فهرست مطالب mortaza sharifi

The Dumak ophiolitic mélange in the Baluchistan region is one of the ophiolitic mélanges that contains all of the components of a complete ophiolite, located in the middle parts of the western margin of the Eastern Iranian range. Field studies indicate the presence of a large volume of pillow lavas in different parts of the Dumak mélange. The outcrop of sheeted dikes associated with the Dumak mélange is limited to the Shuru region. These dikes present below the pillow lava and Cretaceous pelagic sediments. Compositionaly, most of pillow lavas and sheeted dikes are basalt. Variations in SiO2 to FeOt/MgO in the pillow lavas and sheeted dikes indicates a tholeiitic trend for their productive magma. The pattern of REE elements and amounts of (La/Sm)N in these rocks are similar to E-MORB. The study of pillow lavas and sheeted dykes of Dumak ophiolitic mélange shows that the MORB ophiolitic body in Dumak has been gradually and continuously evolved in a supra-subduction zone environment and beginning of intra-oceanic subduction. Considering structural evidence of the region, after adding the Dumak ophiolite to the Lut block, during the continuation of tectonic movements related to orocline bending, a new mélange has formed with the presence of Eocene carbonate blocks.

Cenozoic volcanic activities in the Urumieh-Dokhtar Magmatic Arc (UDMA) have occurred in three main pulses of Eocene, upper Oligocene-Pliocene, and Pio-Quaternary (Dilek et al., 2010, Sayari, 2015). Magmatic activities in the UDMA until a few years ago were marked with calc-alkaline and occasionally shoshonitic signatures. Recent studies have reported post-collisional adakites in some parts of the UDMA (e.g., Ghadami et al., 2008; Omrani et al., 2008; Sayari, 2015; Sayari and Sharifi, 2018). Since magmatic genesis of calc-alkaline, shoshoitic, and especially adakites are absolutely different, variation in the volcanism nature of Iran is a key to recognition of geodynamic evolution of Iran. This study tries to analyze the volcanic evolution in the central part of the UDMA by systematically processing of geochemical database for three main Cenozoic volcanic pulses.   

Whole rock reliable ICP-MS analysis data from scientific texts having exact location coordinates were gathered to form a geochemical geodatabase which includes 99 samples. This database spatially covers around 200 km in the central part of the UDMA from 51°15´E and 33°47´N (north of Isfahan) to 52°57´E and 32°35´N (east of Isfahan).  

Analysis of the geochemical geodatabase indicates that none of the samples belong to alkaline and tholeiitic magmatic series. About 71 percent of group 1 (volcanic pulse of Eocene) are calc-alkaline, and the remaining 29 percent are shoshonitic. About 67 percent of group 2 (volcanic pulse of Oligocene-Miocene) are shoshonitic, and the remaining 33 percent are calc-alkaline. About 88 percent of group 3 (volcanic pulse of Plio-Quaternary) are adakite, and the remaining nearly 12 percent are both calc-alkaline/shoshonitic (samples CN4, JS13, OG4 and SK1 of Khodami, 2009). Adakitic samples are situated in two areas in Joshaghan-Ghohrud and Kajan-Kahang. Sayari and Sharifi (2018) showed that there is a correlation between UDMA adakites and positive lithospheric thickness anomalies. They showed that adakites in the central part of UDMA are restricted to 4 regions exactly where lithosphere and crust are anomalously thicker than the surrounding. In the areas where adakites lie, lithosphere-asthenosphere boundary (LAB) is situated deeper than 212 km (Sayari and Sharifi, 2018). The geochemical aspect of the studied adakites which are all related to the third volcanic pulse of UDMA shows that they have been derived from the subducted slab. They do not have adakite-like or crust-derived adakites characteristics.

The results indicate that volcanic activities from Eocene to Quaternary have evolved from calc-alkaline to shoshonitic signatures and then turned into adakitic nature. Calc-alkaline and shoshonitic magmatism resulted from partial melting of the mantle wedge, while adakitic magmatism resulted from partial melting of the subducted slab. This means that the origin of the third volcanic pulse has shifted from mantle wedge to slab. According to the La/Sm versus La diagram (Aldanmaz, 2000) calc-alkaline samples have been derived from about 15% partial melting of the spinel-garnet lherzolite, and the shoshonitic samples have resulted from about 3% partial melting of the spinel-garnet lherzolite. Based on La/Yb versus Yb diagram (Bourdon et al., 2002), adakites from Kajan-Kahang have been derived from about 10% partial melting of the garnet amphibolite. Moreover, the Adakites from Joshaghan-Ghohrud have resulted from about 6% partial melting of the hornblende eclogite.

