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Petrology (15562085)33(2)pp. 139-161
Abstract: Metabasites within the Jandaq Metamorphic Complex (JMC), Iran, offer valuable insights into the region’s magmatic and metamorphic history. Whole-rock geochemical data (major, trace, and rare earth elements) coupled with Sm-Nd isotopes were used to decipher the protolith origin and tectonic setting of formation of these metabasites. Our results demonstrate a predominantly ortho-amphibolitic nature for the JMC metabasites, with igneous protoliths ranging from basalt to andesite based on geochemical discrimination diagrams (Zr versus MgO and Sm/Nd). They exhibit geochemical affinities closer to enriched mid-oceanic ridge basalts (E-MORB) rather than normal MORB, implying a nascent oceanic basin within an intracontinental extensional setting. Trace element signatures (LILE enrichment, HFSE depletion) suggest a metasomatized subcontinental lithospheric mantle (SCLM) or a metasomatized lithospheric mantle beneath the oceanic crust as the parental magma source. Sm-Nd isotopic data suggest a potential plume source for the protoliths. These rocks were metamorphosed further by at least three metamorphic events: M1 (regional metamorphism, Barrovian-type; 616–687°C, 8–11 kbar), M2 (a brittle deformation event), and a later retrograde metamorphism (M3). These findings provide a comprehensive understanding of the geochemical characteristics, tectonic setting, and metamorphic evolution of JMC metabasites, shedding light on the geological history of the Jandaq region as a Paleo-Tethyan remnant. © Pleiades Publishing, Ltd. 2025.
Arian, H.,
Alaminia, Z.,
Ahmadi, H.,
Pour, A.B.,
Tabatabaei manesh, S.M.,
Lentz, D.R.,
Parsa, L. Remote Sensing Applications: Society and Environment (23529385)38
The demand for critical minerals is increasing swiftly as they are essential components for clean energy technologies. Nowadays, lithium (Li) is considered critical due to its wider use in various battery chemistries and the rapid growth of the electric vehicle industry. Pegmatites are considered one of the main sources of lithium worldwide. The pegmatite belt in Afghanistan, known for its enormous resources of critical metals, has recently emerged as an important region for lithium exploration. Multispectral remote sensing imagery is the only technique with large spatial coverage to map lithium-bearing pegmatites on a regional scale. In this study, ASTER and Sentinel 2MSI multispectral remote sensing imagery was used to map lithium-bearing pegmatites in the Tagablor pegmatite field in central Afghanistan. Various spectral mapping methods such as False Color Composite (FCC), Band Ratio (BR) and Spectral Angle Mapper (SAM) as well as supervised classification algorithms, i.e. Support Vector Machine (SVM), Minimum Distance (MD) and Maximum Likelihood (ML), were used to discriminate between altered minerals and lithologies as well as to identify areas with high potential for lithium-bearing pegmatites. Of the classification algorithms tested, SVM showed the highest efficiency in separating pegmatite bodies from their host rocks when applied to Sentinel 2 MSI data. The current study identified six promising pegmatite zones in the Tagablor pegmatite field, five of which were newly discovered and proposed for a comprehensive field campaign. In this study, an overall accuracy of 89 % was achieved in the detection of pegmatites and their surrounding formations, highlighting the potential of multispectral remote sensing for lithium exploration at a regional scale in arid and semi-arid regions. Further geochronological, geochemical and mineralogical investigations are recommended to better understand the age and mineralization potential of these pegmatites in the Tagablor pegmatite field, central Afghanistan. This study highlights the significant potential of multispectral remote sensing in mapping potential zones of critical minerals to enhance the sustainable utilization of minerals for green energy technologies in the future. © 2025 Elsevier B.V.
Journal of the Geological Society (2041479X)182(5)
This study explores the Oligocene–Miocene subduction-related plutonic rocks (OMPs) from the central Urumieh–Dokhtar Magmatic Arc (UDMA) in the centre of the Alpine–Himalayan Orogenic Belt (AHOB). OMPs range in composition from gabbro/diorite (c. 34–32 Ma) to tonalite (c. 20 Ma) with geochemical signatures of metaluminous calc-alkaline I-type granitoids. Geochemical analyses reveal enrichment in large ion lithophile elements and light rare earth elements relative to high-field-strength elements and heavy rare earth elements (LaN/YbN = 3.05–4.45). Mineral and whole-rock chemical variations reflect lower crust melting to crustal contamination over time, and magmatic chamber evolution. OMP chemical evolution can be attributed to two key factors: (1) incorporation of Th-rich sediment/crustal components from progressive lower crustal melting and (2) injection of fertile mantle melts altering magma chamber composition. These factors rendered the OMPs barren in Cu-mineralization but suggest a possible potential Cu mineralization in Miocene intrusive rocks, where the enriched mantle fluids, derived from the subducted slab, were more pronounced. This study proposed a geodynamic model to improve our understanding of the UDMA magmatic evolution. Comparison of subduction-related magmatism plutonic rocks from the central UDMA, southern Tibet and western Anatolia highlights the evolution of slab dynamics, crustal thickening and extensional processes in ‘Oligocene–Miocene’ magmatism during the eastward closure of Neotethys along the AHOB. © 2025 The Author(s). Published by The Geological Society of London. All rights, including for text and data mining (TDM), artificial intelligence (AI) training, and similar technologies, are reserved. For permissions: https://www.lyellcollection.org/publishing-hub/permissions-policy. Publishing disclaimer: https://www.lyellcollection.org/publishing-hub/publishing-ethics.
