جستجوی مقالات مرتبط با کلیدواژه "سنگ کره" در نشریات گروه "زمین شناسی"

The Iranian Plateau is a part of the Alpine–Himalayan orogenic belt located in the western part of Asia. Convergence of the Arabian Plate and Eurasia from the late Cretaceous to the present has generated significant lithospheric deformations such as crustal shortening and thickening in the Plateau and surrounding mountain ranges including the Zagros Fold–Thrust Belt, Alborz and Kopeh Dagh. The convergence across Zagros is accommodated through different mechanisms of diffused shortening and/or thrusting of the Arabian lithosphere beneath Central Iran. This study focuses on the velocity structure of the eastern part of the Iranian Plateau which has not been studied well yet. Our study region also contains Binalud and Kopeh-Dagh deformation domains which were built up by the north-eastern collisional boundary between the Plateau and Eurasia and a small part of the Urumieh-Dokhtar magmatic arc which was the volcanic arc of the past Neotethyan subduction. The lithosphere-asthenosphere system beneath east of Iran is investigated by employing earthquake surface wave tomography. A total of 5862 teleseismic Rayleigh waveforms from 368 events recorded at three permanent networks during a period of three years were used to produce 2-D high-resolution phase velocity maps. We employed a two-plane wave tomography approach to generate phase velocity maps at period ranges of 25–111 s. From a published study of ambient noise tomography, we extracted Rayleigh wave dispersion data at 8–20 s periods to improve resolution in the crust and then inverted them for a 3-D S-wave velocity model. A 3-D velocity model was then constructed by a nonlinear Bayesian Markov chain Monte-Carlo algorithm of local node-wise dispersion data into S-wave velocity models down to a depth of 200 km. The most prominent resolved feature by our 3-D velocity model is a low-velocity asthenospheric channel at 70 and 150 km depths overlaid by a thin lithosphere. We believe that in the lack of an isostatic compensated crustal root in the Iranian Plateau, this feature is supporting high elevation (~1000 m) topography covering the Iranian Plateau. A Moho map for the study region is obtained by mapping the geometry of 4.0 km/s S-wave velocity contour in the 3-D velocity model. It shows that most of the study region is covered by a less deformed crust with a thickness of ~36 km. Two crustal roots are observed, one beneath the Urumieh-Dokhtar magmatic arc and the other beneath the north-eastern part of the study region where an array of the Neotethys suture zones is marked by ophiolite outcrops. Lithospheric scale deformation in a sequence of Neotethys suture zones is high probably responsible for the crustal thickening in NE Iran.

The flexural strength and consequently the elastic thickness (Te) of the lithosphere are often calculated utilizing the statistical relationships between gravity anomalies and topography data. The elastic thickness of the lithosphere is one of the most important parameters in determining the geological properties and characteristics of the crust as well as its rheological behavior. This prospective study was designed to investigate the use of the gravity and topography data in order to calculate the two fundamental functions, i.e. admittance and coherence, which are the basic functions for determining the elastic thickness of the lithosphere. In this research, the theory of the two objective functions is modeled. The study offers some important insights into the involved parameter and how they affected the functions. Additionally, the results show the impact of initial assumptions of different parameters on the retrieved value of the Te parameter. Taking into account the initial assumptions about parameters such as the elastic thickness () of the plate, the loading ratio () and the degree of correlation () between the surface and subsurface loading regimes applied to the plate and using spectral methods, the value of these two functions are calculated. After examining the theoretical models, the real-data analysis is conducted in order to examine the observed values and compare them with the theoretical values. Based on what was mentioned in the following, this function can be able to retrieve the elastic thickness of the lithosphere. We concluded that:One of the more significant findings to emerge from this study, by examining the theoretical models, is that the best function to determine the elastic thickness of the lithosphere is to use the Bouguer coherence function. A comparison of the results reveals that the characteristic curves of the admittance function will change drastically with the change of the involved parameters. Consequently, having complete knowledge of the structure of the region and involved parameters is essential while using free air admittance in order to determining Te. As it was illustrated in this research, the characteristic curve of the coherence function can be used to determine Te based on the roll over wavelength. For the reason that there was no significant change in the shape of characteristic curve of the functions with the initial value of the loading ratio (), this parameter had less impact on the inversion process. Having considered rare correlation between free air gravity and topography, it is reasonable to accept that the free air coherence method is less applicable in determining Te than Bouguer coherence. The findings from previous studies provide support for the key arguments.