The Aliabad area is located in the northwest of Nain. Volcanic rocks of the Aliabad area have andesitic to rhyolitic composition.On the basis of petrographic investigations, porphyritic texture is the main texture of these rocks. Thus, they have experienced two crystallization stages. In these rocks, phenocrysts have been crystallized in the first stage, and in the second stage the cooling processes were fast, resulting in a groundmass of glass and fine crystals.The second stage of crystallization in these rocks took place at (near) the earth surface. The composition of phenocrysts such as amphibole, biotite and pyroxene provide valuable data about magmatic series, pressure, and temperature history of the primary magma during crystallization. In this study, the clinopyroxene of these rocks was analyzed in order to estimate the physicochemical conditions of the parent magma.

Field work in the Aliabad area was carried out to identify volcanic units and their relationships. About 65 samples were collected. Thin sections were prepared for petrographic studies to select suitable samples of the volcanic rocks for more detailed mineralogical and geochemical studies. The chemical composition of minerals was determined using a wavelength dispersive EPMA (Cameca-SX 100) at Iran Minerals Research and Processing Center. Analytical conditions for the minerals were accelerating voltage of and a beam current of 15 nA. 15 kV.  Also, the Minpet software package was used for processing the relevant data and calculating the structural formula of clinopyroxene minerals based on 6 oxygen atoms.

The chemical compositions of clinopyroxenes were used to estimate the chemical evolution and P-T conditions of the magmas during crystallization. Microprobe analyses show that clinopyroxenes in the andesitic rocks are augite (En43-45Wo 38-42 Fs14-18).According to the clinopyroxene thrmobarometry calculations done by several methods, it was inferred that the clinopyroxenes are crystallized at temperatures of 1009-1200 °C and pressures of 2.5-7 kbar.By noting the distribution of aluminum in clinopyroxenes, these phenocrysts were formed in a range of low to medium pressure that shows the crystallization of those during the ascending of magma in different depths of 9 to 18 km. According to the Helz diagram (1973), the amount of water is about 10 percent. Clinopyroxene composition along petrographic investigations in the studied rocks confirm that ƒO2 is high.

The Aliabad area is located in the Urumieh- Dokhtar volcanoplutonic belt, Northwest of Nain- Iran. In the Aliabad area, the exposed Cenozoic volcanic rocks are compositionally from andesite to rhyolite. These rocks show porphyritic, trachytic, and amygdaloidal textures under the microscope and they consist of plagioclase, clinopyroxene, sanidine, quartz, opaque and apatite.The andesitic rocks of the Aliabad area are composed mainly of plagioclase and clinopyroxene phenocrysts in a groundmass of plagioclase microlites and fine crystals of pyroxene and opaque minerals along with glass. According to the ternary diagram of Wo-En-Fs (Morimoto, 1989), the studied clinopyroxenes are augite in composition. The physical (pressure and temperature) conditions of a magma during crystallization is recorded in the chemical composition of the clinopyroxene phenocrysts. Therefore, clinopyroxenes are representative of magma composition and usually are used for identifying the chemical condition i.e. magmatic series and physical conditions, temperature and pressure of a magma at the time when clinopyroxene was crystallized. Several methods that are applied for this purpose are as follows:1- The Soesoo (1997) method Based on this approach, the pressure and temperature formation of the Aliabad clinopyroxenes are about 3.5-6 kbar and 1150-1200 °C, respectively.2- The Sayari and Sharifi (2014) method According to this method, the pressure and temperature formation of the studied samples are about 2.48-4.8 kbar and 1074-1094 °C, respectively. 3- The Nimis and Taylor (2000) method Using this method, the temperature formation of clinopyroxenes in the Aliabad area is about 1009-1083 °C.

The authors of the manuscript would like to thank the respectable reviewers for valuable suggestions and also Dr. Sayari for his help in using the SCG software.

