جستجوی مقالات مرتبط با کلیدواژه « folding » در نشریات گروه « زمین شناسی »

The Ghalajeh anticline with about 60 km length and NW-SE trend is located in Lurestan sub-zone and the Zagros fold and thrust belt. Geometry and kinematic of the folds of this zone are controlled by thrust faults and detachment levels. In this research, geometry and deformational style analysis of the Ghalajeh anticline and the role of the detachment levels on folding style have been investigated interpreting well data and construction of three cross-sections and calculation of geometric parameters. The structure of this anticline is affected by two detachment levels, which include the Pabdeh and Garu formations as the upper and middle detachment levels. Detachment levels and deep-seated and surface thrust faults in the southwestern limb affected the folding geometry and have caused the high thickness of the middle detachment level and inversion of the southern limb which waning southwestern part of the anticline, and the dip of the layers are normal which in turn caused fracturing. Analysis of geometrical parameter along the Ghalajeh anticline indicate that this anticline is an asymmetrical, cylindrical fold is an open half-angle round fold.

The Naft anticline is located in the NW-SE of the N Lurestan sub-zone and the Zagros fold and thrust belt. In this sub-zone, the structural geometry of the folded sequence is significantly influenced by the basemen thrust and strike-slip faults and detachment levels. In this research, for the geometrical analysis of the Naft anticline, we utilized the structural profile perpendicular to the anticline in the central region, information from drilling wells in the study area and neighboring anticlines, and the deformation pattern and structural geometry of the Naft anticline. The anticline has two upper (Amiran Formation) and Middle (Garau Formation) detachment levels. The basement thrust faults and detachment levels in the southwestern limb had a significant impact on the folding geometry and led to the formation of disharmonic folding. An N-S basement strike-slip fault in the middle part of the anticline has shifted the anticline axis from N70W in the northwest to N50W in the southeast. In addition, the minor and shallow thrust faults propagationg from the upper detachment levels or the independent thrusts in the Gurpi Formation resulted in the development ofan axis of two kink and curved hinges in the middle part of the Naft anticline in folded structures. The analysis of the geometrical parameters of the Naft anticline shows that it is an asymmetrical and noncylindrical fold, categorized as an open half-angle fold in terms of tightness.

Estimation of shortening and vergence in northern part of Sistan Suture Zone for determination of kinematic convergent vectors During the evolution of orogenic belts, the rock units are deformed. Aim to the understanding of the amount and condition of deformation, the strain states should be estimated which took place during different deformation phases. By means of superficial sturctures, strain states can be estimated in verious scales from microscopic to regional scale. In this study, estimation of shortening has been measured by using unfolding folds and measurement of strain states during making of faults. Amount of vergence states also evaluated which occurred, for purpose of determining the kinematic convergent vectors. For this reason, in the northern part of strurctural Sistan province in the east of Iran, the study has been done on the section which begins from Nazdasht village in west to eastern part of Khoshab village in east, with trending of N60°. Based on the estimations, the folds and faults experienced 27.3 and 13.6 percent shortening respectively. The vergence vectors situations for folds show 7.4 and 11.6 percent for NE and SW direction, respectively. The vergence vectors situations also which has been made by faulting are 19.35 and 22.82 percent for NE and SW direction, respectively. From beginning of converging between Afghan and Lut plates, the vergence vectors situations of Afghan plate is 7.7 percent more than Lut plate. Finally, direction of subduction and tectonic transfer direction have NE and SW trends, respectively.

he Dara anticline as one of the anticlinal oil structures in the Zagros fold-and-thrust belt within the Dezfol embayment (west of the Kazerun fault) has been carried out at this research. For this aim, after the determination of fold trend and mechanism, some sections at: NW nose, center and SE nose of anticline have been drown by using subsurface data. Analyses of folds exhibit the Dara anticline at Class 3 Ramsay classification. On the base of Fleuty classification, this fold is an open one. Fractures are at three main trends: E-W, N-S and NW-SE. Restoration sections indicate that the rate of shortening along the NW nose (A-A' section) is 6.5% and at B-B' section is 8.4% that illustrates on high folding rate at SE nose of the Dara anticline

Irankuh is located 20 km south of Isfahan. Late Jurassic black shale, silt and sandstones are the oldest rocks in the area that exposed in the northern flank of the Irankuh Mountain. Lower Cretaceous dolomitic limestone with some shale and marl starting with a basal conglomerate, overlay the Jurassic sediments in the area. Folds are trending NW-SE. In the northern flank of Irankuh a Kilometer scale Syncline with vertical axial plane and axis plunges of 35° to the west and an anticline with 32° plunges to the west and its exposure extended toward the southern flank of mountain. According to competency contrast of the rock units, abundant minor folds consistent with the geometry of the major structures are produced in couple of synclines and anticlines. Goushfil-Tapeh Sorkh reverse fault (75° dipping to the NE) thrust the Jurassic sediments over the Cretaceous rocks in Goushfil and Tappeh Sorkh1 Mines. Field observations indicate that it was originally a normal fault dipping to the SW and has been changed during the course of folding process to an inverted high angle reverse fault dipping to the NE close to the surface. NW-SE trending reverse faults are controlling the mineralization in the Irankuh area i.e. Goushfil-Tapeh Sorkh reverse fault.

