مرضیه غدیرپور،
Ghadirpour M.،
Ghadirpour M.،
Ghadirpour M.،
قدرت ترابی،
قدرت ترابی،
قدرت ترابی،
Shirdashtzadeh N.،
Shirdashtzadeh N. و
Shirdashtzadeh N. زمین شناسی اقتصادی (20087306)15(4)pp. 55-79
Ghadirpour, M.,
Torabi, G.,
Shirdashtzadeh, N.,
Meisel, T.C.,
Morishita, T. Journal of African Earth Sciences (1464343X)228
The Eocene Kalut-e-Ghandehari (KG) pluton, located in the Central Eastern Iranian Microcontinent (CEIM), intrudes the Ashin Mesozoic ophiolite and Middle Eocene volcanic rocks. Petrographic and geochemical analyses reveal a calc-alkaline, metaluminous intermediate to mafic composition ranging from gabbro to monzonite. The rocks exhibit characteristic REE and HFSE patterns indicative of subduction-related magmatism. The KG pluton is composed of plagioclase (An = 34–60 %), Alkali-feldspar (Or = 70.8–96.1 %), diopside (Mg# = 0.71–0.90), phlogopite (Fe# = 0.3), and opaque minerals. Geochemical evidence (e.g., enrichment of LREE, LILE (e.g., Cs, Ba, Rb, Th, U), Zr, and Hf; depletion of HREE, Ti, Nb, and Ta, and Y) suggests partial melting of a lithospheric spinel lherzolite that had been previously enriched by an earlier subduction event. The geochemical similarities of parental magmas of the KG pluton and the Soheyl-e-Pakuh pluton (located in the neighboring ophiolite of Nain) indicate that both derive from a subduction-induced partial melting of a mantle peridotite. However, their magma sources temporality and spatially are in accord with eastern and western Neo-Tethys subduction-related magmatisms, respectively. Thus, the cross-cutting relationships between the pluton and the Ashin ophiolite, combined with geochronological data, support a pre-Upper Eocene closure of the eastern Neotethys oceanic crust. This finding provides valuable insights into the Cenozoic tectonic evolution of the Central Iran. © 2025 Elsevier Ltd
Pirnia, Tahmineh,
Bahramnejad, Elham,
Sharifi, Mortaza,
Bahramnejad E.,
Bagheri S.,
Sharifi, M.,
Nurlu N.,
Shi Y.,
Torabi, G.,
Noghreyan, M. GEOCHEMISTRY (00092819)84(1)
The Eastern Iranian Ranges are considered to be either a suture zone produced by closure of a Neo-Tethyan backarc basin between the Lut and Afghan blocks or an oroclinal buckling of multiple terranes accreted to the active margin of the Neo-Tethyan Ocean. Both models are based on the presence of Cretaceous ophiolite complexes and sequences of Eocene turbiditic sedimentary rocks. The Dumak ophiolitic melange, a significant ophiolitic assemblage that crops out in the western portion of the orogen adjacent to Lut, contains all the essential elements of a typical ophiolite in a matrix of serpentinite and clay-rich sediments. Ultramafic-mafic cumulates in the melange are characterized by medium, non-rhythmic bedding in limited outcrops where they are in tectonic contact with other ophiolitic units. The cumulates consist of plagioclase-bearing dunite, troctolite, Cpx-troctolite and gabbro composed chiefly of olivine, plagioclase, and clinopyroxene accompanied by rare orthopyroxene. This assemblage is very similar to the differential crystallization sequence of tholeiitic magma at modern midocean ridges. The clinopyroxene in these rocks is diopside (En = 47-49) and the plagioclase is bytownite (An = 71-77). Whole-rock geochemistry of samples from the crustal sequence of Dumak melange are characterized by low TiO2 (0.03-0.17 wt%). Investigation of this crystalline sequence and geochemical properties of the rocks suggests that they can be considered as the low-Ti ophiolite originated from mid-ocean ridges. Additionally, the positive Eu anomalies as well as comparison of frequency of LREE and HREE in the mafic and ultramafic samples indicate the cumulates formed by fractional crystallization and differentiation of mantle-derived magmas. According to petrographic, geochemical, and structural evidence, it is possible that the Dumak ophiolite, after being formed or displaced between Lut and Afghan blocks, was firstly accreted to the south of the Lut block and then re-mixed into Eocene sediments emplaced in the current position.