The Nabar area that is a part of the Urumieh- Dokhtar volcano- plutonic belt is located in the south of Kashan. Research works such as Emami (Emami, 1993) and Abbasi (Abbasi, 2012) have been done about the geology of this area.
Rock units in the study area contain middle- upper Eocene intermediate to acidic lavas and pyroclastic rocks, green marl, shale and sandy marls of Oligo- Miocene, limestones of Qom formation, intrusive granitoids with Oligo- Miocene age and quaternary travertine and recent alluvium (Emami, 1993). The volcanic and sub volcanic rocks of this area are composed of andesite, trachyandesite, dacite, rhyolite and porphyric pyroxene diorite along with pyroclastic rocks.
In order to achieve the aims of this work, at first field surveying and sampling were done. Then, thin and polished thin sections were prepared. Some of the samples were selected for microprobe analysis and clinopyroxene minerals were analyzed by using JEOL- JXA-8800 analyzer with a voltage of 20 Kv and a current of 12 nA in the Kanazava University of Japan and Cameca-Sx100 analyzer with a voltage of 15 Kv and a current of 15 nA in the Iranian mineral processing research center, Karaj.
On the basis of petrographic investigations, porphyritic, porphyroid, fluidal, amygdaloidal and porphyry with microlitic groundmass are common textures of these rocks. Also plagioclase, clinopyroxene, amphibole, biotite, sanidine and quartz are essential minerals, opaque, zircon and apatite as accessory minerals are observed in the studied rocks. Clinopyroxenes are observed with corona texture that resulted during the uralitization process. On the basis of minerals’ chemistry, pyroxenes are Fe- Mg- Ca type in composition (Morimoto et al., 1988). These clinopyroxenes are augite. Investigations indicate that mineral composition of clinopyroxene can be effectively used to evaluation the P-T conditions during crystallization. Previous research works have proposed several methods such as Soesoo (Soesoo, 1997) and Putrika (Putrika, 2008). Thermobarometric studies of clinopyroxenes reveal that Nabar rocks were formed at temperatures of 900 -1200 ˚C and the pressure of 2-5 kbar. According to the Aoki and Shiba (Aoki and Shiba, 1973) and Helz (Helz, 1973) approaches, the pyroxenes of the studied rocks are in a range of low to medium pressure that shows crystallization of clinopyroxenes during ascending of magma in different depths. Also according to Helz (Helz, 1973), the water vapor content in the crystallization of clinopyroxenes is more than 10 percent. Using AlIV versus AlIV 2Ti Cr diagram which depends on the amount of ferric iron in pyroxenes, we can get oxygen fugacity. Based on this diagram, the pyroxenes which crystalized at high oxygen fugacity, has been situated above the line of Fe3. Furthermore, Cameron and Papike (Cameron and Papike, 1981) have mentioned to the distances of the samples from the Fe3 line and noted that further distances of the samples from this line are indicating more oxygen fugacities in their geological setting. On the basis of this diagram samples were located above the line of Fe3橷 these rocks are formed in high oxygen fugacities. Pyroxene composition depends on the chemical composition and tectonic setting of the host lava which can be used widely to determine tectonic setting of the rocks. On the basis of approaches of Le Bas (Le Bas, 1962) and Sun and Bertrand (Sun and Bertrand, 1991), the chemical composition of clinopyroxenes shows that the studied rocks are related to calc-alkaline series and orogenic settings.
On the basis of mineral chemistry, pyroxenes are Fe-Mg-Ca type in composition. These clinopyroxenes are augite. Thermometric studies of clinopyroxenes reveal that Nabar rocks are formed at temperatures of 900-1200 ˚C. According to the distribution of aluminum in clinopyroxenes, these minerals were formed at 2-5 k bar pressure and water vapor content of more than 10 percent. Therefore, pyroxenes of the Nabar rocks are in a range of low to medium pressure that shows crystallization of clinopyroxenes during ascending of magma in different depths. Moreover, the volcanic rocks in Nabar were formed in high oxygen fugacity. The chemical composition of clinopyroxenes reveals that these rocks are related to calc-alkaline series and orogenic settings.

