Zakipour, Z.,
Torabi, G.,
Kazuo, N.,
Morishita, T. Publication Date: 2022
Periodico di Mineralogia (22391002)91(2)pp. 163-199
The Eocene pluton intrudes the Paleozoic accretionary wedge in the Kal-e-Kafi area (NE of Anarak, Isfahan province, Central Iran). Metaperidotites of this Paleotethys- related accretionary prism consist of metalherzolite, metaharzburgite and metadunite and are associated with the listwaenites and metasediments (schist and marble). Rock-forming minerals of the Kal-e-Kafi metaperidotites are olivine (forsterite and chrysolite, Mg# =0.86-0.92 with CaO<0.02 wt%), orthopyroxene (enstatite, Mg# =0.84-0.86), clinopyroxene (Mg# =0.90-0.94, Al2O3 0.03-2.08 wt%), tremolite, magnesiohornblende, anthophyllite, serpentine, talc, chlorite, chromian spinel (Cr# =0.58-0.72), magnetite and plagioclase. All these minerals are metamorphic products and are not relicts of the primary igneous mineralogy, except the inner parts of Cr-spinels. Chemical composition of the core of Cr-spinel crystals reveal that the protolith of the studied rocks were mantle peridotites which belong to the depleted and moderately depleted peridotite series. The field relationships, petrography evidences, chemical characteristics of minerals and results of the thermobarometry calculations, show that the peridotites in the Kal-e-Kafi area have suffered a regional metamorphism in P-T condition of greenschist facies during the Paleozoic, intrusion of the Kal-e-Kafi pluton, caused a progressive contact metamorphism at 630 to 750 °C under a pressure less than 1 kbar (pyroxene hornfels facies) during the Eocene. © 2022 Edizioni Nuova Cultura. All rights reserved.
Shirdashtzadeh, N.,
Furnes, H.,
Miller, N.R.,
Dantas, E.L.,
Torabi, G.,
Meisel, T.C. Publication Date: 2022
Ofioliti (03912612)47(2)pp. 155-171
Subduction initiation (SI) ophiolites are critical for reconstructing plate tectonic and magmatic evolution along ancient convergent margins. Here we integrate clinopyroxene and whole rock chemical compositions, whole rock Nd isotopic compositions, and zircon U-Pb geochronology to demonstrate that the Ashin ophiolite between the Torbat-e-Heydarieh-Sabzevar and Nain-Baft ophiolitic Belts, records the initiation of late Early Cretaceous subduction mag-matism and formation of Neo-Tethys oceanic crust. Clinopyroxene and whole rock geochemical compositions of Ashin non-metamorphosed pillow lavas and ortho-amphibolites (metamorphosed pillow lavas) and ortho-amphibolitic dikes (metamorphosed diabase dikes) and whole rock compositions of comparable ophiolite exposures from Nain, Dehshir, and Shahr-Babak areas support a basaltic protolith generated during a subduction initiation system. Based on geochemical data, Sm/Nd > 0.4, Lu/Hf > 0.3, CeN/YbN < 1.2, DyN/YbN < 1.2, GdN/YbN < 1, LaN/YbN < 1, Th/Nb < 0.2 ratios, and εNdI > +9 can characterize the forearc basalt (FAB) affinity of ophiolitic mafic rocks. Geochronological (~ 107-94 Ma radiolarian cherts) and geochemical characteristics of the Ashin pillow lavas reflect a MORB-like forearc basin formed during subduction initiation towards the end of the Early Cretaceous. Then a younger group of basic pillow lavas and dikes formed and metamorphosed (to the amphibolites and amphibolitic dikes) in MORB-like (before 104 Ma) to SSZ-like (~ 97 Ma) SI settings based on zircon U-Pb ages and geochemical data. This short-lived oceanic basin (~ 13 Myrs, from ~ 107 to 94 Ma) closed at around 60 Ma (in Paleocene). © 2022, Edizioni ETS. All rights reserved.
Salim h., H.,
Torabi, G.,
Shirdashtzadeh, N.,
Sahlabadi m., ,
Morishita, T. Publication Date: 2022
Geotectonics (15561976)56(2)pp. 241-256
Abstract: The Early Oligocene alkalibasalts exposed in the Central Toveireh area located in the southwest of Jandaq city in Isfahan Province (Iran) and northwest of the Central-East Iranian Microcontinent (CEIM). Field studies reveal that these alkalibasalts crosscut the Eocene calc-alkaline volcanic rocks and granitoids and covered by the Miocene sedimentary rocks. The basaltic magma rose to the surface along the local faults. Based on the petrography, these alkalibasalts are composed of major minerals of olivine and plagioclase, and minor minerals of clinopyroxene, sanidine, Cr-spinel, and magnetite. The microscopic textures are porphyritic, microlithic porphyritic, trachytic, anti-rapakivi, corona, sieved texture, and poikilitic. Olivines are forsterite and chrysolite (Fo 0.90–0.75), plagioclases are labradorite to oligoclase (An63.1–20.7), alkali-feldspars are sanidine (Or50.3–61.5), clinopyroxenes are diopside and augite (Mg# 0.79 to 0.87), and Cr-spinels are hercynite (Cr# 0.24 to 0.25) in chemical composition, spinels (Mg# 0.72 to 0.76) are present as xenocrysts in some samples. The average contents of SiO2 and TiO2 of these rocks are 48.96 and 1.54 (wt %), respectively. The chondrite and primitive mantle-normalized diagrams characterized by enriched LREE relative to HREE, LILE enrichment, and absence of evident Eu anomaly. The normative content of nepheline reaches up to 14.6%. Modal and normative mineralogy, as well as geochemical data of minerals and whole rocks revealed that these rocks are sodic to highly sodic alkalibasalts formed in a within-plate continental tectonomagmatic setting after the cessation of subduction. The whole-rock chemical data indicate that the Central Toveireh alkalibasalts probably formed by relatively medium degrees of partial melting of an amphibole-bearing garnet lherzolite from the asthenospheric mantle of about 105 km in depth, which was previously enriched by subduction of the Neo-Thetyan slab. © 2022, Pleiades Publishing, Inc.
