Petrology
Reza Jamal Omidi; Saeid Hakimi Asiabar; Shahrooz Haghnazar; Mansour Vosoghi Abedini
Abstract
Tarom mountains are located at the southwestern end of the Alborz mountain range with an approximate northwest-southeast direction. Tashvir region is a part of the northern margin of the Tarom mountains. Most igneous rocks in this area include basalt, andesitic basalt, and interlayers of tuff. Enrichment ...
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Tarom mountains are located at the southwestern end of the Alborz mountain range with an approximate northwest-southeast direction. Tashvir region is a part of the northern margin of the Tarom mountains. Most igneous rocks in this area include basalt, andesitic basalt, and interlayers of tuff. Enrichment of LIL elements with positive anomalies of Ce, P, Sm, and depletion of Nb, Ta, Zr, Hf, and Th, elements and also K2O/Na2O and Ba/Rb ratios in the rock samples of Tashvir area, indicate magma contamination with the lower crust. The evidence of crustal contamination and the ratio of Nb/Y and Zr/Y in the samples indicate that the basalts of the Tashvir region belong to the source of the plume. Alkaline, shoshonitic, and peraluminous nature, REE enrichment (i. e. Ba, Rb, and Sr), low titanium content, origin, and depth of magma indicate they're belonging to the rift environment. In this study, in addition to determining the characteristics of igneous rocks in the Tashvir area, the results of several previous studies are plotted on the map of the Tarom mountains. Accordingly, the tectonic setting of the Tarom range is divided into two parallel sub-regions with magmatic arc and rift-type eruptions, which expansion of this rift zone has stopped before it evolve as a back-arc basin.
Stratigraphy and Palaeontology
Nasrollah Abbassi; Reza Aharipour
Abstract
Mila Formation includes five members in the Tuyeh-Darvar section, west Damghan. Fifth Member of formation comprises alternations of calcareous shale, limestone and green shales. Trace fossils of this member includes Cruziana problematica, Gordia isp., Helminthopsis abeli, Helminthopsis tenuis, Palaeophycus ...
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Mila Formation includes five members in the Tuyeh-Darvar section, west Damghan. Fifth Member of formation comprises alternations of calcareous shale, limestone and green shales. Trace fossils of this member includes Cruziana problematica, Gordia isp., Helminthopsis abeli, Helminthopsis tenuis, Palaeophycus striatus, Planolites beverleyensis, Psammichnites gigas, Scolicia strozzii and Treptichnus pedum. Circulichnis montanus abundant in the upper most layers of the fifth Member and is circular cylindrical ring in shape. Circulichnis is a fodinichnion, that produced by progressive and plasticity behaviors of annelids. It seems that these trace fossils are belong to the mid parts of the turbidite rhythmic sequences and formed in the turbidity conditions of the sedimentary environment.
Stratigraphy and Palaeontology
Tayebe Sarbandi Farahani; Mehdi Yazdi; Mahmoud Reza Majidifard
Abstract
This paper focused on the systematic of the benthic foraminifera from the Chaman Bid and Goznawwi sections. At the type locality of the Chaman Bid Formation, consists of alternation of limestone (grainstone to wackstone), argilasious limestone and marl. The age of tha Chaman Bid Formation based on ammonite ...
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This paper focused on the systematic of the benthic foraminifera from the Chaman Bid and Goznawwi sections. At the type locality of the Chaman Bid Formation, consists of alternation of limestone (grainstone to wackstone), argilasious limestone and marl. The age of tha Chaman Bid Formation based on ammonite fauna range from ?Bathonian to late Tithonian. and the age. Near the Azadshar, the Farsian Formation is exposed and consists of fossilferous the soft marl, sandstone, limestone and silt which based on ammonite, age of this sediment considered as Callovian. Two studied sections are bearing well - preserved foraminifera which most belong to Lagenina (most belong to Nodosaridae and Vaginolinidae families) and Rotalina (Epistominidae); total 23 genus and 39 species from Goznawwi and 10 genus and 16 species from Chaman Bid sections. The 28 species of the benthic isolated foraminiferal assemblages are first recorded from Iran. In additional, based on this study, Iranian assemblage of foraminifers at this time are most similar to those of the North of the tetyan releam.
Tectonics
Saeid Hakimi Asiabar
Abstract
Abstract The area of Dona mine is a part of central Alborz. The Dona anticline is a part of pop up structure and located between Kandavan and Azadkuh thrust faults. In this research three sets of major faults are recognized. The first category of faults with W-E trend, dip 40-50, Rake angle more than ...