Volcanic rocks with a porphyritic texture have experienced two crystallization stages. The first is slow, resulting in phenocrysts, and the second, which took place at, or near the surface, or during intrusion into a cooler body of rock, result in a groundmass of glass, or fine crystals. The pressure and temperature history of a magma during crystallization is recorded in the chemical composition of the phenocrysts during both stages. These phenocrysts provide valuable data about the physicochemical conditions of the parent magma during the process of crystallization. The composition of clinopyroxene (cpx) reflects not only the chemical condition and therefore the magmatic series, but also the physical conditions, i.e., temperature and pressure of a magma at the time when clinopyroxene crystallized.
The Ghohrud area lies in the middle part of the Urumieh-Dokhtar Magmatic Arc , which is part of a much larger magmatic province extending in a vast region of convergence between Arabia and Eurasia north of the Zagros-Bitlis suture zone (Dilek et al., 2010). In the Ghohrud area, north of Isfahan, exposed Eocene volcanic rocks belong to the first pulse of Cenozoic volcanism of Iran (Sayari, 2015), ranging in composition from andesitic basalt to basalt. The basaltic rocks of the Ghohrud area are composed mainly of plagioclase phenocrysts surrounded by smaller crystals of clinopyroxene in a groundmass of microlites, glass and opaques. In this study, the clinopyroxene and plagioclase of these rocks were analyzed in order to estimate the physicochemical conditions of the parent magmas.
Clinopyroxene and plagioclase phenocrysts of nineteen samples were analyzed with the electron microprobe. The chemical compositions of the clinopyroxenes were used to estimate both the chemical evolution and temperature and pressure conditions of the magmas during crystallization, using SCG, a specialized software for clinopyroxene thermobarometry (Sayari and Sharifi, 2014). Microprobe analyses show that plagioclases in the Eocene basaltic rocks are labradorite-bytownite (An85-58Ab15-41) and clinopyroxenes are augite (En41-49Di29-38Fs17-26). The compositions of the clinopyroxenes indicate a tholeiitic affinity for the magma. After plotting the cpx thermobarometry results on a P-T diagram, and applying a linear regression, an equation of P-T describing the physical conditions of the ascending magma was obtained.
Several complex thermobarometry equations used to estimate T and P of cpx have been introduced to the Society of Petrology by different researchers (e.g., Sayari, 2012; Sayari and Sharifi, 2014Putirka et al., 1996; Nimis and Ulmer, 1998; Putirka, 2008). Ten well-known barometric and six thermometric equations developed for clinopyroxene were tested for the analyzed samples with the aid of SCG, and then the equations giving the best match were selected and integrated to estimate contemporaneous P and T. According to the systematic cpx-thermobarometry calculations done with SCG software, it was inferred that the clinopyroxenes crystallized over a range of 1120-1170 °C and a range of pressure of 2-6 kbar.
The results of the cpx-thermobarometry were then plotted on a P-T diagram and a linear regression was used to find a function describing P and T for clinopyroxenes. The equation of the regression line is: P (kbar) = 0.0846T (°C)-93.128
The equation has a high coefficient of determination parameter (R2), making it reliable to determine the rate of T-loss against P-reduction. By assuming that the pressure on the magma was lithostatic due to the weight of overlying rocks, and considering the density of continental crust of about 2.7 gr/cm3, this equation shows that while magma was ascending while the clinopyroxenes were crystalizing, pressure was decreasing at a rate of about 84.6 bar per 1 °C temperature loss. This pressure loss indicates a rise of about 320 m in the continental crust.

