Kharazmi Journal of Earth Sciences

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The study area is located in the south of Bardaskan (south west of Khorasan Razavi). Mafic intrusions of Robat-e-Zangiche and Lakh Bargheshi areas from Kooh-e-Sarhangi zone have been injected into granitic basement rocks and Soltanieh dolomite. Plagioclase, amphibole and clinopyroxene are rock forming minerals. According to the petrographic evidences, mineral chemistry and thermobarometry data amphiboles have different generations of igneous and alteration types. The results of amphibole thermobarometry indicate temperature and pressure ranges of 545-911 °C and 2.2 to 5.8 kb respectively. Such wide range of calculated temperature and pressure could be interpreted by various solidification conditions and also secondary altration processes. On the basis of whole rock chemistry, the studied samples are mainly gabbro. The spider diagrams display geochemical signatures of subduction zones magma. Based on tectonic discrimination diagrams, genesis of the studied rocks is related to the both subduction and within plate settings. Furthermore, whole rock chemistry of the studied samples is compatible with spinel lherzolite melting. As the formation of Sabzevar back arc basin was probably triggered by the Neotethys subduction beneath Central Iranian microcontinent, so the Jurassic back-arc magmatism of the Bardakcan area may be affected by the same subduction process and concomitant asthenospheric upwelling in an extensional regime.

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The north of Shahpasand Mountain Pluton, with the age of late Eocene – Oligocene, is located in the northwest of Saveh. Plutonic rocks of Shahpasand Mountain show a various composition of gabbrodiorite, diorite, monzonite, quartzmonzonite, granodiorite and granite. These rocks have granular, intergranular, porphyroid and poikilitic textures.The main minerals are plagioclase, pyroxene, amphibole, biotite, K- feldspar and quartz. The accessory minerals are zircon, apatite, sphene and opaque. From geochemistry, tectonic setting and petrogenesis point of view, the north of Shahpasand Mountain Pluton is compared with Silijerd pluton that is located in the northwest of Saveh. Spider diagrams show that a slight enrichment of LREE to HREE and also higher LILE relation to HFSE. Negative anomalies of Nb, Ti, P show the plutons belong to subduction zone. Geochemical data, suggest that the parent magmas of the studied rocks might be generated by crystal fractionation of arc basaltic magma in magma chambers, coupled with some crustal assimilation. The EPMA analyses on the plagioclase, biotite and pyroxene minerals in granodiorite and gabbrodiorite of the north Shahpasand Mountain Pluton show that plagioclase compositions in granodiorite are in the range of oligoclase to andesine and in the gabbrodiorite samples are from andesine to bytownite. The EPMA analyses of the pyroxene minerals show the existence of two types of pyroxene in the gabbrodiorite samples (orthopyroxene with hyperesthene composition and clinopyroxene with augite – diopside compositions), while in granodiorite clinopyroxene is augite – diopside composition. On the basis of geothermobarometry, crystallization temperature of pyroxenes are estimated to be about 800° C to 970° C and crystallization pressure 7 to 8 kbar for the pyroxenes.
 

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Touyeh- Darvar granitoid pluton is situated in 50 Km SW of Damghan in Semnan province in the eastern Alborz zone. This pluton has intruded into the early Paleozoic rock units (Barout, Zaygun and Lalun Formations). Based on the field observations and petrographic studies, the pluton composed of monzonite, quartz monzonite and monzodiorite. Mineralogically, the pluton consists of plagioclase, alkali feldspar, quartz±biotite±amphibole. It’s accessory minerals include ilmenite, magnetite, zircon, apatite, titanite and chalcopyrite and sericite, epidote, calcite, and chlorite are it’s secondary minerals. The Amphiboles of the Touyeh- Darvar rocks are low pressure calcic type with ferro-hornblende composition and igneous origin. Application of the geothermobarometry methods yielded temperature ranges of 650–730°C and pressures less than 2 Kb for stopping of exchange and final equilibrium of amphibole in the pluton that corresponds to less than 5 km depths for emplacement depth of the pluton. Existence of fine grained hyper-solvous to sub-solvous reaction textures (Perthitic, myrmekitic, graphic and granophyric) in the rocks of pluton and the lack of apparent contact metamorphism around it indicate diapiric ascend and emplacement of the pluton in a relatively cool and solid state in shallow depths of the crust. The Veins of mineral deposits such as Fe-Mn oxide-hydroxides, fluorite, barite, lead and zinc in the pluton host rocks are the obvious evidence for these states.
 

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Soltanabad metamorphic complex cropped out in the ophiolitic range of NE Sabzevar. There is a distinct gneissic body exposed in this complex which is associated with metabasite, serpentinite and adakitic intrusions. Quartz, albite, epidote, amphibole, garnet and chlorite are the rock forming minerals of gneissic samples. Based on abundances of light and dark minerals, different types of felsic, intermediate and mafic gneisses are distinguishable. Metamorphic conditions of the Soltanabad complex gneisses is estimated as 462 (±39)^°C at pressure of 12.4 (±2.15) kb indicating a hot thermal regime of a subduction setting. Based on the whole rock geochemistry gneisses have plagiogranitic composition and formed by partial melting of mafic sequence in oceanic crust. Isotopic ratio of zircon’s Hf and REE pattern confirm a MORB affinity of these gneisses. The Soltanabad metamorphic complex gneissesdisplay considerable compositional similarity with plagiogranite of Iran and Cyprus ophiolitic zones and thier geochemical characteristics are comparable with plagiogranites of supra-subduction zone setting. Probably gneisses and blueschists of the Soltanabad metamorphic complex are plagiogranites and mafic rocks of the Sabzevar oceanic lithosphere that experienced subduction zone metamorphism.  