Petrology (15562085)31(4)pp. 459-474
Abstract: A Permian-Triassic lamprophyric magmatism has developed as dyke and subvolcanic intrusions in the northeast of Isfahan Province, in Central Iran, where is so-called the Chahriseh-Bagherabad area. These rocks mainly consist of olivine, pyroxene, amphibole, and biotite as major minerals and apatite, biotite, muscovite, and opaque as minor minerals with porphyritic texture and with felsic xenoliths and xenocrysts. The Chahriseh-Bagherabad lamprophyres (CBL) magma has undergone significant crustal contamination and fractional crystallization. Based on whole rock geochemistry, these rocks belong to alkaline lamprophyres, derived from a low degree (less than 5%) partial melting of an amphibole-garnet lherzolite mantle and enriched by the lithospheric mantle in the source region. Their 87Sr/86Sr (0.70435–0.70696) and 143Nd/144Nd (0.51260–0.51276) values were supported by an enriched mantle source of the EMІI-type that has been contaminated by the continental upper crust. Thus, the CBL samples are alkaline rock formed by tensional intraplate magmatism in a Paleo-Tethyan subduction zone in the lower Paleozoic to late Permian in which metasomatism and mantle enrichment occurred. The lamprophyres magmas ascend due to tensional stress during rotation and displacement of the central-eastern Iranian microcontinent. © 2023, Pleiades Publishing, Ltd.
Ahmadi-bonakdar s., S.,
Tabatabaei manesh, S.M.,
Nadimi, A.,
Mirlohi a., A.,
Santos j.f., J.F.,
Parfenova o.v., Geotectonics (15561976)56(6)pp. 791-809
Abstract: The Golpayegan metamorphic complex is located in the Sanandaj-Sirjan Zone, Iran. This complex consists of various metamorphic rocks including schists, marbles, slates, gneisses, and amphibolites, most of them have Neoproterozoic age. The presence of structures such as sigma fabrics, boudinage, folded boudinage and interfering fold patterns indicates the occurrence of more than two deformation phases in the Golpayegan metamorphic complex. The measurement of strain intensity in the folds indicated deep immersion of structures and old Precambrian settings that had been influenced by orogenic events in the Neoproterozoic. These deformed rocks were exposed during extensional movements and, subsequently, sheared. The results based on field works shown geochemical relations and initial εNd(600 Ma) values of amphibolites in three sampling points located in Golpayegan region manifested that the protolith of the first (a') and second (b') sampling points had mantle origin (ortho-amphibolite), whilst protolith of the third (c') sampling point had sedimentary origin (para-amphibolite). Geochemically, the Golpayegan ortho-amphibolites showed sub-alkaline basalt-basaltic andesite compositions of tholeiitic affinity. The negative anomalies of Nb and Ti relative to Pb, La, and Ce in the primitive mantle-normalized spider-diagram and εNd(600 Ma) values revealed the subduction environment for ortho-amphibolites. The ortho-amphibolites exhibited the intermediate chemistry between the normal mid-ocean ridge basalt and island-arc tholeiitic basalt. Enrichment in large ion lithophile elements (LILE), light rare earth elements (LREE), and relative depletion in high field strength elements (HFSE) suggest the back-arc basin setting for the Golpayegan ortho-amphibolites. The primitive magma of the ortho-amphibolites was produced by 8–20% melting of spinel lherzolite. According to the Neoproterozoic age of the Golpayegan ortho-amphibolites and their relationship with the Golpayegan granitic gneiss (596‒578 Ma), it shows that they can be related to the Cadomian back-arc basin in the north of Peri-Gondwana at the Neoproterozoic. The high values of 87Sr/86Sr (0.708450‒0.714986) interpreted as result of seawater hydrothermal alteration. © 2022, Pleiades Publishing, Inc.
