Publication Date: 2023
Geodynamics and Tectonophysics (2078502X)14(2)
Within the Urumieh-Dokhtar Magmatic Arc in the central part of Iran, the formation of which is associated with the Neotethys closure, there are many porphyry copper deposits and ore occurrences. One of them is the Astaneh porphyry copper ore deposit, located in the central part of the Saveh-Ardestan ore region southeast of Ardestan city. The purpose of this study is to investigate the petrochemical characteristics of rocks and to determine the relationship between the distribution of porphyry copper mineralization and tectonic position of faults within the study area. To achieve the goal, there were used the structural and geological data obtained in the fieldwork, as well as the results of mineralogical and geochemical analyses. The obtained results show that rocks of different composition of the Astaneh ore deposit (andesite, andesite-basalt, basalt, trachybasalt) were formed in the suprasubduction zone, and probably in the environment prior to the collision of the of continental plates. Paragenetic relationships and mineralogical analysis show that the evolution of mineralization of the Astaneh ore deposit can be divided into three stages: pre-ore, hypogene and supergene mineralization. Geochemical research based on the study of the content of the major chemical elements in the rocks of the region shows that igneous rocks belong to calc-alkaline basalts and geodynamically can be attributed to the products of magmatism of the ensial island arc. The results concluded that the main stages of the formation of a porphyry copper ore deposit in the study area attain maximum spatio-temporal similarity with the tectonomagmatic phases of the development of the Neotethys Ocean. In addition, the Southern Ardestan fault, running through the study area and intersecting the basement structures, forms wide permeable zones favorable for the formation of porphyry copper deposits therein. © Beygi S., Tadayon M., Ilalova R. K., Talovina I. V., Meisel T. C., 2023.
Publication Date: 2022
Journal of Structural Geology (01918141)160
The Central Iranian Micro-plate (CIM) is a dismembered piece of northern Gondwana. The aim of this study is to reconstruct the post-Early Cretaceous structural evolution of the western edge of CIM in the light of the integration of regional to the micro-scale structural data with minor Anisotropy of Magnetic Susceptibility (AMS) analyses. Our original field measurements on the structural architecture of the study area show main NW-SE and E-W structural trends that are accompanied by structural evidence for superposition. However, paleostresses obtained from fault and fold analysis (stress inversion method on faults and statistically π-plane and β-axis solution on folds), statistical Fry center-to-center analysis on the oriented thin-sections integrated with AMS results suggest that the study area has experienced a NE-SW-directed compressional regime since Paleocene time followed by a post-Early Miocene, roughly N–S-directed, regional compressional regime. Furthermore, the results of this work confirm the consistency between regional-micro structural analysis and AMS analysis. The most of samples show composite (sedimentary + tectonic) magnetic fabric and intermediate arrangement in the orientation of the magnetic fabric. Reconciling our results with published structural and AMS data suggests the changes in the regional stress regime in the western CIM has been occurred in response to the long-term stress transition from the infant Late Cretaceous–Paleogene subduction of the Neo-Tethys Ocean to the mature Cenozoic stages of the Zagros collision and the consequent Neogene tectonic reorganization in the hinterland domains of the southern Eurasian plate. © 2022 Elsevier Ltd
Publication Date: 2021
International Journal of Image and Data Fusion (19479832)12(2)pp. 155-175
Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite imagery was used to identify argillic, phyllic and propylitic alteration zones and mapping geological structural features for porphyry copper exploration in the Kacho-Mesqal zone, Urumieh- Dokhtar Magmatic Arc, Iran. The image processing techniques such as specialised band ratio, Selective Principal Component Analysis (SPCA), and Spectral Angle Mapping (SAM) image processing methods were implemented to the visible and near-infrared and shortwave infrared bands of ASTER. Results indicate that the argillic alteration zone is broadly distributed in the granodiorite intrusion, andesitic rock, tuff breccia and ignimbrite. Phyllic alteration is mainly mapped associated with sandstone and some parts of andesitic lithology. Propylitic alteration zone is identified in andesite, sandstone, shale and marl, dacite to rhyodacite, andesite-basalt, tuff and andesite lava and granodiorite intrusion. The fracture density map shows that the argillic alteration is mostly abundant in the high-density fracture zone, whereas propylitic and phyllic zones are located in moderate to low-density fracture zones. Consequently, high potential zones for copper mineralisation in the study area are identified within the high to moderate fracture density zones associated with argillic and assemblage of argillic, phyllic and propylitic alteration zones in granodiorite and andesite units. © 2020 Informa UK Limited, trading as Taylor & Francis Group.
