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.
S. A. Atapourfard; A. Yassaghi; M. Rezaian; E. Shabanian
Abstract
In the east of high Zagros – in Faraghan Anticline- sedimentary cover with more than 10 km thickness has decoupled from basement above the Hormuz salt and has deformed. Mention anticline is cut by High Zagros Fault. By attention to lack of paleostress study and kinematic interpretation on north ...
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In the east of high Zagros – in Faraghan Anticline- sedimentary cover with more than 10 km thickness has decoupled from basement above the Hormuz salt and has deformed. Mention anticline is cut by High Zagros Fault. By attention to lack of paleostress study and kinematic interpretation on north east of Fars Arc structures, in this paper we reconstructed stress field and interoperated its role in evolution of Faraghan Anticline. Inversion method used for determination of reduced stress tensor parameters and discrimination faults of every brittle tectonic phase. Maximum shortening axis determined by using Stylolite's and attitude of Minimum main stress determined by using veins. The present stress field was calculated by inversion of earthquake focal mechanism data. According to our data and the deduced results, some of veins developed with an N27° - 29°E direction of σ1 stress axis before late of middle Miocene (before folding and faulting). During the late Miocene, sedimentary cover deformed as detachment and faults related folds in a general compressional stress regime with an N27° - 29°E direction of σ1. The basement faults were reactivated during late Miocene- early Pliocene in a general strike slip regime with an N4°E direction of σ1 stress axis. The High Zagros Fault was reactivated at that time and cross- cuts the entire cover section and its associated structures. In the late Pliocene, direction of σ1 stress axis temporally changed to N025°W in strike slip tectonic regime. Strike- slip and reverse faults were reactived in new stress field. Earthquakes Focal mechanism data analysis indicate that direction of σ1 stress axis is N-S now.