Petrological Journal (22285210)13(4)pp. 87-106
The occurrence of tourmaline in the metamorphic complex of the north of Golpayegan is observed within the granitoid mass and schists in contact with granitoid and marbles. Speaking of abundance, tourmaline is less frequently a minor mineral found in granites and granitic pegmatites as well as in low-to high-grade metamorphic rocks (Krmícek et al., 2020). The minerals of the tourmaline group can adjust their composition to adapt to varied settings, and therefore show a remarkable stability range in terms of pressure, temperature, fluid composition, and host rock composition (Van Hinsberg et al., 2011). Since tourmaline displays a negligible intra-crystalline diffusion, it can record the physical and chemical conditions of its setting and preserve this information in geological chronicles. Therefore, tourmaline accurately presents the composition of fluids and the melts from which it crystallized (Marks et al., 2013). Although tourmaline is common in many rocks, it is not common in metamorphosed carbonates (Krmícek et al., 2020). A petrographical and geochemical investigation of tourmalines in the north of Golpayegan was undertaken to know the formation mechanism of this mineral and to determine the differences between tourmalines crystallized at the contact, in granitoid and tourmaline in marbles. Regional Geology The Golpayegan Metamorphic Complex is located in the Sanandaj-Sirjan Zone and the occurrence of tourmaline in this complex is observed in two locations. The first location is on the west side of Ochestan farm where tourmaline is found in three forms: 1) In the granitoid mass (Gt); 2) In the amphibole schists (At) in contact with the granitoid mass, and 3) In the mica schists (Mt) in contact with the granitoid mass. The second area is in the north of Esfajerd where tourmaline occurs inside the marbles (Ct). Methodology With the completion of field reconnaissance and preparation of thin sections, a petrographic study was fulfilled to determine the texture and mineralogy of the minerals, and then, some samples were selected for electron microprobe analysis. Petrography The tourmaline in granitoid mass (Gt), appears as idiomorphic and coarse-grained without any inclusions. Micaschists (Mt) in contact with the granitoid mass are sieve-shaped or spongy. Inside the amphibole schists (At) in contact with the granitoid mass, it is idiomorphic without any inclusions. Tourmaline in marbles (Ct) is fine-grained and blue, which can be observed around biotites with corrosion marks, indicating its reaction with fluid. Tourmaline chemistry The tourmalines in Ochestan granite-pegmatite (Gt) are of alkali tourmaline variety with schorl composition, enriched in aluminum, and points to the replacement of Al in the Y (R2) position. The substitution type of these tourmalines is Al(NaFe+2)-1 owing to the high amount of Fe versus Mg, The tourmalines in amphibole schist (At) are alkali tourmaline with schorl-dravite composition and the tourmalines in mica schist (Mt) are alkali tourmaline with dravite composition, and both types are characterized by insignificant amounts of aluminum. This demonstrates the replacement of Al in the position of Y (R2) has not occurred. Due to the change in Mg and Fe content, the At-type tourmalines benefit from both Al(NaFe+2)-1 and Al(NaMg)-1 substitution varieties. However, the substitutions of Mt-type tourmalines are mainly Al(NaMg)-1 due to the high content of Mg versus Fe. Indeed, Fe+3Al-1 substitution can be observed in both types of tourmaline. Tourmalines in marble (Ct) are of the alkaline type of dravite composition and rich in aluminum, which indicates the replacement of Al in the Y (R2) position. Their substitution is Al(NaMg)-1 due to the high content of Mg versus Fe. Discussion The composition of tourmaline in Gt is of schorl type (Fe/Fe+Mg= 0.89-0.91) and has an aluminum replacement in the Y position. The composition of tourmaline in Mt type is of dravite type (Fe/Fe+Mg= 0.45-0.47) and the composition of tourmaline in At type is of schorl-dravite type (Fe/Fe+Mg= 0.49-0.51), which, replacement of aluminum in the Y position does not occur in both types of tourmaline in schists. Consequently, hydrothermal tourmalines have less aluminum (i.e. At and Mt-type tourmalines), and tourmalines in the granite-pegmatite mass have much more aluminum (i.e. Gt-type tourmalines). Based on the values of Fe# (FeO/FeO+MgO), it is possible to determine the formation site of tourmalines. If the amount of Fe# in tourmaline is >0.8, it indicates the closed magmatic system, lack of fluids interference, and their contamination with Al-rich sediments. Meanwhile, if the ratio is <0.6, it means that boron is metasomatic with sediments rich in Al and also is of an extrinsic origin. The Gt tourmaline samples in the range of Li-poor granitoids and related pegmatites and aplites related to them, the At and Mt tourmaline samples placed in the range of Ca-poor metapelites, metapsammites and quartz-tourmaline rocks not coexisting with an Al-saturating phase. The tourmalines in the marbles of the north Esfajard (Ct) are of dravite type with the ratio of Fe/Fe+Mg= 0.42-0.45. In these tourmalines, both aluminum replacement in the Y position and Al(NaMg)-1 substitution can be observed, which manifests the non-magmatic origin of these types of tourmalines. The Ct-type tourmalines in the range of metapelites and metapsammites coexist with an Al-saturating phase. The postmagmatic/residual-hydrothermal fluids related to alkali syenite magma of the north Esfajard along with the fluids from the progressive metamorphism in micaschists, have developed these tourmalines in marble. The discrepancy in the results of two types of thermometers (thermometry based on the amount of Ti in biotite and Mg-Fe exchange between tourmaline and biotite minerals) in meta-carbonates, highlights that at temperatures >566°C biotite, and lower temperatures, Ct-type tourmaline is composed of biotites. Acknowledgment The authors are sincerely grateful to the Geology Department of Isfahan University for all their support. © 2023 The Author (s). Publisher: University of Isfahan.
