Tectonics
Mohammad R. Ghassemi; Ali Aghanabti; Abdollah Saeidi
Abstract
Correlation of the orogenic and epeirogenic events in Iran with the events that have been identified in different parts of the world and in different tectonic environments, has caused some confusion in the Iranian geological literature. After a brief review of the nature of known orogenic processes in ...
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Correlation of the orogenic and epeirogenic events in Iran with the events that have been identified in different parts of the world and in different tectonic environments, has caused some confusion in the Iranian geological literature. After a brief review of the nature of known orogenic processes in the world, examining issues related to the abovementioned correlations, and considering the tectonic history of various parts of Iran, we have tried to systematically describe and name the important orogenic and epeirogenic events of the country. Most Precambrian orogenic events in Iran are dubious due to unknown age and poorly constrained tectonic setting of the rock units attributed to Precambrian. Paleozoic in Iran has been mostly associated with epeirogenic events, and the only sign of a real orogenic event goes back to the Late Carboniferous in northern Iran. The important Mesozoic and Cenozoic orogenic events have shaped the modern tectonic configuration of Iran. The Paleotethys suture in northern and central Iran formed during the Gorgani orogeny, development of the Central Iranian active margin (Sanandaj-Sirjan) occurred in the Ekbatani orogeny, ophiolite obduction in Central Iran and Zagros developed during the Late Cretaceous events, and collision of the Iranian plate with the Helmand block resulted in the Sistani orogeny. The creation of the Zagros and Alborz Mountain ranges started from Oligocene and Miocene times, respectively, and the deformation due to their shortening continues to this day.
Tectonics
Mehdi Tavakoli Yaraki; Seyyed Ahmad Alavi; Mohammad Reza Ghassemi; Iraj Abdollahie fard
Abstract
The significance of mechanical stratigraphy of rocks in kinematics of folds has long been of interest to structural geologists. Parameters such as sedimentary facies variations and thickness of incompetent layers play major role in activity of these layers as detachment horizons. The purpose of this ...
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The significance of mechanical stratigraphy of rocks in kinematics of folds has long been of interest to structural geologists. Parameters such as sedimentary facies variations and thickness of incompetent layers play major role in activity of these layers as detachment horizons. The purpose of this study is to investigate the role of mechanical stratigraphy on fold geometry in the Aghajari and Pazanan anticlines within the Dezful Embayment zone. For this purpose, we have used seismic profiles, stratigraphic data and petrophysical logs as well as the previous stratigraphic works in study area. Results show that the Garau Formation is the major intermediate detachment level in the Aghajari structure, and has a significant control on folding geometry of the competent sequences of the Fahliyan to Asmari Formations. The Dashtak Formation and other incompetent evaporatic Formations of Middle-Upper Jurassic also have been active in the Aghajari structure. In contrast, in most parts of the Pazanan structure, the Garau and the Jurassic Formations do not have appropriate mechanical properties to act as intermediate detachment levels due to their change into hemipelagic facies and limestone (Surmeh Formation) respectively. Based on the evidences, the facies change in the abovementioned Formations occurs between the Pazanan and Aghajari anticlines. It seems that activity of the Hendijan-Izeh paleo-high also has some control on facies of the Garau Formation. Based on geometric characteristics and a geometric conceptual model provided for development of these structures, the folding style of the anticlines is suggested as an asymmetric faulted detachment fold type.
Tectonics
Rojin Hamidi; mohamad reza ghassemi; mohammadreza sheikholeslami
Abstract
Continuation of the compressional regime within the convergence zone between the Central Iran and Turan rigid blocks caused thrusting of old rock complexes over the recent sediments. As a result of multiple thrusts and folds, the area uplifted at the same time and the Binalud range have been shortened. ...
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Continuation of the compressional regime within the convergence zone between the Central Iran and Turan rigid blocks caused thrusting of old rock complexes over the recent sediments. As a result of multiple thrusts and folds, the area uplifted at the same time and the Binalud range have been shortened. This study attempts to evaluate the amount of shortening of the Binalud mountains by reconstruction of a balanced cross-section. Field data from the Dulat-Abad-Neyshbur transect, study of the geological units and décollements along the section, and the Move® software environment are used as the basis for this research. Based on these information, four tests were carried out for balancing the cross section in question. The first test, which used the arc and polygon method for the horizons and a listric fault without floor thrust, failed to display the deformed section. In the second test the section was drawn, however the deformed structure did not balance the section in the process of unfolding the fault bend folds. In the third and fourth tests, we used the kink method to restore the deformed state to an undeformed section. For the third test, deformation was proceeded from the hinterland, and in the process of restoration, a shortening of about 65% was revealed. The fourth test was proceeded from the foreland, and taking into account both the foreland uplifts and shortening, the amount of shortening of Binalud range was estimated to about 26%. The final structural model defined a thin-skinned fold and thrust belt which included fault-bend-folds with out-of-sequence and in sequence duplexes. Major décollement horizons defined in the region include: 1) shale horizons within the Silurian-Devonian rock units, 2) medium-bedded dolomite and limestone layers within the Bahram Formation, and 3) evaporitic layers in the Eocene sediments.
