جستجوی مقالات مرتبط با کلیدواژه « Clinopyroxene » در نشریات گروه « زمین شناسی »

The petrographical examination of peridotites of the Nehbandan ophiolitic complex revealed that the peridotites of Kalateh Shahpouri, Qadamgah, Lah-Kouh, Cheshmeh anjir, Bandan, and Zolfaghari were of harzburgite type and Sefid-Kouh and Nasfandeh-Kouh were of lherzolite type. Generally, the types of clinopyroxenes in the peridotites of this complex were diopside. The geochemical investigation of clinopyroxenes in Mg# vs. Al2O3, Cr2O3, and TiO2 graphs and Ti vs. Nd, Zr, and Sr graphs shows that the peridotites of Nasfandeh-Kouh, Bandan, Zolfaghari, and Sefid-Kouh with a low degree of partial melting belong to the Abyssal tectonic setting and back-arc basin.on the other side, the harzburgites of Kalateh Shahpouri and Cheshmeh anjir were formed in the Supra-subduction zone tectonic setting and fore-arc basin and have a high degree of partial melting. The study of incompatible elements, LILE and HFSE in spider diagrams normalized to the primary mantle and as well as the study of REEs in spider diagrams normalized to the chondrite for clinopyroxenes confirm this issue. Therefore, Nasfandeh-Kouh and Sefid-Kouh lherzolites as well as Qadamgah, Lah-Kouh, Bandan, and Zolfaghari harzburgites with a low degree of depletion were more consistent with the Mid-oceanic ridgestectonic setting, and the harzburgites of Kalateh Shahpouri and Cheshmeh anjir were close to the Supra-subduction zone tectonic setting with a high degree of depletion.

The volcano-plutonic complexes are important for understanding of tectono-magmatic settings in geological terrains (Wilson, 1989). The chemical composition of pyroxenes depends on the chemical composition and physical conditions of their host magmas, therefore, it can be used in determining of magmatic series nature. The Paleogene Eastern Iranian ranges is the product of the large-scale, Indian-Eurasian collisional event and their subsequent convergent involving amalgamation of the Afghan and Lut micro-continents as well as the Neo-Tethyan accretionary complexes and associated island arcs (Bagheri and Damani Gol, 2020). This paper aims to investigate new geochemical data on the Mahirud volcano-plutonic complex which represents a key area of the Sistan fold-and-thrust belt (SFB).

In order to study of the pyroxene chemistry of the MVPC, 10 samples of the fresh Cretaceous volcanic rocks were selected. Electronic micro-processing analyses (EPMA) were performed by the JEOL.JXA-8600M automatic super-probe with an accelerating voltage of 15 kW and a radiation current of 2 × 10-8 am in the Department of Earth and Environmental Sciences of Yamagata University in Japan.

The MVPC, previously known as Cheshmeh Ostad Group located in northeastern part of the SFB, has been interpreted as a rift-related assemblage which was preserved on the Afghan rifted margin (Tirrul et al, 1983; Angiboust et al, 2013). However, our observation indicates the Lower Cretaceous tonalitic stocks intruded the ophiolitic pillow lavas which interbedded with pelagic sediments and associated Upper Cretaceous neritic limestone (Guillou et al, 1981) in this region (figure 1). The volcanic rocks of this complex are diabase, basaltic andesite, andesite, dacite and tuff that were intruded by the Lower Cretaceous tonalitic stocks (Keshtgar et al, 2016; Keshtgar et al, 2019). The clinopyroxene in the diabasic rocks is mainly augite–diopside, while the clinopyroxene in basaltic andesite has augite composition. The low abundance of the HFSE elements, especially Ti, is a common characteristic of these clinopyroxenes. Moreover, the chemical composition of the studied pyroxenes are silica rich compared to the similar types of pyroxene in alkaline rock. This is in consistence with the geochemistry of the host volcanic rocks which are associated with ​​tholeiitic and calc-alkaline magmatic series (figure 2).