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Abstract The area of Dona mine is a part of central Alborz. The Dona anticline is a part of pop up structure and located between Kandavan and Azadkuh thrust faults. In this research three sets of major faults are recognized. The first category of faults with W-E trend, dip 40-50, Rake angle more than 70, are parallel to the major fold axes and second category of faults have NE-SW trend with reverse movement and rake angle less than 65. The third category which truncate the first sets, have nearly N30W to N40W direction with dip more than 75 and rake angle more than 70. The aim of this paper is investigation on the structure of Dona mine and investigations on the mechanism of third category of faults which are not popular in Alborz range and did not discussed before. Some of these faults do not have visible slickensides and the mechanism of these faults held on the basis of preparing geologic map on the scale of 1:1000, structural cross sections and implementing Schmidt net with construction methods. The change of tectonic movements from collision into sinstral, on the pop-up structure created this set of young reverse faults with NW-SE trend.
Mohammad Reza Sheikholeslami
Abstract
Evidence of at least ten different tectonic- controlled sedimentary basins can be recognized in the central part of the Alborz Mountains in the Middle part of the Alpine-Himalayan belt. They formed from Neoprotrozoic to recent time as the results of the relative plate motion in southwest of Asia in Tethyan ...
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Evidence of at least ten different tectonic- controlled sedimentary basins can be recognized in the central part of the Alborz Mountains in the Middle part of the Alpine-Himalayan belt. They formed from Neoprotrozoic to recent time as the results of the relative plate motion in southwest of Asia in Tethyan realm. The basins include: (1) Prototethys Late Neo-Proterozoic to Early Ordovician epi-continental/platform basin; (2 Paleotethys Middle Ordovician to Devonian rift basin; (3) Devonian to Middle Triassic continental shelf basin; (4) Upper Triassic to Lower Jurassic foreland basin; (5) Shemshak back arc rift basin; (6) South Caspian carbonate platform basin; (7) Paleocene clastic sedimentary basin; (8) Karaj back arc basin; (9) Oligo-Miocene foreland basin; (10) Pliocene-Pleistocene intramontane basin. Each basin has its own unique history connected to the different stages of the birth, development and destruction of the Prototethys, Paleotethys and Neothethys Oceans in the Middle East region in the southwest of Asia.
B. Hosseini; M. Mohammadi Siyani; A. R. Ahmadi
Abstract
Quaternary volcanic activities in Alamut Valley occurred in three stages and covered Neogene red sedimentary rocks. The volcanic rocks are intermediate in composition and are classified as hornblende trachyandesite. The SiO2 content of the rocks varies in a range from 55.48-61.88 wt%. Chondrite normalized ...
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Quaternary volcanic activities in Alamut Valley occurred in three stages and covered Neogene red sedimentary rocks. The volcanic rocks are intermediate in composition and are classified as hornblende trachyandesite. The SiO2 content of the rocks varies in a range from 55.48-61.88 wt%. Chondrite normalized REE patterns exhibit a steep arrangement of LREEs and MREEs (La/Ho)N =85 and a relatively flat HREE (Ho/Lu)N =1.3., Large ion lithophile elements (LILE) do not show strong enrichment compared to LREEs in mantle normalized multi-element spider diagrams. Nb andTa are slightly depleted compared to neighboring light rare earth elements. These rocks have high Sr/Y (140-205), La/Yb (113-142) ratios, accompanied by high K2O/Na2O (0.7-0.9) and resemble C-Type adakites. Geochemical evidence suggest that these rocks are resulted from partial melting of thickened eclogitic lower crust in presence of abundant residual garnet. Partial melting of lower continental crust probably triggered by thickening of crust as a result of late Cenozoic orogenic phases especially the Passadenian Orogenic phase.
M Khazaee; M Hosseini-Barzi; A Sadeghi; H Mosaddegh
Abstract
The Jeirud Formation (Upper Devonian) in Deh-Sufian section of northeast of Shahmirzad consists of siliciclastic and carbonate deposits. In the study area lower boundary of the Jeirud Formation with fine grain clastic deposits of the Mila Formation is erosional (Disconform) and has been conformably overlain ...
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The Jeirud Formation (Upper Devonian) in Deh-Sufian section of northeast of Shahmirzad consists of siliciclastic and carbonate deposits. In the study area lower boundary of the Jeirud Formation with fine grain clastic deposits of the Mila Formation is erosional (Disconform) and has been conformably overlain by dark carbonate deposits of the Mobarak Formation. The clastic deposits of the Jeirud Formation include conglomeratic, sandy and muddy facies. The conglomeratic deposits comprises three facies A1, A2 and A3 that are equivalent to Gcm, Gt and Gmm/Gmg of Miall facies respectively. Also, five sandy facies of B1, B2, B3 and B4 equivalent to St, Sh, Sm and Sr of Miall respectively and B5 (Shc) with hummocky cross stratification (HCS) sedimentary structure have been identified. Muddy facies including C1 and C2 are equivalents to Miall’s Fsm and Fl facies. Carbonate facies (D) comprising small amounts of the stratigraphic column is almost entirely dolomitized. Field and petrographic studies provide five facies association: fluvial, foreshore-backshore, shoreface, offshore transitional zone and offshore and carbonate facies interpreted as Proximal carbonate tempestites and distal carbonate tempestites based on evidences such as basal erosional surface, normal grading, HCS and coexisting clastic facies . In the study area, the Jeirud Formation deposits initiate with fluvial sequences that have been followed by storm dominated marine deposits as foreshore-backshore deposits and alternations of shoreface to offshore deposits. Study of sequence stratigraphic surfaces especially important subaerial unconformities and also stratal stacking patterns of the formation resulted in determination of three subaerial unconformity bounded depositional sequences plus transgressive part of the 4th sequence.
