeghi‐Bagherabadi et al () proposed that both the lithospheric and the asthenospheric mantle contribute to the SKS splitting observations in Iran and the relative contribution of each layer in a given region is determined by the thickness of the lithosphere.…”

Section: Introductionmentioning

confidence: 99%

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Seismic Anisotropy and Its Geodynamic Implications in Iran, the Easternmost Part of the Tethyan Belt

et al. 2018

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In this study, we use the results of seismic anisotropy as inferred from shear wave splitting analyses of SKS phases to propose a geodynamical model of the Arabia‐Eurasia collision zone. A detailed analysis of the 202 non‐null splitting and 196 null splitting measurements obtained from a dense temporary network are utilized to investigate the possibility of lateral and vertical variations in the anisotropic parameters and the hypothesis of a dipping anisotropic layer. A 2‐D geodynamical model of the western part of the collision zone is constructed. The preferred 2‐D model suggests that the belt‐parallel orientation of fast axes in the western Zagros originates from a lithospheric transpressional deformation. The plate motion‐parallel pattern in central Iran and western Alborz coincides with the decrease in the lithospheric thickness. Thus, we believe this trend has its origin in the asthenosphere. A combination of the keel effect of the thickened Zagros lithosphere, the asthenospheric edge‐driven convection flow and the lithospheric deformation in the shear zones can cause the NW‐SE‐oriented splitting pattern reported in some parts of central Iran. The asthenospheric flow beneath the thinner lithosphere to the south of the Bitlis suture in northern Iraq is likely the causative mechanism for our observed plate motion‐parallel splittings there. The variation of the convergence obliquity along the Alborz and Zagros inferred from analysis of geodetic data implies that a change in the pattern of lithospheric deformation and the consequent anisotropy is expected.

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Section: The Alborzsupporting

confidence: 84%

Section: Discussionmentioning

confidence: 99%

Section: Supporting Informationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Seismic Anisotropy and Its Geodynamic Implications in Iran, the Easternmost Part of the Tethyan Belt

et al. 2018

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“…They contended that the complex and variable pattern of fast polarization directions (FPD) under central Iran could reflect a small-scale organization of the mantle flow field under a lithosphere with a significant thickness gradient. Also, Sadidkhouy et al (2008) observed fast SKS directions in northern Iran that were subparallel to the APM vector, suggesting an asthenospheric origin for the observed anisotropy. Also, on the Anatolian side of the Turkish-Iranian plateau, SK(K)S studies (Sandvol et al 2003;Paul et al 2014;Confal et al 2016Confal et al , 2018 show a dominant NE-SW oriented FPDs, with almost no abrupt changes in directions across the main tectonic boundaries.…”

Section: R E G I O N a L T E C T O N I C S E T T I N G A N D P R E V I O U S A N I S O T Ro P Y S T U D I E Smentioning

confidence: 79%

Seismic anisotropy and mantle deformation in NW Iran inferred from splitting measurements of SK(K)S and direct S phases

Arvin

Sobouti

Ghods

et al. 2021

Geophysical Journal International

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Summary We present the results of a shear wave splitting analysis performed on the teleseismic SK(K)S and direct S wave recordings of 68 temporary broadband stations to investigate the mantle deformation on the northern side of the Arabia-Eurasia collision zone in NW Iran. We used the Reference Station Technique to overcome potential contamination from the source-side anisotropy on the direct S-wave signals. This method enabled us to expand our splitting measurement database beyond the usual SK(K)S phases. The average splitting delay time over the entire region was found to be 1.14 ± 0.42 s for the SK(K)S wave and 1.36 ± 0.26 s for the direct S wave. In most parts of the study area, the fast polarization directions for both shear phases are consistent and show a uniform NE-SW direction with an average of 36° and 37° for SK(K)S and S wave-derived results, respectively. This direction is in close agreement with the direction of the absolute plate motion vector in NW Iran (N39° E). The fast directions are associated with neither the surface geological trends, nor the geodetic strain fields. We propose that the observed anisotropy is mainly controlled by the LPO fabric developed due to the shearing of the asthenospheric layer in response to the motion of the lithosphere relative to the deeper mantle. Only in a narrow region near the tectonic boundaries of central Iran with NW Iran and the Alborz, NW-SE oriented SK(K)S fast directions tend to align with the major geological structures. Fast directions obtained from direct S-wave indicate significantly smoother variations in the same regions and mostly continue to be aligned in the NE-SW direction. We attribute these differences to the change in the structure of the lithosphere in the tectonic boundary zone. The western margins of central Iran possess a strong deformational fabric as evidenced by the major active strike-slip zones there. Considering that the depth extent of this fabric expands over a relatively narrow zone in the mantle, it can locally influence the SK(K)S phases. The direct S-waves, on the other hand, have a larger footprint and therefore average over a larger region, and relative to the SK(K)S phases, are influenced more strongly by the asthenospheric fabric due to their larger angles of incidence, which results in a larger zone of influence for station average anisotropy parameters.

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A new calibration of seismic velocities, anisotropy, fabrics, and elastic moduli of amphibole‐rich rocks

Shao

Michibayashi

et al. 2013

JGR Solid Earth

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A large portion of the middle to lower crust beneath the continents and oceanic island arcs consists of amphibolites dominated by hornblende and plagioclase. We have measured P and S wave velocities (Vp and Vs) and anisotropy of 17 amphibole‐rich rock samples containing 34–80 vol % amphibole at hydrostatic pressures (P) up to 650 MPa. Combined petrophysical and geochemical analyses provide a new calibration for mean density, average major element contents, mean Vp‐P and Vs‐P coefficients, intrinsic Vp and Vs anisotropy, Poisson's ratios, the logarithmic ratio Rs/p, and elastic moduli of amphibole‐rich rocks. The Vp values decrease with increasing SiO2 and Na2O + K2O contents but increase with increasing MgO and CaO contents. The maximum (≤0.38–0.40 km/s) and minimum S wave birefringence values occur generally in the propagation direction parallel to Y and normal to foliation, respectively. Amphibole plays a critical role in the formation of seismic anisotropy, whereas the presence of plagioclase, quartz, pyroxene, and garnet diminishes the anisotropy induced by amphibole crystallographic preferred orientations (CPOs). The CPO variations cause different anisotropy patterns illustrated in the Flinn diagram of Vp(X)/Vp(Y)‐Vp(Y)/Vp(Z) plots. The results make it possible to distinguish, in terms of seismic properties, the amphibolites from other categories of lithology such as granite‐granodiorite, diorite, gabbro‐diabase, felsic gneiss, mafic gneiss, eclogite, and peridotite within the Earth's crust. Hence, amphibole, aligned by dislocation creep, anisotropic growth, or rigid‐body rotation, is the most important contributor to the seismic anisotropy of the deep crust beneath the continents and oceanic island arcs, which contains rather little phyllosilicates such as mica or chlorite.

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Seismic anisotropy in the crust and upper mantle of the Central Alborz Region, Iran

Cited by 24 publications

References 35 publications

Seismic Anisotropy and Its Geodynamic Implications in Iran, the Easternmost Part of the Tethyan Belt

Seismic Anisotropy and Its Geodynamic Implications in Iran, the Easternmost Part of the Tethyan Belt

Seismic anisotropy and mantle deformation in NW Iran inferred from splitting measurements of SK(K)S and direct S phases

A new calibration of seismic velocities, anisotropy, fabrics, and elastic moduli of amphibole‐rich rocks

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