Tectonics
Masoud Biralvand; Mohammad Mohajjel; Mohammad Reza Ghassemi
Abstract
In Takht-e-Suleiman region, travertine deposits are widespread in the footwall of the Chahartagh fault. Three factors played roles in forming travertine in this area: magmatism and high geothermal gradient, existence of carbonates between thermal source at depth and travertine springs on the ground, ...
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In Takht-e-Suleiman region, travertine deposits are widespread in the footwall of the Chahartagh fault. Three factors played roles in forming travertine in this area: magmatism and high geothermal gradient, existence of carbonates between thermal source at depth and travertine springs on the ground, so that the hydrothermal solution can provide the necessary ingredients for the formation of travertine. The third factor is extensional faults and fractures to conduct water containing dissolved calcium carbonate up to the surface. Absence of travertine on the top of the metamorphic basement, even in the footwall of the Chahartagh fault, highlights the essential role of second factor in formation of the travertine. Sources of travertines in this area are carbonates from the Jangoutaran and Qom formations, with the more emphasis on the latter based on our data. Right-lateral kinematics on the Chahartagh fault led to an NNW extension in the southeastern termination of the fault, paving the way for emergence of the travertine. However, there is evidence for a regional NE extension responsible for NW-SE normal faults in the area. Such an extension may be associated with slab rollback and slab breakoff of the Neotethian oceanic lithosphere, lithosphere delamination deformation or basement-involved thick-skinned deformation in this area.
M. Jamali; M. R. Ghassemi; M. Lotfi; A. Solgi
Abstract
Kuh-e-Ahan is a high-standing single relief within a rather flat plain, which is located in the north of the Tabas block, near the intersection of the Nayband and Kalmard faults and there are great outcrops of fe-oxide, along with eastern-western faults and fractures in Kooh-e-Ahan area.. ...
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Kuh-e-Ahan is a high-standing single relief within a rather flat plain, which is located in the north of the Tabas block, near the intersection of the Nayband and Kalmard faults and there are great outcrops of fe-oxide, along with eastern-western faults and fractures in Kooh-e-Ahan area.. The present study uses structural and remote sensing methods to discover the mechanism for evolution of the Kuh-e-Ahan, and to understand style of mineralization in the mountain, emphasizing on the role of fractures and major faults. In our remote sensing approach, we used DEM data and Aster satellite images and their filtering in main directions to detect displacements and sudden offsets of lithologic units and changes in drainage patterns. In our field studies, we studied mechanism of the faults, emphasizing on the faults within the Kuh-e-Ahan mining district. The results show N-S faults (Nayband fault trend) and NE-SW faults (Kalmard trend) have a general right-lateral mechanism, and the E-W faults are left-lateral with a reverse component. Structural model developed in this study suggest that strike-slip displacement on conjugate fault provided the space required for ascend and development of hydrothermal mineral deposits within the mine district.
A. Naeimi; M. R. Ghassemi; M. R. Sheikholeslami; A. Hajihosseini
Abstract
The Attary Fault is an oblique fault with a mapped length of ~20 km. It is concealed by Quaternary deposits both northeastward and southwestward. However, there is a fault in the north of Kavir-e-Chah Jam that can be considered as the northeast continuation of the Attary Fault in this area. In addition, ...
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The Attary Fault is an oblique fault with a mapped length of ~20 km. It is concealed by Quaternary deposits both northeastward and southwestward. However, there is a fault in the north of Kavir-e-Chah Jam that can be considered as the northeast continuation of the Attary Fault in this area. In addition, satellite imagery reveals that the Mayamey Fault System extends southwestward into north of the Kavir-e-Chah Jam. Therefore, the Attary Fault may join the Mayamey Fault System in the north of Kavir-e-Chah Jam and hence reach a length of ~127km, considering the concealed parts. There is another major fault with maximum reported uplift of 4km, called the Peyghambaran Fault, to the northwest of the Attary Fault. To the west, the Peyghambaran Fault is linked to the Semnan Fault. The connection of the Attary Fault to the Peyghambaran Fault, Semnan Fault and Mayamey Fault System leads to creation of a greater fault system that could have served as the boundary between Alborz and Central Iran, despite the fact that the Attary Fault does not represent significant uplift and mostly cuts the Eocene volcanics. Additionally, since the Attary fault steeply dips to SSE (60-75◦), the so-called “positive flower structure” which is widely regarded as the general framework for the Central Alborz has not formed in this part of the range. Our study also shows that a left-lateral motion has been initiated on the Attary Fault following the westward motion of the south Caspian basin in the Late Cenozoic.