Neues Jahrbuch fur Mineralogie, Abhandlungen (00777757)199(1)pp. 37-54
Calc-alkaline to shoshonitic Eocene and alkaline Oligocene volcanic rocks are exposed in Godar-e-Siah and Toveiereh areas, respectively, northwest of the Central-East Iranian Microcontinent (CEIM). Granulitic xenoliths have been found in these volcanic rocks. The Godar-e-Siah xenoliths comprise the Ca-poor plagioclase (An33) + phlogopite + corundum + sillimanite + spinel ± garnet. This mineral assemblage corresponds to conditions characteristic of peak of granulite facies metamorphism. The Toveireh xenoliths consist of spinel and plagioclase as major minerals and corundum, rutile, ilmenite and magnetite as accessory ones. The presence of Al-rich minerals and the absence of quartz suggest the Al-saturated but Si-undersaturated nature for the xenoliths. Mineralogical characteristics, thermobarometry estimates and use of experimental petrogenetic grids indicate that the estimated P-T conditions for Toveireh (8 –10 kbar, 800 – 900 °C) and Godar-e-Siah (7.8 kbar, 780 °C) xenoliths are consistent with the granulite facies rocks near anatectic condition. The Toveireh xenoliths are Al-rich granulites (Al2O3 = 33 – 34 wt%) and have LREE-enriched patterns with large positive Eu anomalies (Eu/Eu* = 3 – 5). These patterns indicate that the plagioclase rich restites of the lower continental crust devel-oped as a result of the removal of Neoproterozoic-Cambrian S-type granitic magma. The Aeirakan S-type granites and the xenolith bearing rocks are located at the northwest of the CEIM along the Great Kavir Fault. The parental magma of the Aeirakan S-type granite which is located at northeast of the xenolith bearing sites (Toveireh and Godar-e-Siah) is formed by anatexis and dehydration melting of such Al-saturated Si-undersaturated crustal granulites during Pan-African orogeny. It is probable that some parts of these dehydrated materials are brought to the surface as granulitic xenoliths by Eocene and Oligocene volcanism in Godar-e-Siah and Toveireh areas, respectively. © 2024 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany.
Salim h., ,
Torabi, G.,
Shirdashtzadeh, N.,
Sahlabadi m., ,
Morishita, T. 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.
Petrology (15562085)30(6)pp. 671-689
Abstract: Eocene volcanic rocks with basaltic-trachyandesite and trachybasalt composition which cross-cut the Cretaceous sedimentary rocks, are exposed in the northwestern part of the Central-East Iranian Microcontient (CEIM) (SE of Khur, Isfahan Province, Iran). The rock-forming minerals of these volcanic rocks are olivine (chrysolite and hyalosiderite, Mg# = 0.69–0.71), clinopyroxene (augite with Mg# = 0.74–0.84), orthopyroxene (enstatite with Mg# = 0.61–0.62) and plagioclase (andesine and labradorite with An48.3-65.1). Phenocrysts set in a fine-grained matrix of the same minerals plus sanidine (Or59.1Ab36.6An4.3) with minor amounts of opaque minerals (magnetite and ilmenite). Secondary minerals are chlorite and calcite. The main textures of these volcanic rocks are porphyritic, microlitic porphyritic, poikilitic, and glomeroporphyritic. The Eocene volcanic rocks of the Khur area are characterized by SiO2 content of 51.8 to 54.9 wt %, Al2O3 amounts of 14.35 to 16.47 wt %, and TiO2 values of 0.88 to 0.92 wt %. They exhibit strong enrichment in light rare earth elements (LREE) relative to heavy REE (HREE) (La/Lu ratio up to 102.35), enrichment in large ion lithophile elements (LILEs), depletion in high field strength elements (HFSE), and present negative anomaly in Eu (Eu/Eu* = 0.72–0.87). Chemical characteristics and homogeneity of these volcanic rocks reveal their calc-alkaline nature and suggest that they were derived from a same parental magma and underwent a similar melt extraction. Major and trace elements geochemical features of the analyzed samples indicate that the parental magma was possibly derived from relatively low degrees of partial melting of a mantle wedge spinel lherzolite which was previously enriched by fluids/melts released from the Neo-Tethyan subducted slab. © 2022, Pleiades Publishing, Ltd.
Torabi, G.,
Salim h., ,
Nosouhian, N.,
Salim h., ,
Torabi, G.,
Nosouhian, N. Journal of Economic Geology (20087306)14(2)pp. 115-141
Introduction In the northeastern part of the Isfahan province and 65 km northeast of the Anarak city (Kal-e-Kafi area), an I-type granitoid pluton cross cut the Paleozoic metamorphic rocks and Eocene volcanic rocks. In the contact of this granitoid body with sourrounding rock units, skarn and hornfels have been formed (Ahmadian, 2012; Ranjbar, 2010). The Kale-Kafi Eocene intrusive body presents a wide range of mineralogical and petrological compositions, from gabbro to alkali-feldspar granite. Presence of mafic to acidic rocks in this mostly-granitoid body indicates that fractional crystallisation has played an important role during magma evolution. The field and petrographical studies indicate the presence of anorthosite veins within the gabbro section. The mafic and basic parts of this pluton have not been studied yet. The mineralogy and chemistry of rock-forming minerals in the anorthosites and gabbros are the subject of this research study. © 2022 The author(s). This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, as long as the original authors and source are cited. No permission is required from the authors or the publishers.
Samadi, R.,
Torabi, G.,
Dantas, E.L.,
Morishita, T.,
Kawabata, H. 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.
