University of Isfahan Petrological Journal 2228-5210 15 1 2024 04 20 Cenozoic magmatism petrogenesis and evolution in the Sangan mining district: using zircon mineral chemistry Cenozoic magmatism petrogenesis and evolution in the Sangan mining district: using zircon mineral chemistry 1 58 27445 10.22108/ijp.2023.136429.1290 FA Majid Ghasemi Siani ِAssociate Professor, Department of Geochemistry, Faculty of Earth Sciences, Kharazmi University, Tehran, Iran Behzad Mehrabi Professor, Department of Geochemistry, Faculty of Earth Sciences, Kharazmi University, Tehran, Iran 0000-0002-8184-1623 Franz Neubauer Professor, Department of Environment and Biodiversity, Geology Division, Paris-Lodron-University of Salzburg, A-5020 Salzburg, Austria Journal Article 2023 01 12 Zircon is a significant mineral due to its ubiquitous occurrence, chemically resistant and refractory, that can survive both weathering and transport processes as well as high-temperature metamorphism and anatexis (Ballard et al., 2002). It can, therefore, be found in many igneous, metamorphic, and sedimentary rocks and is particularly common in plutonic rocks. Zircon acts as a valuable archive of geochemical information regarding geochronology studies (Hoskin and Schaltegger, 2003), a record of the parent rock oxygen isotopic ratio (Hawkesworth and Kemp, 2006), provide a proxy for processes such as crustal recycling by Hf isotopic composition (Scherer et al., 2007), reflect the oxidation state of parent magma by Ce and Eu anomalies (Trail et al., 2012), and temperature estimation by Ti content (Hofmann et al., 2014). The Sangan mining district, the largest skarn iron ore district in Iran, is located in the northeastern part of the Alborz Magmatic Arc. Fourteen skarn anomalies occur along the contact of the syenite to the syenogranite Sarnowsar pluton in the north and the Sarkhar and the Bermani plutons in the southeast (Mehrabi et al., 2021). Previous works have used the zircon U–Pb geochronology, whole rock geochemistry, and zircon chemistry to constrain the emplacement age, fertility of magmatism, and petrogenesis of these granites (Malekzadeh Shafaroudi et al., 2013; Golmohammadi et al., 2015; Mazhari et al., 2017; Mehrabi et al., 2021; Ghasemi Siani et al., 2022), but neglected the importance of zircon trace element concentrations when interpreting the parental magma evolution. Here, we examine the trace elements of zircons from Sarnowsar and Sarkhar-Bermani intrusions, to verify the origin of these zircons and the evolution of the parent magma. Regional Geology The oldest rocks in the Sangan mining district include weakly metamorphosed Precambrian slates and metasiltstones. The Lower Jurassic Shemshak Formation consists of chert, weakly metamorphosed and metasomatized shale, siltstone, and red sandstone. The Middle Jurassic rocks are characterized by limestones and marls of the Dalichay Formation. The overlying Upper Jurassic Lar Formation composed of limestone, dolostone, and dolomitic limestone. Cretaceous formations are dominated by massive limestone, conglomerate, and intercalated crystal tuff. These metasedimentary formations are uncomfortably covered by the intermediate to felsic volcanic rocks crosscutting by plutonic rocks. Intermediate to felsic volcanic rocks cover an area of 10 km2 in the southwestern part of the Sangan mining district and extended within central ore bodies. Volcanic rocks include dacite, andesite, rhyolite, latite, and their pyroclastic equivalents. Analytical methods Zircon from Sarkhar and Bermani granitoids were analyzed at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, using a laser ablation system, ICP-MS instrument (Agilent 7700a ICP-MS instrument). Also, samples from Sarnowsar granitoids were analyzed at the Nanjing Hongchuang Geological Exploration Technology Service Co. Ltd., China. Zircons were analyzed for trace elements using a laser energy density of 3.6 J/cm2, a spot size of 30 μm, and a repetition rate of 5 Hz. Results Analytical data of zircon trace element concentrate are presented in the supplementary Table. Results are plotted against the 206Pb/238U date for each zircon grain. Zircons from the intrusions have scattered geochemical signatures that show no correlation with U–Pb dates. Conversely, some geochemical parameters of zircons from the intrusive rocks show distinct temporal trends. For example, zircon Yb/Dy and Ce/Nd values broadly increase with age younging. It should be noted that the Th/U and Ce/Nd of the Sarnowsar zircons are higher than those