Publication Date: 2021
Petrological Journal (22285210)12(2)pp. 125-148
Anarak ophiolite, belonging to Paleozoic, formed along with the tectonic evolution of the Paleo-Tethys Ocean, consisting of meta-peridotites of mantle and crust, cumulate rocks, massive gabbros, pillow lava, basic and ultrabasic dikes, rodingite and listwanite covered all by schist and marble units. The olistolithic patches of Anarak ophiolite have commonly exposed in Sebarz schist, within the sole of Chah-Gorbeh complex. Olistoliths composed of listwanite, meta-mafic, serpentinite and meta-peridotite olistoliths varying from centimeter to several hundred meters in size. The results of electron microprobe analyses show that the fundamental rock-forming minerals of the listwanitized olistoliths are chromian spinel and pyroxene, secondary minerals including calcite, garnet, tremolite, chlorite, magnetite and opaque minerals. Meta-mafic olistoliths composed of chromian spinel, sphene, epidote, chlorite and opaque minerals. Serpentinized olistoliths consist of chromian spinel, magnetite, tremolite, talc and chlorite. It also shows that the meta-peridotite olistoliths composed of chromian spinel, chrome-bearing magnetite, chlorite, calcite, garnet and antigorite. Based on the geochemical analyses, Cr# in the listwanite patches, meta-mafic, serpentinite and meta-peridotite olistoliths are 87.40-97.92, 49.38-51.89, 49.22-60.05 and 29.76-55.97 respectively with very low amount of TiO2. The different in chemical composition of minerals in the North Anarak complex shows different petrogenesis for ophiolitic olistoliths suggests characteristic of the MORB and/or supra-subduction zone. © 2021 The Authors. Published by University of Isfahan.
Publication Date: 2021
Journal of Asian Earth Sciences (18785786)217
The upper plate of the Arabia-Eurasia collision zone experienced orogen-perpendicular to orogen-parallel extension from 25–22 to 10–9 Ma. Although such an extension occurred during widespread collisional deformation, it is not clear if it is a local feature or if represents a major phase of upper plate extension. In this study we combine anisotropy of magnetic susceptibility (AMS) with fault kinematic analysis and sedimentologic data from 16.2- to 7.6-My-old deposits of the Upper Red Formation of the intermontane Tarom Basin (NW Iran). These strata present syndepositional, normal faults and offer the possibility to gain new insights into the spatial extent of such a Miocene extension. AMS data from the central and northern sectors of the basin document a tectonic fabric with a magnetic lineation parallel to the strike of the orogen, suggesting a compressional tectonic overprint. Conversely, the southern margin of the basin presents a purely sedimentary magnetic fabric despite a ~NE–SW orogen-perpendicular extension. This suggests that basin formation was not driven by extensional tectonics. Rather, the normal faults are gravity instabilities induced as also documented by coeval landslide deposits. This allows concluding that the orogen-perpendicular extension observed in few sectors of the collision zone is not regionally pervasive and hence it is not controlled by large-scale processes. Combined, our results indicate that if orogen-parallel extension associated with tectonic denudation and metamorphic core complex development occurred in certain sectors of the collision zone (Takab complex), it must have ended before 19–16 Ma, when widespread upper plate contractional deformation started. © 2021 Elsevier Ltd
Publication Date: 2021
Chemical Geology (00092541)566
The Triassic carbonate-hosted Komsheche deposit of Central Iran, in the central segment of the Alpine-Himalayan orogen, is an ideal test site for tectonic-controlled ore formation processes. The mineralization consists of barite, fluorite, minor galena, and subordinate pyrite and chalcopyrite, and gangue minerals of dolomite, quartz, siderite, organic material, and calcite. Radiogenic isotopes point to multiple sources. The Pb composition in galena indicates an origin of Pb from upper crustal material. Barite generations II and III have 87Sr/86Sr = 0.709147 to 0.709595, higher than those of the Triassic host rocks, but more similar to the composition of Paleozoic basement and Miocene seawater. The chondrite-normalized REE patterns of fluorite crystals are subhorizontal with slightly negative or no Eu anomalies and weak enrichment of the MREE. The composition of fluorite, combined with the Pb and Sr isotopic data, reflects a process of fluid-rock interaction for the mineralizing fluids along favorable lithological and structural sites. The anatomy of the Komsheche deposit is dominantly controlled by the fault architecture. The (U-Th)/He thermochronology of fluorite grains from Komsheche yields a range of ages from Early Cretaceous to Pliocene, in concordance with the multistage tectonic evolution of the Zagros orogen. Our proposed model is that the barite-fluorite deposits of Central Iran formed during alternating tectonic episodes, including Early Cretaceous extension, post-Cretaceous - Oligocene compression, Oligo-Miocene extension, and finally Miocene and younger compression. The spatial-temporal correlation of our results with those of other studies along the Alpine-Himalayan and Atlas Mountains domains reveal a tight coupling between tectonism and formation of sediment-hosted fluorine-bearing (±Ba, Pb±Zn) deposits throughout the Mesozoic and Cenozoic. Incipient deposits formed in the Mesozoic along extension-related basement faults and subsequent deposit generations formed during reactivation / inversion of pre-existing structures. © 2021