Publication Date: 2022
Journal of Economic Geology (20087306)14(1)pp. 157-184
Introduction Subduction-related magmas are characterized by enrichment of large ion lithophile elements (LILEs), light rare earth elements (LREEs) and depletion in high field strength elements (HFSEs) (Harangi et al., 2007). These geochemical signatures of magmatic rocks are commonly explained by the addition of hydrous fluids from subducting oceanic lithosphere combined with the flux of melts from subducted sediments to the mantle wedge, lowering the mantle solidus and leading to magma generation (Aydınçakır, 2016). Asthenospheric mantle, subcontinental lithospheric mantle and/or lower crust may be the principal source of these rocks (Eyuboglu et al., 2018). In addition, magma differentiation processes, such as fractional crystallization, crustal contamination, and magma mixing may also play an important role in the genesis of these rocks. This research study presents new petrological and geochemical data from the volcanic rocks with NW-SE trending, which are situated in the northwestern margin of the Central -East Iranian Microcontinent (CEIM) (south-east of Khur, Isfahan Province) which have been formed during the peak activity of Eocene. Study of this typical small volume subduction- related magmatism will be useful in understanding the origin and geological evolution of the Central Iran in Cenozoic. Analytical Methods The petrographic investigations on Eocene volcanic rocks from the SE of Khur area were carried out with an optical microscope (OlympusBH2) in the petrology Laboratory of the University of Isfahan, Iran. Major and trace element concentrations of samples from whole- rocks were obtained by a combination of inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) at the Als Chemex Laboratory of Ireland. The chemical compositions of 4 samples (B865, B866, B867, and B868) were determined by Neutron Activation Analysis (NAA) in the Isfahan Activation Center. The detection limit was 0.01% for all major element oxides and 0.01 ppm for rare earth elements. Mineral abbreviations were adopted from Whitney and Evans (2010). Results and Discussion Eocene volcanic rocks with trachy-basalt and trachybasaltic andesite composition are exposed in the northwestern part of the Central-East Iranian Microcontinent (CEIM) (SE of Khur, Isfahan Province, Central Iran). These rocks which have a dominant northwest-southeast trend crosscut the Cretaceous sedimentary rocks. Petrography and mineral chemistry analyses indicate that the predominant rock-forming minerals of volcanic rocks are olivine, plagioclase, clinopyroxene and orthopyroxene. Phenocrysts set in a fine to medium grained matrix of the same minerals plus sanidine with minor amounts of opaque minerals. Secondary minerals are chlorite and calcite. The most common textures of these rocks are porphyritic, microlitic porphyritic, poikiolitic and glomeroporphyritic. Geochemical analyses of whole rock samples show that these rocks have been enriched in alkalies and large ion lithophile elements (Cs, K, Rb, Sr, Ba,), and have been depleted in high field strength elements (HFSE) (Ta, Nb, Ti). All samples indicate moderate to high fractionation in LREE patterns. These geochemical signatures point out to the subduction-related calc-alkaline nature of these rocks and their similarity to volcanic rocks of continental arcs or convergent margins (Yu et al., 2017). Pb enrichment and low values of Nb/La, Nb/U and Ce/Pb ratios reveal that crustal contamination has played an important role in magma evolution (Srivastava and Singh, 2004; Furman, 2007). The large volume of hydrous fluids coming from the subducted slab rather than sediments have caused enrichment and metasomatism of the subcontinental lithospheric mantle source. The geochemical characteristics of the studied rocks suggest that the parental magma have been derived from partial melting of a metasomatized spinel lherzolite of lithospheric mantle, which was previously modified by dehydration of a subducting slab. The tectonic environment, in which these rocks were formed has probably been a volcanic arc. Subduction of oceanic crust around the Central-East Iranian Microcontinent (CEIM) is the most reasonable mechanism which can be used to explain enrichment in volatiles of the mantle, and the calc-alkaline magmatism of the study area in Eocene times. © 2022 The author(s)
Samadi, R.,
Torabi, G.,
Dantas, E.L.,
Morishita, T.,
Kawabata, H. Publication Date: 2022
International Geology Review (00206814)64(15)pp. 2151-2165
This study investigates relicts of some granitic Gondwanan basement unexpectedly outcropping in the northwest of Central-East Iranian Microcontinent (CEIM) and incorporated into an ophiolitic mélange. Based on petrographical (e.g. high modal content of muscovite (~10 vol.%), absence of hornblende, inherited zircons (>541 Ma)), geochemical (peraluminous and calc-alkaline S-type affinity, high silica, high ‘light rare earth element (LREE)/heavy rare earth element (HREE)’ ratios, negative Nb and Ti anomalies), and geochronological (magmatic zircon age ~448 Ma) results, it is an Ordovician anatectic granite formed from a sedimentary source during crustal thickening in a syn-collisional setting. It shows some signatures of metamorphic deformation (cataclastic fabric, quartz bulging recrystallization, and foliation) likely developed in the Devonian (~410 Ma). The U-Pb zircon ages from this granite are analogous to the other Ordovician collision-related magmatic events in the CEIM (Chahak to Airekan, Balvard). Our results confirm that Cadomian subduction and closure of the Proto-Tethys Ocean to the north of the Gondwana supercontinent resulted in crustal thickening during Ordovician collision-related magmatism and Devonian-Carboniferous regional metamorphism in the CEIM. © 2021 Informa UK Limited, trading as Taylor & Francis Group.