Petrology (15562085)30(1)pp. 107-132
Abstract: The Urumieh-Dokhtar Magmatic Arc (UDMA) appears as a nearly linear suite of magmatic rocks that extends from NW to SE Iran parallel with the orogenic suture of the Zagros Fold-Thrust belt. The Qazan granitoids formed along the central part of UDMA and span a wide range of felsic rocks, including granodiorite, quartz diorite, diorite, and monzogranite. Their common rock-forming minerals are mainly quartz, feldspar, amphibole, biotite and clinopyroxene. These granitoids contain abundant mafic microgranular enclaves (MME). Bulk-rock major and trace element compositions returned a relatively low SiO2 content (ca. 51–55 wt %) and high Mg# (ca. 40–50) for MME samples, potentially reflecting a mantle-derived origin. The granitoid host rocks are metaluminous (A/CNK = ca. 0.7–1) I-type rocks with arc-related calc-alkaline affinity. They yield higher SiO2 contents with a comparatively larger variation (ca. 57–66 wt %) and lower Mg# (ca. 35–48), consistent with derivation from partial melting of lower continental crust. Mixing of two contrasting mafic (sourced from an enriched subcontinental lithospheric mantle wedge) and felsic (derived from lower continental crust) melts in the Neo-Tethyan subduction-related oxidizing system has resulted in generation of Qazan granitoid melts. Thermometry of Qazan intrusive rocks indicates that the ascending melt was crystallized at 1200–1100°C in lithospheric mantle to lower continental crust. © 2022, Pleiades Publishing, Ltd.
Tabatabaei manesh, S.M.,
Moghaddam I.R.,
Shirdashtzadeh, N.,
Amani E.,
Moghaddam I.R.,
Tabatabaei manesh, S.M.,
Shirdashtzadeh, N.,
Amani E. Journal of Economic Geology (20087306)13(4)pp. 719-740
Granitoids are one of the most abundant and common igneous rocks in the continental crust and they formed the world's largest batholiths. They are widely distributed in Precambrian to Cenozoic orogenic belts (e.g., Raymond, 2002), but some are formed in non-orogenic zones (Blatt et al., 2006). Because much of the continental crusts in orogenic belts are composed of granitoids, they are of particular importance in explaining the petrologic processes in orogenic belts. Cenozoic magmatism of Urmieh-Dokhtar magmatic arc is intruded by Oligo-Miocene plutonic rocks in some regions (Arvin et al., 2004). An outcrop of Oligo-Miocene granites is found in Zafarghand area in the southeast of Ardestan in Isfahan Province. Sarjoughian et al. (2018), Aminoroayaei Yamini et al. (2017), Sadeghian and Ghaffary (2011), Khalatbari Jafari et al. (2016), and Ghalamghash et al. (2019) suggested that this magmatism is a result of lower crust melting during mantle wedge metasomatism, occurred by Neo-Tethys subduction. This study aims to investigate the Oligo-Miocene granodiorites of East Bideshk, which is exposed in the central part of the Urumieh-Dokhtar magmatic arc in the northeast of Isfahan city. Despite the tectonomagmatic importance of this pluton in completing the geological history of Urumieh-Dokhtar magmatic arc, there are no comprehensive petrological studies performed on Bideshk granitoid. Thus, this study considered the mineralogy, geochemistry, tectonic environment, and origin of this granodiorite. © 2021 The author(s)
Geotectonics (15561976)55(4)pp. 584-599
Abstract: The Qazan granitoid pluton (South of Kashan, Iran) is situated in the central part of the Urumieh–Dokhtar Magmatic Arc. The plutonic body includes in its composition granodiorite, quartzdiorite, tonalite, and monzogranite. Granodiorite is the most predominant rock unit, which is composed of quartz, plagioclase, K-feldspar, hornblende, and biotite as main mineral phases. The Qazan pluton intruded into the Eocene volcano-sedimentary and Qom formation units. The Qazan pluton consists of mafic microgranular enclaves ranging from a few centimeters to meters in size. The Qazan pluton rocks with SiO2 content of 57.37 to 66.89 (wt %) are metaluminous to weakly peraluminous with A/CNK ratios of (>1.1) and show calc-alkaline I-type affinity. Primitive mantle-normalized spidergrams show enrichment of large ion lithophile elements (Rb, Ba, Th, U), as well as depletion of high-field strength elements (Nb, Ti). Field research suggested the magma ascended mainly in the NE–SW and NE–SW faults direction. The Qazan granitoids were injected along the extensional shear zones relevant to the dextral transpressional replacements. Petrographic and geochemical characteristics in combination with geodynamic evidence, offer that host rocks and associated enclaves originated by interaction between lower crust‒derived felsic and mantle derived mafic magmas in an active continental margin arc environment, during the subduction of the Neotethyan oceanic plate under the Central Iran continental crust. © 2021, Pleiades Publishing, Inc.