L. Ebadi; S. A. Alavi; M. R. Ghassemi
Abstract
In this paper a part of the Shahr-e-Babak area in NW-Kerman is studied, which is geologically located in Central Iran and Urumiyeh- Dokhtar Belt. The basin was strongly affected by compression in Miocene times, in which deformation is characterized by development of NW-SE trending fold and thrust belt. ...
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In this paper a part of the Shahr-e-Babak area in NW-Kerman is studied, which is geologically located in Central Iran and Urumiyeh- Dokhtar Belt. The basin was strongly affected by compression in Miocene times, in which deformation is characterized by development of NW-SE trending fold and thrust belt. In this paper, we aim atdeciphering polyphase deformation and paleostress history of part of the Central Iran in the Shahr-e-Babak area, and that how various geological aspects may be related to a stress field that has been reoriented through time. Also, we indicate how the brittle deformation studies and paleostress analyses may contribute in the interpretations of the post-collisional tectonic evolution of this area. In this paper, by using systematic brittle tectonic analyses, including stress tensor inversion form fault-slip data, we decipher the succession of deformational events that resulted in present-day structures. Therefore, a statistical view of the brittle tectonic reconstructions taken as a whole leads one to better understand the relationships between the different stress fields and folding events that governed the history of compression in this area .The systematic reconstruction of brittle tectonic regimes led us to characterize an anticlockwise change in the main direction of compression through time. Thus, it can be seen that the late Cretaceous to late Miocene pre-folding N055° and N084° compression was followed by syn-folding N040° compression in the Miocene. The Miocene compression then continued into the Pliocene post-folding N029° direction, and changed afterward to the Pleistocene-Recent post-folding N003° direction. Although this general anticlockwise rotation of compression has probably been progressive through time, our data suggest three distinct stress regimes that (1) predate, (2) are contemporaneous with, and (3) post-date the more consistent compressional stress regime of the folding and thrusting process. According to this reconstruction, it is confirmed that many local right-lateral strike–slip faults were reactivated from NW-SE reverse faults in the Sahahr-e-Babak area of SW Central Iran .These results could properly support the hypothesis of a significant anticlockwise change in the movement direction of the Arabian plate with respect to the Eurasian plate and block rotation in Central Iran.
L. Aghajari; S. A. Alavi; M. R. Ghassemi; M. A. Kavoosi
Abstract
Different geological, structural and morphological characteristics of the eastern Kopeh-Dagh Province in NE Iran resulted in identification of several morphotectonic domains separated by major basement faults. Based on various field surveys, seismic reflection data, satellite images and cross-sections ...
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Different geological, structural and morphological characteristics of the eastern Kopeh-Dagh Province in NE Iran resulted in identification of several morphotectonic domains separated by major basement faults. Based on various field surveys, seismic reflection data, satellite images and cross-sections construction we introduce the fault-bounded deformed areas with different characteristics as the structural domains. These domains are the Hezar-Masjed, Darreh-Gaz- Sarakhs, and the Kopeh-Dagh foredeep from southwest to northeast, respectively. They are bounded by the Kashafrud, Mozduran, and the North Kopeh-Dagh faults. The domains were formed on the Turan plate since Middle Jurassic times when the extensional phase commenced in the Kopeh-Dagh Province. The bounding faults were initially of normal mechanism which generated grabens and half-grabens within the sedimentary basin. The maximum extension and subsidence in the basin occurred during Middle Jurassic, synchronous with the deposition of the Kashafrud Formation. Differential subsidence and configuration of the basin resulted in lateral lithofacies variations and thickness changes of the Kashafrud Formation throughout the basin. The main compression event in the Kopeh-Dagh Province started following the closure of the Neo-tethys ocean between the Iranian and Arabian plates in the Late Eocene, which caused inversion tectonics and reactivation of pre-existing normal faults as well as folding of sedimentary cover.
M Biralvand; M Mohajjel; M.R Ghassemi
Abstract
In this study, brittle deformation in Takab complex is discussed. Deformation in the Takab area has been controlled by two sets of major faults. The first set is characterized by NNW-SSE trending steeply-dipping dextral strike-slip faults with reverse component. The second set includes WNW-ESE trending ...
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In this study, brittle deformation in Takab complex is discussed. Deformation in the Takab area has been controlled by two sets of major faults. The first set is characterized by NNW-SSE trending steeply-dipping dextral strike-slip faults with reverse component. The second set includes WNW-ESE trending moderately-dipping reverse faults which have been obviously displaced by the first set. The basement metamorphic rocks are exposed in the hangingwall of the faults indicating thick-skinned type of deformation and exhumation in the area. The major strike-slip reverse faults have resulted in dextral inclined transpression in the Takab complex area. Fault-related folds in hangingwall and footwall of the faults especially in the Cenozoic sediments indicate young activity and uplift in the area. Development of normal faults and local folds, as well asthe occurrence of earthquakes in the area imply that it is tectonically active. Structural analysis in this area reveal that the major steeply-dipping strike-slip reverse faults have controlled deformation and changedthe homogeneous strain to partitioned strain.Deformation of Cenozoic rocks overlying the basement metamorphic rocks indicate a dextral inclined transpression. Deformation in the younger sedimentary cover (Cenozoic sediments) is related to thick-skinned deformation in the basement metamorphic rocks.