F Vaez-Javadi
Abstract
The East Yurt mine, SE Azadshahr, Golestan Province contains well preserved plant macrofossils containing nineteen species allocated to thirteen genera of various orders viz., Equisetales, Filicales, Cycadales, Bennettitales, Ginkgoales, and Coniferales. The plant macrofossils in this area are studied ...
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The East Yurt mine, SE Azadshahr, Golestan Province contains well preserved plant macrofossils containing nineteen species allocated to thirteen genera of various orders viz., Equisetales, Filicales, Cycadales, Bennettitales, Ginkgoales, and Coniferales. The plant macrofossils in this area are studied for the first time. Based on the occurrence of Pterophyllum bavieri, Pterophyllum nathorsti,and Baiera muensteriana a Rhaetian age is suggested for this assemblage. Since, there was no differentiation between formations in geological map, these flora confirms spreading of the Kalariz Formation in this area. The East Yurt mine flora is correlated to the plant macrofossil assemblages of Minoodasht, Narges-Chal, Zirab, Tazareh, Ashtar, Abiek, and Jajarm (Alborz Mountains), Ghadir Member of the Nayband Formation in the Parvadeh mines (Tabas Block), and Darbid-Khun (Kerman Basin). Moreover, this assemblage evidenced in Europe (Germany, Austria, Sweden, Greenland, France, Denmark), China, Turkistan, and the Central Asia. Therefore, there were close floristic relationships between North and Central-East Iran (Kerman Basin and Tabas Block) and these area were palaeogeographically closely related, probably forming a uniform paleoenvironment and palaeoclimate during the Late Triassic. Furthermore, Iran was located at the Middle Asia Province among the Euro-Sinian Region of Vakhrameev climatic belt subdivisions and the South-western Region of Dubroskina’s subdivisions during this time.
B Taherkhani; H Nazari; M Pourkermani; M Arian
Abstract
The E-W trending North Qazvin Fault is situated in north & northeast of Qazvin city in south-central Alborz. Across the fault, Karaj formation (Eocene) is thrusted over Hezardarreh Formation (A) and the alluvial B Formation. It could be the source for the 1119 AD earthquake with an estimated magnitude ...
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The E-W trending North Qazvin Fault is situated in north & northeast of Qazvin city in south-central Alborz. Across the fault, Karaj formation (Eocene) is thrusted over Hezardarreh Formation (A) and the alluvial B Formation. It could be the source for the 1119 AD earthquake with an estimated magnitude of Ms: 6.5. The North Qazvin Fault is a seismically active fault, therefore it is one of the most important earthquake threats for the Qazvin as an industrial city of Iran. Morphotectonicand detailed field studies along a part of the North Qazvin Fault allows us to measure horizontal and vertical offsets caused by recent movements on this fault. One of the measured horizontal and vertical displacements due to the recent movements on the fault is 4 and 3.5 meters, respectively. The geometry (strike, dip and rake) of the North Qazvin Fault in this part is 090˚, 45˚, 51˚ respectively. Our investigations show that the North Qazvin Fault is a north-dipping compressional fault. The North Qazvin Fault and its surrounding faults such as Najm-abad fault appear as a propagating fault system which has left-lateral compressional kinematics in southern part of the west-central Alborz.
N Afsari; F Taghizadeh-Farahmand; M.R Ghassemi
Abstract
The AlborzMountains are part of the Alpine-Himalayan orogenic belt, situated to the south of the Caspian Sea and north of the Central Iran. . The region is undergoing extensive crustal deformation and shortening between the north-central Iran and the rigid SouthCaspianBasin crust. In this study, we used ...
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The AlborzMountains are part of the Alpine-Himalayan orogenic belt, situated to the south of the Caspian Sea and north of the Central Iran. . The region is undergoing extensive crustal deformation and shortening between the north-central Iran and the rigid SouthCaspianBasin crust. In this study, we used the P-wave receiver function modeling to investigate the crustal structure beneath the eastern part of the AlborzMountains from data recorded between 2004-2010 in Sari and Semnan seismic networks of short-period seismographs, permanently deployed across the area. We observed clear conversions (Ps) from the Moho boundary, and we used them to define a model for the crust of the eastern Alborz. Our analysis indicates a thickening of the crust from ~51±2 km beneath the northern part of the eastern Alborz to ~62±2 km beneath the central part of the region, then a thinning of the crust to ~52±2 km towards south of the eastern Alborz Mountains.