of Sarkhar and Bermani intrusions. Discussion Correlations between rock type and the trace element compositions of zircon from a wide range of igneous rocks can be illustrated with a series of discriminant plots. For example, plots of Nb vs. Ta, Y versus Yb/Sm, and Y vs. Ce/Ce* and similar plots (Belousova et al., 2002) indicate that the studied zircons are classified as granitoid igneous type as a parental magma. The uniformly high Hf contents of zircons in this study point to their crystallization derived from a more evolved felsic magma, particularly Sarkhar and Bermani intrusions. The accompanying low Eu/Eu* ratios are indicative of plagioclase crystallization. The U/Yb ratio of zircons can be used to distinguish their origin (Grimes et al., 2015). Continental-arc zircons have U/Yb ratios mostly between 0.1 and 4, and low U/Yb ratios (<0.1) are characteristic of zircons derived from a mantle source. In the discrimination diagrams of U/Yb vs. Hf and U vs. Yb, all the obtained data are plotted in the continental-series area and are distinguishable from ocean crust zircons. In the U/Yb versus Nb/Yb diagram, both the whole-rock and zircon compositions show the characteristics of a magmatic-arc array. Overall, a continental-crust source for the zircons, mirroring the origin of the parent magma. The disparate geochemical behaviors of Hf, Th, and Nb within zircon provide a potential method for establishing the tectonic setting of host magma. The Nb content of arc magmas is depleted relative to magmas formed in within-plate settings (Pearce and Peat 1995), and as such, arc zircons possess lower Nb/Hf and higher Th/Nb ratios at a comparable degree of magmatic fractionation. Accordingly, bivariate discrimination diagrams of Th/U vs. Nb/Hf and Th/Nb vs. Hf/Th are meaningful tools for distinguishing within-plate (anorogenic) from arc-related (orogenic) settings (Hawkesworth and Kemp, 2006). The majority of zircons are plotted in the orogenic field, signifying a magmatic-arc or orogenic setting and a calc-alkaline parent magma. Conclusion Based on the trace-element composition of zircon grains, whole-rock trace-element contents, and patterns of two granitoid intrusions in the Sangan mining district, the following conclusions can be drawn: - The disparate geochemical behaviors of U, Hf, Th, and Nb indicate a continental-crust source in a magmatic-arc tectonic setting. - All of the studied zircons are located in the granitoid igneous rocks fields with a series of discriminant plots. - The studied zircon grains of the Sarnowsar show relatively high Ce4+/Ce3+ ratios, pointing to their formation in an oxidized magmatic medium. Zircon is a significant mineral due to its ubiquitous occurrence, chemically resistant and refractory, that can survive both weathering and transport processes as well as high-temperature metamorphism and anatexis (Ballard et al., 2002). It can, therefore, be found in many igneous, metamorphic, and sedimentary rocks and is particularly common in plutonic rocks. Zircon acts as a valuable archive of geochemical information regarding geochronology studies (Hoskin and Schaltegger, 2003), a record of the parent rock oxygen isotopic ratio (Hawkesworth and Kemp, 2006), provide a proxy for processes such as crustal recycling by Hf isotopic composition (Scherer et al., 2007), reflect the oxidation state of parent magma by Ce and Eu anomalies (Trail et al., 2012), and temperature estimation by Ti content (Hofmann et al., 2014). The Sangan mining district, the largest skarn iron ore district in Iran, is located in the northeastern part of the Alborz Magmatic Arc. Fourteen skarn anomalies occur along the contact of the syenite to the syenogranite Sarnowsar pluton in the north and the Sarkhar and the Bermani plutons in the southeast (Mehrabi et al., 2021). Previous works have used the zircon U–Pb geochronology, whole rock geochemistry, and zircon chemistry to constrain the emplacement age, fertility of magmatism, and petrogenesis of these granites (Malekzadeh Shafaroudi et al., 2013; Golmohammadi et al., 2015; Mazhari et al., 2017; Mehrabi et al., 2021; Ghasemi Siani et al., 2022), but neglected the importance of zircon trace element concentrations when interpreting the parental magma evolution. Here, we examine the trace elements of zircons from Sarnowsar and Sarkhar-Bermani intrusions, to verify the origin of these zircons and the evolution of the parent magma. Regional Geology The oldest rocks in the Sangan mining district include weakly metamorphosed Precambrian slates