According to the tectonic setting geochemical diagrams (Le Base, 1962), the MVPC has properties similar to the magmas were originated in the supra-subduction zone (SSZ) and Island arcs (IAT) (figure 3). The presence of an island arc complex in the Sistan fold-and-thrust belt, which some of its parts are considered here as the MVPC, is comparable to the Pakistani Chagai-Raskoh and Kuhistan Cretaceous-Eocene island-arcs (Siddiqui, 2004; Siddiqui et al, 2012), in the east (figure 4). The subduction of the Neo-Tethys oceanic lithosphere under Eurasia, including the Lut and Afghan blocks, has been divided into two zones; the southern one which was an intra-oceanic subduction zone resulted in the island arcs development and on the other side, the northern one was a continental margin brought accretionary prisms and magmatic arc along the Cimmerian block.

There are discontinuous outcrops of volcanic rocks in the West Azarbaijan province and in the north of Maku city. These volcanic complex were bimodal and compose of acidic and basic lava and pyroclastic rocks. Mineral chemistry studies show that clinopyroxenes in the studied rocks are diopside. These pyroxenes have a high magnesium number (0.87 to 0.99). Magma series and tectonic determination diagrams show that the basaltic rocks that make up the studied clinopyroxenes have an alkaline nature and were formed in a whitin plate environment. According to geothermobarometry studies, clinopyroxenes were formed at temperature 1100 - 1250 ° C and pressure of 3 - 9 Kbar. The depth for generation of magma was at about 22 kilometers.

The Bostanabad-Hashtrood gabbro-diorite intrusive body in the south of Tikmehdash has intruded the Eocene volcanic-sedimentary rocks. The chemistry of the constituent minerals in this intrusive body shows that the plagioclases and clinopyroxenes have labradoritic and diopsidic composition, respectively, and are accompanied by the subordinate amounts of Mg-rich biotite and gangue minerals. The chemistry of the existing diopsides in these rocks indicates that their parent magma belongs to subalkaline magmatic series with a continental arc tectonic setting. The thermometric considerations showed that the clinopyroxene was crystallized at temperatures around 1200°C. Based on AlVI content (0.048-0.102) in the crystal lattice of the clinopyroxenes, it was ascertained that this mineral was formed under the pressure range of 6 to 9 kbars equivalent to depths between 19 and 28 km. Additionally, this study revealed that the clinopyroxenes in these rocks were formed from a magma which contained 10% water. The presence of some ferric iron in these clinopyroxenes with titanomagnetite is indicative of high oxygen fugacity in the parent magma.

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 Kal-e-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.

The mineralogical and petrographical studies have been done by using Olympus BH-2 polarizing microscope in the mineralogy laboratory of the University of Isfahan. EPMA and LA-ICP-MS analyses were used to obtain chemical characteristics of rock-forming minerals. Major-elements composition of minerals were performed by JEOL JXA-8800, WDS microprobe electron analyzer with accelerator voltage of 15 kV, current of 15 nmA, diameter of 3 μm, and a counting time of 40 seconds at the Kanazawa University of Japan. Natural and synthetic minerals and compounds were used as standards. The ZAF program was used for data correction.Trace element values of plagioclases and clinopyroxenes were analyzed by LA-ICP-MS (laser ablation-inductively coupled plasma-mass spectrometry) using an ArF 193 nm Excimer Laser coupled to an Agilent 7500S at the Earth Science Department of the Kanazawa University, Japan. The diameter of the analyzed points was 110 µm at 10 Hz with energy density of 8 J/cm2 per pulse.Mineral abbreviations in tables and photomicrographs are adopted from Whitney and Evans (2010). 

