Tectonics
Tahmoores Yousefi; Kouros Yazdjerdi; Manouchehr Ghorashi; Alireza Shahidi
Abstract
The current form of the folded Zagros is the result of the oblique collision the Arabian and Iranian plates in Late Cenozoic. In this study, Cenozoic stress field changes in Zagros Simply folded belt and structural evolution after collision in Shiraz Area have been evaluated. The geological formations ...
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The current form of the folded Zagros is the result of the oblique collision the Arabian and Iranian plates in Late Cenozoic. In this study, Cenozoic stress field changes in Zagros Simply folded belt and structural evolution after collision in Shiraz Area have been evaluated. The geological formations under investigation are from Late Cretaceous to Neogene (Late Cenozoic). In this regard, geometry and kinematics of the faults, stylolites and other tectonic and stratigraphic evidence in geological formations outcrops in the study area at 30 stations were taken. The tension main axes (σ1, σ2, σ3) were calculated by Inversion Method for the categorized data. The results of the reconstruction of the paleo stress show compressional and Strike- Slip tectonic regime in Cenozoic. Moreover, anticlockwise rotation of the direction of compressive stress over time is about 60 degrees. As pre-folding compressional stress direction (σ1) is about N60E and its time is Miocene and before that. Whereas syn-folding stress direction is N35E and its age is equivalent to Pliocene that is the same age as old Bakhtiary formation. Stress changes in post-folding indicate N20E and its age equivalent to Pleistocene that is the same age as young Bakhtiary formation. At the present time, the maximum stress direction that is about N-S affects the area.
Tectonics
Tahmoores Yousefi; Kooros Yazdjerdi; 2Manouchehr Ghorash; Alireza Shahidi
Abstract
Abstract: The brittle tectonic history expresses different tectonic events in the Zagros Simply Folded Belt. Consequence of Mesozoic extension, rifting and the shortening derived from the Cenozoic Eurasia – Arabia collision. In order to reconstruction the ancient tensions in the Mesozoic deposits ...
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Abstract: The brittle tectonic history expresses different tectonic events in the Zagros Simply Folded Belt. Consequence of Mesozoic extension, rifting and the shortening derived from the Cenozoic Eurasia – Arabia collision. In order to reconstruction the ancient tensions in the Mesozoic deposits in the east and south-east of Shiraz, geometry and kinematics of the faults data simultaneously with sedimentation was investigated using the inversion method, to evaluated rifting time, the former of Neo-Tethys and its collisions in Cretaceous and Paleocene. In this regard 21 stations have been exposed in Khanekat to Pabdeh Formations. The resulted geometry and kinematics of the faults data were calculated situation main tension axes (σ1, σ2, σ3 ), tension ellipsoid figure or ratio of difference (ɸ). The results are as follows: from Triassic to upper Cretaceous (Mastrichtian) in Khanekat,Surmeh, Fahlian, Darian, Sarvak, Ilam, Gurpi, Tarbur Formations and Ghorban Member; extensional tectonic regime was dominant and having NE-SW direction (N052°) but in Pabdeh Formation with Paleocene age, tectonic regime has changed into compression with NE-SW compressional stress direction(N045°). So it was concluded that in simply folded Zagros of interior Fars, time of rifting and the forming of Neo-Tethyan basin was Triassic or older (Permian) with NE-SW extensional direction. The beginning of compressional tectonic regime with the same direction has been in Paleocene.
M Roustaee; B Zamani; P Navabpour; M Moayyed
Abstract
Siah Cheshmeh- Khoy fault system is one of the principal faults in NW of Iran and that its right- lateral strike- slip activity has reported for different segments of this fault zone. Landsat 7 satellite images of the area, confirm the right- lateral strike- slip motion of this fault system by deflected ...