Publication Date: 2021
Geotectonics (15561976)55(4)pp. 600-617
Abstract: The combination of geochemical analyses and geochronological data of Eocene volcanic rocks reveals a gradual shift in the dominant magmatic series from calc-alkaline to high-K calc-alkaline and shoshonitic in Central Iran. Transitional high-K calc-alkaline Eocene volcanic rocks with predominantely trachy-andesite composition are exposed in western part of the Central-East Iranian Microcontient (CEIM) (NE of Anarak, Isfahan Province, Central Iran). Petrography and mineral chemistry analyses indicate that the rock-forming minerals of these trachy andesites are clinopyroxene (diopside and augite, Mg# = 0.840–0.94), plagioclase (andesine and oligoclase, An18–39), sanidine (Or65–69), amphibole (Magnesio-hastingsite and magnesio-hornblende, Mg# = 0.576 to 0.787), and phlogopite (Mg# = 0.54‒0.58) with minor amounts of opaque minerals (magnetite and titanomagnetite), zircon, titanite and apatite. Secondary minerals, as the result of alteration, are calcite, chlorite (diabantite), kaolinite, hematite and prehnite. Geochemical analyses of whole rock samples show that these rocks are characterized by SiO2 content of 55.1 to 62.5 wt %, Al2O3 amounts of 14.3 to 16.70 wt %, K2O contents of 2.92 to 4.83 wt % and TiO2 values of 0.55 to 0.72 wt %. They are enriched in alkalis (Na2O + K2O up to 10.43 wt %) and large ion lithophile elements (LILE) (Cs, K, Rb, Sr, Ba), depleted in high field strength elements (HFSE) (Ta, Nb, Ti) and exhibit weak negative Eu anomaly (Eu/Eu* = 0.70‒0.92). These Eocene volcanic rocks present strong enrichment in light rare earth elements (LREE) relative to heavy REE (HREE) (La/Lu ratio up to 131.29), and a flat HREE pattern. All these chemical cheriteria point to the subduction-related high-K calc-alkaline magmatic rocks. The occurrence of this potassic volcanism can be attributed to the former subduction of the CEIM confining oceanic crust beneath the CEIM from Triassic to Eocene. Geochemical features of these trachy andesites suggest that the parental magma were possibly derived from relatively low degrees of partial melting of a mantle wedge spinel lherzolite experienced strong metasomatism by fluids/melts released from the Neo-Tethys subducted slab. These high-K calc-alkaline volcanic rocks are generated at the late stages of the orogeny and after the cessation of subduction. © 2021, Pleiades Publishing, Inc.
Jamshidzaei, A.,
Torabi, G.,
Morishita, T.,
Tamura, A. Publication Date: 2021
Journal of Geodynamics (02643707)145
The Eocene felsic stock and dike swarm with intermediate composition from Central Iran (southwest of Jandaq) are studied to understand geodynamic evolution of the Central-East Iranian Microcontinent (CEIM). Field relationships show that the dikes, composed of trachyandesite and basaltic trachyandesite, cross-cut the felsic stock. Whole rock geochemical data reveal the calc-alkaline nature of stock and high-K calc-alkaline to shoshonitic nature of dikes. The felsic stock and intermediate dikes show LREE and LILE enrichment and HFSE (Ta, Nb and Ti) depletion, suggesting that they probably formed in a subduction zone and are similar to the volcanic arc rocks. The rock samples of felsic stock have geochemical characteristics of the high silica adakites (HSA) produced by melting of a subducted oceanic crust. On the other hand, the dikes have characteristics of low silica adakites (LSA) produced by partial melting of a lithospheric mantle peridotite previously metasomatized by slab-derived melts. The Eocene felsic stock and dikes probably formed by subduction of the CEIM-confining oceanic crusts beneath the CEIM. The field and geochemical studies indicate that the magma originated from melting of basic section (amphibolite) of the subducted slab (HSA) will arrive to the Earth surface before the magma formed by melting of mantle wedge peridotites (LSA). © 2021
Samadi, R.,
Torabi, G.,
Kawabata, H.,
Miller, N.R. Publication Date: 2021
Lithos (00244937)386
Chemical compositions of Fe-Mg biotite have been used to understand the petrogenesis of metamorphic and igneous rocks. However, biotite is affected by sub-solidus hydrothermal alteration, metamorphism, and chemical exchange with other common coexisting phases such as garnet and muscovite. Therefore, the interpretation of igneous and metamorphic processes using biotite compositions is not always straightforward. Here we compare biotite compositions in igneous rocks, meta-igneous rocks, and meta-sedimentary rocks from localities in northeast (Dehnow, Khalaj, Khajeh Morad) and central (Jandaq and Airekan) Iran, with similar rock types in the global GEOROC database and from other localities, in order to constrain associated petrogenetic classification schemes. We find important compositional contrasts in biotite associated with muscovite and/or garnet (in both igneous and metamorphic rocks), suggesting careful use of common discrimination schemes. For example, magmatic biotite associated with garnet and/or muscovite (i.e., Bt + Ms, Bt + Ms + Grt, Bt + Grt) is often enriched in Al and depleted in Fe, Mg, and Ti, likely due to crystallization prior to muscovite but synchronous with or following garnet crystallization. Metamorphic biotites in garnet- and/or muscovite-bearing rocks tend to be enriched in Ti, Fe, and Mg and depleted in Al. The contrasting compositional behavior of magmatic and metamorphic biotites also poses problems for garnet-biotite, biotite-muscovite, and Ti-in-biotite thermometers. Our analysis indicates that biotite rare earth and trace element concentrations are strongly influenced by co-existing garnet and muscovite. When magmatic biotite crystallization occurs with muscovite and garnet, HREE concentrations respectively decrease and increase. © 2021
Publication Date: 2021
Journal of Economic Geology (20087306)13(1)
Granitoids are the main rock units in the continental crust. Study of granitoids reveals significant information on tectonic mantle and upper crust. Many researchers have investigated petrogenesis and origin of granitoids (e.g., Chappell and White, 2001; Barbarin, 1999; Frost et al., 2001). For example, Chappell and White (1992), Pitcher (1993) and Chappell et al., (1998) have divided granites into two major groups of: (1) I-type granites (high-temperature or Cordellerian granitoids, including low-K granitoid to high-Ca tonalite, without inherited zircons) formed by partial melting of mafic rocks at >1000 ℃ in mantle or subduction zones of continental margins, and (2) S-type (low-temperature or Caledonian granitoids with inherited zircons) granites formed by partial melting of felsic crust at ~700-800 ℃. Northeast of Iran is a key location for studying the Cimmerian Orogeny, which is related to the Late Triassic collision between it and Eurasia, and the closure of the Paleo-Tethys (Samadi et al., 2014). Mesozoic Mashhad granitoids have cropped out along with the Paleo-Tethys suture zone. Distinct granitoid suites, i.e., monzogranite, granodiorite, tonalite, and diorite occur in Mount Khalaj located in the south of Mashhad. It comprises of monzogranite and granodiorite. However, monzogranite is the most abundant. To study the plutonic events during the Turan and Central Iran collision, the origin and tectonic setting of monzogranite of Mount Khalaj are investigated in this study based on whole rock geochemical data. © 2021 Ferdowsi University of Mashhad. All rights reserved.