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)
Nosouhian, N.,
Torabi, G.,
Morishita, T.,
Arai, S. Periodico di Mineralogia (22391002)91(2)pp. 113-142
The Paleozoic Jandaq ophiolite is situated in the western part of the Central-East Iranian microcontinent and is a remnant of the Paleo-Tethys oceanic crust. This ophiolite consists of mantle peridotites and serpentinized mantle peridotites, metagabbro, basic and ultrabasic metamorphosed dykes and lavas, metapyroxenite, amphibolite, rodingite and listwaenite which are covered by the Late Paleozoic schist and marble. The open spaces of joints and cracks of gabbroic dykes and stocks are filled by hydrothermal minerals such as calcite, prehnite, garnet (grossular-andradite), epidote, clinopyroxene (diopside), chlorite, albite and sericite. The calcite and garnet are the latest minerals in this association. The most predominant mineral is calcite with coarse-grained morphology. The main textures are granoblastic and poikiloblastic. The very low abundances of Al, Ti, Na, Cr and rare earth elements (REEs) in clinopyroxenes support their metamorphic origin. The high modal abundance of calcite, the presence of clinopyroxene, garnet, prehnite and epidote as the Ca-bearing minerals, as well as the positive anomaly of Eu in the chondrite-normalized REE patterns of minerals possibly point to the seawater- derived penetrating fluids ingression through the oceanic crust-covering sediments and the uppermost portion of oceanic crust into the gabbros. The involved fluids in the Jandaq area have leached the calcite-bearing sediments (e.g., limestone) and calcic plagioclase-rich lithologies (e.g., basic pillow lavas and sheeted dykes) before reaching to the gabbros, caused to the CO2, calcium and Eu enrichment of fluids. Accordingly, the hydrothermal veins in the Jandaq ophiolite are possibly formed by high temperature circulation of seawater-originated fluids throughout the uppermost oceanic crust. © 2022 Edizioni Nuova Cultura. All rights reserved.
Shirdashtzadeh, N.,
Furnes, H.,
Miller, N.R.,
Dantas, E.L.,
Torabi, G.,
Meisel, T.C. 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.
Zakipour, Z.,
Torabi, G.,
Kazuo, N.,
Morishita, T. 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.
Samadi, R.,
Torabi, G.,
Kawabata, H.,
Miller, N.R. 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
Jamshidzaei, A.,
Torabi, G.,
Morishita, T.,
Tamura, A. 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
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.
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.
Pirnia, T.,
Saccani, E.,
Torabi, G.,
Chiari, M.,
Goričan, Š.,
Barbero, E. Geoscience Frontiers (16749871)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
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
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.
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.
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.
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.
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
Journal of Economic Geology (20087306)10(2)
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.
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.
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.
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.
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.
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.
Shirdashtzadeh, N.,
Torabi, G.,
Meisel, T.C.,
Arai, S.,
Bokhari, S.N.H.,
Samadi, R.,
Gazel, E. Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen (00777749)273(1)pp. 89-120
The Nain Ophiolite is one of the most complete harzburgitic-ophiolite suites exposed along the Nain-Baft Fault, around the Central-East Iranian Microcontinent (CEIM). It is a remnant of the Nain Ocean (Early Jurassic to upper Early Cretaceous-Paleocene). During the Cretaceous (~Albian to Cenomanian), ascending melts and serpentinization overprinted the Jurassic melt-rock reactions and metamorphism of peridotites in most of the ophiolite. However, metamorphosed peridotites of the Darreh Deh massif in the eastern part of Nain Ophiolite remained intact, with the lowest degree of alteration and serpentinization and slightly higher degrees of partial melting and melt - rock reactions. Clinopyroxene and Cr-spinel compositions together with bulk rock geochemistry of Darreh Deh peridotites indicate a mid-ocean ridge affinity for lherzolite but later compressional tectonics led to an intra-oceanic subduction and supra-subduction zone (SSZ) in which harzburgite and dunite formed due to ascending melt reacting with the mantle lherzolite. Further indications are the presence of replacive olivine, incongruent melting of orthopyroxene and increase of Cr# of Cr-spinel in harzburgite. The extensional to compressional evolution in the Jurassic ended with accretionary and/ or collisional processes induced by convergence between the Sanandaj - Sirjan zone and the CEIM. These caused a regional metamorphism that affected the Darreh Deh massif by forming antigorite, talc, metamorphic olivine, tremolite and chlorite metamorphic assemblages in mantle peridotites at amphibolite facies (~630-700 °C / 7-15 kbar) conditions, similar to the metamorphosed diabasic dikes, basalts and pillow lavas of this ophiolite. © 2014 E.
