M Gharailou; A Yassaghi; J Bagheri
Abstract
The NW-SW trending Garmsar Anticline is located in the Abardej area in northwestern part of the Garmsar city, 110 km east of the Tehran province. The aim of this paper is to investigate folding style of the Garmsar Anticline and its relationship with the Kavir thrust and also the influence of tectonic ...
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The NW-SW trending Garmsar Anticline is located in the Abardej area in northwestern part of the Garmsar city, 110 km east of the Tehran province. The aim of this paper is to investigate folding style of the Garmsar Anticline and its relationship with the Kavir thrust and also the influence of tectonic regime inversion on the structures of the study area. Furthermore, the study aims at determining spatial development of the structures based on field observations and subsurface data interpretation. The presence of a thrust fault along the southern limb of the Garmsar anticline suggests that this anticline is a fault-related fold, whose specifications are characteristic of faulted-detachment folding style. The existence of the Lower Red Formation evaporates as a ductile horizon has influenced folding style in the Garmsar Anticline, which is clearly observed in seismic lines. The anticline axis is also cross-cut by secondary strike-slip faults that are the youngest structures in the area. Fold amplifications during compressional regime has resulted in development of this set of strike-slip faults across the axis of the Garmsar Anticline.
E Tavakolian; A Yassaghi
Abstract
The Zagros fold-thrust belt has been cut out by various transverse faults with segments displaying en-echelon pattern. Depending on the type of overlapping and fault mechanisms, restraining and releasing zones have been developed between these en-echelon segments. The NW-trending dextral Sabzpushan fault ...
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The Zagros fold-thrust belt has been cut out by various transverse faults with segments displaying en-echelon pattern. Depending on the type of overlapping and fault mechanisms, restraining and releasing zones have been developed between these en-echelon segments. The NW-trending dextral Sabzpushan fault is one of these transverse strike-slip faults located in the Fars province of the Zagros belt. Since the Sabzpushan fault zone consists of several en-echelon segments of clockwise pattern, restraining zones have been generated between them. One of these restraining zones is developed on the NW nose of the Chaghal anticline. Detailed field studies and interpretation of satellite images resulted in identification of several dextral en-echelon faults in the western part of the Chaghal anticline. This fault zone consists of two en-echelon faults called Qir and Harm. Different kinds of structures such as dextral faults with reverse component, thrust faults, minor duplexes and young minor folds were mapped in these restraining zones. These structural assemblages are similar to those that are developed in the restraining zones produced in physical models of en-echelon strike-slip faults. In addition, similar restraining zones which are also observed across the Ghol Ghol and Sefidar anticlines to the south and north of the Chaghal anticline, respectively, are attributed to other en-echelon segments of clockwise array along the Sabzpushan fault zone. These dextral en-echelon faults along the Sabzpushan fault, which are interpreted as surface ruptures in the sedimentary cover with basal detachment zone, formed as a result of the activity of Sabzpushan fault in the basement.
Y Jalili; M.M Khatib; A Yassaghi
Abstract
Fracture intensity-controlling factors, which include folding mechanism, lithology and thickness of layers, have been investigated in the Asmari Formation of the Kuh-e- Asmari using field studies and satellite images. Parameters such as structural position, spacing and vertical extension of the fractures ...
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Fracture intensity-controlling factors, which include folding mechanism, lithology and thickness of layers, have been investigated in the Asmari Formation of the Kuh-e- Asmari using field studies and satellite images. Parameters such as structural position, spacing and vertical extension of the fractures in the limestone and argillaceous limestone units of different thicknesses in the Asmari Formation sequence in Kuh-e Asmari anticline were studied. The existence of large amounts of low-strength and high-porous clay minerals in the argillaceous limestone has resulted in the overall low strength of the rock, which eventually led to lower intensity of fractures in argillaceous limestone than of that in limestone. Variations in the fracture intensitiesin these two rock types showed that the thickness of the units does not much affect the fracture intensity. Hinge-parallel and hinge-perpendicular fractures resulted from flexural-slip folding and outer-arc extension in the hinge area of the fold exhibit the largest development, and exert the highest effect on wellbore instabilities. Results show that the maximum fracture intensity is in the hinge area of the fold, and that folding mechanism is the most important factor in controlling the intensity of the fractures.
M Najafi; A Yassaghi; A Bahroudi; SH Sherkati; J Vergés
Abstract
The long-lived Fars paleo-high, located in SE Zagros Mountains is a prolific hydrocarbon province as it contains 15% of the world’s proven gas reserves. Subsurface data sets acquired during the recent hydrocarbon exploration in the region indicated fold style variation and structural complexity ...