P Gholami Zadeh; M.H Adabi; M Hosseini-Barzi; A Sadeghi; M.R Ghassemi
Abstract
Petrography and geochemistry of the Neyriz Miocene sediments at RoshanKuh and Kuh-e Asaki sections were carried out to determine their provenance, tectonic setting and paleoclimate conditions in the proximal part of Zagros Basin. The Miocene sediments are limited to the Zagros Main Fault at the northeast ...
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Petrography and geochemistry of the Neyriz Miocene sediments at RoshanKuh and Kuh-e Asaki sections were carried out to determine their provenance, tectonic setting and paleoclimate conditions in the proximal part of Zagros Basin. The Miocene sediments are limited to the Zagros Main Fault at the northeast and the Neyrizophiolite zone at the southwest in the Neyriz region. They contain about 700 m red and green sandstone, conglomerate and marl which overlay the Jahrum Formation with a disconformity and covered by Bakhtiari conglomerate with an angular unconformity.Petrography of thin sections indicates that the rock fragments are the most constituent, and then quartz and feldspar respectively. The low compositional and textural maturity of the studied samples (angular grains and poorly sorted sandstones) shows the proximity to the source area. Petrography of the rock fragments and the bulk chemical composition of samples display that their provenance is multiple and the sediments were derived from Sanandaj-Sirjan Zone (Cretaceous limestone- metamorphic rocks- Eocene volcanic) and Zagros Zone (ophiolite sequence- radiolarites- Eocene limestone). Also, point-count data plotted on the QFL and QmFLt triangles indicate the recycled orogen and magmatic arc provenance. Based on geochemical data tectonic setting of Neyriz Miocene sediments is continental island arc and active continental margin. The averages of Cullers' index, CIW΄ (for calculation of the chemical weathering), ICV Index (to determine the maturity source), and SiO2versus Al2O3 + K2O + Na2O diagram for these sediments show a poor weathering and dry climatic condition during their deposition which is supported by the high percentage of calcareous cement and frequency of the rock fragments. The results of this study suggest a sedimentlogical framework for the proximal part of Zagros Basin and the Miocene syn-depositional processes.
L Ebadi; A Alavi; M.R Ghassemi
Abstract
The study area is located in the SW Rafsanjan city and central Iran. In the area, strike- slip faults effected the Cenozoic unites. This paper analysis subsidiary fault data collected from damage zones associated with the Cenozoic Rafsanjan intraplate right-lateral strike-slip fault systems in SW Rafsanjan ...
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The study area is located in the SW Rafsanjan city and central Iran. In the area, strike- slip faults effected the Cenozoic unites. This paper analysis subsidiary fault data collected from damage zones associated with the Cenozoic Rafsanjan intraplate right-lateral strike-slip fault systems in SW Rafsanjan city. Fault sets, arranged in a consistent kinematic architecture that is compatible with the Cenozoic regional strike-slip environment. In the paper, kinematic architecture of fault zone interpret in the subsidiary fault. The results show that five peaks is prominence. Angular and kinematic relation among subsidiary fault set show that right-lateral strike- slip and revers fault are the dominant kinematic type in the area. Based on, the angular analysis in the damage zone, we have 5 subsets. 2 subsets of 5 subsets named 1rev (NW-SE trending) and 2rev (E-W trending). In the strike- slip fault mechanism, 3 subsets is demined, three azimuth named 1rl (NW-SE striking), 2rl (E-W striking) and 3rl (WNW-ESE striking). Average strike of set 1rl and 1rev indicate the orientation of the PDZ for fault systems and the PDZ be produced by early localization of the principal displacement zone along pre-existing mechanical discontinuities inherited. Early formation of the PDZ by re-activating pre-existing mechanical discontinuities.The azimuthal value of the faults set in the kinematic architecture are similar to predicted by the simple shear Reidel model. By analysis with kinematic architecture in damage zone of strike- slip fault system indicated that the linking damage zone is very important to increase permeability and created void. The void is low pressure stress and magma can intrude in the area and the dikes formed. The PDZ induced stress and the second and third order fracture is created. Stress analysis in the study are show shear – compression regime convert to compression. The maximum principle axis show N20E to N-S in the Cenozoic. The change of stress regime is correlated by formation fault and fold with E-W trend. The change regime caused reactive pre-exiting fault.
R Entezari; S.A Alavi; M.R Ghassemi
Abstract
Metamorphic rock assemblage of southern Salmas area is located in the northwestern terminal part of Sanandaj-Sirjan zone, and includes various rock types. This study uses field observations plus mineralogy and petrography of samples to describe and interpret the microstructures in the area. Different ...