Z Hamidi Beheshti; H Alimohammadian; M Talebian; A Shahidi; M.R Ghassemi
Abstract
Geomagnetism is one of the most applied techniques of geophysics in geology. Today, this method is applied in different disciplines such as Magnetic fabric of rocks, palaeomagnetism and environmental magnetism. Each of these magnetic methods is suitable for a particular lithology. Therefore, the potential ...
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Geomagnetism is one of the most applied techniques of geophysics in geology. Today, this method is applied in different disciplines such as Magnetic fabric of rocks, palaeomagnetism and environmental magnetism. Each of these magnetic methods is suitable for a particular lithology. Therefore, the potential of sandstones of Shemshak Group, in central AlborzMountain range were examined to record their response to the application of some conventional magnetic methods. This rock unit is formed during two major tectonic events of early and middle Cimmerian and has great coverage not only in the study area but also in a vast majority of Iran. The total number of 135 oriented core samples was taken from 18 stations. In this study combination of magnetic and petrographic data are examined. The result of magnetic mineralogy analysis of all samples (except samples from stations 10 and 15) show irreversibility i.e. minerals such as hematite and magnetite, have formed during the heating stage. The results of thermal demagnetization analysis showed that ferromagnetic minerals present in the samples (except samples from stations 10, 14 and 15) have demagnetized below 400 °C and by proceeding heating, samples show zigzag pattern or show abnormal increase in susceptibility. This indicates that, the magnetic minerals are formed during heating in one stage and due to unstability lose its susceptibility in other stage. The magnetic susceptibility (Km) vary from 200-400×10-6 SI for more stations of study area, indicating abundance of paramagnetic mineral in this rock unit. From petrography point of view all the sandstone samples are classified as arenites and ratio of quartz to lithic fragment and feldspar is relatively low, which may indicate low mineral maturity. Comparison of magnetic mineralogy and thermal demagnetization data for two stations S10 and S15 show that there is an inverse potential relationship between amount of stable ferromagnetic mineral in a sample and amount of its alteration during heating stage. The results of this study reveal the poor nature of Shemshak Group sandstones for palaeomagnetic studies due to their low mineral maturity and water percolation which increase the possibility of acquisition of chemical remanent magnetization (CRM). The high sedimentation rate of sandstones cause magnetic inclination and declination error, and low ferromagnetic mineral fraction in samples, make them unsuitable to record magnetic directionsduring formation of rocks. However, abundance of paramagnetic minerals such as biotite in these rocks, proves their applicability for magnetic fabric studies.
M Haj Manuchehri; M Arian; M Ghorashi; A Solgi; A Sorbi
Abstract
Geomorphic indices of active tectonics are useful tools to analyze the influence of active tectonics. These indices have the advantage of being calculated from ArcGIS and Remote Sensing software packages over large areas as a reconnaissance tool to identify possible geomorphic anomalies related to active ...
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Geomorphic indices of active tectonics are useful tools to analyze the influence of active tectonics. These indices have the advantage of being calculated from ArcGIS and Remote Sensing software packages over large areas as a reconnaissance tool to identify possible geomorphic anomalies related to active tectonics. This method is particularly new and useful in areas where relatively little work has been carried out on active tectonics based on this method. Based upon the values of stream length-gradient index (SL), drainage basin asymmetry (Af), hypsometric integral (Hi), ratio of valley-floor width to valley height (Vf), index of drainage basin shape (Bs), and index of mountain front sinuosity (Smf), we used an integrated index (Iat) that is a combination of the other indices. This index divides the landscape into four classes of relative tectonic activity. According to the Iat results, sub-basins 4 and 6 show zones of low tectonics activity (Class 4), sub-basins 1, 2, 7, 9, 10, 11, 12, 14, 15 and 19 fit to areas of moderate tectonic activity (Class 3), and high tectonic activity is represented by sub-basins 3, 5, 8, 13, 16, 17 and 18 (Class 2). The Tranverse Topographic Symmetry (T) was also studied using morphometric measurements, which finally gave a plot of T-vectors defining anomalous zones of basin asymmetry. A comparison between T index and map of relative tectonic activity showed a consistent coincidence between areas of higher Iat classes with zones of greater asymmetry.
Sh Haghnazar; S Malakotian; Kh Alahyarii
Abstract
The pillow basalts, Cretaceous in age, outcrop in the northern part of Alborz in the East of Guilan province (north of Iran). The pillow lavas are mainly olivine basalts. From geochemical point of view, these rocks are transitional or mildly alkalic series and negative anomaly of Nb-Ta, Zr, Ba; positive ...