and metasiltstones. The Lower Jurassic Shemshak Formation consists of chert, weakly metamorphosed and metasomatized shale, siltstone, and red sandstone. The Middle Jurassic rocks are characterized by limestones and marls of the Dalichay Formation. The overlying Upper Jurassic Lar Formation composed of limestone, dolostone, and dolomitic limestone. Cretaceous formations are dominated by massive limestone, conglomerate, and intercalated crystal tuff. These metasedimentary formations are uncomfortably covered by the intermediate to felsic volcanic rocks crosscutting by plutonic rocks. Intermediate to felsic volcanic rocks cover an area of 10 km2 in the southwestern part of the Sangan mining district and extended within central ore bodies. Volcanic rocks include dacite, andesite, rhyolite, latite, and their pyroclastic equivalents. Analytical methods Zircon from Sarkhar and Bermani granitoids were analyzed at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, using a laser ablation system, ICP-MS instrument (Agilent 7700a ICP-MS instrument). Also, samples from Sarnowsar granitoids were analyzed at the Nanjing Hongchuang Geological Exploration Technology Service Co. Ltd., China. Zircons were analyzed for trace elements using a laser energy density of 3.6 J/cm2, a spot size of 30 μm, and a repetition rate of 5 Hz. Results Analytical data of zircon trace element concentrate are presented in the supplementary Table. Results are plotted against the 206Pb/238U date for each zircon grain. Zircons from the intrusions have scattered geochemical signatures that show no correlation with U–Pb dates. Conversely, some geochemical parameters of zircons from the intrusive rocks show distinct temporal trends. For example, zircon Yb/Dy and Ce/Nd values broadly increase with age younging. It should be noted that the Th/U and Ce/Nd of the Sarnowsar zircons are higher than those of Sarkhar and Bermani intrusions. Discussion Correlations between rock type and the trace element compositions of zircon from a wide range of igneous rocks can be illustrated with a series of discriminant plots. For example, plots of Nb vs. Ta, Y versus Yb/Sm, and Y vs. Ce/Ce* and similar plots (Belousova et al., 2002) indicate that the studied zircons are classified as granitoid igneous type as a parental magma. The uniformly high Hf contents of zircons in this study point to their crystallization derived from a more evolved felsic magma, particularly Sarkhar and Bermani intrusions. The accompanying low Eu/Eu* ratios are indicative of plagioclase crystallization. The U/Yb ratio of zircons can be used to distinguish their origin (Grimes et al., 2015). Continental-arc zircons have U/Yb ratios mostly between 0.1 and 4, and low U/Yb ratios (<0.1) are characteristic of zircons derived from a mantle source. In the discrimination diagrams of U/Yb vs. Hf and U vs. Yb, all the obtained data are plotted in the continental-series area and are distinguishable from ocean crust zircons. In the U/Yb versus Nb/Yb diagram, both the whole-rock and zircon compositions show the characteristics of a magmatic-arc array. Overall, a continental-crust source for the zircons, mirroring the origin of the parent magma. The disparate geochemical behaviors of Hf, Th, and Nb within zircon provide a potential method for establishing the tectonic setting of host magma. The Nb content of arc magmas is depleted relative to magmas formed in within-plate settings (Pearce and Peat 1995), and as such, arc zircons possess lower Nb/Hf and higher Th/Nb ratios at a comparable degree of magmatic fractionation. Accordingly, bivariate discrimination diagrams of Th/U vs. Nb/Hf and Th/Nb vs. Hf/Th are meaningful tools for distinguishing within-plate (anorogenic) from arc-related (orogenic) settings (Hawkesworth and Kemp, 2006). The majority of zircons are plotted in the orogenic field, signifying a magmatic-arc or orogenic setting and a calc-alkaline parent magma. Conclusion Based on the trace-element composition of zircon grains, whole-rock trace-element contents, and patterns of two granitoid intrusions in the Sangan mining district, the following conclusions can be drawn: - The disparate geochemical behaviors of U, Hf, Th, and Nb indicate a continental-crust source in a magmatic-arc tectonic setting. - All of the studied zircons are located in the granitoid igneous rocks fields with a series of discriminant plots. - The studied zircon grains of the Sarnowsar show relatively high Ce4+/Ce3+ ratios, pointing to their formation in an oxidized magmatic medium.

