ایران مرکزی

Open Access Article

1 - The Study of alteration, mineralization, and fluid inclusion in the Howz-e-Sefid zinc-lead deposit (Central Iran)
Mansor Adelpour godratollah Rostami Paydar

The Howz-e-sefid zinc-lead deposit is located 17 km northeast of Ardakan town in the central Iran tectonic zone. Host rock of this deposit is lower Cretaceous dolomitized carbonate rocks. In this area there are three major rock units. The Sangestan Formation as the lowe More

The Howz-e-sefid zinc-lead deposit is located 17 km northeast of Ardakan town in the central Iran tectonic zone. Host rock of this deposit is lower Cretaceous dolomitized carbonate rocks. In this area there are three major rock units. The Sangestan Formation as the lowest unit, is composed of shale and siltstone with calcarenitic interbeded layers. This unit is overlain by ankeritic massive dolomite and dolomitic limestone of the Taft Formation. The Abkouh Formation at the top, is composed of cherty or argillaceous limestone with massive reefal limestone. The host rock of deposit in the lower Cretaceous carbonate horizon along with other geological evidence indicate that this deposit has been primarily formed similar to the Mississipi Valley-type deposits. This conditions include carbonate and evaporatic sequences, special hydrothermal dolomitized horizons, lack of the effects of igneous intrusions and the presence of the important controling faults. Based on the observations, it can be concluded that the primary ores have been of the sulphide type including sphalerite, galena and pyrite. Due to their exposure to superficial oxidizing conditions and undergoing changes, the primary sulphide ores, have been converted into nonsulphide ore body. As a result, the primary sulphide ores have been changed into secondary minerals such as hemimorphite, smithsonite, cerusite and anglesite. In many cases, the nonsulphide minerals established in the structural fractures and fissures, shows the colloform texture. Therefore, it can be accepted that this type of minerals were formed under the effect of low temperature hydrothermal fluids.There are two types of fluid inclusions (type I: L and type II: L+V) in the carbonaceous ore bearing veins. On the basis of microthermometric study, the homogenization temperatures is between 150-260 °C. The salinity of fluid inclusions is low to intermediate (0.33-14.26 wt. % NaCl equivalent). Heating depressurization due to reduced pressure to boiling with low CO2 bearing fluid (0.62-0.98 gr/cm3) is the main mechanism of deposition. Based on evidence such as the nonhomoginity in filling degree of fluid inclusions, existence of a few vapor-rich phase shows boiling of ore fluid in faulted and fracture zones. Manuscript profile

Open Access Article

2 - Late Cretaceous Island-arc subduction magmatism in northern edge of central Iran, SW Sabzevar
Elham Mirzakazemi Habibollah Ghasemi Fardin Mousivand Wilyam Griffin

A thick sequence of Late Cretaceous volcano-sedimentary rocks crops out on the northern margin of Central Iran, in the southwest of the Sabzevar. The igneous rocks include extrusions (trachy-andesite, dacite and rhyolite) and shallow depth intrusions (gabbro, gabbrodior More

A thick sequence of Late Cretaceous volcano-sedimentary rocks crops out on the northern margin of Central Iran, in the southwest of the Sabzevar. The igneous rocks include extrusions (trachy-andesite, dacite and rhyolite) and shallow depth intrusions (gabbro, gabbrodiorite, diorite and granite). These igneous rocks have geochemical signatures of magmatic rocks of island-arc subduction zones and plot within field in different tectonic setting discrimination diagrams. The parental magma of these rocks has island arc tholeiitic nature and was produced via partial melting of a depleted spinel lherzolite mantle source during closing of the Sabzevar Neo-Tethyan oceanic basin in the Late Cretaceous. This depleted mantle source was affected by the metasomatic fluids released from dehydration of the Neo-Tethys subducted oceanic slab. Manuscript profile

