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.
H Hajialibeigi
Abstract
The E-W trending deep-seated Balarud fault zone is formed the part of Mountain Front Fault in north of Andimeshk. This strucutre has been separated the Lurestan zone (in North) from the Dezful Embayment (in South) that has operated as a faulted zone. Several subsurfaial and surface anticlines are affected ...
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The E-W trending deep-seated Balarud fault zone is formed the part of Mountain Front Fault in north of Andimeshk. This strucutre has been separated the Lurestan zone (in North) from the Dezful Embayment (in South) that has operated as a faulted zone. Several subsurfaial and surface anticlines are affected by this fault zone. In this paper for some of these anticlines have been drawn the cross-sections that based on well data, interpreted seismic profiles and field observations. The geometrical characteristics of these anticlines analyzed from cross-sections. The achievement of these analyses is used for distinguishing the tectonics and the deformational pattern in the Balarud fault zone. These anticlines formed by following mechanism: detachment folding, fault-propagation folding and fault-bend folding. The change of the deformational style and type of these anticlines are related to present and absence of the intermedate detachment horizons and also contorted by influence of this fault zone. These anticlines that have less 100 km lengths are En echelon arrayeh, asymmetric, disharmonic, noncylindrical, convolute folds with SW vergence and helicoidally axial surfaces. The Lurestan zone is more folded than the Dezful Embayment zone. The Balarud fault zone is a sinistral simple shear zone due to influence of strike-slip fault with E-W trending in basement. It seams the strike-slip movement sinisteral component of deap-seated fault is provided a helicoidally geometry in the study area. Different mechanism of fault-related folds of these anticlines and the results of the demonstration of the style of layer folded confirm the helicoidally geometry. Direction of fault is generally due to North and gradually become vertical to subvertical in adjacent to basement. The Balarud fault zone is an oblique footwall-ramp system with oblique convergence and the Kazerun fault zone is also another member of this system. The sinistral and dextral movements respectively, have been caused by a part of the promontory of Arabian plate between these fault zones. A transition zone is formed that the structural geology process and tectonics mechanism in duration of this ramp are different. The Balarud fault zone is not continuous, and has been displaced by many strike-slip basement involved faults. A NW-SE basement fault (α fault) as a tear fault cuts the sheet of the Balarud fault parallel to the Kabir Kuh anticline.
Kh Sarkarinejad; Z Kamali
Abstract
The NE oriented Dasht-e-Arjan graben with orientation is located in 65 Km west of ShirazCity. This graben is resulted from the active Kare-e-Bas fault segmentations. This extensional graben system is part of the Zagros Simply Folded Belt and bounded by two boundary fault system perpendicular to the Shahneshin ...
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The NE oriented Dasht-e-Arjan graben with orientation is located in 65 Km west of ShirazCity. This graben is resulted from the active Kare-e-Bas fault segmentations. This extensional graben system is part of the Zagros Simply Folded Belt and bounded by two boundary fault system perpendicular to the Shahneshin anticline and Salamati anticline. These two boundary faults were named the East-Arjan and West-Arjan faults in this paper. The oriented samples and slabs from slickensides and slickenlines of these two faults were collected in order to reconstruct paleostress orientations for the Dasht-e Arjan graben activities. The paleostress analysis based on the fault-slip inversion method was performed from the striations or the slickenlines data collected from the two faults planes. This showed that the orientations of the maximum principal stress (σ1) of the graben is 70°, N 26° E and the minimum principal stress (σ3) is 25°, S 40°E. Microscopic examination of the oriented thin sections (XY- and XZ- planes) indicated that they consist of the type І and type П calcite e-twins. The measurements of the e- twin and c- axis were carried out using an optical polarizing microscope equipped with 5-axis Universal Stage in order to determine orientations of "Compression"(P) and "Tension" (T) axes. The mean orientation of the sub-vertical maximum principal stress (σ1) is N 35° E ± 11. 72º and mean orientation of the minimum principal stress (σ3) is S 35° E ± 9،32°. The stress field around the boundary faults of the graben is related to the stress field of the Kare-e Bas fault activities.