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The pillow basalts, Cretaceous in age, outcrop in the northern part of Alborz in the East of Guilan province (north of Iran). The pillow lavas are mainly olivine basalts. From geochemical point of view, these rocks are transitional or mildly alkalic series and negative anomaly of Nb-Ta, Zr, Ba; positive anomaly of Kand Pb; low ratios of Ce/Pb, Nb/U and high ratios of Th/Nb and Ba/Zr are geochemical evidences of crustal contamination. In tectonic setting diagrams, the pillow lavas plots in intra-continental rift Basalts terrain and is comparable with the Transitional Ethiopian Rift Basalts. The geochemical studies show that the pillow basalts are derived from the spinel-lherzolite mantle source and originated from less than 60km depth with less than %15 partial melting.
K Orang; M Mohajjel; G.R Tajbakhsh
Abstract
The kinematic analysis of the Koushk-e-Nosrat Fault (striking WNW-ESE) at north Saveh city indicates that since a time after early Miocene it has been inverted from dextral strike-slip (and reverse-dextral-oblique slip) to reverse-sinistral (and sinistral strike-slip( displacement. The Kinematic evidences ...
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The kinematic analysis of the Koushk-e-Nosrat Fault (striking WNW-ESE) at north Saveh city indicates that since a time after early Miocene it has been inverted from dextral strike-slip (and reverse-dextral-oblique slip) to reverse-sinistral (and sinistral strike-slip( displacement. The Kinematic evidences of right-lateral strike-slip displacement are: 1) Generation of the Koushk-e-Nosrat pull-apart basin along the bended segment of the fault in north Saveh city where a thin sequence of the Qom Formation (late- Oligocene to early Miocene) has been deposited in this narrow basin. 2) Shear bands and other kinematic indicators of right-lateral strike-slip and reverse-dextral-oblique slip displacements exist in the fault zone. 3) Synthetic right-lateral and antithetic left-lateral strike-slip faults are observed in wall damage zones around the main fault zone. The evidences of left-lateral strike-slip displacements after slip sense inversion are: sinistral- reverse faults, pure reverse faults, sinistral strike-slip faults and folds are generated in the Koushk-e-Nosrat Fault zone. The younger left-lateral reverse kinematic of the Koushk-e-Nosrat Fault is another significant evidence for the main role of the left-lateral reverse faults in deformation of the Qom-Saveh district in NW part of the Central Iran Block that has been tested before by structural and morphological kinematics of other major faults in the area like the Ipak (south Boin-zahrah) and Alborz (north Qom) Faults and seismological evidence of earthquake in the Boin-zahra areas.
H Amin-Rasouli; Y Lasemi; S Zaheri
Abstract
The middle Cambrian-early Ordovician transgression in the AlborzMountains resulted in the deposition of members 1 through 3 of the Mila Formation showing an overall transgressive trend. This succession is bounded unconformably by the Top-Quartzite of the Lalun Formation at the below and member 4 of the ...
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The middle Cambrian-early Ordovician transgression in the AlborzMountains resulted in the deposition of members 1 through 3 of the Mila Formation showing an overall transgressive trend. This succession is bounded unconformably by the Top-Quartzite of the Lalun Formation at the below and member 4 of the Mila Formation at the top. It consists of tidal flat to open marine facies, which have been deposited in an extensive ramp on the Proto-Paleotethys passive margin of northern Gondwana. It is composed of six depositional sequences aged middle to early- late Cambrian, related to Sauke 2 supersequence. These sequences are correlated with those recognized in other parts of the world including Oman, China, and North America suggesting that they were formed as the consequence of global relative sea level fluctuation.
M Derakhshi; H Ghasemi; T Sahami
Abstract
The Soltan Maydan Basaltic Complex indicates the most important, thickest, and most voluminous early Paleozoic magmatic activity in Iran outcropping in the eastern Alborz structural zone, in the north-northeast of Shahrud. This complex overlies the late Ordovician Ghelli Formation and is overlain by ...
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The Soltan Maydan Basaltic Complex indicates the most important, thickest, and most voluminous early Paleozoic magmatic activity in Iran outcropping in the eastern Alborz structural zone, in the north-northeast of Shahrud. This complex overlies the late Ordovician Ghelli Formation and is overlain by the early Devonian Padeha Formation. The field evidences show more than 50 lava flows erupting frequently in the sub-aerial and submarine environments. This complex comprises of a continuous fractional spectrum including basalt, basaltic andesite, trachybasalt and basaltic trachyandesite that has undergone medium to high degrees of alteration. The geochemical data and diagrams signify transitional to alkaline nature of the primary magma, genetic relationship among all rocks of this complex due to fractional crystallization, none or weak role of magmatic contamination in magma evolution, and generation of primary magma by 15-17 percent partial melting of an enriched garnet peridotitic mantle source in an intra-continental extensional rift setting. This tectonic setting is concordant with the known extensional rift setting governed on the Alborz and Central Iran zones during the early Paleozoic, especially late Ordovician-Silurian, primary stages of generation and development of the Paleotethys.