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Metamorphic rock assemblage of southern Salmas area is located in the northwestern terminal part of Sanandaj-Sirjan zone, and includes various rock types. This study uses field observations plus mineralogy and petrography of samples to describe and interpret the microstructures in the area. Different rock units are classified into three groups based on their parent rocks, and consist of 1) metabasite, 2) quartz-feldespathic, and 3) marble. Most of these rocks have mylonitic texture but the grade and the intensity of mylonitization are different. Presence of mylonitic foliation and lineation along with other microstructures such as various porphyroclasts, mica fish, S-C fabric, and S-C' fabric demonstrate different mylonitic zones in this area. Due to differences in strain rate, parent rock type, and depth of deformation, we could distinct three mylonitic zones in the metamorphic complex. Most of these mylonitic samples show features characteristic of low to medium grade mylonites, in which mylonitization grade increases from west to east and center of the study area. Presence of ultramylonites in the central part of the area indicates increases in strain rate. Also presence of high-grade mylonites (T> 650 ºC) and migmatite imply that the deformation occurred at depths of middle to lower crust. We could discern two metamorphic phases (M1 and M2) and six deformation phases (D1, D2, D3, D4, D5, D6). Compressional deformation phase D1 occurred after Precambrian magmatism, then a metamorphic phase (M1) impressed these rocks by the Latest Cambrian. During Late Permian to Early Cretaceous, two deformation phases (D1 and D2) with a major simple shear component strongly affected the metamorphic complex, leading to the development of mylonitic zones. Synchronous with the deformation phase D2, a retrograde metamorphic phase (M2) affected the complex. At Late Cretaceous to Early Paleocene, deformation phase (D4) caused obduction of ophiolites over the metamorphic complex. Eventually, two brittle deformation phases (D5 and D6) affected all older rocks.
M Baghernejhad; M.R Ghassemi; B Oveisi
Abstract
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 ...
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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 from other structures within the area, as well as from 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 from those estimated forthe neighboring Alborz and Zagros Orogens, where 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.
M Ramazani; M.R Ghassemi
Abstract
The erosional window of Aghdarband, located in NE Iran and SE of Mashhad is a unique place to study of the Eo-Cimmerian event. This event (Late Triassic-Middle Jurassic) resulted from closure of the PaleotethysOcean and collision between the Iran and Turan plates. In this study, we have tried to analyze ...
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The erosional window of Aghdarband, located in NE Iran and SE of Mashhad is a unique place to study of the Eo-Cimmerian event. This event (Late Triassic-Middle Jurassic) resulted from closure of the PaleotethysOcean and collision between the Iran and Turan plates. In this study, we have tried to analyze the microstructural features of the exposed carbonate units (the Sefid Kuh formation of the Early Triassic age and some Paleozoic units) in the Aghdarband area. The average of ellipticity calculated for the calcite grains is about 0.78 located in the oblate part of the Flinn diagram. The estimated kinematic vorticity number is 0.6 - 0.7. The calcite twining in the carbonate units exposed in the Aghdarband area indicate temperatures of about 180-200˚C and differential stresses of about 180-240 MPa during the main deformational event of the area (Eo-Cimmerian).
M Nemati; J Hollingsworth; M.R Ghassemi
Abstract
Our research focuses on the seismotectonics of the north of Eastern Alborz and southeast of the Caspian Sea. Eastern part of the Caspian fault, and seismological active plain situated in north of the area have been studied. The seismological data of microearthquakes (ML>4.5) recorded by the local ...
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Our research focuses on the seismotectonics of the north of Eastern Alborz and southeast of the Caspian Sea. Eastern part of the Caspian fault, and seismological active plain situated in north of the area have been studied. The seismological data of microearthquakes (ML>4.5) recorded by the local network of the Geological Survey of Iran (installed during 2009 and 2010) and regional seismicity located by seismological networks of the Geophysics Institute of University of Tehran and International Institute of Earthquake Engineering and Seismology of Iran were used. Also geomorphological evidences in the area and dynamic parameters of the 1985 Gorgan earthquake, MS=6.0, are included for getting a better justification. Although deep thrust mechanisms of the 1999, 2004 and 2005 earthquakes indicate N-S compressional regime at depth and normal component of shallow earthquakes (ML>4.5) shows extensional regime at near surface in southeast of the Caspian Sea. The morphological evidences confirm this normal kinematics. In addition, the dynamical parameters of the 1985 Gorgan earthquake and its focal mechanism introduce the Caspian fault as the source of this thrust earthquake. All evidences confirm probable underthrusting of southeast of the CaspianBasin beneath the Eastern Alborz.
Y Jalili; M.M Khatib; E Gholami; M.R Ghassemi
Abstract
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 ...
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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.
S Alimardan; Sh Solaymani Azad; M Ghorashi; M.R Ghorashi; B Oveisi; A Hatami
Abstract
Due to urban population growth in recent decades and the need for decentralization of cities with limited facilities and increasing marginalization in the larger cities, construction of new cities around large towns has been considered by decision makers to develop a plan to create new cities around ...