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The long-lived Fars paleo-high, located in SE Zagros Mountains is a prolific hydrocarbon province as it contains 15% of the world’s proven gas reserves. Subsurface data sets acquired during the recent hydrocarbon exploration in the region indicated fold style variation and structural complexity deep in the sedimentary cover, understanding of which is essential for petroleum system modelling and selection of new targets for gas at depth. In order to analyse the fold style in Fars paleo-high, this study presents a new regional balanced cross-section with a length of ~130 km and a depth of 12 km, across the Fars paleo-high. The section was constructed using seismic profiles, exploration wells and field data. The results show that variation of fold style happens in accordance to variation in mechanical properties of rock units across the Fars paleo-high, as well as from surface down to the depth of sedimentary cover. Detachment folding, followed by limb thrusting, which happens above 8-12 km below sea level, is the main deformation mechanism of sedimentary cover. In the middle of sedimentary cover, however, tectonically over-thickened Triassic evaporitic rocks efficiently decouple the geometry of post Triassic succession with respect to the underlying Permo-Triassic reservoir carbonates. Restoration and balancing of the regional cross-section indicated 20% of shortening across the Fars Paleo-high, accommodated by folding and thrusting. Abrupt change in the level of synclines accompanied with trends of seismicity and linear exposure of old geological units, proposes involvement of at least two main basement reverse faults in the deformation of cover sequence.
N Sahabi-Fard; A Yassaghi; M.G Hassan-Goodarzi
Abstract
Zagros fold-thrust belt has been crossed by different transverse faults with NNW-SSE trend and dextral mechanism. These faults often show en-echelon geometries on the surface because of presence of detachment layers at base and within the cover sequence. The Karehbas fault is one these faults located ...
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Zagros fold-thrust belt has been crossed by different transverse faults with NNW-SSE trend and dextral mechanism. These faults often show en-echelon geometries on the surface because of presence of detachment layers at base and within the cover sequence. The Karehbas fault is one these faults located in Fars province about 65 km to the east of the Kazerun Fault zone. Presence of the Hormoz salt as a basal detachment and ductile horizons within the sedimentary cover have caused the fault to appear on the surface as several north-northwest-trending en echelon segments. At least six segemnts have been recognized in northern and southern parts of the Karehbas fault. In this study two southern segments, the Mengharak and Kalagh segments of the Karehbas fault zone to the south of Firuzabad are introduced and their mechanism are analyzed. Riddle and anti-riddle faults and drag folds and terminations are used to analyze the dextral kinematic for both segments. These strike-slip fault segments terminate in thrusts that are sub-parallel to the regional the Surmeh and Kalagh thrusts in the south. These fault terminations are in the hanging-wall of the Surmeh and Kalagh thrusts, and expose formations that are older than those in the hanging-wall of the latter thrusts. Therefore, the Mengharak and Kalagh segments introduced in this study have strike-slip mechanism, and according to this mechanism, their geometry and their structural position in continuation of the northern and central segments of the Karehbas fault, they are introduced as the southern segments of the Karehbas fault . Based on the thrusting of the Asmari Formation over the Bakhtiari Formation in the positive flower structure along the Mengharak segment, the minimum amount of displacement on these fault segments are evaluated equal to the thickness of the Mishan Formation.
S Rezaei; A Yassaghi
Abstract
The aspect ratio of folds is among the most important parameters indicating geometrical features of folds. Based on the aspect ratio, folds are categorized into two groups of buckle and forced folds. The NW-SE trending Qitoleh anticline, which is located in NW of the Lurestan structural subzone and in ...
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The aspect ratio of folds is among the most important parameters indicating geometrical features of folds. Based on the aspect ratio, folds are categorized into two groups of buckle and forced folds. The NW-SE trending Qitoleh anticline, which is located in NW of the Lurestan structural subzone and in the vicinity of the High Zagros Fault, has unique structural characteristics that make it different from other folds in the Zagros Folded Belt. In rock units older than Cretaceous, the anticline consists of four en-echelon buckle folds whereas shows high aspect ratio and forced fold geometry in Tertiary units. Such a variation in the fold style from the surface down to the depth is interpreted as the imposed influence of the High Zagros Fault on intermediate detachment horizons. Such a fold style, which is also observed in other anticlines neighboring the SE part of High Zagros Fault, can be used as a model to interpret similar folds adjacent to the major reverse basement faults in other parts of the Zagros belt.