Journal of African Earth Sciences (1464343X)154pp. 120-135
Meso-Cenozoic magmatic belt of Urumieh–Dokhtar resulted from subduction of Neothetys oceanic crust beneath the Central Iran Block with Gondwanic signature is dominated by calc-alkaline to alkaline igneous rocks. The magmatic rocks has mainly occurred in submarine environments as volcanic-volcanoclastics with interlayers of sedimentary rocks in the Eocene, while it has occurred as intrusive and subvolcanics in the Neogene. In the Nabar area volcano-sedimentary rocks of Eocene have been covered unconformably by Oligo-Miocene sedimentary rocks (Qom Formation). The Eocene and Oligo-Miocene sequences are intruded by Middle-Upper Miocene intrusive and subvolcanic bodies. Igneous rocks of Eocene and Middle-Upper Miocene are of I-type and calc-alkaline belonging to arc and post-collisional setting of continental margin, respectively. The mineralization consists of pyrrhotite, pyrite, minor chalcopyrite and sphalerite, mainly hosted by Eocene volcanoclastics and particularly by the contact metamorphic halos of Qom formation. Irregular veinlets (stringer zone) in the lower part change to massive lenses upward which conformable with Eocene enclosing rocks, and have sharp contact with overlying Qom formation. Low grad ores with irregular shape (patches, veinlets, cavity and fracture filling) which are resulted from remobilization of previous mineralization, occurred within the contact metamorphic halos of Middle-Upper Miocene intrusions. According to geochemical analysis and mineralogical studies, iron, copper, gold, silver, arsenic, lead and zinc are enriched in the ore zone. Two types of fluid inclusion (L-V and L-V[sbnd]S) were distinguished in quartz veinlets. The homogenization temperature and salinity of fluid inclusions vary from 121 °C – 537 °C and 9–45 wt% NaCl equivalent, respectively. These data indicating the mixing of magmatic water with meteoric water in the later stage of mineralization. The δ 34 S values of pyrite and pyrrhotite which varies from 10.5 to 11.6 wt% compatible with massive sulfide and skarn type deposits. Field observations, mineralogical, geochemical, fluid inclusion and isotopic data suggest that, the Nabar deposit is probably a Kuroko type massive sulfide deposit which has been partly changed to skarn during penetration of Middle-Upper Miocene subvolcanic intrusions. The Kuroko type barite deposit of Dorreh and exhalative Mn deposit of Venarch and Shahrestanak were formed at the same time, within the Eocene volcanoclastic sequences. © 2019
Geotectonics (15561976)52(2)pp. 281-296
The Darreh Sary metapelitic rocks are located in the northeast of Zagros orogenic belt and Sanandaj-Sirjan structural zone. The lithological composition of these rocks includes slate, phyllite, muscovitebiotite schist, garnet schist, staurolite-garnet schist and staurolite schist. The shale is the protolith of these metamorphic rocks, which was originated from the continental island arc tectonic setting and has been subjected to processes of Zagros orogeny. The deformation mechanisms in these rocks include bulging recrystallization (BLG), subgrain rotation recrystallization (SGR) and grain boundary migration recrystallization (GBM), which are considered as the key to estimate the deformation temperature of the rocks. The estimated ranges of deformation temperature and depth in these rocks show the temperatures of 275–375, 375–500, and >500°C and the depths of 10 to 17 km. The observed structures in these rocks such as faults, fractures and folds, often with the NW-SE direction coordinate with the structural trends of Zagros orogenic belt structures. The S-C mylonite fabrics is observed in these rocks with other microstructures such as mica fish, σ fabric and garnet deformation indicate the dextral shear deformation movements of study area. Based on the obtained results of this research, the stages of tectonic evolution of Darreh Sary area were developed. © 2018, Pleiades Publishing, Inc.
Geochemistry International (00167029)56(7)pp. 670-687
The metabasites of Chadegan, including eclogite, garnet amphibolite and amphibolite, are forming a part of Sanandaj–Sirjan Zone. These rocks have formed during the subduction of the Neo–Tethys ocean crust under Iranian plate. This subduction resulted in a subduction metamorphism under high pressuremedium temperature of eclogite and amphibolites facies condition. Then the metamorphic rocks were exhumed during the continental collision between the Afro–Arabian continent and the Iranian microcontinent. In the metabasite rocks, with typical MORB composition, garnet preserved a compositional zoning occurred during metamorphism. The magnesium (XMg) gradually increases from core to rim of garnets, while the manganese (XMn) decreases towards the rim. Chondrite–normalized Rare Earth Element patterns for these garnets exhibit core–to–rim increases in Light Rare Earth Elements. The chondrite–normalized REE patterns of garnets, amphiboles and pyroxenes display positive trend from LREEs to Heavy Rare Earth Elements (especially in garnet), which suggests the role of these minerals as the major controller of HREE distribution. The geochemical features show that the studied eclogite and associated rocks have a MORB origin, and probably formed in a deep–seated subduction channel environment. The geothermometry estimation yields average pressure of ~22 kbar and temperature of 470–520°C for eclogite fomation. The thermobarometry results gave T = 650–700°C and P ≈ 10–11 kbar for amphibolite facies. © 2018, Pleiades Publishing, Ltd.