https://ijp.ui.ac.ir/article_27445_0d70a17b435a74436a230b9c734bed58.pdf

University of Isfahan Petrological Journal 2228-5210 15 1 2024 04 20 Mineral chemistry and thermobarometry of gabbroic rocks from the Pargeh area (NE Qazvin): A key for understanding the crystallization conditions Mineral chemistry and thermobarometry of gabbroic rocks from the Pargeh area (NE Qazvin): A key for understanding the crystallization conditions 59 84 27722 10.22108/ijp.2023.137922.1303 FA Nahid Naseri Ph.D. Student, Department of Geology, Faculty of Sciences, Lorestan University, Khorramabad, Iran, Reza Zarei Sahamieh Professor, Department of Geology, Faculty of Sciences, Lorestan University, Khorramabad, Iran, Matthew Leybourne Professor, Queen’s Facility for Isotope Research, Department of Geological Sciences and Geological Engineering, Queen’s University, Kingston, Ontario, Canada K7L 3N6, Anderson Costa Dos Santos Professor, Rio de Janeiro State University (UERJ), Geology Faculty, Departamento de Mineralogia e Petrologia Ígnea (DMPI), Brazil, Ahmad Ahamadi Khalaji Associate Professor, Department of Geology, Faculty of Sciences, Lorestan University, Khorramabad, Iran, Journal Article 2023 06 04 Introduction Mineral chemistry data as well as petrography provide a comprehensive picture of magma crystallization conditions that support the conclusions based on geochemical data. In addition, the chemical composition of minerals such as clinopyroxene, olivine, biotite, feldspar, and Fe-Ti oxides reflect physicochemical parameters (pressure, temperature, and oxygen fugacity), crystal growth history, and melt origin. The pressure, temperature and oxygen fugacity parameters are estimated from chemical data of various rock-forming minerals to provide information regarding the crystallization of magmas. The essential purposes of present study are to determine the physicochemical conditions (temperature and pressure), to identify the tectonic environment and to propose an emplacement model for Pargeh mafic magmas formation. Regional Geology The Pargeh area is a part of the Central Alborz Magmatic Belt (AMB) (Figure 1). There are extensive magmatic sections in this zone including the Cenozoic calc-alkaline and alkaline (potassic) magmatism generated in an arc and back-arc setting in an extensional environment (post collision). This belt is mainly composed of Upper Precambrian to Eocene sedimentary and volcanic sequences intruded by Mesozoic to Cenozoic plutons, in the central and western parts of the belt. The igneous rocks of the north and northeast of Qazvin were formed during three volcanic phases, of which only two phases can be seen in the study area. These Late Eocene-Oligo-Miocene plutonic rocks are related to post-collisional magmatic activities originated in back-arc extensional basins and have calc-alkaline to high-potassium shoshonitic characteristics. According to U–Pb dating, the age of the syenite and monzonite rocks is Late Eocene. But the exact age of the Pargeh gabbroic rocks is not known, considering that these intrusions were injected into Eocene tuffs, they are Late Eocene and possibly Oligocene. Analytical Methods The main minerals were analyzed by an electron microprobe at the Queen’s Facility for Isotope Research (QFIR), Queens University, Kingston, Canada. Operating conditions were as follows: the acceleration voltage was 15 kV, the beam current was 20 nA, and the diameter of the probe was 3 µm (Tables 1 to 6). Petrography Field and petrographic observation show that most of the Pargeh pluton is monzogabbro and olivine gabbros make up only a small part of the pluton. Olivine gabbro is a medium- to coarse-grained mesocratic-melanocratic rock. Olivine gabbro and monzogabbro are texturally varied. In both samples, intergranular, poikilitic, sub-ophitic and granular textures were identified. Olivine gabbro are dominated by olivine (20-25%vol), clinopyroxene (15-20 %vol), plagioclase (50-55 %vol), biotite (~ 5 %vol) and K-feldspar (~ 5 %vol). Accessory minerals include apatite and