The Eocene Kal-e-Kafi pluton includes a wide range of rocks from gabbro to alkali-feldspar granite, which points to an extensive magmatic differntiation. Field relationships indicate presence of at least 4 magmatic phases, and gabbro is the first and oldest phase. The most predominant rock unit in the Kal-e-Kafi intrusive body is granitoid. However,  in the northern parts, the gabbro and anorthosite present substantial exposures. The anorthosites and gabbros are associated with each other in the field. Anorthositic veins with up to 15 cm thickness cut the gabbro.Gabbro is composed of bytownite and anorthite plagioclase (An= 84 – 94 %; some of them have been altered to bytownite, andesine and oligoclase), clinopyroxene (diopside, Mg#= 0.75), orthoclase (Or0.88), apatite, magnetite, and prehnite. Anorthosite rock-forming minerals are anorthite plagioclase (An= 89 – 95 %; some anorthite plagioclase have been altered to bytownite and labradorite), sphene and zircon. The main texture of these rocks are granular, intergranular and poikilitic. Field studies suggest that anorthosites are associated with gabbros which have filled the fractures of gabbros.Very simmilar petrography and chemical composition of plagioclases in the anorthosites and gabbros possibly reveal their cogenetic nature. It seems that the primary magma in the magma chamber, first crystallized the clinopyroxene and plagioclase, which caused formation of gabbros. In the next stage, by occurrence of a tectonic activity, the gabbros have broken and the remaining magma which was rich in plagioclase components, crystallized the anorthosites in the fractures. This reveals that the anorthosites of the study area are the plagioclase rich part of the primary basic magma which have formed the gabbros.According to the field relationships, it is generally believed that anorthosites are differentiates of gabbroic magmas. The studied anorthosite veins and gabbros of the Kal-e-Kafi area are consanguineous. These anorthosites are perhaps generated by the process of collection of plagioclase crystals from a gabbroic magma under the action of gravity and tectonic activity (filter pressing).Pyroxene is one of the common minerals. The chemical composition of this mineral provides valuable information about the nature of magma, H2O content, Oxygen fugacity, type of magmatic series, tectonic setting, as well as temperature and pressure of crystallisation (Schweitzer et al., 1979; Leterrier et al., 1982; D’Antonio and Kristensen, 2005).Chemistry of clinopyroxens within the gabbros of the Kal-e-Kafi  area shows that the parental magma belongs to the sub-alkaline and calc-alkaline magmatic series and these rocks are similar to those of volcanic arcs. The time and place of formation of these plutonic rocks possibly indicate that they are formed by subduction of the Central-East Iranian Microcontinent (CEIM) – confining oceanic crust beneath the CEIM. AcknowledgmentsThe authors thank the University of Isfahan for financial supports.

The study area is located in the Eastern Alborz zone (Gansser, 1951) which is a part of the northern margin of Gondwana during the Paleozoic (Stöcklin, 1974; Salehi Rad, 1979; Berberian and King, 1981; Şengor, 1990; Alavi, 1991, 1996; Stampfli and Borel, 2002; Allen et al., 2003; Horton et al., 2008; Sinha, 2012, 2013). According to studies conducted by Gansser (1951) and Hubber (1957), the gabbro masses of South Gorgan (Nahar Khuran Valley) belong to the ophiolite collection. Meanwhile, 6km South-East of Galougah city, Gorgan schists have been covered by underlying Jurassic sandstones with s steep discontinuity. The parts resulting from the erosion of Gorgan schists were observed in the sequence conglomerate of the underlying Jurassic. At the beginning of the Ziarat Valley, about 800 meters above the Nahar Khuran, two small tectonic masses (the thickness of about 11 meters) are placed on the layers. These masses are mostly metamorphic. The metamorphic rocks (Gorgan schists), as one of the important geological units in Iran, are mainly formed from low-metamorphic rocks such as slate, phyllite, chlorite schist, greenschist and micaschist along with volcanic rocks and gabbrodiorite masses infiltrating them.

To prepare a geological map of the study area, field sampling and fieldwork were first done from the various units in the region. Over 100 samples were collected from the area. Approximately 70 thin cross-sectional samples of the tectonic rocks of the area were selected from them and investigated using a polarizing microscope. In this paper, 11 points of clinopyroxene were selected for microprobe analysis. The point analysis done on these minerals was conducted using the EPMA method using a microprobe analysis set in the Center of Mineral Processing of Iran (Karaj). The structural formula is calculated using the Excel (Spreadsheet) and dividing them was done by the MinPet 2.02 software package. Given that microprobe analysis is unable to distinguish Fe2+ and Fe3+ and given that it reports total iron as FeO*, it is necessary to separate these two from each other in order to calculate the minerals’ structural formula.