Publication Date: 2020
Ore Geology Reviews (01691368)117
The Abbas-Abad volcano-sedimentary-hosted Fe-Cu skarn deposit, NE Isfahan, is one of the most important skarns in the central Urumieh-Dokhtar magmatic arc. It was formed along the contact with the Dorojin granitoid massif next to the Zefreh Fault. The plutonic rocks are of I-type, volcanic arc affinity with normal-K, metaluminous, calc-alkaline to calcic quartz diorite, tonalite, and granodiorite, similar to many other Fe-type skarn-related granitoids worldwide. The parent magma involved in this skarn system is high temperature and relatively oxidized. Amphibole geobarometery in quartz diorite yielded a crystallization pressure lower than 200 MPa (2 kb, ~7 km) at 724° to 785 °C. Granitoid compositions around the ore deposit are mainly granodiorite. U-Pb zircon dating yields Early Miocene ages of 23.0 ± 1.6 Ma for a quartz dioritic rock and 21.3 ± 1.5 Ma for a tonalitic sample. The injection and cooling of the granodiorite produced a hornblende hornfels aureole with endoskarn. Paragenetic relationships and microprobe data indicate that Abbas-Abad calcic skarn evolution can be subdivided into three stages as follow: (I) Prograde skarn associated andradite-rich garnet (Adr93-98Grs0-4Spe1-2) and pyroxene, (II) Retrograde skarn starting with garnet (Adr53-69Grs28-43Spe2-4), magnetite, and sulfide minerals associated with calcic-alteration, and (III) Post-ore with pyrite, chalcedony, epidote, quartz, calcite, and zeolite veinlets. Textural and compositional studies of garnet and magnetite from the garnet-bearing exoskarn zone reveal the multiple events associated with skarn formation. Garnets are characterized by low TiO2 and relatively high CaO that are indicative of a calcareous wall-rock among Eocene volcaniclastic rocks. They are grouped into garnet-1 (low w/r) and garnet-2 (inverse zoning at high w/r) with notable Cu-contents (up to 743 ppm). Petrographically, magnetite morphology is divided into fine-grained granular, needle-like, and polycrystalline aggregates. Mineral chemistry of needle-like type reveals impure components (Al2O3, CaO, and SiO2). This type formed from dissolution-reprecipitation processes during a stage of reequilibration in the skarn system. Mixing with cooler external fluid (rich in oxygen and poor in Fe2+) is reflected in individual features during infiltration metasomatism during garnet and magnetite growth, such as oscillatory zoning and needle-like textures. Thus, we infer increasing pH (decreasing acidity) and decreasing T related to carbonate neutralization reactions affecting Fe- and Cu-chloride complexing as the main controls on mineralization. The structural studies of the area show that movement of the dextral transtensional Zefreh Fault provide local zones for emplacement of Dorojin granitoid during the Early Miocene. Consequently, the dextral transtensional Zefreh Fault and dextral transpression associated with the Marbin-Rangan Fault uplifted the skarn and host units and Dorojin body under the roughly N-S directed maximum compression direction. Furthermore, the interplay of Zefreh and Marbin-Rangan faults within the N-S regional compressional regime formed an anticlinal structure that exposed the Dorojin body within the core. © 2020 Elsevier B.V.
Publication Date: 2020
International Geology Review (00206814)62(11)pp. 1359-1386
The Early Cretaceous was an important epoch in the evolution of the Earth system in which major tectonic episodes occurred, especially along the Alpine–Himalayan belt. The paucity of reliable palaeogeographic data from the central segment of this geological puzzle, however, hampers the reconstruction of a panoramic view of its Early Cretaceous palaeogeography and geodynamic setting. Here we present multidisciplinary provenance data from Lower Cretaceous strata of the overriding plate of the Neo-Tethyan subduction zone (the Sanandaj–Sirjan Zone; SSZ, of central Iran), including structural, basin-fill evolution, petrographic and geochemical analyses. Sandstone provenance analysis of Lower Cretaceous red beds suggests the occurrence of sub-mature litho-quartzose sandstones attributed to an active continental arc margin in convergent setting predominantly derived from plutonic, quartzose sedimentary and metamorphic rocks exposed in the central SSZ. Weathering indices indicate moderate chemical weathering in the source area which may be related to close source-to-sink relationships or arid climate. Our palaeogeographic reconstructions and original geological mapping indicate that the erosion of uplifted basement rocks exposed in horst blocks provided the sediment sources for the syn-extensional deposition of uppermost Jurassic–lowermost Cretaceous conglomerates and Lower Cretaceous siliciclastic red beds within a continental retro-arc basin during initiation of the ‘Neo-Tethys 2ʹ. The polyphase tectonic reactivation along the principal fault of the study area controlled the syn- and post-extensional tectonostratigraphic evolution that reflect the corresponding mechanical decoupling/coupling along the northern Neo-Tethyan plate margin. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.