Open Access Article

3 - Geochemistry and petrology of Qareh-Dash rhyolites from Shahindej- NW Iran: Geochemical features of post- collision volcanism
Masoumeh Ahangari معصومه نظری Mohsen Moazzen

Qareh-Dash rhyolites from the Shahindej area are peraluminous rocks with high SiO2 and K2O contents. These rocks are mainly composed of quartz, K- feldspar and rare plagioclase phenocrysts in a fine-grained K-feldspar rich matrix. Geochemically, Qareh-Dash rhyolites sho More

Qareh-Dash rhyolites from the Shahindej area are peraluminous rocks with high SiO2 and K2O contents. These rocks are mainly composed of quartz, K- feldspar and rare plagioclase phenocrysts in a fine-grained K-feldspar rich matrix. Geochemically, Qareh-Dash rhyolites show enrichment in LREEs and LILEs and depletion in HREEs. Field studies, textural and petrographical relations, along with whole rock geochemistry, demonstrate that the parental magma of the Qareh-Dash rhyolites was originated from the crust. The composition of the parental magma was modified due to fractional crystallization of plagioclase and titanomagnetite evidenced by negative Eu, Sr and Ti anomalies in multielement diagrams. The chemical characteristics of Qareh- Dash rhyolites such as Rb/Nb, K/Rb, Rb/Sr, Rb/Ba and Ga/Al ratios are similar to A-Type granites/ rhyolites associated with post- collision tectonic settings. According to Precambrian age for the Qareh-Dash rhyolites, formation of these rocks might be related to extensional phases which were probably taken place after closure of proto- Thetys Ocean. Manuscript profile

Open Access Article

4 - Evidence of transpressional tectonics in NW of central Iran sedimentary basins based on reflective data and geomorphic indices
Mohammad Mokhtari S.Ahmad Alavi Leila Mahshadnia

The depressed basins of northwest central Iran are located in the structural Step and between Soltanieh-Ipac-Koshk-e-Nosrat and Qom –Zefreh system (the Indes - Qom –Khurabad faults). The main process of deformation within the basin with extension and compression of spec More

The depressed basins of northwest central Iran are located in the structural Step and between Soltanieh-Ipac-Koshk-e-Nosrat and Qom –Zefreh system (the Indes - Qom –Khurabad faults). The main process of deformation within the basin with extension and compression of specific structures are comparable and verifiable using experimental models. The extensional structures include roll-over folds and normal faults, resulting in deep sedimentary basins during deposition of the lower and upper red formations. The younger structures, includes back-thrusts and for-thrusts, shortcut, and pop up structures represents the reversal of tectonic of primary extensional basin. These sedimentary basins have been created in relation to the growth faults and hanging wall blocks So In the presence of roll-over fold and antithetic and synthetic faults therefore are suitable for entrapment of hydrocarbons during migration. The active structural features have been identified using combination of geomorphic characteristic and seismic reflection data. Accordingly, none of the old normal faults in the Saveh- Qom and Aran basin show at the present any extensional movement and the fault activity of boundary faults and extensional folding are compressional. The active parts are: hanging wall of Saveh, restraining bending at the end of Indes fault that has stream Length-Gradient (SL) index and high value hypsometric index (Hi). The central part of Saveh-Qom and Aran basin, although show high Hi but the SL is low. This situation is due to the moderating effects of the thick lower and upper red formations and evaporative layer within the basin. In the Aran basin due to incomplete coverage of seismic lines the absence of normal faults cannot be definitively confirmed. However, the center of Aran basin as of Qom-Saveh formed push up which marks the compression of this basin and also activity of reverse and thrust faults. Based on the existing surface and subsurface data set, active deformation in this area now is transpression basin and the interior domains are in the uplift. Manuscript profile

Open Access Article

5 - Basic steps in determining the provenance of terrestrial sedimentary sequences, with examples from central and north west of Iran
عبدالحسین امینی