Kinematic evidence of shear deformation in strain fringes of sphalerite mineral in an overturned limb of a fold structure are studied. Structural observation in Cretaceous rocks of Tiran Mine Area in west Esfahan, reveals a shear deformation in overturned limb of a hanging-wall anticline that has generated with reverse fault in the area. Orientation of strain fibers and their rotations in strain fringes of sphalerite minerals are used for determination of stress orientations and its changes during shear deformation process. This fabric indicates kinematic evolution of the overturned limb of a hanging-wall anticline and related reverse fault during folding. In this study, amount of stretching in strain fringes and their rotation are measured by object-centre path model.

In the east of Tabriz city, south of Eskandar village, Upper Cretaceous rock units are exposed. The structures in these rock units include meso-scale folds inclined towards NNE, and a thrust system which has transported Upper Cretaceous units in three thrust sheets towards NW. This thrust system has cut the NNE-verging folds in Upper Cretaceous units. These deformed rock units are unconformably overlain by the Miocene beds. The vergence of folds in the Miocene units is toward SSW. There are SW-verging thrust faults and right-lateral strike-slip faults parallel to the North Tabriz fault in the study area. We conclude that the N-verging structures in Upper Cretaceous rock units has been formed in the time interval between Upper Cretaceous and Miocene and were cut by the North Tabriz fault. The structural characteristics of the Upper Cretaceous rocks as the remnants of the Upper Cretaceous oceanic crust in the Neotethyan marginal basin indicate that the probable subduction direction of this basin was towards south.

There is a close relationship between resistance to slip along decollement surfaces and presence of deep and shallow decollement levels in thin-skinned fold and thrust wedges. Decollement units in lower (Upper Red Formation) stratigraphic levels in Mianeh-Mahneshan fold belt have an effective role onthe geometry and kinematics of deformation of the area. In order to understand the fold geometry and folding mechanisms, and to exploredepth-to-the-decollement surface, we carried out data collection and field study in an area between Mianeh and Mahneshan cities. Folded structures in the study area are different other structures within the area, as well as the structures in the neighboring Alborz Mountains.The rise of salt domes along with the plasticity of marls in the Upper Red Formation have resulted in extreme complexities in folding pattern. In order to analyze syn-sedimentary structural features and interpret the geological evolution of the area, we used detailed structural measurements, sedimentological and sedimentary environment features, sedimentary rock studies, and paleogeography.One of the results of this study was the interpretation of syn-sedimentary growth structures in the Mianeh-Mahneshan area, which helped us to construct six structural cross-sections (AA’, BB’, CC’, DD’, EE’ and FF’)across the folded structures. Measured shortening along two Sections AA’ and DD’is 46.65% and 38.05%, respectively, with an average of 42.3%. These values are different those estimated forthe neighboring Alborz and Zagros Orogens, shortening ranges between 16-30%. We attribute this difference to local intense shortening in the study area caused by several factors such as basin slope, deep faults and weak beds along decollement surfaces. This study indicates that dominant folding mechanisms in the study area are detachment folding, and fault-propagation or fault-bend folding. The presence of evaporitic material (gypsum and salt) within the succession has played a major role in the kinematics of folding.

The Chelounak area in northwest of Birjand located in the Sistan suture zone extremity with middle-upper Eocene sedimentary and pyroclastic rocks, folded with different axes and exposed between the Chahak-mosavieh and Mohammadieh-Hessarsangi faults. These folds have a dominant characteristic of the dispersion axis trends of NE-SW, NW-SE, and N-S. Geometric-Kinematic Analysis of these folds was carried out by data that taken from the structural interpretations, satellite images, geological maps, structural cross sections and mathematical functions. Aspect ratio, percent shortenings and the rotation folds axes are respectively for folds with NE-SW axis, 0.356-1.6, 20-77% and 28-40°; for folds with NW-SE axes0.352-0.620, 25-41% and 25-40°; and for folds with N-S axes 0.352, 25% and 24°. In this analysis the Chahak and Chelounak synclines and the Chahak anticline with NE-SW axis have maximum shortening and the Shavangan syncline with NW-SE axis has minimum shortening. This Study demonstrated the aspect ratio rises with increasing of shortening. Analysis of the structural elements demonstrates axis change of the Chelounak, Chahak and Hoj noj synclines and the Chahak and Chelounak anticlines with NE-SW Dominant axes affected by the Chahak-Mosavieh fault (~N-S trend) as well as the axis change of the Taj kouh, Shavangan and Hessar sangi synclines with NW-SE dominant axes affected by the Mohammadieh-Hessar sangi fault (~N-S trend). Dispersion of folds axial respect to compressive component has caused difference in aspect ratio, shortening and rotation of fold axes values.