Pirnia, T.,
Arai, S.,
Tamura, A.,
Ishimaru, S.,
Torabi, G. Lithos (00244937)196pp. 198-212
Melt impregnated plagioclase lherzolites from the Nain mélange, central Iran, contain pyroxenes enriched and chemically zoned with Sr. Pyroxenes from the lherzolite and the clinopyroxenite seams, which have been precipitated from the impregnating melt, show similar trace element geochemical characteristics, including a similar Sr anomaly. The associated plagioclase, precipitated from the impregnating melt, has been selectively altered to isotropic saussurite. Strontium concentration increases in the pyroxenes from the core to the rim and toward crosscutting saussurite trails in orthopyroxene porphyroclast cores. The highest Sr content (up to 10.8. ppm in clinopyroxene and 3.8. ppm in orthopyroxene) is found in the finer pyroxenes surrounded by thicker saussurite layers.The Sr enrichment within pyroxenes is neither caused by metasomatism nor modified by fluids involved in hydrothermal alteration because pyroxenes are extremely depleted in fluid-mobile and light rare earth elements. Also, Sr enrichment cannot be related to the melt impregnation, since the Sr supply from the impregnating melt was consumed by plagioclase crystallization. The Sr enrichment in the pyroxene postdates the melt impregnation and is due to the relatively high-temperature (375. °C-850. °C) of saussuritization, that is, the breakdown of plagioclase. Plagioclase decomposition has released appreciable amounts of Sr to enrich adjacent pyroxenes. Saussurite shows significantly lower Sr contents than the plagioclase. Sr enrichment in peridotite pyroxenes, which is ascribed primarily to the metasomatism of slab-derived fluids, should be treated carefully, particularly when altered plagioclase is present. © 2014 Elsevier B.V.
Pirnia, Tahmineh,
Pirnia, T.,
Pirnia, T.,
Pirnia, T.,
Arai, S.,
Arai, S.,
Arai, S.,
Torabi, G.,
Torabi, G.,
Torabi, G. JOURNAL OF GEOLOGY (00221376)121(6)pp. 645-661
Detrital chromian spinels from adjacent sediment (recent sands and a Tertiary sandstone) were used to obtain a general view of the lithological and petrological characteristics of the Nain ophiolitic melange, Iran. They display a wide chemical range in terms of Cr# (=Cr/(Cr + Al) atomic ratio), from 0.10 to 0.92. Except for some grains (11% of the total), the spinels show low TiO2 contents (<0.25 wt%), typical for the spinels of mantle peridotites. Relatively high-Ti spinels (TiO2 content 10.25 wt%, up to 1.26 wt%) are relatively low in Mg# (=Mg/(Mg + Fe2+) atomic ratio), from 0.15 to 0.65, and were possibly derived from mantle peridotite that reacted with impregnating melt (e. g., dunite or plagioclase-bearing peridotites). The high-Cr# (0.55-0.92) spinels, which are dominant in the Tertiary sandstone, are chemically homogenous and clearly different from high-Cr# altered spinels (ferritchromite and Cr-magnetite), which are formed by low-T alteration, and are low in Mg# and high in Fe3+. The higher abundance of the high-Cr# spinels in the Tertiary sandstone than in the recent sands indicates higher abundance of refractory lithologies in the Paleo-Nain ophiolite than the present one. The refractory lithologies for the source of the high-Cr# spinels have not been reported from the Nain melange, which implies that the refractory dunite and harzburgite were effectively sheared to provide the melange matrix and then eroded during later stages of emplacement. This indicates uplift and intermittent protrusion of a vertical slice of heterogeneous upper mantle in the Nain since the late Cretaceous. This is in good agreement with the geological situation of the Nain melange located on a fossil transcurrent fault (Nain-Baft fault zone), which was involved in the opening of the Nain-Baft basin along an active margin of the central-east Iranian microplate (the Sanandaj-Sirjan block). The initial presence of the high-Cr# spinels implies an origin from a spreading center above a subduction zone (e. g., back-arc basin) for the Nain melange.
Petrology (15562085)21(4)pp. 393-407
Late Paleozoic blueschists present good exposures in the Pateyar metamorphic complex (south of Chupanan, Isfahan Province). They are formed by metamorphism of primitive basaltic lavas. Petrography and microprobe analyses show that the studied rocks consist of glaucophane, actinolite, actinolitic hornblende, plagioclase (albite), sphene, magnetite, quartz and apatite. Secondary minerals are epidote, chlorite, pyrite, hematite and calcite. Mineralogical assemblages are consistent with blueschist facies metamorphism, which is followed by a retrograde metamorphism in greenschist facies. Estimation of the metamorphic conditions suggests 300-400°C and 7-11 kbar. Chemical signatures of the studied metamorphic rocks conclude that they retain main geochemical characteristics of the protoliths, which allow the petrochemical interpretations. Geochemical analyses of these blueschists show that they were originally tholeiitic basalts. Evident negative anomalies of Nb, Ta and Ti relative to Th, La and Ce, in the primitive mantle normalized spider-gram, reveal subduction role in their petrogenesis. The studied metavolcanics exhibit an intermediate chemistry between the N-MORB (normal mid-ocean ridge basalt) and IATB (island arc tholeitic basalt). Enrichment in LREE (light rare earth elements) and LILE (large ion lithophile elements) and relative depletion in HFSE (high field strength elements) suggest a back-arc basin paleotectonic setting for the Chupanan samples. The primitive magma of the analyzed samples possibly have been produced by 8-13% melting of a spinel lherzolite. The field and petrological data propose that the studied Paleozoic metavolcanics were formed in a back-arc basin above the northward subduction of Paleo-Tethys oceanic lithosphere in Central Iran. The chemical criteria of the LILE/HFSE ratio suggests that the subduction zone was young and immature during the volcanism. © 2013 Pleiades Publishing, Ltd.