Petrographic studies identified rocks including gabbro, olivine gabbro, monzonite, gabbro to monzogabbro altered, metagabbro, and catalactic porphyry diorite. Mineralogically, these rocks consist of phenocrysts of plagioclase with labradorite composition, clinopyroxene and olivine with accessory minerals of apatite, sphene, biotite, and metal minerals. Secondary minerals are chlorite, sericite, clay mineral and epidote. The dominant textures in these rocks are granular and ophitic. The results of electron microprobe analysis of these clinopyroxenes show that they have augite compositions. In addition, gabbros also mostly show alkaline composition.

To precisely investigate the rocks in the research area, the results of the chemical analyses of minerals were used in determining their petrogenesis. Felsic minerals mainly include altered plagioclase, the main combination of which is labradorite and which is converted to the secondary albite due to hydrothermal alteration processes. The combination of clinopyroxenes available in the volcanic rocks is in Quad range and has a composition of augite. The temperature calculated for the clinopyroxenes in gabbros is 1277.7 to 1353.1°C and the pressure is more than 10 Kbars.  (On the baseline of 3.65kbar per 1km in depth), the formation of clinopyroxenes in the parent magma was over 37km. The primary water content of the gabbro magmas is estimated to have been between 0.5 and 5 wt.%. Distribution of aluminum in tetra and octa positions of clinopyroxenes depends on pressure and the amount of water available in the crystallization environment. Accordingly, the amount of AlIV decreases as the amount of water increases. Tectonomagmatic diagrams suggest that the host rocks are alkaline and are related to volcanic arc setting.

The Gaz Boland area is located in Kerman Province, northwest of Shahr-e-Babak. This area is a part of the volcanic-plutonic belt of Urumieh-Dokhtar. Most of the exposed rocks in this region belong to Eocene age, however, the basalts with Pleio-Pleistocene age have also a relatively limited distribution in the region. The main texture of the basalts is microlithicporphyric and olivine, clinopyroxene and plagioclase form the main minerals. Due to the weathering and alteration processes, secondary minerals such as calcite, chlorite, and iron oxides have formed in these rocks. Based on the analysis of X-ray microprobe, the composition of pyroxenes is diopside-augite. The chemical composition of clinopyroxenes confirms the calc-alkaline nature for their parent magma of, which originates from the subduction-related tectonic setting. Based on clinopyroxene thermobarometric studies, the parent magma of the rocks, when crystallization of the clinopyroxene mineral with approximately 10% water under a pressure of 2 to 8 kbar occured, formed during uplift and before the eruption. The magma temperature variations during the crystallization of clinopyroxenes ranges between 1130 and 1249 °C.

Basaltic volcanic rocks with pillow structures are exposed at the southeasternmost extremity of the Sanandaj-Sirjan zone.They belong to volcanic-sedimentary complexes that formed in a general northwest-southeast to north-south trend. In this research, the mineral chemistry of clinopyroxene and plagioclases are employed to study physicochemical conditions and paleo-tectonic setting during generation of basaltic rock. Basalts with plagioclase and clinopyroxene, as the major constituents, have porphyritic texture, which groundmass marked by fine grained plagioclase, clinopyroxene, apatite, opaque minerals and chloritized glass with intergranular to intersertal textures. Electron probe micro-analyzer (EMPA) data indicate most of the feldspars are calcic plagioclase with bytownite composition and clinopyroxenes are augite. High Al and low- Ti and Fe3+contents in clinopyroxenes show the major role of Tschermak’s components, specially CaAlAlSiO6 and minor presence of acmite component. Low TiO2 and Na2O and high SiO2 content indicate their tholeiitic affinity. Based on thermobarometric approaches Mata clinopyroxenes were formed at temperatures of about 1150-1200 ˚C and pressures in the range of 5–6 kbars, which approximately corresponds to a crystallization depth of 15-18 km. Clinopyroxenes have geochemical characteristics similar to ones generated in an extensional environment related to back-arc basin setting.