Publication Date: 2020
Neues Jahrbuch fur Mineralogie, Abhandlungen (00777757)196(3)pp. 179-191
The petrography and mineral chemistry of the metamorphosed lherzolite in Darreh-Deh massif (east of Nain Ophiolite, Central Iran) is investigated in order to find the calcium source for rodingitization and tremolitization. In com-parison with olivine and orthopyroxene, the clinopyroxene has lower modal content and is more alteration-resistant. The microprobe data and petrography of these lherzolites indicate that Ca2+ cations can be released during serpentinization of orthopyroxene (with ~18 vol% and CaO~2.7 wt%) and clinopyroxene (with ~6 vol% and CaO~ > 20 wt%). In contrast, per-vasive serpentinization of mantle olivine with ~70 vol% and CaO~0.02 – 0.07 wt% is another expected source for producing Ca2+ rather than metamorphic olivine with CaO~ < 0.02 wt%. The released Ca2+ cannot be completely accommodated in crystal lattice of produced serpentine (with CaO~0.02 – 0.06 wt%), talc and chlorite (with CaO~0.015 wt%), but it can par-ticipate in formation of Ca-bearing tremolite (CaO~13 wt%), as a result of serpentinization of clinopyroxenes or subsequent metamorphism of peridotites at amphibolite facies and in formation of coarse-grained clinopyroxene blades and tremolite during rodingitization. Therefore, the calcium content in clinopyroxene, orthopyroxene and olivine of a plagioclase–free peridotite is a potential source of Ca2+, depending on the degree of serpentinization or chloritization. © 2019 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany.
Publication Date: 2020
Island Arc (10384871)29(1)
This study is focused on a plagioclase-bearing spinel lherzolite from Chah Loqeh area in the Neo-Tethyan Ashin ophiolite. It is exposed along the west of left-lateral strike-slip Dorouneh Fault in the northwest of Central-East Iranian Microcontinent. Mineral chemistry (Mg#olivine < ~ 90, Cr#clinopyroxene < ~ 0.2, Cr#spinel < ~ 0.5, Al2O3 orthopyroxene > ~ 2.5 wt%, Al2O3 clinopyroxene > ~ 4.5 wt%, Al2O3 spinel > ~ 41.5 wt%, Na2Oclinopyroxene > ~ 0.11 wt%, and TiO2 clinopyroxene > ~ 0.04 wt%) confirms Ashin lherzolite was originally a mid-oceanic ridge peridotite with low degrees of partial melting at spinel-peridotite facies in a lithospheric mantle level. However, some Ashin lherzolites record mantle upwelling and tectonic exhumation at plagioclase-peridotite facies during oceanic extension and diapiric motion of mantle along Nain-Baft suture zone. This mantle upwelling is evidenced by some modifications in the modal composition (i.e. subsolidus recrystallization of plagioclase and olivine between pyroxene and spinel) and mineral chemistry (e.g. increase in TiO2 and Na2O of clinopyroxene, and TiO2 and Cr# of spinel and decrease in Mg# of olivine), as a consequence of decompression during a progressive upwelling of mantle. Previous geochronological and geochemical data and increasing the depth of subsolidus plagioclase formation at plagioclase-peridotite facies from Nain ophiolite (~ 16 km) to Ashin ophiolite (~ 35 km) suggest a south to north closure for the Nain-Baft oceanic crust in the northwest of Central-East Iranian Microcontinent. © 2020 John Wiley & Sons Australia, Ltd
Pirnia, T.,
Saccani, E.,
Torabi, G.,
Chiari, M.,
Goričan, Š.,
Barbero, E. Publication Date: 2020
Geoscience Frontiers (1674-9871)11(1)pp. 57-81
The Nain and Ashin ophiolites consist of Mesozoic mélange units that were emplaced in the Late Cretaceous onto the continental basement of the Central-East Iran microcontinent (CEIM). They largely consist of serpentinized peridotites slices; nonetheless, minor tectonic slices of sheeted dykes and pillow lavas - locally stratigraphically associated with radiolarian cherts - can be found in these ophiolitic mélanges. Based on their whole rock geochemistry and mineral chemistry, these rocks can be divided into two geochemical groups. The sheeted dykes and most of the pillow lavas show island arc tholeiitic (IAT) affinity, whereas a few pillow lavas from the Nain ophiolites show calc-alkaline (CA) affinity. Petrogenetic modeling based on trace elements composition indicates that both IAT and CA rocks derived from partial melting of depleted mantle sources that underwent enrichment in subduction-derived components prior to melting. Petrogenetic modeling shows that these components were represented by pure aqueous fluids, or sediment melts, or a combination of both, suggesting that the studied rocks were formed in an arc-forearc tectonic setting. Our new biostratigraphic data indicate this arc-forearc setting was active in the Early Cretaceous. Previous tectonic interpretations suggested that the Nain ophiolites formed, in a Late Cretaceous backarc basin located in the south of the CEIM (the so-called Nain-Baft basin). However, recent studies showed that the CEIM underwent a counter-clockwise rotation in the Cenozoic, which displaced the Nain and Ashin ophiolites in their present day position from an original northeastward location. This evidence combined with our new data and a comparison of the chemical features of volcanic rocks from different ophiolites around the CEIM allow us to suggest that the Nain-Ashin volcanic rocks and dykes were formed in a volcanic arc that developed on the northern margin of the CEIM during the Early Cretaceous in association with the subduction, below the CEIM, of a Neo-Tethys oceanic branch that was existing between the CEIM and the southern margin of Eurasia. As a major conclusion of this paper, a new geodynamic model for the Cretaceous evolution of the CEIM and surrounding Neo-Tethyan oceanic basins is proposed. © 2019 China University of Geosciences (Beijing) and Peking University
Publication Date: 2019
Geotectonics (15561976)53(6)pp. 786-805