This paper, a two-dimensional model of Lali oil field and faults of the northern and southern edges of the relations with ABAQUS software based on finite element methods. The model results from Geodynamic Geodesy area networks and the tectonic stress as a constraint problem has been logged and various field formations on the elastic properties is considered. Fault surface is covered with contact elements that have authority to slip influence and change their shape and according to this properties in surface properties can well indicate the fault. Modeling results and geological criteria (Geodesy results) were compared and good coordination is observed between the results of the validation criteria. Results with a different coefficient of friction compared to the rate of displacement of GPS stations that coordination is more pronounced in the coefficient of friction 0.02. Displacement of southern edge of the fault in both friction 0.02 and 0.1 are obtained, respectively, 6.3 and 11 mm/year. The modeling results also showed that fault at different depths has different displacements and at depths less, move more expressive. Faults north and south edges of the integration Lali anticline that the most stress have focused on their, is Stress concentration and critical fault location of the fault.

Marun Oil Field is located in the southern part of Dezful embayment, in the mid part of the zagros simple folded mountain range and along the Ramin and Aghajari anticlines. In this study, based on the subsurface data and using subsurface analytical methods the folding mechanism and fractures of this anticline has been studied. In this research, using the primary results of geophysical data, analysis methods, geometric curvature changes, mud loss and reservoir engineering data, geometry of anticline and fractures associated with folding have been analyzed. Folding mechanisms in this anticline is a combination of flexural-sliding folding and folding with neutral surface. In other words, the Marun subsurface anticline is a thrust fault- related fold and also a faulted detachment fold. Seismic profiles showthat the Marun anticline as a concentric fold that from surface to depth space has been decreased. This decrease of space associated with faulting in the southern flank and these faults disappear in the Gachsaran formation. A good conformity among geometric analytical methods, mud loss data, index productivity on bending region in the Marun anticline and presence of fractures in this region exist. The data analysis shows that the highest density of fractures is related to the bending region in the Marun Oil Field. Finally, using these parameters, it is recommended that for further drilling of development and production wells these parameters must be regarded and the northeastern part of the Oil Field as well as southern flank of the anticline must be given full consideration.

Structural analysis of folds in the Kharapeh area clears tow co-axial folding stages in the Cretaceous metamorphic rocks, in this part of the Sanandaj-Sirjan zone. First stage folds are tight to isoclinal recumbent folds that were co-axially refolded by second stage upright open to close folds. Normal faults, mafic dykes and abundant quartz veins oriented sub-parallel to the axial surface of the kharapeh antiform implying that the extensions were synchronous with folding perpendicular to the fold axis, during second stage folding process in the area. This is well concordant with tangential longitudinal strain folding mechanism for the second stage folding. By this folding mechanism, tension was produced at the outer arc of the Kharapeh anticline and quarts veins were generated by compression in the core area and filled in the tension fractures that were mostly produced in the fold hinge area during the folding process. In fractures where it was accompanied with shearing, some clasts from wall rocks were engaged in the fault zone breccias. The field observations reveal that the fractures were produced synchronous with the second folding stage in the Kharapeh anticline and filled by the gold bearing quartz veins.

The marine facies of the Qom Formation was deposited between two detritus continental facies of the Lower and Upper Red Formations. The type section of the Qom Formation was observed in Qom city, but its most thickness has been reported from the Dokhan area in west Saveh. Stratigraphic studies revealed that its thickness has sudden changes in the Dokhan area through short distances. Geometry of the structures was strongly influenced by change of thickness in different rocks of the Qom Formation. The main question that has been answered in this study is what caused change of thickness in short distances. The geometry and kinematic observations of the major faults in the Dokhan area showed that their displacement style during sedimentation influenced on change of the thickness and folding style during deformation of the Qom Formation. This study showed that the Dokhan area is located in the extension termination of the NW-SE trending major strike-slip faults such as the Tafresh, Talkhab and Indus faults.

The ptygmatic folds are intestinal folds that violent bends and twisting in manes can be seen in them. These folds are seen in many of the evolved migmatites and migmatitic schists in Simin area. But they are not present in migmatites evolved from hornfelses. Growing and expanding of ptygmatic folds in migmatites occurs during separation of leucosome and mesosome. This process develops in second process by the active folding boundaries of leucosome and increasing of branches of veins. A sharp rheological differences between folded veins with background is the most important reasons of growth and separation of ptygmatic shapes. Probably development of shear zones, presence of schistosity and the large size of minerals present in evolved migmatites is compatible with development of these folds in the area.

The outcrop of northern part of North Eshtehard Thrust has been ed for study of structural evolution and geological processes. The study area includes folding structures with different scales regional to outcrop which belong to fault related folding category. Analysis of joints in the region among upper red formation strata shows two main sets which are usually tensional (j1 & j2). These joints are visible in sandstone units of upper red formation and most of them are filled with gypsum. It is obvious that the j1 joints are younger than j2. j1 and j2 joints are related to folding processes. The local stress field which could be measured the joint study is σ1=337/75, σ2=189/13 and σ3=077/03 and corresponds with the given paleostress direction for southern part of central Alborz.