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen (00777749)267(2)pp. 171-192
There are two types of ophiolites in the western part of Central Iran: Mesozoic ophiolites (Naein and Ashin), and Paleozoic ophiolites (e.g., Anarak and Jandaq). Field studies show that the Mesozoic ophiolites contain considerable amounts of chromitite, but the Anarak and Jandaq ophiolites do not. Study of Mesozoic ophiolites reveals that they contain two different types of chromitites. The Naein chromitites have high Cr contents, whereas the Ashin chromitites are high-AI in composition. The field, petrographic and chemical studies suggest that melt/mantle interaction caused the formation of chromitites in the Naein and Ashin ophiolites. The reason of chromitite absence in the Anarak ophiolite is an insufficient degree of partial melting of mantle rocks, as well as a low content of Cr203 in pyroxenes and the mantle source. Despite suitable Cr203 contents in clinopyroxenes in the Jandaq ophiolite, the intact fertile lherzolitic system of the mantle and its low Cr203 amount explain the chromitite absence. The high-AI composition of chromitites in the Ashin ophiolite can be ascribed to the high-AI (MORB-like) composition of percolating melts, lower degree of partial melting, lower Cr# [Cr/(Cr+AI)] of orthopyroxenes and lower CrP3 content of mantle peridotites in the Ashin ophiolite, compared to those in the Naein area. The high-Cr characteristic of chromitites in the Naein ophiolite are attributed to the boninitic composition of the percolating melt, high Cr# of orthopyroxenes and high Cr203 value of mantle peridotites. It is concluded that the chromitites of the Central Iran Mesozoic ophiolites were formed in a supra-subduction zone setting. © 2012 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.
Island Arc (10384871)21(3)pp. 215-229
Late Permian trondhjemites in the Anarak area occur as stocks and dykes, which cross cut the Anarak ophiolite and its overlying metasedimentary rocks, and are exposed along the northern Anarak east-west main faults. These leucocratic intrusive bodies have enclaves of all ophiolitic units and metamorphic rocks. They are composed of amphibole, plagioclase (oligoclase), quartz, zircon and muscovite. Secondary minerals are chlorite (pycnochlorite), epidote, albite, magnetite and calcite. Whole-rock major- and trace-element analyses reveal that they are characterized by high SiO 2 (67.8-71.0wt%), Al 2 O 3 (14.9-17.1wt%) and Na 2 O (5.3-8.6wt%), low K 2 O (0.1-1.5wt%; average: 0.8wt%), low Rb/Sr ratio (0.01-0.40; average: 0.09), low Y (3-6ppm), negative Ti, Nb and Ta anomalies, slightly negative or positive Eu anomaly, LREE enrichment and fractionated HREE. These rocks present 2 to 40 times enrichment in inclined chondrite-normalized REE patterns. Geochemical characteristics of the Anarak trondhjemites all reflect melting of a mafic protolith at more than 10kbar. The field evidence and whole-rock chemistry reveal that these rocks have been crystallized from magmas derived from melting of subducted Anarak oceanic crust. This study reveals that melting of garnet amphibolite was an important element of continent formation in the study area. © 2012 Wiley Publishing Asia Pty Ltd.
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen (00777749)265(1)pp. 49-78
The Surk ophiolitic melange, as a narrow belt, is located between the southwest of the Central Iran and Urumieh-Dokhtar magmatic arc, along the Naein-Dehshir-Baft fault. This ophiolitic melange consists of mantle peridotites (harzburgite, lherzolite and dunite in decreasing order), gabbro, diabasic dykes, dacite, serpentinite, listvenite, rodingite, chert and Upper Cretaceous limestones. Petrography and mineral chemistry of mantle peridotites reveal formation of excess olivines by incongruent melting of orthopyroxenes, occurrence of K-free pargasitic amphibole in lherzolites and increasing value of Cr# of spinels from lherzolite to harzburgite to dunite. Whole rock chemistry of volcanics in this ophiolite suggests the effect of subducted oceanic slab on their productive magma, cause to presence of silica-oversaturated volcanic rocks (dacite). All above petrography and mineral chemistry evidences and field relationships (such as transitional succession of lherzoliteharzburgite- dunite, and absence of lherzolite-dunite contact) suggest melt/mantle peridotite reaction. This reactive melt originated from a subducted oceanic slab that decreases the melting temperature of the lithospheric mantle and leads to widespread ascending melt/rock reaction. The Surk ophiolitic mélange is a HOT type ophiolite and has characteristics of supra-subduction zone (back arc basin) ophiolites. © 2012 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.