Abstract—: The Lower Oligocene Kal-e-kafi (East of Anarak, Central Iran) lamprophyres occur as stocks and dikes, which cross-cut the Eocene volcanic and Cretaceous sedimentary rocks. The predominant minerals of these lamprophyres are hornblende (magnesiohastingsite) and clinopyroxene (diopside) phenocrysts set in a fine- to medium-grained matrix of the same minerals plus plagioclase (labradorite to bytownite), sanidine, apatite, and magnetite. Secondary minerals are chlorite, magnetite, calcite, and epidote. Petrography, mineral chemistry, and whole rock compositions classify these rocks as calc-alkaline lamprophyre, in general, and spessartite in particular. These samples have intermediate compositions (SiO2 ~ 58 wt %). The chondrite-normalized REE patterns and primitive mantle-normalized multi-element spider diagram of Kal-e-kafi lamprophyres are remarkably parallel and suggest that these dikes and stocks were derived from the same parental magma and underwent similar melt extraction. These rocks are enriched in alkalies, large-ion lithophile elements (e.g., Rb, Ba, K), and light rare-earth elements (e.g., La, Ce), and exhibit moderate to high fractionation in LREE patterns, with an average La/Lu ratio of 112. The large amount of hydrous fluids coming from the subducted slab rather than sediments caused to the enrichment and metasomatism of subcontinental lithospheric mantle source. Crustal contamination and assimilation of host rocks also played role in the genesis of these lamprophyres. Geochemical characteristics of the studied rocks suggest that parental magma have been derived from partial melting of a metasomatized amphibole-bearing spinel lherzolite of lithospheric mantle, which was previously modified by dehydration of a subducting slab. Subduction of oceanic crust around the Central-East Iranian Microcontinent (CEIM) is the most reasonable mechanism to explain enrichment in volatiles of the mantle, and the lamprophyric magmatism of the Kal-e-kafi area in Lower Oligocene times. Several tectonomagmatic discrimination diagrams indicate that the Kal-e-kafi lamprophyres occurred during postcollisional period of lithospheric extension. © 2019, Pleiades Publishing, Inc.
Publication Date: 2019
Geotectonics (15561976)53(1)pp. 110-124
Abstract: The Ashin ophiolite is situated in the western part of Central Iran and presents two stages of Jurassic and Cretaceous spreading. The Ashin ophiolite represents fragments of the Neo-Tethys oceanic lithosphere. Plagiogranite intrusions of this ophiolite have good exposures. Plagiogranites of Cretaceous are more fresh than the metamorphosed samples of Jurassic. The main minerals of plagiogranites from the Ashin ophiolite are plagioclase, quartz and amphibole. Plagiogranites of the Jurassic have tholeitic nature with higher amounts of amphibole, $${\text{F}}{{{\text{e}}}_{2}}{\text{O}}_{3}^{*},$$ TiO2, Co and lower values of Mg#, Th and Sr than the Cretaceous calc-alkaline plagiogranites. The chondrite-normalized REE patterns of these plagiogranites are characterized by higher values of REEs and negative Eu anomalies for the Jurassic samples and low values of REEs and positive Eu anomalies for the Cretaceous ones. Very low values of HREEs in the Cretaceous plagiogranites indicates a non-peridotitic source rock. We suggest that the Jurassic plagiogranites are formed by fractional crystallization of a low-K tholeitic magma; and the adakitic Cretaceous plagiogranites are formed by partial melting of an amphibolite in the subducting slab. Geochemical criteria of the Ashin plagiogranites indicate changing the Ashin ophiolite tectonic setting from a mid-ocean ridge system in the Jurassic to a supra-subduction zone in the Cretaceous. © 2019, Pleiades Publishing, Inc.
Publication Date: 2019
Turkish Journal Of Earth Sciences (1303619X)28(4)pp. 558-588
The Middle Eocene Toveireh plutonic body is located in the western margin of the Central-East Iranian Microcontinent (CEIM). This plutonic body consists of granodiorite, syenogranite, and monzogranite compositions. Granodiorite is the most predominant rock unit, which is composed of quartz, plagioclase, K-feldspar, hornblende, and biotite main mineral phases. The Toveireh pluton is metaluminous to weakly peraluminous (A/CNK = 0.85–1.04) and shows a calc-alkaline I-type affinity. Primitive mantle-normalized spidergrams show enrichment of large ion lithophile elements (Rb, Ba, Th, U) and light rare earth elements (REEs) (La/YbN = 6.8–8.24), as well as depletion of high-field strength elements (Nb, Ta, Ti, P). These rocks are characterized by unfractionated heavy REEs [(Gd/Yb)N = 1.02–1.80] and a moderate negative Eu anomaly (Eu/Eu* = 0.39–0.77) in the chondrite-normalized REE patterns. The geochemical data suggest that the Toveireh pluton was derived from a low degree of partial melting of a mixed source, primarily of mafic and metasedimentary rock, in the middle crust by underplating of mafic magma. Geochemical and petrological features of the studied samples, such as a wide range of Mg# values (21.3–62.2, average: 35.6) and low amounts of mafic microgranular enclaves, indicated minor involvement of the mantle-derived magma components in the source and about 10% mixing with a felsic melt. Magma chamber processes, including melting, assimilation, storage and homogenization, magma mixing, and assimilation and fractional crystallization, played an important role in the magmatic evolution. The hornblende thermobarometry yielded 720 °C to 840 °C ± 23.5 °C and 0.6–1.4 ± 0.16 kbar for the granodiorites, and the biotite thermobarometry revealed 700 °C to 750 °C and 0.77–0.78 kbar for the syenogranites. The combined results suggest that the studied rocks were crystallized in shallow crustal magma chambers. The Toveireh pluton was formed by the subduction of the eastern branch of Neo-Tethyan oceanic crust beneath the CEIM during the Late Triassic to Early Tertiary. © TÜBİTAK.