The Upper Triassic gabbroic bodies of Dehsard is located in southwest of Kerman in the southern parts of the Sanandaj-Sirjan zone. According to field observation and petrographic studies, the mafic bodies consist of hornblende gabbro. The studied gabbroic bodies are composed of plagioclase, clinopyroxene, amphibole, titanite, apatite, epidote and chlorite. Mineral chemistry studies reveal that the composition of plagioclase is albite-oligoclase and clinopyroxenes have diopsidic composition. The clinopyroxenes are classified as Ca-Mg and Fe clinopyroxenes. The amphiboles belong to calcic amphiboles group (magnesio-hornblende and actinolite). The geothermometry studies of the clinopyroxene and amphibole of the studied hornblende gabbro display that these rocks have crystalized at temperature of 1000 to 1200°C. The geobarometry of studied clinopyroxene estimate the crystallization of gabbroic rocks occurred in 2.05-5.58 kb, equivalent 14 km depth. The chemical compositions of the clinopyroxene and the amphiboles show the minerals have crystallized from a subalkaline- calcalkaline magma. The tectonic setting of these magmas are volcanic arc that are derived from the subduction zone.

Basalts in the Gasht-Masuleh area crop out in the SW Fuman, Gilan Province, and are exposed in the Jurassic and Late Cretaceous units in this area. Whole rock chemistry shows that the rock samples have Mg numbers between 30 and 31.7. Rare earth element patterns (REE) indicate light REE (LREE) enrichment and heavy REE (HREE) depletion (LaN/YbN= 7.7-9.8). Nb, Ta and Ti negative anomalies in primitive mantle normalized multi-element diagrams indicate the formation of parent melt in an arc-related tectonic setting. Clinopyroxene phenocrysts have diopside compositions, crystallized from a calc-alkaline basic parent melt in an extensional tectonic setting. These geochemical features indicate that the basalts of the Gasht-Masuleh area probably formed in an extensional related tectonic setting and inherited their arc signatures from a previous subduction event, possibly of the Paleo-Tethys Ocean crust subduction.

The study area known as ‘Chahar-Dahaneh’ is part of the Iranian southeast ophiolites related to Alpian-Himalayan Mesozoic orogeny belt, and is located in the western margin of the Makran subduction zone. Chahar Dahaneh peridotite section consists of three major lithologies including: 1.dunite lenses 2. harzburgites and 3. Lherzolite. Based on electron microprobe analysis ,we estimated pressure of 5kb with 10%wt H2O for magma with temperature of about 1150-1200C for the origin of clinopyroxene crystallization and chrome spinels are ferrian palenaste in composition. Enrichment of Al3+ ratio to Fe3+ in spinels from lehrzolites suggest that they formed in lower oxygen fugacity and higher pressure than those spinels in dunites and olivines are forsterite in type with  88-91 Mg#. Based on microprobe datas, Chahar Dahaneh peridotites are related to back arc metasomatised mantle in SSZ tectonic setting.

The Horjand area is located in northeast of Kerman in the Central Iran zone and the Kashmar-Kerman tectonic belt. In this area, gabbroic rocks and doleritic dykes are intruded into the sedimentary rocks of Desu Series with Infra-Cambrian age. The gabbros and doleritic dykes have relatively same composition. The main minerals are plagioclase and clinopyroxene. Their texture is medium to fine granular and ophitic to sub-ophitic. The plagioclase minerals of the rocks have labradorite composition (An53-67), but as a result of saussuritization in gabbros and doleritic dykes, the plagioclase changed to oligoclase and albite composition, respectively. The mineral chemistry of clinopyroxenes display Mg-Ca-Fe type which are diopside and augite. The distribution of aluminum in clinopyroxenes structure show that the minerals were crystallized from a magma with water vapor pressure less than 10 percent. On the basis of the chemical charaterstions of the clinopyroxenes, the magma source has predominantly had tholeiitic to minor alkaline affinities with a tectonic setting related to within plate environments. Geothermobarometry evaluations of the clinopyroxenes reveal that the mafic rocks were formed at temperatures of 1127-1200 ˚C and pressure less than 6 Kbar.