Petrology (15562085)19(7)pp. 690-704
In western part of the CEIM (Central-East Iranian Microcontinent) (Bayazeh area, Isfahan province, Iran), a series of Paleozoic basaltic rocks, occur. Major minerals of these basalts are olivine, clinopyroxene (diopside, augite), plagioclase (albite), sanidine, amphibole (kaersutite), phlogopite, ilmenite and magnetite. Secondary minerals include epidote, pumpellyite, albite, calcite and chlorite. Olivine and clinopyroxene are as phenocryst, while feldspars are restricted to groundmass. Chemical composition of clinopyroxenes indicates crystallization during ascending of magma. Geochemical analysis of whole rock samples shows that these rocks are characterized by low SiO2 (43.21-48.45 wt %), high TiO2 (1.81-3.00 wt %) and P2O5 (0.18-0.34 wt %). Petrography, chemistry of clinopyroxenes and whole rock analyses reveal an alkaline nature of these basalts. They are enriched in alkalis (Na2O + K2O = 4.1-7.7 wt %), LILE, HFSE and LREE. The Bayazeh alkali-basalts present strong enrichment in LREE relative to HREE (La/Lu ratio = 77.6-119.6) and were dominantly derived from partial melting of a metasomatized asthenospheric garnet-amphibole lherzolite. Field relationships reveal that junction of faults in west of the Bayazeh prepared a suitable path for ascending of magma from deep regions to surface and intra-plate continental magmatism. The Paleo-Tethys subduction from lower to upper Paleozoic is too enough for mantle enrichment in volatiles and basaltic alkaline magmatisrn in upper Paleozoic of Bayazeh area. © 2011 Pleiades Publishing, Ltd.
Island Arc (10384871)20(3)pp. 386-400
Paleozoic lamprophyres exhibit good exposures in the western part of the Central-East Iranian microcontinent. These rocks crop out as volcanoes, dykes, and plugs. The constituent minerals are amphibole, clinopyroxene, plagioclase, K-feldspar, olivine, Cr-spinel, titanite, biotite, and ilmenite. The main textures in volcanic lamprophyres are porphyritic, trachytic, microlithic, and variolitic, whereas in dykes and plugs, intergranular texture is common. These lamprophyres are regionally metamorphosed in some areas. Petrographical and geochemical characteristics of the studied rocks suggest that they are classified as alkaline lamprophyres and camptonites. They are enriched in alkalis (Na2O+K2O), large ion lithophile elements, and light rare earth elements, and the features of trace element concentrations are similar to those of within-plate basalts. This study suggests that the lamprophyres were derived from different degrees of partial melting of metasomatized amphibole-bearing spinel lherzolite. Subduction of Paleo-Tethys oceanic crust from the Early to late Paleozoic resulted in enrichment in fluids in the mantle, and lamprophyric magmatism occurred along the minor and major faults. This limited but typical lamprophyric magmatism in a broad area of Central Iran suggests that, in spite of the long length of the Paleozoic (~250my), it was a relatively calm era from the viewpoint of magmatism in Central Iran. © 2011 Blackwell Publishing Asia Pty Ltd.
Revista Mexicana de Ciencias Geologicas (10268774)28(3)pp. 544-554
Anarak Paleozoic ophiolite is located in western part of the Central - East Iranian Microcontinent. This metaophiolite is covered by Paleozoic schist and marble. Blueschists of the Anarak ophiolite are exposed along the northern Anarak east-west main faults and are considered as remnants of the Paleo-Tethys suture zone in Central Iran. Anarak blueschists are formed by metamorphism of primitive basic lavas. In some cases, they preserve the primary pillow structure. Petrography and microprobe analyses show that they are composed of riebeckite, actinolite, plagioclase (albite), sphene, magnetite, white mica and apatite. Secondary minerals are chlorite (pycnochlorite), epidote, pyrite and calcite. Mineralogical assemblages are consistent with blueschist facies metamorphism, which is followed by a retrograde metamorphism in greenschist facies. Estimation of the metamorphic conditions suggests 300-450 °C and 4-9 kbar. Whole rock geochemical analyses show that these rocks can be classified as alkaline basalts. Chondrite-normalized rare-earth element (REE) patterns of the studied rocks display 10-150 times enrichment, high light REE and relatively low heavy REE contents. These geochemical characteristics are representative of mantle-derived magmas. Primitive mantle normalized spidergram of the Anarak samples exhibit negative anomalies of Ba, U, K and Sr, and positive anomalies of Cs, Rb, Th, Nb, Ta and Zr. Similar geochemical features of all analyzed rocks indicate that they were all derived by more than 12% partial melting of an enriched/carbonated garnet lherzolite and underwent similar degree of partial melting. Geochemically, the studied blueschists resemble intraplate alkali-basalts. The presence of Paleozoic ophiolitic rocks along the main faults of central and northern Iran are indicative of a multisuture closure of the Paleo-Tethys ocean.