Publication Date: 2019
Periodico di Mineralogia (22391002)88(2)pp. 155-184
The Paleozoic Bayazeh ophiolite is situated in the western part of the Central-East Iranian Microcontinent (CEIM). This ophiolite consists of serpentinized peridotite, metagabbro, metapicrite, serpentinite and amphibole-bearing listwaenite, which are covered by schists and marbles. Serpentinites in the Bayazeh ophiolite are produced by serpentinization of a mantle protolith. The composition of primary chromian spinel cores (with average content of Cr~9.9, Mg~4.3, Ti< 0.01 and Fe3+<0.5 apfu) in the Bayazeh serpentinites suggests an origin from high degrees of partial melting of a depleted harzburgite source in a supra-subduction zone setting. The texture and mineral assemblage of amphibole-bearing listwaenites and their association with serpentinites indicate that the studied listwaenites were generated by prograde metamorphism under upper greenschist to lower amphibolite facies conditions from a carbonated serpentinite. Geochemical characteristics of the Bayazeh metagabbros, indicate high value of large ion lithophile elements, high content of light rare earth elements, low HREE fractionations [e.g. (Gd/ Yb)CN=0.95-1.21], low contents of high-field strength elements and large variation of the LILE/HFSE ratios (e.g. Sr/Sm=47.83-564.67). These compositions are similar to cumulate gabbros and point to a possible role of melts from a lithospheric mantle and effect of fluids derived from the subducted slab in their formation. Mineralogical characteristics (e.g. presence of primary hydrous minerals such as phlogopite up to 10 vol%) and chemical composition of the Bayazeh metapicrites suggest derivation from a metasomatized asthenospheric mantle. Metasomatic enrichment of the mantle source probably occurred by fluids released during subduction of the Paleo-Tethys Ocean beneath the Central Iran. Subduction of the Paleo-Tethys from the Early to the Late Paleozoic is the cause of volatile enrichment and mantle metasomatism in the western part of the Central-East Iranian Microcontinent. © 2019 Edizioni Nuova Cultura. All rights reserved.
Publication Date: 2018
Journal of Asian Earth Sciences (18785786)166pp. 35-47
This paper presents petrographic and U-Pb LA-ICP-MS isotopic data of a single peraluminous intrusion (alkali-feldspar granite of Airekan) with partial gneissic foliation on the north western margin of the Yazd Block in the west of the Central-East Iranian Microcontinent (CEIM) to discuss the evolution of this terrain. This intrusion typically suggests a continental collision orogenesis along the northern frontier of Gondwana in the CEIM. The U-Pb dating of zircons indicates that Airekan granite has a distinctive inherited magmatic component at ∼518.2 ± 4.9 Ma but zircons with 892, 679, 614 and 554 Ma ages. These zircons were likely to be ultimately sourced from neighboring Neoproterozoic – Cambrian leucogranite terrains, similar to the other localities in the northern margin of Gondwana, along the Alpine-Himalayan belt from Europe, Turkey, NE Iran, CEIM, Pakistan, India to southern Tibet. The zircons and overgrowths around the inherited components with igneous morphology indicate a plutonism at Lower Ordovician (∼483 ± 2.9 Ma). Petrographic features and morphology of zircon crystals indicate that partial resetting of the U-Pb system in zircons have occurred at ∼382.6 ± 3.2 Ma in Devonian, during the Paleo-Tethys evolutions in Khur region (Anarak-Jandaq terrane) in the southern active margin of Laurasia. © 2018 Elsevier Ltd
Publication Date: 2018
Journal of Economic Geology (20087306)10(2)
Publication Date: 2017
Petrology (15562085)25(1)pp. 114-137
The Naein ophiolite is the most complete ophiolitic exposure in Cental Iran and considered as a remnant of the Mesozoic Central East Iranian microcontinent (CEIM) confining oceanic crust. In the northeastern part of this ophiolite (Darreh Deh area) within the mantle peridotites, a few hundred meters below the top of the Moho transition zone (MTZ), the hornblendites are present as dykes (former cracks and joints) from a few millimeters to nearly 50 cm wide. They have sharp boundaries with the surrounding mantle harzburgites and dunites. These hornblendites are pale green and coarse-grained in hand specimen and composed of magnesio-hornblende (Mg# = 0.93), chlorite (penninite and clinochlore, Mg# = 0.95), Cr-spinel (chromite, Cr# = 0.67 and Mg# = 0.55), tremolite, calcite and dolomite. Tremolites were formed by retrograde metamorphism of hornblendes. Calcite and dolomite occur as late-stage veins. Very high amount of primary hydrous phases (~94 vol % hornblende and chlorite), as well as peculiar mineralogical and chemical characteristics of the Naein ophiolite mantle hornblendites, do not match a magmatic origin. They are possibly products of the reaction between mantle peridotites and seawater-originated supercritical fluids, rich in silicate components. The presence of primary hydrous phases (hornblende and chlorite) may reveal high activity of H2O in the involved solution. The chemical composition of chromite in the hornblendites is near to the average chromite composition from the surrounding harzburgite and dunite. This suggests that the main source of Cr should be chromites of nearby peridotites, which were totally or partly dissolved by hydrothermal fluids. The positive anomaly of Eu in the chondrite-normalized REE patterns of hornblendes, high modal abundance of Ca-rich hornblende, as well as presence of calcite and dolomite, point to seawater ingression through the gabbros in to the uppermost mantle peridotites. The higher value of MgO than CaO, presence of high-Cr chromite and Cr-enrichment of hornblendes and chlorites indicate a higher contribution of peridotites rather than gabbros to the chemical characteristics of the involved fluids. This study shows that circulation of possibly seawater-derived high temperature hydrous fluids in the upper mantle can leach and provide necessary elements to form hornblendite in joints and cracks of the uppermost mantle. © 2017, Pleiades Publishing, Ltd.