By stating the fundamental differences between terrestrial and detrital facies, this paper emphasizes on the limitations of provenance studies in terrestrial facies. Considering the presence of coarse-, medium- and fine-grained facies in most of terrestrial sedimentary More

By stating the fundamental differences between terrestrial and detrital facies, this paper emphasizes on the limitations of provenance studies in terrestrial facies. Considering the presence of coarse-, medium- and fine-grained facies in most of terrestrial sedimentary sequences, the differences in textural and mineralogical characteristics, their study methods and possible differences in the provenance of these facies, the basic and necessary steps in studying these facies for determining the sedimentary provenance was investigated. In explaining these steps, some examples from terrestrial formations of Central Iran (Upper Red Formation) and north west of Iran (Zivar Formation) are presented. The role of diagenesis, structural deformation and paleogeography in the provenance study and their importance in this type of studies are explained. Finally, it is discussed how to proof the accuracy of the interpretations for the studied sedimentary sequences. Manuscript profile

Open Access Article

6 - Karst geology of carbonate rocks mass in Abegarm area, south of Qazvin province
P. Armani M. Karimi M. Tajabadi

Understanding the geological phenomena created by dissolution can be a great help in understanding karst systems. Hence, geology is usually the first step in studying the karstification process. Abegarm is located in the Central Iran structural zone and includes the For More

Understanding the geological phenomena created by dissolution can be a great help in understanding karst systems. Hence, geology is usually the first step in studying the karstification process. Abegarm is located in the Central Iran structural zone and includes the Formations of the Paleozoic, Mesozoic and Cenozoic eras. The most important carbonate formations in Abegarm are Soltanieh, Ruteh, Elika, Lar and Qom formations. In this study, karstification potential was investigated after field work and sampling of carbonate rock units and comparing them in terms of the development of karst landforms. Sampling of karst springs in both dry and wet periods, as well as measurement of EC, pH and temperature on the ground were performed. Remote sensing studies were performed by ILWIS software on Landsat satellite images for isolation and calculation of the area of carbonate formations. AqQa software was used to review and interpret the findings of chemical analyses and Phree Qc software was used to model water chemistry. The most important karst landforms in the region include karrens, vugs, caves, and karst springs. Based on the combination of field studies and remote sensing data, the intensity of karstification in the Abegarm area graded from high to low, include: Qom, Soltanieh, Lar and Cretaceous formations. Based on karst development classification, Abegarm karstification is merokarst (incomplete) and shallow; and based on the karst cycle classification it is classified as juvenile to young. Manuscript profile

Open Access Article

7 - Structural evolution of the southern Natanz region and its role in the distribution and concentration of Pb-Zn mineralization
Firouzeh Shavvakhi Saeed Madanipour M. Tadayon Ebrahim Rastad M.J. Kupaei

The studied area is structurally located in the western part of the Central Iranian structural zone atthe southwestern termination of the Qom-Zefreh Fault. Our structural data represent the older generation of E-W to NW-SE trending thrust faults that juxtapose Permia More

The studied area is structurally located in the western part of the Central Iranian structural zone atthe southwestern termination of the Qom-Zefreh Fault. Our structural data represent the older generation of E-W to NW-SE trending thrust faults that juxtapose Permian- Triassic (Nayband and Shotori Formations) over younger rock units. Most of the thrust faults have been crossed cut with the younger generation of the strike-slip fault system. Major thrust faulting of the area occurred during post Late Cretaceous time. The final post Oligocene strike slip faulting related to the activation of the Qom- Zefreh fault overprinted and crossed cut older structural features. Our economic geological studies in the south Natanz area represent syngeneic strati bond or Sedex-Like type Pb-Zn epigenetic occurrence of these deposits in Permian-Triassic carbonates and barite developed in the Lower Cretaceous carbonate and clastics. The ore deposit development in Permian-Triassic Carbonates have occurred along thrust faults and then redistributed along strike slip faults with normal component. Therefore, genetically, stratiform deposits developed in the Lower Cretaceous carbonates and clastics (Yazdan and Pinavand Ore deposit) occurred in a regional early Cretaceous extensional regime. However, epigenetic deposits developed in Permian-Triassic carbonates (Changarzeh deposit) were generated during the regional post Late Cretaceous compressional regime and redistributed during post Oligocene strike slip deformation. Manuscript profile