Fe-Ti oxides. Monzogabbros are characterized by a high proportion of plagioclase (55-60 %vol) and clinopyroxene (20-25 %vol), biotite (5-10%vol) and K-feldspar (8-10%vol).. Fe-Ti oxides and apatite are common accessory minerals in monzogabbros. Discussion Based on research on the distribution of Ti in silicates and oxides of magmatic rocks, Verhoogen (1962) proposed that the crystallization temperature of clinopyroxene is positively correlated with its Ti content. Therefore, the higher clinopyroxene, crystallization temperature, the more Ti clinopyroxene likely to contain. The TiO2 content of clinopyroxenes in olivine gabbros is slightly higher than that of monzogabbros, pointing to the clinopyroxenes in olivine gabbro having a relatively higher crystallization temperature compared to that of clinopyroxenes in monzogabbro. In the 9-A and B diagram, all the samples are in the range of alkaline basalt, so the parental magma can be an alkaline magma. As mentioned above, clinopyroxenes have high amounts of Al and Ti, consistent with the evolution of an alkaline magma. High amounts of calcium in the studied clinopyroxenes indicate that the parental magma may have an alkaline nature. This tectonic setting discrimination diagram can distinguish basaltic clinopyroxenes from volcanic arc basalt (VAB), ocean floor basalt (OFB), intraplate tholeiite (WPT) and intraplate alkaline environments (WPA). In the F1-F2 tectonic environment discrimination diagram, all the study samples fall within the range of volcanic arc basalts (VAB+OFB), which shows that these rocks are probably formed in a volcanic arc and arc-related tectonic setting environment. In general, all tectonic discrimination diagrams based on clinopyroxene chemistry indicate an arc-related environment for the parental magma. Conclusion The mafic rocks of Pargeh are composed of olivine gabbro and monzogabbro which are characterized by the presence of olivine, plagioclase, clinopyroxene, biotite and K-feldspar. The mineral chemistry results show the role of fractional crystallization as the main process in the formation of the parental magma of the rocks under study The chemical features of clinopyroxenes point that the parental magma must belong to a silica under-saturated alkaline series, characterized by high temperature, low pressure, low Si and high Ca contents possibly formed in a volcanic arc tectonic setting environment. As the xamined thermobarometers data show, the olivine gabbros generated at higher temperature and pressure than that of monzogabbros indicating that the olivine gabbros probably crystallized at a greater depth. Introduction Mineral chemistry data as well as petrography provide a comprehensive picture of magma crystallization conditions that support the conclusions based on geochemical data. In addition, the chemical composition of minerals such as clinopyroxene, olivine, biotite, feldspar, and Fe-Ti oxides reflect physicochemical parameters (pressure, temperature, and oxygen fugacity), crystal growth history, and melt origin. The pressure, temperature and oxygen fugacity parameters are estimated from chemical data of various rock-forming minerals to provide information regarding the crystallization of magmas. The essential purposes of present study are to determine the physicochemical conditions (temperature and pressure), to identify the tectonic environment and to propose an emplacement model for Pargeh mafic magmas formation. Regional Geology The Pargeh area is a part of the Central Alborz Magmatic Belt (AMB) (Figure 1). There are extensive magmatic sections in this zone including the Cenozoic calc-alkaline and alkaline (potassic) magmatism generated in an arc and back-arc setting in an extensional environment (post collision). This belt is mainly composed of Upper Precambrian to Eocene sedimentary and volcanic sequences intruded by Mesozoic to Cenozoic plutons, in the central and western parts of the belt. The igneous rocks of the north and northeast of Qazvin were formed during three volcanic phases, of