The study area is located in the Shurab area that is about 50 Km Southeast of Qom. Volcanic rocks of the Shurab area have basaltic composition that is associated with salt and marl units. Igneous rocks of the Shurab area have not been comprehensively studied thus far.
Clinopyroxene composition of volcanic rocks, and especially the phenocrysts show Magma chemistry and can help to identify magma series (Lebas, 1962; Verhooge, 1962; Kushiro, 1960, Leterrier et al., 1982), tectonic setting (Leterrier et al., 1982; Nisbet and Pearce, 1977) as well as temperature formation and pressure of rock formation. Some geologists have estimated temperature of clinopyroxene formation by clinopyroxene composition (Adams and Bishop, 1986) and clinopyroxene-olivine couple. So, clinopyroxene is used in this study in order to identify magma series, tectonic setting, plus the temperature and pressure of volcanic rocks of the Shurab.
Material and Clinopyroxene analyses were conducted by wavelength-dispersive EPMA (JEOL JXA-8800R) at the Cooperative Centre of Kanazawa University (Japan). The analyses were performed under an accelerating voltage of 15 kV and a beam current of 20 nA. The ZAF program was used for data corrections. Natural and synthetic minerals of known composition were used as standards. The Fe3 content in minerals was estimated by Droop method (Droop, 1987).
In the Shurab area, the volcanic rocks area with basaltic composition are located 50 km Southeast of Qom. Their age is the early Oligocene and they are associated with the salty marl units of the Lower Red Formation (LRF). The hand specimens of the studied rocks look green. These rocks are intergranular, microlitic, porphyric, vitrophyric and amygdaloidal and they consist of olivine, pyroxene and plagioclase. Accessory minerals contain sphene, apatite and opaque.
According to Wo-En-Fs diagram (Morimoto, 1988), clinopyroxenes indicate diopside composition.
Clinopyroxenes are representatives of magma composition and they are usually used for identifying magma series. There are several diagrams that are used for this purpose as follows.
1 - Al2O3 – SiO2 diagram (Lebas, 1962): According to this diagram, the studied clinopyroxenes were plotted in sub-alkaline field.
2 - Al2O3 – TiO2 diagram (Lebas, 1962): In this diagram, the studied clinopyroxenes show to be calcalkaline.
Some diagrams that are used for determining tectonic setting according to clinopyroxene composition are as follows: 1 - F1 – F2 diagram (Nisbet and Pearce, 1977): Based on this diagram, the Shurab clinopyroxenes rocks lie between volcanic arc and mid ocean ridge basalt fields.
2 - Al2O3 - SiO2 diagram (Lebas, 1962): Using this diagram, the studied clinopyroxenes are located in the sub-alkaline field.
Some methods that are used for determining temperature formation and pressure of clinopyroxene are as follows: 1 – Kretz method (Kretz, 1994): Using this method, temperature formation of clinopyroxene is about 1200- 1250oC.
2 – Soesoo method (Soesoo, 1997): Using this method, pressure formation of clinopyroxene is about 6-10 Kb.
In Al�븊 against Na diagram, Clinopyroxenes are located above the Fe=0 line (Schweitzer et al, 1979). This case and abundant hematite and magnetite in the Shurab area rocks confirm that oxygene fugasity is high. Based on Helz diagram (Helz, 1973), the content of magma water during clinopyroxene formation is about 2-5 percent.
Using various methods, the temperature and pressure of clinopyroxene formation are about 1200 oC and 6-10 Kb, respectively. Clinopyroxene composition and the abundant hematite and magnetite in the studied rocks confirm that oxygene fugasity is high. According to Helz diagram, the amount of water is about 2-5 percent.
Additionally, the parent magma of the studied area rocks is calc alkaline and tectonic setting is subduction-related based on the clinopyroxene composition.

The Bultaq shear zone is located 185 km north-west of Isfahan. The study area is a part of the Sanandaj–Sirjan zone, which is affected by ductile and brittle–ductile deformation and consists of slate, schist(garnet-muscovite schist, enriched quartz-muscovite schist and biotite-muscovite schist), amphibolite marble, metavolcanic, andesite and tuff. There are several duplex structures and thrusts with NW-SE-trend and NE dip in the Bultaq shear zone. This shear zone is parallel to the Zagros Organic thrust. Also, boudinage structures geometric analysis, mesoscopic scale asymmetric folds, microscopic studies of S-C, S-Ć cleavages and σ- type porphyroclast confirmed right-lateral strike-slip movement. These fabrics show right rounded cuts in region in some parts. Mylonitic foliations were used to calculate elongation (e) and stretch (s) in this area. The microstructures were formed under green schist to amphibolite facies conditions. The metamorphic rocks have been formed in a Barrovian metamorphism type (medium temperature - pressure) and affected by three metamorphic and deformation phases. The metamorphic phases include dynamothermal, dynamic and retrograde and the deformation phases are D1, D2 and D3.