Fathabad area is located in northwest of the city of Zarand (Kerman province) in the Posht-e-Badam block of the central Iran structural zone. The Ordovician–Silurian gabbroic stocks have intruded into volcanic-sedimentary rocks of the Rizu series. The gabbros are mainly composed of clinopyroxene, kaersutite, plagioclase and biotite. Electron microprobe analyses demonstrate that the clinopyroxenes are aluminous diopside with alkaline-to-peralkaline affinity. Thermobarometry studies reveal a temperature ranging between 1121°C to 1184°C for the formation of clinopyroxene, in which the pressure varies from 6 to 11 kb. The chemical composition of clinopyroxene grains exhibit their association with oceanic island basalts that are related to intraplate rift environments. It seems that the Fathabad alkalic gabbroic stocks are related to the Ordovician–Silurian Paleo-Tethys rifting events that were emplaced during the back-arc extension in the northern margin of the Gondwana supercontinent.

The exposed volcanic rocks in south west of the Khoy area consist of basalts with minor amounts of plagioclase-phyric basalts. These rocks are composed of clinopyroxene plus plagioclase and plagioclase phenocrysts, respectively. The basaltic rocks are highly altered and contains high amounts of secondary minerals mainly chlorite and epidote. According to mineral chemistry, the composition of clinopyroxenes varies from diopside to augite. The clinopyroxenes are characterized by normal zoning and were formed from a primitive subalkaline magma. The studied clinopyroxenes were crystalized at pressure of 2 to 5 kbars, temperature ranging from 1100- 1150 °C and high oxygen fugacity. On the tectonic setting discrimination diagrams, the south west of Khoy basalts plot mainly in the areas of overlap between IAT, BABA and MORB. The comparison between studied basalts and basaltic rocks in the Khoy ophiolitic complex reveal that the south west of Khoy basalts might have been formed in back- arc basin settings.

The Ahmadabad, Tahmoures and Ghareh-toreh volcanoes are part of the volcanic centers located on the Qorveh-Bijar axis and constitute a part of the magmatic outcrops of the northern arm of the Sanandaj Sirjan Zone, Hamadan-Tabriz. Volcanic rocks have basaltic composition and show porphyritic, microlithic porphyry and glomeroporphyritic textures. Major phenocrysts include clinopyroxene and olivine. The abundance of clinopyroxene is found to be lower in Ghareh-toreh basalts, olivine is major phenocryst in this center. Clinopyroxene phenocrysts show normal, in some cases, reverse zoning and gulf corrosion indicating disequilibrium with the host's melt. The results of thermobarometric calculation (temperature and pressure) using clinopyroxene mineral indicate the temperatures of 1100-11300 °C and pressures of 3 to 11 kbar for Ahmadabad and Tahmoures volcanoes, and volcanic basalts at Ghareh-toreh reveal the temperature of 800 Up to 1100 °C and pressure of 0 to 3 kbar. The high oxygen fugacity in these rocks and the coherence of the temperature and pressure of the olivine phenocryst in this region with the temperature and pressure of the clinopyroxene in Ahmedabad and Tahmoures, all show that clinopyroxene crystals of Ghareh-toreh volcano formed at a lower depth and possibly in a shallow reservoir

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.

With the east–west exposure trend, Peshtasar basalts are in the sedimentary basin of Moghan (Talesh structural zone), in the northwest of Iran.The Peshtasar complex lithologically includes basalt, andesitic basalt or basaltic andesite, megaporphyric andesite, leucite tephrite and volcanic breccia. The main constituent minerals are plagioclase, clinopyroxene, and iddingsitized olivine in basalts and plagioclase megacryst, clinopyroxene, and leucite in tephrite. The results of the microprobe analyses of clinopyroxene reveal the diopside composition. Clinopyroxenes of Peshtasar basalts have igneous nature originated from alkaline and continental magmatic serries. The results of termobarometry studies indicate the crystallization range from 800 -1200 degrees centigrade and crystallization pressure less than 5 kb. There was no water in composition of the parent magma of these rocks. The titanium contents of clinopyroxenes were low, indicating the presence of titano-magnetite (opaque minerals) in the rock. The ferric iron values in clinopyroxenes represents a high oxygen fugacity of magma.