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Due to urban population growth in recent decades and the need for decentralization of cities with limited facilities and increasing marginalization in the larger cities, construction of new cities around large towns has been considered by decision makers to develop a plan to create new cities around these towns. One of the most important parameters for the construction of new population centers is seismotectonic studies. Hashtgerd New Town in southern slopes of the Alborz (located 65 km northwest of Tehran) is located on the uplifted deposits of the Plio-Quaternary. Vertical tectonic movements in the range caused the height difference of about 300 m between Hashtgerd and its southern plain elevations. Due to the emplacement of the city on the uplifted Plio-Quaternary deposits, and the lack of information about the causative active fault in this region, an attempt has been made to investigate the morphotectonic characteristics of the area on the basis of survey satellite image, aerial photo, digital elevation model, and field observations. In the present study, an active fault zones with NW-SE trends has been identified with oblique-slip movements (compression with left-lateral strike-slip component). The N-NE stress direction, in regards to the abovementioned trend is oblique, and hence, the result could be a transpressional regime for the area. Recognition of mentioned active faults is very important for earthquake hazard assessment studies for the new town.
A Salehpour; B Oveisi; M.R Ghassemi
Abstract
In thin-skinned fold-thrust belts, the style of deformation is critically depends not only on the resistance to sliding along basal detachment, but also on the presence of intermediate decollement levels or/and ductile units within the wedge. In ZFTB the incompetent units known as detachment levels like ...
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In thin-skinned fold-thrust belts, the style of deformation is critically depends not only on the resistance to sliding along basal detachment, but also on the presence of intermediate decollement levels or/and ductile units within the wedge. In ZFTB the incompetent units known as detachment levels like the Gachsaran formation (Shallow level) and the Hormuz salt series (deep) affect strongly the deformation style. However, in many cases shallow level detachment of the Gachsaran unit controls this shallow deformations, but owing to the different facies of this unit in the studied area it is reasonable to other incompetent shallow units (e.g. the middle Miocene Mishan Fm. and the Upper part of Aghajari Fm.) to partially decoupling deformation form the underlying sedimentary units, and have permitted the re-activation of pre-existing syncline structures, through upward extrusion of the syncline core. Owing to the concentration of significant amounts of young deformation across the structure (specially northern hinge) in the style of erosional surfaces, the East-West trending Anve syncline in north of the Bastak town, considered to be one of the most active structures in the region. In this study, we try to define the vertical deformation of a geomorphic marker as well as using tectonic morphology techniques to shed light on the deformation extend and pattern in the eastern and western parts of the structure . However, the microseismic data do not suggest any significant event related to this kind of deformation, but studying deformation style and relative uplift rate estimation could be beneficial dealing with earthquake hazards in the region.
N Saboor; M.R Ghassemi; M Eskandari; A Nazari F; B Oveisi
Abstract
Erosion agents diffuse the scarps created by the earthquakes, are and their primary sharp shapes are gentled. This process is accomplished with the definite rate, which is accounted with the diffusion equation. Rate of diffusion depends on primary shape of scarp and diffusion coefficient that is coefficient ...
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Erosion agents diffuse the scarps created by the earthquakes, are and their primary sharp shapes are gentled. This process is accomplished with the definite rate, which is accounted with the diffusion equation. Rate of diffusion depends on primary shape of scarp and diffusion coefficient that is coefficient of diffusion equation. The coefficient depends on various parameters such as the climate and the value of erosion of scarp material. The coefficient is accounted with the modeling of earthquake scarp with the definite age and initial shape. We afforded three profiles from the Salmas earthquake scarp created in 1930. We diffused the reconstructive primary shape of them by the code that we wrote in the Matlab software. We present diffusion coefficient of the Salmas area, and the mean of definitive coefficient. This coefficient is used for other earthquake scarps and traces in this and other areas with the same climate. The age of their formation was calculated by this coefficient and the prepared profiles.
A Ahmadi-Torkmani; M.R Ghassemi
Abstract
The present research uses precise field data to provide a balanced cross-section of the Mahneshan area, and investigate nature of depth distribution of its major structures. Our structural studies indicate that the Mahneshan and Anguran faults are two major faults, which penetrate deep into the crust ...