Geochemistry International (00167029)54(5)pp. 423-438
Grossular-andradite (grandite) garnets, precipitated from hydrothermal solutions is associated with contact metamorphism in the Kal-e Kafi skarn show complex oscillatory chemical zonation. These skarn garnets preserve the records of the temporal evolution of contact metasomatism. According to microscopic studies and microprobe analysis profiles, the studied garnet has two distinct parts: the intermediate (granditic) composition birefringent core that its andradite content based on microprobe analysis varies between 0.68–0.7. This part is superimposed with more andraditic composition, and the isotropic rim which its andradite content regarding microprobe analysis ranges between 0.83–0.99. Garnets in the studied sample are small (0.5–2 mm in diameter) and show complex oscillatory zoning. Electron microprobe analyses of the oscillatory zoning in grandite garnet of the Kal-e Kafi area showed a fluctuation in chemical composition. The grandite garnets normally display core with intermediate composition with oscillatory Fe-rich zones at the rim. Detailed study of oscillatory zoning in grandite garnet from Kal-e Kafi area suggests that the garnet has developed during early metasomatism involving monzonite to monzodiorite granitoid body intrusion into the Anarak schist- marble interlayers. During this metasomatic event, Al, Fe, and Si in the fluid have reacted with Ca in carbonate rocks to form grandite garnet. The first step of garnet growth has been coeval with intrusion of the Kal-e Kafi granitoid into the Anarak schist- marble interlayers. In this period of garnet growth, change in fluid composition may cause the garnet to stop growing temporarily or keep growing but in a much slower rate allowing Al to precipitate rather than Fe. The next step consists of pervasive infiltration of Fe rich fluids and Fe rich grandite garnets formation as the rim of previously formed more Al rich garnets. Oscillatory zoning in the garnet probably reflects an oscillatory change in the fluid composition which may be internally and/or externally controlled. The rare earth elements study of these garnets revealed enrichment in light REEs (LREE) with a maximum at Pr and Nd and a negative to no Eu anomaly. This pattern is resulted from the uptake of REE out of hydrothermal fluids by growing crystals of calcsilicate minerals principally andradite with amounts of LREE controlled by the difference in ionic radius between Ca++ and REE3+ in garnet x site. © 2016, Pleiades Publishing, Ltd.
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen (00777749)279(3)pp. 311-322
The metabasites of Chadegan belong to the Sanandaj-Sirjan Zone and include eclogite, garnet amphibolite and amphibolite that have been affected by several tectono-metamorphic events. These rocks were metamorphosed during subduction of Neo-Tethys ocean crust under Eurasia. Subsequent exhumation occurred by upwards-directed mass flow in a subduction channel during continental collision between the Afro-Arabian continent and the Iranian micro-continent. Trace element geochemistry and high total REE concentrations show that the protoliths of the studied metabasites has an E-MORB character and formed in an ocean ridge setting. Slightly positive initial εNO values (+1.5 to +3.8 at 190 Ma) agree with an origin of the parental magmas in a mantle source that did not undergo severe depletion events, whilst a large range of (87Sr/86Sr)I values (0.70690 to 0.71624) testifies for the strong influence of continental crustal fluids during regional metamorphism. ©2016 E. Schweizerbartsche Verlagsbuchhandlung, Stuttgart, Germany.
Geotectonics (15561976)50(3)pp. 313-326
The metabasites and mylonitic granites of the East and South East of Chadegan in the Isfahan province are a part of the Sanandaj-Sirjan Zone. This region is a large-scale ductile shear zone which has experienced different phases of deformation and dynamothermal metamorphism. There are at least three phases of deformation in this area. During the first phase which was related to the subduction of the Neotethys oceanic lithosphere under the Iranian microcontinent, the study rocks have experienced regional metamorphism. The second deformational phase was concurrent with the collision between the Arabian plate and the Iranian plate in the Late Cretaceous and caused mylonitization of the metamorphic rocks. The NW–SE trending fold and thrust faults have formed in this stage. The mylonitization have been formed along the dextral transpressional faults. During the third stage of deformation and exhumation of the metamorphic complex, the mylonitic zones have been uplifted to the surface. In this the deformation phase, developed the current morphology of the rocks. The granites have been injected along the extensional shear zones related to the dextral transpressional displacements. These granites are related to the continental collision granites type and have been formed synchronous to the collision between the Arabian and the Iranian plate. Enrichment in LREEs comparison to HREEs and the negative Eu anomaly in the primitive mantle-normalized spidergram and Chondrite-normalized REE patterns support an intra-crustal origin for these granites. Upper continental crust-normalized REE patterns show that in terms of LREEs, are similar to Upper continental crust. © 2016, Pleiades Publishing, Inc.