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Siah Cheshmeh- Khoy fault system is one of the principal faults in NW of Iran and that its right- lateral strike- slip activity has reported for different segments of this fault zone. Landsat 7 satellite images of the area, confirm the right- lateral strike- slip motion of this fault system by deflected drainage of large rivers, cutting and displacement of alluvial fans across the segments of the fault zone. The amount of alluvial fans displacement in -Dasht e zurabad- (along the segment of the Kamarkassan fault) was estimated nearly 1.8 km. In this research, the neotectonics and mechanism of the Siah Cheshmeh- Khoy fault zone has been studied by Inversion method, based on the combination of focal mechanisms of earthquakes and different shear- fault planes. In this paper, we utilized all of the focal mechanism solutions of earthquakes existent in this area. Besides, the data measured conclude shear planes whit slickenside and the measured fault planes across the Siah Cheshmeh- Khoy fault zone. These data were gaged in 7 sites and 45 shear planes with slickenside. Initially the main axis were obtained in all sites by Inversion method; then by combination of focal mechanisms of earthquakes and the measured data, the stress state of this region was evaluated. The results obtained of this analysis indicate strike- slip stress with NNW-SSE (N162°) direction of compression component and ESE-WNW (N255°)direction of extension component in this area. It can be stated that the mentioned stress regime was the main factors controlling the recent kinematic movements of faults and strong earthquakes in the region. Also the right- lateral strike- slip motion of the Siah Cheshmeh- Khoy fault segments are affected by this stress (under the influence of this stress). The results of this research are compatible with the results of the geodetic studies and the GPS measurements in the region that were done by other researches.
M. Saadat; S. A. Alavi; A. Saeedi
Abstract
To analyze the paleostress in Sorkheh Hessar – Khodjir area, different shear – fault planes and the associated slickenside lineations are measured. The stress tensor and the variation of the stress direction in the upper Triassic to Oligocene formations are discussed. Numerous shear data ...
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To analyze the paleostress in Sorkheh Hessar – Khodjir area, different shear – fault planes and the associated slickenside lineations are measured. The stress tensor and the variation of the stress direction in the upper Triassic to Oligocene formations are discussed. Numerous shear data are determined from different locations in the study area and categorized into 16 sites according to the stratigraphic age. The main criteria used to identify the sense of slip are accretionary mineral steps, tectonic tool marks, polished and rough facets, and riedel shears. According to the inversion method which includes determination of the mean stress tensor orientation and sense of slip on numerous faults ,all data are classified based on tectonic events and the principal stress axes and corresponding compressional and extensional directions are calculated.
Based on the derived results from the diagrams, it is suggested that a prominent NE- SW compressional stress direction, which is obvious in Mesozoic and the younger Cenozoic formations, caused the deformation of the Mesozoic strata after Mesozoic and was continuous in Tertiary (Oligocene). It seems that a younger N-S stress direction exists and has had effects on both older and younger formations. It is believed that it would be related to one of the last Alpine orogenic phases.
S. Bahiraie; M. Abbasi; M. Almasian
Abstract
Generally the most important factor in the structural evolution of Alborz is thrust and reverse faulting that often has an east-west trend, parallel to the mountain chain. Mosha fault, one of the main faults, in this study covers the area between longitudes 51˚, 30´ to 51˚, 45´ including ...
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Generally the most important factor in the structural evolution of Alborz is thrust and reverse faulting that often has an east-west trend, parallel to the mountain chain. Mosha fault, one of the main faults, in this study covers the area between longitudes 51˚, 30´ to 51˚, 45´ including central-western part of Mosha fault. The stress evolution on the available faults in northeast of Tehran city was studied by means of inversion of 120 striated fault planes and related striations. Finally, two different movement systems were identified. One of them generated dextral reverse faulting and the other one which is younger created sinistral reverse faulting. The dextral system, known to resulted from the movement of the Arabian plate toward the north, is determined to be Miocene and probably older. The sinistral system originates from structural transition of AlborzMountain (progressive deformation in Alborz). Obtained result shows that the movement vector on the thrust Mosha is the consequence of the combination of sinistral and reverse faulting. The ages of stress changes were determined by using the cross cutting