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The present research uses precise field data to provide a balanced cross-section of the Mahneshan area, and investigate nature of depth distribution of its major structures. Our structural studies indicate that the Mahneshan and Anguran faults are two major faults, which penetrate deep into the crust and cause a considerable amount of horizontal shortening in the area. In a more specific way, the Anguran fault roots deep into the middle crustal levels of about 21 km, and thrusts the whole Phanerozoic sequence and even parts of the Precambrian basement rocks over the younger strata. We believe that the abovementioned thrust originates not from a low-competency decollement plane, but from a ductile shear zone in deep crust. Evidences for development and conditions of such shear zone are present in the Precambrian basement rocks of the Anguran fault’s hanging-wall. We suggest that the decollement surface for the Mahneshan thrust, which is located in the shallower depths (13 km), is related to probable occurrence of evaporitic materials equivalent to the Hormoz Series beneath the Kahar Formation. Syn-sedimentary deformation within the Qom Formation in the hanging-wall of the Anguran thrust, as well as other evidences present in Neogene deposits of the area suggest that the thrust fault has been active since Oligocene. Restoration of displacements across the Anguran fault, and comparing the results with inception age for the fault suggests that the Anguran fault has been active with a slip rate of about 1 mm/yr. The structural features in the Mahneshan area indicate that thick-skinned faulting along with thin-skinned tectonics have resulted in a considerable amount of thickening of the crust in the region; this observation is in accordance with abovementioned characteristic of the crust in the Sanandaj-Sirjan zone.
S Afzali; N Nezafati; M Ghaderi; J Ghalamghash; M.R Ghassemi; A Karimi Bavandpur
Abstract
The Gazestan magnetite–apatite deposit is situated 78 km east of Bafq. The Gazestan deposit is located in Bafq-Poshtebadam subzone of Central Iran structural zone. The rock units in the area belong to the Rizu series and consist of carbonate rocks, shale, tuff, sandstone and volcanics. In addition ...
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The Gazestan magnetite–apatite deposit is situated 78 km east of Bafq. The Gazestan deposit is located in Bafq-Poshtebadam subzone of Central Iran structural zone. The rock units in the area belong to the Rizu series and consist of carbonate rocks, shale, tuff, sandstone and volcanics. In addition to sedimentary and volcanic rocks, intrusive rocks in the form of stock and dyke outcrop as diorite gabbro, gabbro, diabase, quartz-monzonite and granite in various places. The green rocks with acidic to intermediate composition (trachyte and dacite demonstrate green color due to alteration) host iron and phosphate mineralization which in some localities, show subvolcanic facies. The alteration is more obvious in the volcanic rocks and includes chloritization, argillic, silicification, and also formation of mafic minerals such as epidote, tremolite and actinolite. The host rocks are strongly altered. Mineralization at the Gazestan deposit comprises a combination of iron oxides and apatite with various ratios accompanied by quartz and calcite, observed in different forms mainly within the trachytic-dacitic rocks and a small proportion in the rhyolites. Five forms of mineralization are distinguished in the area including massive iron ore with minor apatite, apatite-magnetite ore, irregular vein-veinlets (stockwork) in the brecciated green rocks, disseminated, and pure massive apatite veins. The host rocks in the Gazestan area plot on calc-alkaline field. Comparison of the most important characteristics of the Gazestan deposit (including tectonic setting, host rock, mineralogy, alteration, structure and texture) with those of various types of mineralization in the world suggest that the deposit is quite similar to the iron oxide - apatite deposits.
H Amini; M Fattahi; M.R Ghassemi
Abstract
The Doruneh fault is the second longest fault systems in Iran. This fault is 700 km long and extended from the Afghanistan-Iran border to the central Iran desert. Despite of its length, and position in the convergence zone between the Arabian and Eurasian plates and its seismic potential, only one historical ...
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The Doruneh fault is the second longest fault systems in Iran. This fault is 700 km long and extended from the Afghanistan-Iran border to the central Iran desert. Despite of its length, and position in the convergence zone between the Arabian and Eurasian plates and its seismic potential, only one historical earthquake (M>7) and two instrumental (M>6) earthquakes are recorded on this fault. Therefore, study of this fault is very important for evaluation of its seismic hazard. In our study, we used the Landsat images, aerial photographs, topography maps, geological maps and field work data to identify and estimate the amount of displacements of rivers, rock units, and some alluvial fans along this fault. Three branches of the Doruneh fault investigated in this study, named as the north, middle and south branches according to their geographical locations. This study demonstrates that both of the maximum and minimum fault displacements have occurred on the southern branch. Furthermore, the amount of displacements of the rivers, which have cut the alluvial fans during the Quaternary period, suggests that this branch, particularly between 57˚00΄ and 58˚50΄E, is more active than the other branches. Although, several slip rates were previously determined using different methods for some parts of this fault by the authors and other researchers, we suggest further dating and geodetic methods in the same regions and other part of the fault to estimate and compare the slip rate of different branches of this important fault.
E Hajizadeh Naddaf; B Oveisi; M.R Ghasemi; M.J Bolurchi
Abstract
The analytical models in rock mechanics represent suitable analysis of deformation and failure conditions of the samples bearing simple geometry and mechanical properties. Nowadays different methods of numerical modeling, like finite difference method (FDM), are used for analysis of continuous, non- ...