The Seranjic skarn occurs as invading of Late Jurassic intrusive body with granite composition within impure carbonate rocks. Field observation and mineralogical investigations show the exoskarn is the most widespread skarn in the Seranjic skarn and is mostly calcic skarn together with magnesium skarn as a narrow marginal zone. The mineral assemblages indicate two stages of evolutions: the prograde and the retrograde stages. The prograde stage is characterized by garnet and clinopyroxene. The texture evidences and EPMA chemical analysis of clinopyroxene and garnet show two types of clinopyroxene and three types of garnet in various zones during the prograde skarn. Type 1 clinopyroxene show salitic (Hd27-40 Di58-51 Jo8-14) and ferrosalitic (Hd58-75 Di27-16 Jo8-13) compositions in the forsterite- clinopyroxene and garnet- vesuvianite- clinopyroxene zones respectively. Type 2 clinopyroxene has the intermediate compositions of salitic and ferrosalitic (Hd36-48 Di43-51 Jo7-12) in the garnet- vesuvianite- clinopyroxene zone, which is accompanied by scheelite crystallization. Garnet mostly occurred in the center near the exoskarn zones to the plutonic body. Type 1 garnet is characterized by grossular-rich granditic composition (Grs65 And25 to Grs45 And40) with pyralspite< 10 mol percent, and the textural evidences show coexisting type 1 garnet and type 1 clinopyroxene that is widespread in the garnet- vesuvianite- clinopyroxene zone. Type 2 garnet (Grs50 And25 Pyr25 to Grs45 And20 Pyr35) and type 3 garnet (Grs70 Pyr30 to Grs60 Pyr40) have the highly pyralspite and occurs as proximal zones from the plutonic bodies. Based on mineral assemblages, the formation of type 1 garnet, comparative to type 2 and type 3 garnet, is in more oxidized condition in the distal zones of the skarn. Moreover, garnet/clinopyroxene ratios observed at the skarn is affected by the F high volume of magma-fluid. Also, the abundance of F in the volatile phase is probably largely responsible for the abundance of F-bearing minerals, such as vesuvianite, and the scarcity of pyroxene in the skarn. Composition of the variation types of clinopyroxene and garnet show the prograde skarn can be stable at relatively oxidized to relatively reduced and LogfO2 = -18 to -30.

The studied area is situated in northeast Varzeghan in East Azerbaijan Province. In the classification of the structural unites of Iran, this area is a part of Ahar-Arasbaran magmatic arc. The Cenozoic magmatism in the Ahar-Arasbaran region started in the Eocene with an intensive volcanic activity that produced widespread basic to felsic rocks and continued in the Oligo-Miocene with the emplacement of large granitoid plutons. The Plio-Quaternary basaltic and trachyandesitic rocks cover the older magmatic units, particularly in the Varzaghan area. This Quaternary alkaline volcanism in northwest Iran occurred after late Miocene calc-alkaline magmatism.

Minerals from representative samples were analyzed at University of Tasmania (UTAS), Australia with a Cameca Sx-100 electron microprobe with combined WDS and EDS systems. A range of natural minerals were used as standards. The microprobe operated with a 5μm beam diameter, an accelerating voltage of 20 kV and a beam current of 15 nA. Precision, as indicated by replicate determinations on an in-house standard, was better than 2% for the major elements.

Volcanic rocks consist of alkali basalts, trachybasalts , basaltic tracyandesite, tracyandesite, andesite, dacite and rhyodacite. Alkali basalts and trachybasalts display microlithic porphyritic texture with phenocrysts of Chrysolite (XFo: 0.74-0.8), Diopside and Augite (Wo42-48، En37-45، Fs10-16), and plagioclase (XAn: 31-93) in microlithic groundmass. The Olivine composition shows that these minerals are not in equilibrium with liquids similar to the whole-rock composition.  According to melt and clinopyroxene compositions and olivine and clinopyroxene -melt equilibrium, estimated crystallization temperature varies between 1170 C to ~1270 C. The equilibrium pressure calculated using clinopyroxene compositions is close to 8kbar which corresponds to an approximate depth of ~25 km.

The clinopyroxene compositions of the basic rocks display an alkaline nature which indicates an extensional setting. Also, clinopyroxene compositions indicate that parental magma this rocks origin from enriched and primitive source. The petrographic and mineral chemistry evidences reveal that magma evolution processes have been occurred in open-system thermodynamics and fractional crystallization has played the most vital role in the evolution of basaltic magma.