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen (00777749)261(2)pp. 129-150
Mantle peridotites of the Jandaq ophiolite are composed of metamorphosed lherzolite and harzburgite, with lherzolitic mineralogical and bulk chemical compositions prevailing over harzburgite. They are closely associated and isofacial with amphibolites and Paleozoic metasedimentary rocks (schist and marble). Rock forming minerals of metalherzolites are clinopyroxene, Cr-spinel, olivine, tremolite, chlorite, serpentine, magnetite and calcite. Metaharzburgites are composed of olivine, orthopyroxene, talc, anthophyllite, magnetite, Cr-spinel ± low amounts of chlorite and tremolite. The olivine and orthopyroxene in these rocks are metamorphic products, not relicts of the primary igneous mineralogy. Early relict phases (mantle phases) include clinopyroxene and Cr-spinel. Petrography, mineral chemistry, as well as major and trace element geochemistry of the metamorphic lherzolites indicate that they are relicts of undepleted mantle material and have experienced less than 3% partial melting. Metamorphic assemblages in metaperidotites, mineral chemical studies, together with additional geological constraints, indicate that the Jandaq mantle peridotites are metamorphosed under upper amphibolite facies conditions (8 to 9 kbars and 714 to 737 °C), followed by a retrograde metamorphism under greenschist facies conditions. The maximum temperature of regional metamorphism was not sufficient to replace calcic amphibole (tremolite) by calcic pyroxene. Textures (magnetite inclusions in metamorphic olivines) and associated rock types (meta-listwaenite) indicate the studied rocks were partly altered (M1) before being progressively metamorphosed under upper amphibolite facies conditions (M2). Late-stage retrograde metamorphism (M3) led to formation of chlorite and thin irregular serpentine veinlets, partially to serpentinization of metamorphic olivine and orthopyroxene, and partial replacement of chromian spinel by ferritchromite and magnetite. These three metamorphic episodes can be attributed to the Early, Middle and Late Cimmerian orogenies of Iran, respectively. © 2011 E. Schweizerbart'sche Verlagsbuchhandlung Stuttgart Germany.
Petrology (15562085)19(7)pp. 675-689
In western margin of the CEIM (Ashin area), Middle Eocene volcanic shoshonites present very good exposures. This shoshonitic association comprises of all shoshonite group members from basic to acidic. Major minerals of basic members (absarokite and shoshonite) are olivine, clinopyroxene (augite), plagioclase (labradorite), K-feldspar (sanidine and anorthoclase), analcime, calcite, apatite, ilmenite and magnetite. Secondary minerals include chlorite, calcite, epidote and zeolite (mesolite). The Ashin shoshonitic rocks consist of SiO2 undersaturated (absarokite or phonotephrite) to SiO2 oversaturated (toscanite or rhyolite) units. The studied rocks are characterized by wide range of SiO2 (48 to 70 wt %), low content of TiO2 (0.35 to 1.17 wt %), and high values of Alkalis [(Na2O + K2O) = 7.03 to 11.4 wt %]. Other main geochemical characteristics of Ashin shoshonites are potassic to ultra-potassic nature (K2O/Na2O = 1.04 to 5.06), high ratios of LREE/HREE (e.g. La/Yb up to 19.16), and enrichment in LILEs. Primitive mantle normalized spidergram of the studied rocks shows positive anomalies of Cs, U, K, Pb, Hf and negative spikes of Nb, Ta, Sm, Ti and Y. All analyzed samples display markedly negative Nb, Ta, and Ti anomalies, typical features of orogenic magmas. These geochemical signatures point out to the subduction-related nature of Ashin shoshonites and their similarity to potassic volcanic rocks of continental arcs or convergent margins. The parental magma of these shoshonites is an alkalibasalt (absarokite) which produced by low-degree of partial melting of a metasomatized enriched mantle source. Petrographical evidences together with geochemical characteristics (e.g., high values of Pb and U) of the studied rocks conclude crustal contamination of magma during ascending throughout the continental crust. The former subduction of CEIM confining ocean from Triassic to Eocene is too enough for volatile enrichment of the mantle and shoshonitic magmatism in middle Eocene of Ashin area. © 2011 Pleiades Publishing, Ltd.
Torabi, G.,
Shirdashtzadeh, N.,
Arai, S.,
Koepke, J. Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen (00777749)262(2)pp. 227-240
Paleozoic of Jandaq and Posht-e-Badam ophiolites and Mesozoic ophiolitic mélanges of Nain and Ashin are located in the western part of the Central East Iranian Microcontinent. They are metamorphic relicts within the amphibolite faciès of Paleo-Tethys and Neotethys Oceans. Petrological and geochemical studies of these Paleozoic and Mesozoic ophiolites suggest that they include oceanic basic dykes, pillow and massive lavas formed during mid-oceanic rifting processes. Parental basic rocks from Paleozoic ophiolites of Jandaq and Posht-e-Badam have tholeiitic to alkaline affinities. They are supposed to have been generated by lower partial melting of a relatively enriched mantle peridotite. Parental basic rocks from Mesozoic ophiolites have typical N-MORB affinity and were generated by partial melting of a depleted mantle source. © 2011 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.