A Bayat Gol; N Abbassi
Abstract
A detailed ichnological study on the Geirud Formation (Late Devonian-Early Carboniferous) from the Zaygon area, central Alborz shows a diverse trace fossils, which include 14 ichnogenera represented by 23 ichnospecies. These trace fossils contains various ethological patterns, such as domichnia, fodinichnia, ...
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A detailed ichnological study on the Geirud Formation (Late Devonian-Early Carboniferous) from the Zaygon area, central Alborz shows a diverse trace fossils, which include 14 ichnogenera represented by 23 ichnospecies. These trace fossils contains various ethological patterns, such as domichnia, fodinichnia, grazing, equilibrichnia, and fugichnia. These trace fossils are: Arenicolites, Asterosoma, Chondrites intricate, Chondrites targionii, Diplocraterion parallelum, Arenicolites isp., Asterosoma isp., Chondrites intricate, Chondrites targionii, Chondrites isp., Diplocraterion parallelum, Helminthoidichnites isp., Helminthopsis abeli, Helminthopsis isp., Palaeophycus heberti,Palaeophycus tubularis, Planolites beverleyensis, Planolites isp., Phycodes cf. palmatus, Rhizocorallium jenense, Rhizocorallium irregular, Rosselia soccialis, Taenidium serpentinum, Taenidium satanassi, Talassinoides horizntalis, Thalassinoides suevicus, Thalassinoides paradoxicus, Zoophycos isp. Studied beds consist by alternations of laminated mudstones and siltstones, and thick- to medium-bedded sandstones with wavy lamination. Hummocky, trough and low angle to planar cross-bedding are common in layers. It seems that these beds were deposited in the delta to open marine environments. Determined ichno-assemblage represents characteristic of a moderately shallow-marine environment, which effected occasionally by high-energy conditions. A trace fossil assemblage has been examined from the uppermost dark-colored shale layers of the Geirud Formation in the Devonian/Carboniferous (D-Ca) boundary. This assemblage include Chondrites targionii, Zoophycos isp., which involved by Hangenberg event.
R. Elyaszadeh; M. Mohajjel; B. Farahani; S. R. Jafari
Abstract
Structural analysis of the NW-SE oriented Alborz fault in north Qom, demonstrates young left-lateral reverse displacement evidence, based on the rake of the striations on young fault planes (45-53). Strong structural evidence exists for its previous right-lateral reverse displacement. Young left-lateral ...
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Structural analysis of the NW-SE oriented Alborz fault in north Qom, demonstrates young left-lateral reverse displacement evidence, based on the rake of the striations on young fault planes (45-53). Strong structural evidence exists for its previous right-lateral reverse displacement. Young left-lateral displacement evidence in NW-SE oriented oblique and strike-slip faults recently was documented in central-west (eg. Mosha and Talegan faults) and south Alborz mountains (eg. Ipak and Kusk-e-Nosrat faults) due to the compression direction of the south Caspian oceanic crust with Alborz mountains. Replacement of right-lateral reverse mechanism by young left-lateral reverse mechanism in the Alborz fault in north Qom implies that the inversion of the central-west Alborz faults is being transferred through to the same oriented faults in south Alborz mountain up to the Qom area.
A. Bayat Gol; N. Abbassi; A. Mahboubi; R. Moussavi-Harami; H. Amin Rasouli
Abstract
Some of Paleozoic sediments from Alborz and Central Iran subzones from Mid-Iran zone evaluated for distinction of Palaeophycus and Planolites ichnofossils. These sediments include Shale Member of Lalun Formation, Shirgesht Formation, member 5 of Mila Formation and Geiroud Formation. A diverse ichnofauna ...
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Some of Paleozoic sediments from Alborz and Central Iran subzones from Mid-Iran zone evaluated for distinction of Palaeophycus and Planolites ichnofossils. These sediments include Shale Member of Lalun Formation, Shirgesht Formation, member 5 of Mila Formation and Geiroud Formation. A diverse ichnofauna has been found in these Formations, so Planolites and Palaeophycus are abundant between them. Ichnotaxa diagnosis and some determination problems of these ichnogenera was discussed here. Overall characteristics of Palaeophycus suggest dwelling structure made by predator or suspension-feeder and passive sedimentation in the open burrow. Planolites, on the other hand imply active backfilling structure in ephemeral burrows, which constructed by a mobile deposite-feeder. Planolites include unlined burrows with infilled sediments differ texturally from host rock. Whereas Palaeophycus is lined burrow filled by same sediments of surrounding matrix. Accordingly, Palaeophycus assemblage members made by opportunistic communities with r-selected population strategies in physically-controlled and unstable environment, whereas ichnofossils of Planolites assemblage are related to benthic communities with displaying K-selected or climax strategies in the stable environments and rather predictable conditions. Recognized ichnospecies of Planolites are P. montanus, P. annularis, P. terraenovae and P.beverleyensis. and ichnospecies of Palaeophycus include P. heberti, P. tubularis, P. striatus. P. sulcatus and P. alternates.