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The analytical models in rock mechanics represent suitable analysis of deformation and failure conditions of the samples bearing simple geometry and mechanical properties. Nowadays different methods of numerical modeling, like finite difference method (FDM), are used for analysis of continuous, non- and quasi- continuous behavior. This paper represents logical estimate of geomechanical properties of the Asmari formation with usage of the results of triaxial tests on intact rock samples of the upper limy part of this formation and also the finite difference methods. For this purpose, we designed some models containing simple boundary condition and only one rheological unit. To simulate the failure conditions of the samples, a geomechanical simulative software (Flac 2D) was used. The failure of samples under the experienced stress conditions in laboratory were of basic data for simulation of failure conditions by finite difference method. The results show that the cohesion coefficient and uniaxial tensile strength are of sensitive parameters in controlling the failure conditions. This study suggests that the values of Young's and Bulk modulus are 260GPa, 23GPa, respectively, when the uniaxial tensile strength and cohesion coefficient are considered 29MPa and 26MPa, respectively.
M Foroutan; H Nazari; B Meyer; M Sébrier; M Fattahi; K Le Dortz; M Ghorashi; Kh Hessami; M. R Ghassemi; M Talebian
Abstract
The Dehshir fault system (DFS) including six fault segments forms the western border of NS-striking active dextral strike-slip fault cutting the Sanandaj-Sirjan, Uromieh-Dokhtar magmatic arc, and Central Iran. This active fault system right-laterally offset Eocene volcanic rocks and Quaternary alluvial ...
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The Dehshir fault system (DFS) including six fault segments forms the western border of NS-striking active dextral strike-slip fault cutting the Sanandaj-Sirjan, Uromieh-Dokhtar magmatic arc, and Central Iran. This active fault system right-laterally offset Eocene volcanic rocks and Quaternary alluvial fans. Geomorphic evidence imply the activity of the DFS in the Late Quaternary, and paleoseismic investigations revealed seismic movements along the Marvast fault segment during the Late Pleistocene and Holocene timescales. In order to unravel the seismic history of the DFS over the intermediate geologic (103 -105 yr) time scale, and based on the morphotectonics and sedimentary-stratigraphic properties, three paleoseismic sites have been selected along the 35-km-long stretch of the Marvast fault segment. The southern site (Harabarjan) shows steep fault branches of N140±10º strike with sub-horizontal striations in dextral component. Another trench has been excavated at the North Marvast site whitin the Late Pleistocene-Holocene alluvial and colluvial deposits. OSL analysis of loose quartz rich deposits yielded an age of ~72 ka for the oldest exposed sediments. Paleoseismic stduies along the Marvast fault segment provide evidence for the occurrence of several large seismic events associated with surface ruptures along the DFS. The chronology of paleoearthquakes on the Marvast segment indicates that at least 7 large (≈Mw > 7) earthquakes occurred in the last 43 ka with an average recurrence time of 3650±150 years. The most recent earthquake, event I, occurred ~2200 years ago, which associated with 2-4 m of dextral slip and >40 km surface rupture along the Marvast fault segment. These investigations are compatible with the lack of destruction in the Marvast historical (~1300 years) castle, located
A Pireh; S.A Alavi; M.R Ghassemi; A Shaban
Abstract
A major part of source rocks in the Zagros Fold Belt were deposited during Neocomian time; the lowermost part of the Garau Formation has charged the Early Cretaceous Petroleum System of the Lurestan province. These source rocks are widely distributed in the Lurestan Depression and in the NW part of the ...
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A major part of source rocks in the Zagros Fold Belt were deposited during Neocomian time; the lowermost part of the Garau Formation has charged the Early Cretaceous Petroleum System of the Lurestan province. These source rocks are widely distributed in the Lurestan Depression and in the NW part of the Dezful Embayment. The Kabir-Kuh anticline, which is a prominent structure of the Lurestan province, is more than 200 km long, and contains outcrop of the Garau Formation. Natural fracture systems have an important role in increasing of permeability and sometimes porosity of many reservoirs, and are necessary for the primary migration of hydrocarbons from the source rock to the reservoir. We have collected and analyzed field data on fracture set densities andtypes in Garau Formation and in parts of Sarvak Formation which outcrop in the Kabir kuh anticline of Zagros Belt. According to our analyses we have identified 8 fracture sets in 4 fracture systems: 1) a NNE-SSW transverse fracture system (sets A and B), 2) an ESE-WNW longitudinal fracture system (sets C and D), 3) a NE-SW and NNW-SSE oblique fracture system (sets E and F), 4) a SE-NW and ENE-WSW oblique fracture system (sets G and H). The transverse fractures and their orthogonal stylolites are Early Cretaceous to pre-late Miocene in age, while longitudinal and oblique fracture systems have formed since Late Miocene. Some transverse fractures show calcite infillings. We suggest that there have been two phases of counterclockwise rotation in orientation of the stress fields that produced these fractures, 1) a counterclockwise rotation of the stress field between development of non-mineralized fractures and open fractures and 2) a counterclockwise rotation of the stress field between development of the oblique fracture system (sets E and F) and the extension fractures (sets A and B). These rotations in the stress field have probably occurred due to rotation of the Arabian plate during its convergence to the Eurasian plate.