which only two phases can be seen in the study area. These Late Eocene-Oligo-Miocene plutonic rocks are related to post-collisional magmatic activities originated in back-arc extensional basins and have calc-alkaline to high-potassium shoshonitic characteristics. According to U–Pb dating, the age of the syenite and monzonite rocks is Late Eocene. But the exact age of the Pargeh gabbroic rocks is not known, considering that these intrusions were injected into Eocene tuffs, they are Late Eocene and possibly Oligocene. Analytical Methods The main minerals were analyzed by an electron microprobe at the Queen’s Facility for Isotope Research (QFIR), Queens University, Kingston, Canada. Operating conditions were as follows: the acceleration voltage was 15 kV, the beam current was 20 nA, and the diameter of the probe was 3 µm (Tables 1 to 6). Petrography Field and petrographic observation show that most of the Pargeh pluton is monzogabbro and olivine gabbros make up only a small part of the pluton. Olivine gabbro is a medium- to coarse-grained mesocratic-melanocratic rock. Olivine gabbro and monzogabbro are texturally varied. In both samples, intergranular, poikilitic, sub-ophitic and granular textures were identified. Olivine gabbro are dominated by olivine (20-25%vol), clinopyroxene (15-20 %vol), plagioclase (50-55 %vol), biotite (~ 5 %vol) and K-feldspar (~ 5 %vol). Accessory minerals include apatite and Fe-Ti oxides. Monzogabbros are characterized by a high proportion of plagioclase (55-60 %vol) and clinopyroxene (20-25 %vol), biotite (5-10%vol) and K-feldspar (8-10%vol).. Fe-Ti oxides and apatite are common accessory minerals in monzogabbros. Discussion Based on research on the distribution of Ti in silicates and oxides of magmatic rocks, Verhoogen (1962) proposed that the crystallization temperature of clinopyroxene is positively correlated with its Ti content. Therefore, the higher clinopyroxene, crystallization temperature, the more Ti clinopyroxene likely to contain. The TiO2 content of clinopyroxenes in olivine gabbros is slightly higher than that of monzogabbros, pointing to the clinopyroxenes in olivine gabbro having a relatively higher crystallization temperature compared to that of clinopyroxenes in monzogabbro. In the 9-A and B diagram, all the samples are in the range of alkaline basalt, so the parental magma can be an alkaline magma. As mentioned above, clinopyroxenes have high amounts of Al and Ti, consistent with the evolution of an alkaline magma. High amounts of calcium in the studied clinopyroxenes indicate that the parental magma may have an alkaline nature. This tectonic setting discrimination diagram can distinguish basaltic clinopyroxenes from volcanic arc basalt (VAB), ocean floor basalt (OFB), intraplate tholeiite (WPT) and intraplate alkaline environments (WPA). In the F1-F2 tectonic environment discrimination diagram, all the study samples fall within the range of volcanic arc basalts (VAB+OFB), which shows that these rocks are probably formed in a volcanic arc and arc-related tectonic setting environment. In general, all tectonic discrimination diagrams based on clinopyroxene chemistry indicate an arc-related environment for the parental magma. Conclusion The mafic rocks of Pargeh are composed of olivine gabbro and monzogabbro which are characterized by the presence of olivine, plagioclase, clinopyroxene, biotite and K-feldspar. The mineral chemistry results show the role of fractional crystallization as the main process in the formation of the parental magma of the rocks under study The chemical features of clinopyroxenes point that the parental magma must belong to a silica under-saturated alkaline series, characterized by high temperature, low pressure, low Si and high Ca contents possibly formed in a volcanic arc tectonic setting environment. As the xamined thermobarometers data show, the olivine gabbros generated at higher temperature and pressure than that of monzogabbros indicating that the olivine gabbros probably crystallized at a greater depth.