Open Access Article

8 - Geology, mineralization, mineralogy, structure and texture in the Ghezeljeh Cu, Pb-Zn deposit, NW Zanjan
Seyedeh Aliyeh Seyedeh Aliyeh Ghasem Nabatian Afshin Zohdi Armin Salsani

Ghezeljeh deposit is located in the Central Iranian zone, in the Zanjan province and northeast of the Mahneshan city. The rock units in this area belongs to the Oligo-Miocene, which contain Lower Red, Qom and Upper Red formations. The Upper Red Formation in Ghezeljeh re More

Ghezeljeh deposit is located in the Central Iranian zone, in the Zanjan province and northeast of the Mahneshan city. The rock units in this area belongs to the Oligo-Miocene, which contain Lower Red, Qom and Upper Red formations. The Upper Red Formation in Ghezeljeh region has about 750 m thickness and mainly consists of brown to green marl intercalations with sandstones. In this area, the alternation of marl and sandstone sequences contain sandstone layers with thickness about 2 to 8 meters, which in two horizons, the copper-lead and zinc mineralization has occurred. Copper mineralization, in addition to being observed inside the sandstone unit. In the Ghezeljeh deposit, the host rocks of the copper ores, are gray sandstones and conglomerates which are intercalated with red and gray marl units. According to field and microscopic studies, the main ore mineral consist of pyrite, chalcocite, chalcopyrite, bornite, galena and sphalerite which associated with the secondary minerals such as serosite, malachite, azurite, covellite, smithzonite and goethite. The ore mineral textures consist of disseminate, framboidal pyrite, solution seams, interparticle cement, replacement and relict. Preliminary fieldwork studies in the Ghezeljeh region also show that organic matter including plant remains and diagenetic pyrite are the effective factors to concentrate and mineralization. It is considerable that the grade of lead, zinc and copper, in Ghezeljeh deposit are 6%, 3% and 1%, respectively. Generally, host rock, tectonic setting, sedimentary environment, mineralogy, texture, mineralization control factors all confirm that the studied mineralization has more similarities with Redbed type copper deposits. Manuscript profile

Open Access Article

9 - Biostratigraphy and palaeoecology of Qom formation in the Ghamsr section (SW of the Kashan)
tayyeb binazadeh Amrollah Safari Hosyen Vaziri moghadam

In order to study the biostratigraphy and palaeoecology, the Qom Formation has been studied in the Ghamsar section of Kashan. The studied section, with a thickness of 314 m, consists of medium to thick-bedded to massive limestones and shale. The Qom Formation overlies t More

In order to study the biostratigraphy and palaeoecology, the Qom Formation has been studied in the Ghamsar section of Kashan. The studied section, with a thickness of 314 m, consists of medium to thick-bedded to massive limestones and shale. The Qom Formation overlies the Eocene volcanic rocks in the Ghamsar section and is covered by the Recent alluvial sediments. A total of 21 genera and 9 species of benthic foraminifera were identified in this section and the results indicated the age of Rupelian-Chattian. According to the above palaeoecological conditions, in the lower parts of this section (Rupelian), light conditions are euphotic and nutrient conditions are first eutrophic and then Meso-oligotrophic with mainly normal sea salinity. During Chattian, the trophic state was mainly meso-oligotrophic with normal salinity, and salinity varied between 40 and 50 PSU. Light conditions also were between aphotic and mainly meso-oligophotic. Large benthic foraminifera with hyaline walls, such as Amphistegina, Lepidocyclinide and Nummulitide, in shallow environments with high energy, have thicker shells and smaller shell size, and in deep environments, due to reduced light intensity and low water circulation, they have thinner and more elongated shells. The results of the morphometry of 186 samples of Amphistegina show that the seawater depth in Ghamsar section (Rupelian-Chattian) fluctuated from less than 11 meters to less than 44 meters. Manuscript profile