Ali Shekarifard; F. Baudin; K. Seyed-Emami; J. Schnyder; H. Rahimpour-Bonab
Abstract
Geochemical characteristics (Rock-Eval pyrolysis and elemental analysis of kerogen), palynofacies and organic petrography (using light transmitted-reflected-uv microscopy) of the basal black shale from the Shemshak Group (Upper Triassic- Middle Jurassic) in the Tazareh section (Eastern Alborz) have been ...
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Geochemical characteristics (Rock-Eval pyrolysis and elemental analysis of kerogen), palynofacies and organic petrography (using light transmitted-reflected-uv microscopy) of the basal black shale from the Shemshak Group (Upper Triassic- Middle Jurassic) in the Tazareh section (Eastern Alborz) have been investigated. The basal black shale is rich in amorphous organic matter with fewer amounts of vitrinite particles that was deposited in lacustrine environment under anoxic to suboxic conditions. According to vitrinite reflectance values (mean VRr=2.1%), organic matter of the basal black shale has experienced high thermal maturity during deep burial. In this study samples residual organic carbon content is 1 wt.% on average. Thermal modeling results using 1D Genex4 software show that the basal black shale of the Shemshak Group became mature during the Middle Jurassic-Lower Cretaceous time and generated hydrocarbon. At the present day, this organic facies in the Tazareh section is thermally over-mature and depleted in hydrogen and is located in the dry gas generation window. Presently, these sediments are considered as shale gas resources.
A. Fallah; B. Hamdi; H. Mosaddegh
Abstract
The studied section (Kiyasar)is situated in Central Alborz,75 Km. southeast of Sari. The thickness of Carboniferous sequences (Mobarak Formation) is 385 meter and consists of thin-bedded limestone at the base and various thickness of limestone (mostly with medium thickness) with intercalations of shales ...
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The studied section (Kiyasar)is situated in Central Alborz,75 Km. southeast of Sari. The thickness of Carboniferous sequences (Mobarak Formation) is 385 meter and consists of thin-bedded limestone at the base and various thickness of limestone (mostly with medium thickness) with intercalations of shales at the top. Because of lithological similarity and the lack of index microfossils in the uppermost of Devonian and lowermost of Carboniferous, deposits, determination of this boundary was impossible in the field and the approximate boundary has been identified after study of lab by conodont elements. Apparently, this boundary is conformable and continual that the rocks at the bottom of its attributed to Khoshyeilagh Formation. This boundary is located in the interval of samples 4.1(late Devonian) and 4.3(lower Carboniferous) which the distance between them is 4m.(thin to medium-bedded limestones).The limit of boundary is distinct with extinction of Genera and Species for example Icriodus costatus, Pelekysgnathus sp. and Polygnathus semicostatus in the late of Devonian(sample4.1)and appearance of species for example Polygnathus spicatus, Spa. crassidentathus, Po. thomasi and Cly. gilwernensis in early Carboniferous (sample4.3). in summery, limestone rocks in alternation with shale of upper Famenian is attributed to lower-middle costatus zone form lower part of Carboniferous rocks in the region. The top of Mobarak Formation is overlaid by alternations of sandstone, shales and limestone (in the middle part), belong of Dorud Formation (lower Permian) with a disconformity. Carboniferous conodonts (20 Genus, 36 Species, 7 Subspecies are reported from Mobarak Fm.,Kiyasar region, for the first time as well as the distinguished following 7 conodont zones: 1) sulcata zone 2) duplicata zone 3) sandbergi-L. crenulata zone 4) typicus zone 5) anchoralis-latus zone 6) texanus- A. scalenus zone 7) Gn. bilineatus zone. According to conodont data Carboniferous sequences in Kiyasar section were deposited from lower Tournaisian to upper Visean time interval.
Alireza Shahidi; E. Barrier; M.-F. Brunet; A. Saidi
Abstract
In northern Iran the Eo-Cimmerian orogeny resulting from this collision is associated with a regional unconformity and a major change in sedimentation. From Norian to middle Bajocian (Shemshak group), 030° trending extension is indicated by syndepositional normal faults. We assign this extensional ...