The collision of Arabian-Eurasia continental plates in consequence of Neo-Tethys subduction, produces a zone of very complex tectonic structures in Iran. The study area is hinterland of the Zagros Orogen in central part of the Urumieh-Dokhtar magmatic arc, northeast Isfahan. Major brittle structures in the study area consists of dominant NW-SE-trending longitudinal, N-S and E-W-trending oblique faults sets. Comparison of brittle structures and mineral deposits in the area indicated that the mineralizations are mainly formed along the active tectono-magmatic arc. In the study area, NW-SE trending Zefreh fault and it’s branches faults have created a dextral horsetail splay architecture. Analysis of the lineaments interpreted out of satellite images and field observations is recognized as another technique for locating porphyry type copper mineralization. There is a close correlation between increasing the intensity of fractures and the repoted copper mineralization in the area. © 2019 Taylor & Francis Group, London.
Publication Date: 2019
Geological Journal (00721050)54(3)pp. 1454-1479
A better understanding of intraplate deformation requires the knowledge of the space–time scales involved in its development and to decipher possible links with the dynamic evolution of the plate boundaries. Central Iran provides an ideal test site to approach this scientific issue, since it is characterised by a prolonged history of Mesozoic–Cenozoic intraplate deformation that has been interfering with the spatio-temporal re-organization of the Zagros convergence zone along the Eurasia plate boundary. This study focus on the Doruneh Fault (DF) region that is considered as the northern mechanical boundary of the Central East Iranian Microcontinent. By combining field investigations with apatite low-temperature thermochronology, we present a revised tectono-stratigraphic scenario for the DF region, typified by a punctuated history of fault-related exhumation, burial and cooling history back to the Upper Cretaceous. When framed at regional scale, these results attest that the Zagros convergence zone, and its hinterland domain were fully mechanically coupled since ca. 40–35 Ma, a time lapse that is here referred as to the onset of continental collision along the Arabia–Eurasia plate boundary. In this scenario, the DF region operated throughout the Cenozoic as a major zone of residual stress accommodation and transfer in the hinterland domain of the Zagros convergence zone. Results of this study also suggest that the tectonic evolution along the Arabia–Eurasia plate boundary was modulated by the plate-boundary dynamics and by the modes of tectonic reactivation of the intracontinental weak zones of Central Iran and at its tectonic boundaries. Copyright © 2018 John Wiley & Sons, Ltd.
Publication Date: 2017
Tectonics (02787407)36(12)pp. 3038-3064
The Cenozoic deformation history of Central Iran has been dominantly accommodated by the activation of major intracontinental strike-slip fault zones, developed in the hinterland domain of the Arabia-Eurasia convergent margin. Few quantitative temporal and kinematic constraints are available from these strike-slip deformation zones, hampering a full assessment of the style and timing of intraplate deformation in Iran and the understanding of the possible linkage to the tectonic reorganization of the Zagros collisional zone. This study focuses on the region to the north of the active trace of the sinistral Doruneh Fault. By combing structural and low-temperature apatite fission track (AFT) and (U-Th)/He (AHe) thermochronology investigations, we provide new kinematic and temporal constraints to the deformation history of Central Iran. Our results document a post-Eocene polyphase tectonic evolution dominated by dextral strike-slip tectonics, whose activity is constrained since the early Miocene in response to an early, NW-SE oriented paleo-σ1 direction. A major phase of enhanced cooling/exhumation is constrained at the Miocene/Pliocene boundary, caused by a switch of the maximum paleo-σ1 direction to N-S. When integrated into the regional scenario, these data are framed into a new tectonic reconstruction for the Miocene-Quaternary time lapse, where strike-slip deformation in the intracontinental domain of Central Iran is interpreted as guided by the reorganization of the Zagros collisional zone in the transition from an immature to a mature stage of continental collision. ©2017. American Geophysical Union. All Rights Reserved.