The Ghaidou monzogranite in the southeast of Khomein constitute a part of rock complex from the northern part of the Sanandaj-Sirjan zone. This body intruded into the Jurassic micaschists and created a metamorphic aureole. Also، aplitic veins، tourmaline bearing pegmatitic dikes، felsic microgranular enclaves and surmicaeous enclaves are observed in this area. The predominant minerals of these rocks are K-feldspar (orthoclase and microcline)، Na-plagioclase (Albite- oligoclase in the monzogranite and oligoclase in the felsic microgranular enclaves)، quartz and black mica (Annite) -as the main minerals- with minor amount of tourmaline (schorle)، garnet، white mica (phengite)، sillimanite، kyanite، zircon، apatite and ilmenite. On the basis of biotites mineral chemistry، these phases are enriched in FeO and Al2O3 and relatively low in TiO2. These minerals are magmatic and primary and thermometry results yielded 660-690 ºC. According to the chemical composition of primary igneous biotites in the enclaves and monzogranites، these rocks have calc-alkaline، peraluminous and an orogenic continental collision affinity characteristics of S-type granites. Also، the biotite composition and the presence of ilmenite point to low oxygen fugacity and redox conditions during magma crystallization. Based on the available data، the generation of these rocks can be related to Arabian-Eurasia collision zone.

Volcanic rocks of interest are situated in the middle part of the Urumieh-Dokhtar Magmatic Arc (UDMA). They are parts of a vast magmatic province located in the north of Bitlis-Zagros suture zone. Having a prevailing porphyritic texture، these rocks include phenocrysts of plagioclase، amphibole and biotite in a matrix composed of feldspar، quartz، opaque، glass and microlite and mineralogically show composition of dacite to andesite. Minerals are mostly fresh. Effects of alteration are limited to weak chloritization and saussuritization in some amphiboles and rim of plagioclases، respectively. All of the analyzed biotites in the Miocene-Pliocene volcanic rocks in the east of Kamu are of Mg-biotite. According to a widespread classification of micas to 6 general end-members، biotites of interest are averagely composed of 55. 45% phlogopite، 15. 90% talc، 12. 72% Ti-phlogopite، 11. 44% eastonite، 3. 71% ferri-eastonite and 0. 78% muscovite. Chemical composition of biotites indicates a calk-alkaline magmatic series for the magma from which biotites are crystallized. Estimation of the oxygen fugacity of magma، based on chemical composition and Fe3+ content of biotite، shows that the oxygen fugacity was limited to FMQ buffer in quality and was about 10-15 bar in quantity. This value accords the oxygen fugacity for intermediate-acidic volcanic rocks.

The studied volcanic rocks، in the middle part of the Central Iranian volcanic belt (Urumieh-Dokhtar magmatic arc) belong to a vast magmatic province located in the north of the Bitlis-Zagros suture zone. Petrographically، these rocks show dacite to andesite composition and include phenocrysts of plagioclase، amphibole and biotite with a prevailing porphyritic texture in a matrix composing of feldspar، quartz، microlite and glass. Having a relatively invariable composition، plagioclases are all andesine. Amphiboles are calcic and tschermakite type. Estimation of temperature and pressure of crystallization resulted from graphically integrating amphibole and amphibole-plagioclase geothermo-barometry equations indicates that the amphibole-plagioclase phenocrysts were crystallized in the temperature range of 763-823 °C with average of 797 °C and in the pressure range of 2. 2-4. 5 kbar with the average of 3. 4 kbar. The maximum depth of crystallization is evaluated at 17 km in continental crust.

The skarns of the Ochestan area are located in the Sanandaj- Sirjan zone، about 60 Km south of Mahallat. The rock complex in this area consist of intrusive bodies and metamorphic rock such as: schist، phyllite، slate، hornfels، amphibolite and metavolcanic. The injection of magma in the Cretaceous-Paleocene with syenogranite and monzogranite composition into the Paleozoic limestone and dolomite led to formation of skarn and marble. Clinopyroxene (diopside)، olivine (forsterite)، tremolite، talc، serpentine، phlogopite، margarite، wollastonite، opaque minerals، calcite and quartz are observed minerals in contact metamorphism rocks. According to the mineralogical studies، the Ochestan skarns are exoskarn-type and the presence of minerals such as: forsterite، diopside، tremolite، antigorite and phlogopite show that the host rock is dolomitic the in study area. These skarns show zoning of intrusive body into the host rock: wollastonite skarn، pyroxene skarn، forsterite- serpentine marbles، mica marbles، tremolite- talc marbles، calcite and dolomite marbles.