Ofioliti (03912612)36(2)pp. 191-205
The Mesozoic ophiolitic mélanges of Nain and Ashin-Zavar are located in the western part of the Central-East Iranian microcontinent (CEIM), along the major faults of Nain-Baft and Dorouneh. They contain two different groups of highly metamorphosed rocks (amphibolitic rocks, schists, marbles and quartzites) formed through metamorphism of oceanic basaltic and sedimentary units, and also some less metamorphosed rocks (sheeted dikes, pillow lavas, limestones and radiolarian cherts), that were tectonically melanged. These features show that they formed in two distinct phases. Geochemical data point to an island arc tholeiitic affinity for the amphibolitic rocks, and to a MORB nature for the pillow lavas and sheeted dikes that are related to a back-arc basin. Accordingly, oceanic crust extensional processes should have been active during two phases: a- In Early Jurassic, the Nain and Ashin-Zavar oceanic crust segments started spreading and producing diabasic dikes and pillow lavas, covered by pelagic sediments, then they suffered a high-grade metamorphism during the closure of this oceanic sector around the Middle Jurassic. b- During Early-Late Cretaceous to Paleocene, oceanic spreading produced sheeted dikes, massive basalts, and basaltic pillow lavas throughout the Austrian orogenic phase. There is no evidence of high-grade metamorphism as amphibolitic rocks. Radiolarian cherts and Globotruncana limestones of Late Cretaceous age cover the basaltic rocks.
Island Arc (10384871)19(2)pp. 277-291
The Jandaq lamprophyres occur as eight mostly parallel dykes, which cross-cut Eocene volcanic and sedimentary rocks of the Pis-Kuh Formation in dominant north to south direction. These lamprophyres are mainly composed of kaersutite, clinopyroxene, olivine, feldspar, ilmenite, and spinel as primary minerals. The rocks studied here are enriched in alkalis, TiO2, large ion lithophile elements, and light rare-earth elements (LREE), with SiO2 content between 41.7 and 46.2 wt%, and are classified as camptonite and alkaline lamprophyre according to the mineralogical and chemical characteristics. These rocks exhibit positive Eu anomalies (Eu/Eu* = 1.08-1.39) and are characterized by strong enrichment in LREE relative to heavy REEs, and also by varied Zr/Hf ratios. The geochemical features of the rocks suggest that the lamprophyre magmas were derived from low-degree melting of an amphibole garnet lherzolite that experienced strong metasomatism by carbonate-rich fluids in response to dehydration melting from the subducted slab. The Jandaq lamprophyric magmatism has been attributed to the former subduction of the Central-East Iranian microcontinent confining oceanic crust from the Triassic to Eocene, and decompression melting induced by the extensional basin of the Jandaq area in the early Oligocene. © 2010 Blackwell Publishing Asia Pty Ltd.
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen (00777749)255(3)pp. 255-275
This ophiolite has experienced several metamorphic events since its formation. During Jurassic times, a regional metamorphism (Ml) caused the formation of amphibolitic rocks from the oceanic basic rocks. These amphibolites were often covered by skarns formed during M2 metasomatism of carbonates. There are also evidences claiming a retrograde regional metamorphism (M3) that has affected both skarns and amphibolites. Additionally, some less highly metamorphosed sheeted dykes and pillow lavas occur in this ophiolite. Based on their geochemistry they were originally different from the amphibolitic rocks. Therefore, two phases of magma generation can be recognized: The first one, in Lower Jurassic, led to the formation of the basaltic protolith of the amphibolites. The second one, in Upper Cretaceous, caused the generation of sheeted dykes and pillow lavas. © 2009 E. Schweizerbart'sche Verlagsbuchhandlung, D-70176 Stuttgart.
Pirnia, Tahmineh,
Pirnia, T.,
Pirnia, T.,
Pirnia, T.,
Arai, S.,
Arai, S.,
Arai, S.,
Torabi, G.,
Torabi, G.,
Torabi, G. JOURNAL OF MINERALOGICAL AND PETROLOGICAL SCIENCES (13456296)105(2)pp. 74-79
Plagioclase lherzolites of Nain melange, Iran, show peculiar textures that indicate melt impregnation (1) droplet or bleb-like grains of plagioclase distributed in the peridotite matrix, (2) plagioclase-hearing clinopyroxenite seams, and (3) trails of plagioclase crosscutting pyroxene porphyroclasts The textural characteristics show post-deformational igneous formation of plagioclase, and possibly, associated clinopyroxene, from the impregnating melt The melt has precipitated the clinopyroxenite seams and chemically modified all the peridotite minerals Highly refractory compositions of the precipitated minerals suggest involvement of a highly depleted MORB-like melt The melt was an increment of partial melt produced by 8% to 10% fractional melting from the MORB source This is in contrast to the involvement of ordinary MORB in melt impregnation in abyssal plagioclase peridotites Integration of increments of mantle partial melts to form MORB was possibly incomplete in the very incipient mid-ocean ridge as in the short-lived Nain back-arc basin
Journal of Applied Sciences (discontinued) (18125654)8(11)pp. 2031-2040
There are leucocratic gabbro intrusions in serpentinized mantle peridotites of Central Iran ophiolites (Jandaq, Anarak Naein and Ashin-Zavar). In contacts of gabbro intrusions and serpentinized mantle peridotites, ultramafic hornfelses are formed by contact metamorphism. These ultramafic hornfelses are different with host mantle peridotite in petrography, texture and mineral chemistry. Two-pyroxene thermometry of hornfelses and intact mantle peridotites that are far from contact metamorphism, present 987 and 1200°C, respectively. To occurring the reaction between the gabbro intrusions and mantle peridotites, the host rock should be serpentinized previously. © 2008 Asian Network for Scientific Information.