Petrology (15562085)24(1)pp. 100-115
The metamorphic rocks of the Aligudarz-Khonsar region can be divided into nine groups: slate, phyllite, sericite schist, biotite-muscovite schist, garnet schist, garnet-staurolite schist, staurolite schist, mylonitic granite, and marble. In this metamorphic region, four phases of metamorphism can be identified (dynamothermal, thermal, dynamic and retrograde metamorphism) and there are three deformation phases (D1, D2 and D3). Paleozoic pelagic shales experienced prograde metamorphism and polymetamorphism from the greenschist to amphibolite facies along the kyanite geotherm. The metapelites show prograde dynamothermal metamorphism from the greenschist to amphibolite facies. Maximum degree of dynamothermal metamorphism is seen in the Nughan bridge area. Also development of the mylonitic granites in the Nughan bridge area shows that dynamic metamorphism in this area was more intense than in other parts of the AligudarzKhonsar metapelitic zone. The chemical zoning of garnets shows three stages of growth and syn-tectonic formation. With ongoing metamorphism, staurolite appeared, and the rocks reached amphibolite facies, but the degree of metamorphism did not increase past the kyanite zone. Thus, metamorphism of the pelitic sediments occurred at the greenschist to amphibolite facies (kyanite zone). Thermodynamic studies of these rocks indicate that the metapelites in the Aligudarz-Khonsar region formed at 490–550°C and 0.47–5.6 kbar. © 2016, Pleiades Publishing, Ltd.
Arabian Journal of Geosciences (discontinued) (18667538)8(11)pp. 9501-9516
Urumieh-Dokhtar Magmatic Arc (UDMA) resulted from subduction of the Arabian plate beneath the Eurasian plate. Miocene–Pliocene volcanic rocks in the middle part of UDMA located in the north of Isfahan (Central Iran) are mainly dacite. They are chiefly composed of phenocrysts of plagioclase, amphibole, and biotite lying in a matrix made of feldspar, quartz, opaque, glass, and microlite. Having a relatively invariable composition, plagioclases are all andesine. Amphiboles are calcic and tschermakite type. The chemical composition of biotites hardly varies. All of them are Mg-biotite. On average, they are composed of 55.3 % phlogopite, 15.7 % talc, 12.8 % Ti-phlogopite, 11.6 % eastonite, 3.7 % Ferri-eastonite, and 0.9 % muscovite. The chemical composition of biotite indicates the nature of calcalkaline for magmatic series of magma generating biotites. An estimation of the temperature and pressure of crystallization resulted from integrating amphibole and amphibole-plagioclase thermobarometry equations indicates that amphibole-plagioclase phenocrysts were crystalised in the temperature range of 763–823 °C with average of 797 °C and in the pressure range of 2.2–4.5 kbar with the average of 3.4 kbar. An estimation of the oxygen fugacity of the magma, based on chemical composition and Fe3+ content of biotite, shows the oxygen fugacity was equal to that of the FMQ buffer. Quantifying oxygen fugacity shows that logfO2 was about −15. © 2015, Saudi Society for Geosciences.
Arabian Journal of Geosciences (discontinued) (18667538)8(11)pp. 9599-9623
The Oligo–Miocene Ghohroud granitoid is located in the north of Isfahan, in the Urumieh–Dokhtar magmatic arc (UDMA). The rock composition ranges from granodiorite to tonalite. Rocks mainly include quartz, plagioclase, and alkali feldspar with minor biotite and amphibole. Dacitic and basaltic rocks outcrop as dykes. Geochemical data show that these rocks are subalkaline, calc-alkaline, and metaluminous. Microgranular enclaves, sieve texture, oscillatory zoning in plagioclase, and clear roundness of quartz pieces demonstrated magma mixing. The magma has experienced fractional crystallization that has led to the presence of different petrological units. Large-ion lithophile element (LILE) and Pb enrichment is evidence of crustal contamination. Considering the clear negative anomaly of Nb and Ti, the magma has been formed in a volcanic arc environment. The geochemistry of major and rare earth elements reveals that initial magma has been formed by partial melting of lower crustal protoliths. An underplating magma can supply heat source for the dehydration melting of lower crust and generation of Ghohroud granitic melt by melting of a mafic source during the subduction of the Neotethyan oceanic plate and the Central Iran continental crust. © 2015, Saudi Society for Geosciences.
Environmental Earth Sciences (18666299)74(6)pp. 5221-5232
Geological features play a key role in determining variations in elemental concentrations in an area. Among different geological phenomena, intrusion of igneous bodies and associated alteration contribute significantly to the introduction of heavy metals into the area. This study has focused on Ghohroud, in central Iran, which is situated in the Urmieh–Dokhtar magmatic arc (UMDA) belt, and magmatism has developed as a result of the intrusion of a granodiorite body. The area has later been affected by hydrothermal fluids, resulting in argillic and propylitic alteration and contact metamorphism. The objectives of this study were to assess the degree of contamination and to describe the surface soil geochemical variations in relation to the geology, lithology, and hydrothermal activity in the Ghohroud area. Soil sampling was used for the geochemical study, and 96 samples were collected and analyzed by ICP-OES. Among the analyzed elements, the concentrations obtained for Pb, Zn, Ni, Cu, As, Co, V, and Mo were selected for statistical treatment. Different geoenvironmental indices were calculated, and the results showed that Cu, Mo, Pb, and Zn were present at a contaminating concentration. Remote sensing studies were employed in this study for alteration mapping. It was concluded that the development of different alteration types and proximity to intrusive bodies were the main contributors to the increased heavy metal concentrations in the area. © 2015, Springer-Verlag Berlin Heidelberg.