Publication Date: 2016
Geotectonics (15561976)50(3)pp. 295-312
Late Cretaceous Bayazeh dyke swarm is situated in the western part of the Central-East Iranian Microcontinent (CEIM). These dykes with a dominant northeast-southwest trend occur in the Eastern margin of the Yazd block. They cross cut the Lower Cretaceous sedimentary rocks. The length of the Bayazeh dykes occasionally reaches up to the 2 km. Rock forming minerals of these dykes are plagioclase (andesine and oligoclase), amphibole (magnesio-hastingsitic hornblende, magnesio-hornblende and tschermakitic hornblende), quartz, K-feldspar (orthoclase), zircon and apatite. Secondary minerals are chlorite (pycnochlorite), albite, magnetite and calcite. The main textures are porphyritic, glomeroporphyritic and poikilitic. The felsic character of the Bayazeh dacitic dykes is shown by their high SiO2 (62.70 to 64.60 wt %) and low [Fe2O3* + MgO + MnO + TiO2] (average 4.64 wt %) contents. These dykes represent the peraluminous to metaluminous nature and their Na2O and K2O values are 5.20–7.14 and 1.51–2.59 wt %, respectively, which reveal their sodic chemistry. The trace element characteristics are the LREE enrichment relative to HREE, [La/Yb]CN = 13.27–22.99, and slightly negative or positive Eu anomaly. These geochemical characteristics associated with low Nb/La (0.16–0.25), Yb/Nd (0.04–0.05) and high Zr/Sm (37.60–58.25) ratios indicate that the melting of a metamorphosed subducted oceanic crust is occurred where the residual mineral assemblage is dominated by garnet amphibolite. The chemical compositions of the Bayazeh dykes resemble those of slab-derived tonalite-trondhjemite-granodiorite (TTG) series. They were formed by subduction of Mesozoic Neo-Tethys -related Nain and Ashin oceanic crusts. © 2016, Pleiades Publishing, Inc.
Publication Date: 2016
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen (00777749)280(1)pp. 59-77
The Posht-e-Badam ophiolite is situated in the Central-East Iranian Microcontinent CEIM and central domain of the Posht-e-Badam Block. This ophiolite of Paleozoic age is a remnant of the Paleo-Tethys ocean. The rock suite comprises metamorphosed peridotites, metagabbro, ampbibolite and listwaenite. Peridotites form the most important rock types of the Posht-e-Badam ophiolite and metalherzolites are the least altered metaperidotite. They are closely associated with amphibolites and cover Paleozoic metasedimentary rocks schist and marble. Rock-forming minerals of metalherzolites are olivine chrysolite; Mg# = 0.80, tremolite average MgO and CaO content 23.31 and 12.88 wt%, respectively, chlorite penninite; Mg#~0.92, serpentine, chromian magnetite, magnetite and calcite. The main textures of these metamorphosed lherzolites are porphyroblastic, granoblastic, nematoblastic, poikiloblastic, jack-straw and mesh texture. Metamorphic mineral assemblages in the metaperidotites, mineral chemistry of amphibolites, together with regional geologic constraints, led to the conclusion that the Posht-e-Badam partially serpentinized peridotites M1 were metamorphosed under lower amphibolite-facies conditions M2, which was followed by a retrograde stage of metamorphism under greenschist-facies conditions M3. The maximum temperature of regional metamorphism M2 was not sufficient to replace calcic amphibole tremolite by calcic pyroxene. The presence of magnetite inclusions in the olivine neoblasts reveals that the studied metalherzolites were partly altered M1 before being progressively metamorphosed under lower amphibolite-facies conditions M2. Latestage retrograde metamorphism M3 led to partial serpentinization of metamorphic olivine and partial replacement of tremolite by chlorite. These three metamorphic episodes can be attributed to, respectively, the Early, Middle and Late Cimmerian orogenies of Central Iran. © 2016 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.
Publication Date: 2016
Italian Journal of Geosciences (20381719)135(1)pp. 109-119
The Paleozoic Bayazeh ophiolite is situated in the western part of the Central-East Iranian microcontinent (CEIM). This ophiolite consists of serpentinised peridotites, metagabbros, metamorphosed ultrabasic dykes, metapicrites, serpentinites and metamorphosed listwaenites which are covered by Late Paleozoic schists and marbles. The unique petrological characteristic of this ophiolite is due to regional metamorphism, which produced listwaenites by carbonation of serpentinites. The mineral association of the Bayazeh metamorphosed listwaenites is represented by amphiboles (tremolite and actinolite), carbonates (dolomite and calcite), quartz, serpentine (antigorite), chromian spinel, ferritchromite and chlorite (pycnochlorite). The main textures are nematoblastic and granoblastic. Rockforming minerals and the association of the outcrops with serpentinites indicate that the amphibole-bearing listwaenites were generated by regional metamorphism of serpentinites. The mineral assemblage of these rocks and the chemical composition of chromian spinels and amphiboles reveal that these minerals were metamorphosed under upper greenschist to lower amphibolite facies P-T conditions. Relicts of well-preserved chromian spinel cores in the studied rocks were used as a petrogenetic indicator. The high Cr and Mg values, together with the low Fe3+ and Ti contents of the serpentinite chromian spinels confirm their magmatic nature. The chemical characteristics of the investigated chromian spinels suggest that the protolith should have been a harzburgite belonging to a suprasubduction zone geotectonic setting. © Società Geologica Italiana, Roma 2016.