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Gabbroic-dioritic rocks of Hurjand area in northeast of Kerman within the Posht-e-Badam block of the Central Iran microcontinent have intruded into the Precambrian-Cambrian sedimentary units of Desu Series. Amphibole, pyroxenes and plagioclase are the main minerals with granular and poikilitic textures in these rocks. Mineral chemistry studies show that clinopyroxene composition is augite and diopside. The plagioclase has a range of chemical composition from bytownite (An_75.2Ab₂₃.₈Or₁.₁) to andesine (An₄₀.₂Ab₅₅.₉Or₃.₉). Amphibole crystals present in these rocks are calcic and magmatic types with chemical composition of magnesio-hastingsite. Geothermometry of Ti content in amphibole composition shows a range of crystallization temperatures of 769 to 889°C. Geothermometry of coexisting amphibole-plagioclase pair shows the crystallization temperature of 793 to 896°C. Results of the geobarometry show that amphibole crystals formed at pressure of about 6.3 to 8.8 kbar, equivalent to the depth of 23 to 30 km. Mineral chemistry studies indicate the formation of these rocks from magma of alkaline to sub-alkaline nature related to intra-plate tectonic setting.
 

 

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Pelitic schists containing high-pressure mineral assemblage were found from the Sanandaj-Sirjan metamorphic belt in northwest of Nahavand city in western Iran. Textural observation as well as chemical analyses of minerals shows that pelitic schists of the Nahavand area recorded two metamorphic stages. The earlier stage (M1) is testified by relicts of pyroxene, glaucophane and phengite inclusions in core of albitic plagioclase and winchite and phengite cores in chemically zoned amphibole and white mica, respectively. While the second stage (M2) is documented by tremolite, chlorite and muscovite in the main schistosity and in the pressure shadow of albitic plagioclase blasts. P-T estimation of M1 and M2 metamorphic stage by using calibrated thermobarometers and Thermocalc software revealed an average pressure and temperature of 15.5 kbar and 575 ^◦C for the M1 stage, whereas the M2 stage has been constrained at P= 4.5 kbar and T= 600 ^◦C. The obtained P-T pattern show a clockwise path in which the high-pressure metamorphic stage of M1 continued by the retrograde low-pressure metamorphic stage of M2. This P-T path could be formed during subduction of Neo-Tethys oceanic plate under Iranian plateau.
 

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Ophiolitic mélange of south Dehshir is a slice of Nain-Baft ophiolitic belt. Blocks of metamorphic rocks that consist of amphibolite, banded Px-Ep amphibolite, Grt-Px amphibolite, Grt-Am gneiss and Grt-Ep hornblendite are cropped out along with crustal and mantle sequence of ophiolites from south Dehshir. Thermoberometry results of three samples of Grt-Px amphibolite, Grt-Am gneiss and Grt-Ep hornblendite are compatible and indicating an average temperature and pressure of 664°C and 8.8 kb, respectively. PT conditions of metamorphic rocks of south Dehshir ophiolitic mélange are in accordance with the conditions of those from the other worldwide ophiolitic sutures. Intimate spatial relation between investigated metamorphic rocks and adjoining ophiolites, PT conditions of metamorphism and whole rock chemistry indicate that these rocks representing oceanic lithosphere of suprasubduction zone and have derived from sole metamorphism event in the subduction initiation setting.
 

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In the southwest of Khuni mountain and the north of Kal-e-Kafi intrusion (northeast of Anarak), the igneous rocks of Khuni are cropped out. They dominantly show porphyritic texture and are similar to monzodiorite in composition. The phenocrysts mainly are clinopyroxene (diopside), amphibole (magnesiohastingsite to magnesian hastingsite), and feldspar (orthoclase in the rim and andesine in the core). Accessory minerals include primary biotite, apatite, sphene, and magnetite. The secondary minerals are biotite, calcite, epidote, tremolite- actinolite, and chlorite. Anti-rapakivi texture in feldspar is petrographic evidence of magma contamination. Application of various geothermobarometric methods for clinopyroxene and amphibole crystals in Khuni rocks yielded a crystallization temperature of ~1150°C for clinopyroxene and pressure range of 7-8 kb and temperatures of ~900-950°C for the amphibole phenocryst. Thermobarometry and chemistry of clinopyroxene and amphibole phenocrysts indicate that the rock-forming melt was formed by melting the continental crust in the Anarak area, as a result of the subduction-related magmatism of Eocene during the Neo-Tethys subduction beneath Central Iran.

 
 

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