Petrology (15562085)22(3)pp. 310-328
The Nabar pluton with the age of Oligo-Miocene located northwest of Isfahan, the Urumieh-Dokhtar magmatic belt, is composed of gabbro, gabbro diorite, diorite, quartz diorite, tonalite, and quartz monzonite. These rocks contain plagioclase, quartz, alkali-feldspar, magnesiohornblende, actinolite, tremolite-hornblende, actinolite-hornblende, anthophyllite, biotite, and Na-poor pyroxene. Application of the Al-in-hornblende barometry indicates pressures of 2-2.15 kbar, whereas the clinopyroxene barometry shows a pressure of 5 kbar. The temperature (i.e., 750-800°C) is estimated using the amphibole-clinopyroxene thermometry in a dioritic sample. Magmatic water content was greater than 10% at the time of formation of dioritic rocks in the Nabar pluton. Based on chemistry of mafic minerals and geochemical data, the Nabar plutonic complex comprises medium-K, calc-alkaline, and I-type granitoid. The rocks are characterized by enrichment of lithophile elements (LILEs) and depletion of high-field-strength elements (HFSEs). The Nabar rocks have weak concave-upward rare earth element (REE) patterns, suggesting that amphibole played a significant role in their generation during magma segregation. Low (Al2O3/(FeO + MgO + TiO2) and (Na2O + K2O)/(FeO + MgO + TiO2) ratios, and the patterns of trace and rare earth elements suggest that these rocks formed along a destructive plate margin and were derived from a lower crustal source. The magma probably formed by partial melting of lower crustal protoliths (amphibolites). Lower crust contamination with magma derived from partial melting of the upper mantle has an important role in the formation of this intrusive body, and a fractional crystallization of melts in higher crustal levels generated this spectrum of rock types. Mantle-derived gabbroic magmas emplaced into the lower crust are the most likely heat sources for partial melting. © 2014 Pleiades Publishing, Ltd.
Petrology (15562085)20(7)pp. 658-675
The metapelitic schists of the Golpayegan region can be divided into four groups based on their mineral assemblages: (1) garnet-chloritoid schists, (2) garnet schists, (3) garnet-staurolite schists, and (4) staurolite-kyanite schists. Paleozoic pelagic shales experienced progressive metamorphism and polymetamorphism from greenschist to amphibolite facies along the kyanite geotherm. Mylonitic granites are concentrated in the central part of the region more than in other areas, and formed during the dynamic metamorphic phase by activity on the NW-SE striking Varzaneh and Sfajerd faults. The presence of chloritoid in the metapelites demonstrates low-grade metamorphism in the greenschist facies. The textural and chemical zoning of garnets shows three stages of growth and syntectonic formation. With ongoing metamorphism, staurolite appeared, and the rocks reached amphibolite facies, but the degree of metamorphism did not increase past the kyanite zone. Thus, metamorphism of the pelitic sediments occurred at greenschist to lower amphibolite facies. Thermodynamic studies of these rocks indicate that the metapelites in the north Golpayegan region formed at 511-618°C and 0. 24-4. 1 kbar. © 2012 Pleiades Publishing, Ltd.
Petrology (15562085)18(3)pp. 308-317
The metapelitic schists of Jandagh or simply Jandagh metapelites can be divided into four groups based on mineral assemblages: (1) quartz-muscovite schists, (2) quartz-muscovite-biotite schists, (3) garnet-muscovite-chlorite schists, and (4) garnet-muscovite-staurolite schists. The Jandagh garnet-muscovite-chlorite schists show the first appearance of garnets. These garnets contain 58-76% almandine, 1-18% spessartine, and 8-20% grossular. Microprobe analysing across the garnets demonstrates an increase in Mg# from core to rim. This is a feature of the prograde metamorphism of metapelites. Well-preserved garnet growth zoning is a sign that metapelites were rapidly cooled and later metamorphic phases had no effect here. The appearance of staurolite in garnet-muscovite-chlorite schists signifies a beginning of the amphibolite facies. The absence of zoning in staurolite suggests that its formation and growth during prograde metamorphism occurred at a widely spaced isograde. Thermobarometric investigations show that the Jandagh metapelites were formed within a temperature range of 400-670°C and pressures of 2. 0-6. 5 kbar. These results are in agreement with the mineral paragenetic evidence and show the development of greenschist and amphibolite facies in the area studied. © 2010 Pleiades Publishing, Ltd.