Open Access Article

10 - A new look at the rotation of Central Iran: A case study of the Anar fault, east block of the Yazd
Hamidreza AfkhamiArdakani farzin ghaemi Fariba Kargaran Bafghi Ahad Nouri

The Anar fault in the east of Yazd city, with a north-northwest-south-southeast strike, is a basement fault that separates the Yazd block from the Posht Badam block, and its current activity is a dextral strike-slip with a reverse component. The paleostress analysis was More

The Anar fault in the east of Yazd city, with a north-northwest-south-southeast strike, is a basement fault that separates the Yazd block from the Posht Badam block, and its current activity is a dextral strike-slip with a reverse component. The paleostress analysis was done on this fault in order to obtain the tectonic history of central Iran in the period from Devonian to Cretaceous. After analyzing 110 fault data in 13 stations of 2 tectonic phases, it was determined that the maximum stress obtained is between the azimuths of 90 to 110 and 190 to 220 and the angle of stress direction changes in the period from Devonian to Cretaceous is 130 degrees. Based on the studies on the barite veins and the dextral displacements that were seen on them, the separation of the stress phases was done, which indicates that the NNE stress direction is older. Further, according to the previous studies of sedimentology and tectonics in central Iran, it was concluded that the cause of this change in tension was the movement towards the northeast along with the 130 degree counter-clockwise rotation of central Iran. Manuscript profile

Open Access Article

11 - Palaeotectonic reconstruction of sandstones from the Triassic Nakhlak Group in Central Iran, using U-Pb zircon dating
S.H. Hashemiazizi peiman rezaie

<p>The Triassic Nakhlak Group in Central Iran is an important sedimentary succession that helps us better understand the closure of Palaeotethys and the Eo-Cimmerian orogeny in the Middle East. The Nakhlak Group consists of the Alam (Olenekian to Middle Anisian), Baqoro More

<p>The Triassic Nakhlak Group in Central Iran is an important sedimentary succession that helps us better understand the closure of Palaeotethys and the Eo-Cimmerian orogeny in the Middle East. The Nakhlak Group consists of the Alam (Olenekian to Middle Anisian), Baqoroq (?Upper Anisian to Middle Ladinian), and Ashin (Upper Ladinian to ? Carnian) formations, which are mainly composed of volcaniclastic sandstones, mixed siliciclastic conglomerates, and marine carbonates. Here we examine the detrital zircon UPb ages from the Nakhlak Group to determine its provenance and constrain its palaeotectonic position within the Palaeotethyan realm. Most detrital zircons from the Nakhlak Group are euhedral and subhedral with Permian–Triassic ages (ca. 280–240 Ma), indicating they likely came from the Silk Road Arc's Permian–Triassic magmatic rocks. Minor zircon populations show pre-Permian Palaeozoic ages, around 320 Ma and 480 Ma, which probably originated from the basement on which the magmatic arc developed. Zircon grains with Neoproterozoic–latest Mesoproterozoic (ca. 550–1100 Ma) and Palaeoproterozoic (ca. 1800–2200 Ma) ages are anhedral or rounded, with the latter being more prominent in the upper Baqoroq Formation (Middle Ladinian), suggesting the recycling of older sedimentary rocks. Sandstone petrography indicates an additional metamorphic provenance for this formation, possibly due to a tectonic uplift in the source area, resulting in the erosion of metamorphosed rocks with a northeast Gondwanan affinity. This suggests that northeast Gondwana-derived continental fragments likely belonging to the Cimmerian blocks had already arrived at the southern Eurasian margin in pre-Late Triassic time.</p> Manuscript profile

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