Publication Date: 2014
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen (00777749)271(1)pp. 1-19
The western part of the Central-East Iranian microcontinent (CEIM) hosts the Anarak, Jandaq, Bayazeh and Posht-e-Badam ophiolites of Paleozoic age. The Bayazeh ophiolite is situated in the Eastern margin of the Yazd Block and is exposed along the Bayazeh Fault. This ophiolite consists of serpentinized peridotites, metagabbro, metamorphosed ultrabasic dykes, metapicrite, serpentinite and metalistwaenite which are covered by Late Paleozoic schist and marble. Mineral association of the metapicrites in the Bayazeh Ophiolite is olivine (completely altered to serpentine), clinopyroxene (diopside), phlogopite, apatite, prehnite, amphibole (tremolite, actinolite and tremolitic hornblende), chlorite (clinochlore, penninite and diabantite), ilmenite and magnetite. Matrix glass is significantly devitrified and chlorite is present throughout the matrix. Clinopyroxene and phlogopite occur as relicts of the primary igneous mineralogy. Petrography and trace element composition of clinopyroxenes indicate near-simultaneous crystallization of clinopyroxene and plagioclase from the magma. The ultramafic character of the Bayazeh metapicrites is shown by their high MgO (25.8 to 28.0 wt%) and low SiO2 (37.5 to 39.4 wt%) contents. They are characterized by high Mg# (80.61 to 81.60), Ni (975 to 1020 ppm) and Cr (1300 to 1431 ppm) contents, suggesting that this melt closely approached the composition of a primitive mantle-derived melt. High-field strength element (HFSE) enrichment, high Mg# and Ni values, enrichment in light rare earth elements (LREE) (e.g. [La/Yb] CN=11.65-12.31), associated with a large variation of large ion lithophile element (LILE) concentrations indicate metasomatic enrichment of an asthenospheric mantle source with a subduction-related components prior to melting. Geochemical characteristics show that the metapicrites were generated by partial melting of a metasomatized asthenospheric amphibole-bearing spinel lherzolite. The presence of phlogopite as a primary hydrous mineral together with high LILE/HFSE ratios (e.g. Sr/Sm = 63.01-104.86) and a negative Ti anomaly reveal the role of previously subducted oceanic crust. Subduction of the Paleo-Tethys from the Early to the Late Paleozoic is the cause of volatile enrichment and mantle metasomatism. Involvement of hydrous fluids related to Paleo-Tethys subduction, enabled the peridotite source to melt despite the absence of abnormal thermal condition.©2014 E. Schweizerbartsche Verlagsbuchhandlung, Stuttgart, Germany.
Publication Date: 2014
Petrology (15562085)22(6)pp. 617-632
The Eocene dyke swarm with east-west general trend intrudes the Cretaceous sedimentary rocks in ∼25 km north of the Khur city (Central Iran). Some of the studied dykes can be followed for over 7 km, but the majority of exposures in the area are less than 5 km long. The dykes commonly exhibit a chilled contact with the wall rocks. These dykes are trachybasalt and basalt in composition. The trachybasalt dykes are much more abundant. The basaltic dykes cross cut the trachybasalt dykes in some locations, indicating that trachybasalt dykes are older than the basaltic ones. Primary igneous minerals of the basaltic dykes are olivine (chrysolite), clinopyroxene (diopside, augite), plagioclase (labradorite), sanidine, magnetite, orthopyroxene (enstatite), spinel and phlogopite, and secondary minerals are zeolite (natrolite and mesolite), chlorite (diabantite), calcite and serpentine. The trachybasalt dykes are composed of clinopyroxene (diopside), plagioclase (labradorite), sanidine, mica (biotite and phlogopite), amphibole (magnesio-hastingsite) and magnetite as primary minerals, and chlorite and calcite as secondary ones. Whole rocks geochemical data of the studied dykes indicate their basic and calc-alkaline nature and suggest that these two set of dykes were derived from the same parental magma. The chondrite-normalized REE patterns and the primitive mantle-normalized multi-elemental diagram of the Khur dykes show enrichment of light rare earth elements (LREE) relative to heavy rare earth elements (HREE), and negative anomalies of high field strength elements (HFSE) (e.g. Ti, Nb and Ta). These rocks show enrichment of the large ion lithophile elements (LILE) (e.g. Cs, Ba, Th and U) and depletion of the HREE and Y relative to MREE, Zr and Hf. In the chondrite-normalized REE diagram, the basalts show elevated REE abundances relative to the trachybasalt samples. Geochemical analyses of the studied samples suggest a spinel lherzolite from the mantle as the source rock and confirm the role of subduction in their generation. The chemical characteristics of the Khur dykes resemble those of continental arc rocks, and they were possibly formed by subduction of the Central-East Iranian microcontinent (CEIM) confining oceanic crust and decompression melting of a lithospheric subcontinental mantle spinel lherzolite enriched by subduction. © 2014, Pleiades Publishing, Ltd.
Publication Date: 2014
Island Arc (10384871)23(2)pp. 125-141
The Oligocene alkaline basalts of Toveireh area (southwest of Jandaq, Central Iran) exhibit northwest-southeast to west-east exposure in northwest of the central-east Iranian microcontinent (CEIM). These basalts are composed of olivine (Fo70-90), clinopyroxene (diopside, augite), plagioclase (labradorite), spinel, and titanomagnetite as primary minerals and serpentine and zeolite as secondary ones. They are enriched in alkalis, TiO2 and light rare earth elements (La/Yb=9.64-12.68) and are characterized by enrichment in large ion lithophile elements (Cs, Rb, Ba) and high field strength elements (Nb, Ta). The geochemical features of the rocks suggest that the Toveireh alkaline basalts are derived from a moderate degree partial melting (10-20%) of a previously enriched garnet lherzolite of asthenospheric mantle. Subduction of the CEIM confining oceanic crust from the Triassic to Eocene is the reason of mantle enrichment. The studied basalts contain mafic-ultramafic and aluminous granulitic xenoliths. The rock-forming minerals of the mafic-ultramafic xenoliths are Cr-free/poor spinel, olivine, Al-rich pyroxene, and feldspar. The aluminous granulitic xenoliths consist of an assemblage of hercynitic spinel+plagioclase (andesine-labradorite)±corundum±sillimanite. They show interstitial texture, which is consistent with granulite facies. They are enriched in high field strength elements (Ti, Nb and Ta), light rare earth elements (La/Yb=37-193) and exhibit a positive Eu anomaly. These granulitic xenoliths may be Al-saturated but Si-undersaturated feldspar bearing restitic materials of the lower crust. The Oligocene Toveireh basaltic magma passed and entrained these xenoliths from the lower crust to the surface. © 2014 Wiley Publishing Asia Pty Ltd.