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In northern Iran the Eo-Cimmerian orogeny resulting from this collision is associated with a regional unconformity and a major change in sedimentation. From Norian to middle Bajocian (Shemshak group), 030° trending extension is indicated by syndepositional normal faults. We assign this extensional tectonics to the rifting phase preceding the oceanic opening of the South Caspian Basin. Dalichai and Lar formations, late-Bajocian to Neocomian in age, conformably cover the Shemshak in central Alborz. They are contemporaneous with the opening of the South Caspian marginal basin. In Alborz, the lower part of the Cretaceous sequence is associated with E-W to WNW-ESE trending normal fault systems associated with magmatism related to an N-S to NNE-SSW trending extension during this period. The Cretaceous-Palaeogene boundary is marked by a major regional unconformity. This unconformity is related to a major inversion of the southern margin of the South Caspian basins. During the early-middle Eocene, southern Alborz is characterized by a rapid subsidence of the Karaj basin. Syndepositional E-W to WNW-ESE trending normal faults are common in the Karaj Formation. They are associated with a well-determined N-S to NNE-SSW extension. We assign the Karaj basin to a back-arc basin related to the NE subduction of the neo-tethyan oceanic lithosphere beneath the southern margin of Eurasia.
F. Khorrami; K. Hessami; H.R. Nankali; F. Tavakoli
Abstract
We present the results of continuous GPS measurements to interpret present-day kinematic along and across northern Iran (i.e. the Alborz mountain range and northern part of Central Iranian Block (CIB)). In this study velocity field and geodetic strain rate of 30 CGPS stations from 2005 to 2009 were calculated ...
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We present the results of continuous GPS measurements to interpret present-day kinematic along and across northern Iran (i.e. the Alborz mountain range and northern part of Central Iranian Block (CIB)). In this study velocity field and geodetic strain rate of 30 CGPS stations from 2005 to 2009 were calculated in order to indicate active deformation of the region. The obtained velocity field suggests that western and central part of the Alborz mountains accommodate the convergence between Arabia and Eurasia mainly through shortening at a rate of ~6 mm/yr and 2 mm/yr left-lateral strike slip motion while the eastern Alborz accommodates the differential motion on either side of the range by left-lateral strike slip faults at ~5 mm/yr, as well as 2 mm/yr shortening across the range. It can be deduced from the velocity vectors that main portion of the shortening (~70%) in the western and central Alborz is mainly taken up along the North Alborz and western Khazar faults. It is also evident from the site velocities that ~3 mm/yr shortening is occurring in CIB, i.e. ~1.5 mm/yr on northern side of CIB (along the Parchin-Pishva-Robatkarim faults) and ~1.5 mm/yr along the Tafresh fault. These observations strongly suggest that CIB is not a rigid block. Principal axes of geodetic strain-rate tensor showed that mainly compressional deformation occurs in western Alborz while transpressional deformation is dominant in eastern Alborz. Strain rate decreases in south and south-western parts of the belt, as approaches the CIB. We also observe copmressional deformation in northern margin of CIB. Finally, we indicate that the present-day kinematics of the Alborz mountains is consistent with geological evidence and active tectonics of the region.
F. Gharib; Y. Lasemi; M. H. Emami
Abstract
The clastic facies of Kahar Formation were identified in the studied sections of coastal, deltaic and fluvial and also carbonate facies in shallow marine environments. The vertical displacements of Kahar Formation in these study sections show an overall major transgressive upward cycle. The petrography ...
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The clastic facies of Kahar Formation were identified in the studied sections of coastal, deltaic and fluvial and also carbonate facies in shallow marine environments. The vertical displacements of Kahar Formation in these study sections show an overall major transgressive upward cycle. The petrography of plutonic and semi- plutonic igneous rocks indicate that they consist mainly of monzogabbro- diorite and in some cases, alkaline syenite. According to the results of Kahar Formation's plutonic rocks petrography and studies of related facies, the basin of this formation was a continental rift.
H. Nazari; J-F. Ritz
Abstract
The Taleghan Fault is located at the southern side of Taleghan valley in Central Alborz, 50 km north west of the Tehran mega city. Usually described as a south-dipping reverse fault, it could be the source of some of the strongest historical earthquakes recorded in the Tehran region, notably the 958 ...
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The Taleghan Fault is located at the southern side of Taleghan valley in Central Alborz, 50 km north west of the Tehran mega city. Usually described as a south-dipping reverse fault, it could be the source of some of the strongest historical earthquakes recorded in the Tehran region, notably the 958 AD (estimated magnitude M 7.7). The fault stands out as one of the major active structure menacing the cities of Tehran and Karadj, representing together 12 millions inhabitants. In order to analyze the recent activity of the fault, a morphological study was carried out along the fault combining satellite imagery, aerial photographs and Digital Elevation Model. We found out an active branch that had never been described whereas the fault classically mapped appears inactive. Detailed field work along the branch allows us to show that the fault had its vertical component recently reverted from reverse movement to normal movement. One of the measured ratios of accumulated horizontal / vertical displacements associated to the left lateral and normal movement is 2.5-5. The strike, estimated dip and rake in the eastern part are 105°, 60° and 40° respectinely making it a left lateral- normal strike slip fault in this part of the Central Alborz.