https://ijp.ui.ac.ir/article_27722_82d2ce94fc22914e4dbb0c786809c681.pdf

University of Isfahan Petrological Journal 2228-5210 15 1 2024 04 20 Geochemistry, petrography, and tectono-magmatic setting of Eocene volcanic lavas in the south of Mamoniyeh, Urumieh-Dokhtar magmatic arc, Markazi Province, Iran Geochemistry, petrography, and tectono-magmatic setting of Eocene volcanic lavas in the south of Mamoniyeh, Urumieh-Dokhtar magmatic arc, Markazi Province, Iran 85 116 28257 10.22108/ijp.2024.139861.1315 FA Mohammad Goudarzi Ph.D. Candidate, Department of Geology, Faculty of Sciences, Lorestan University, Iran, Hassan Zamanian Professor, Department of Geology, Faculty of Science, University of Tehran, Iran, Urs KlÃtzli zamanian.h@lu.ac.ir 3 Professor, Department of Lithospheric Research, Faculty of Earth Sciences, Geography and Astronomy, University of Vienna, Austria, Journal Article 2023 11 20 The study area lies in the south of Mamoniyeh, a part of the Zaviyeh 1:100000 geological map, which covers the middle part of the Urumieh-Dokhtar magmatic arc. The volcanic phases and the intrusive masses constitute the predominant rocks of the area which has been subjected to magmatic and tectonic activities. Thus, owing to the lack of detailed studies on the volcanic rocks of this area, we try to link the tectonic setting and the magmatic evolution of the rocks under study. In addition, magma evolution processes, such as fractional crystallization, crustal contamination, and magma mixing may play an important role in the genesis of these rocks. The present paper presents new petrological and geochemical data on these volcanic rocks, which were formed during the Eocene. The Urumieh Dokhtar Magmatic arc is characterized by a series of volcanic and plutonic rocks that formed during the Late Cretaceous to Early Miocene, approximately 95 to 20 million years ago, and extends for about 2,000 kilometers. The magmatic rocks in the Urumieh Dokhtar Magmatic Arc are lavas, pyroclastic deposits, and plutonic rocks (i.e., granites and diorites) believed to have originated in the course of subduction of the Arabian plate beneath the Eurasian plate. which gave rise to the melting of the mantle. In this area, the Eocene volcanic units have been completely disrupted due to the influx of intrusive masses and high displacement by shear-compressional faulting. Volcanic rocks in the region with over 4 km thick are composed of flows, pyroclastic layers, tuff, and ignimbrite. Regional Geology The Urumieh Dokhtar Magmatic arc is characterized by a series of volcanic and plutonic rocks formed during the Late Cretaceous to Early Miocene, approximately 20 to 95 million years ago, extending for about 2,000 kilometers. The magmatic rocks in Urumieh Dokhtar Magmatic Arc include a variety of lithologies, such as lavas, pyroclastic deposits, and plutonic rocks (i.e., granites and diorites). These rocks were formed as a result of the subduction of the Arabian plate beneath the Eurasian plate, which led to the melting of the mantle and the formation of magma. In this area, the Eocene volcanic units have been completely disrupted due to the influx of intrusive masses and high displacement by shear-compressional faulting. Research methodology Preparation of a 1:20000 geological map of the area, sampling of surface volcanic units, and drilled boreholes were carried out simultaneously. Based on lithological diversity, 50 samples of volcanic rocks were collected, and 15 of those with the least amount of alteration were analyzed by ICP-MS and XRF methods. Using GCDkit software, petrogenesis and the development of the studied volcanic rocks were investigated. Petrography The main rock-forming minerals are plagioclase, K-feldspar, quartz, amphibole, biotite, and pyroxene, with small amount of olivine, apatite, zircon, and Fe-Ti oxides. Minor minerals include opaques, quartz, carbonate, epidote, chlorite, sericite, apatite, sphene, and zircon, accompanied by rare tremolite and actinolite. Fine-grained and idiomorphic apatites as well as short prismatic zircon crystals are found as inclusions in plagioclase. and biotite. respectively. The predominant textures are clastic and porphyritic with trachytic and cryptocrystalline. Also. sieve intergranular, intersertal, hyalomicrolitic hyaloporphyritic, and microgranular are common textures. Geochemistry The amounts of SiO2 and Al2O3 vary from 47 to 73 wt% and from 11.6 to 17.8 wt%, respectively. The total amounts of alkali elements in the investigated samples range from 4.5 to 10.1 wt%. As the different charts of rare elements display the magmatic series of rocks are in the range of basalt-andesite, calc-alkaline series, and dacite-rhyodacite of the calc-alkaline series. The ratios of Nb versus Nb/Zr, Sr/Zr versus Ti/Zr, Rb versus Rb/Sr, and Rb/Sr versus Ti/Zr show the effect of crystal segregation and mixing processes during magma ascent, and the presence of large plagioclase and clinopyroxene crystals also support the hypophysis. In the spider diagram (primitive mantle-normalized multi-element spider) samples show enrichment in large ion lithophile elements (LILE), especially Rb, Ba, K, and Cs and depleted in high field strength elements (HFSE) (i.e., Ti, Yb, and Zr). The positive Pb and K anomaly can be caused by crustal involvement in magmatic processes. On the chondrite-normalized REE diagram, samples show an LREE-enriched and HREE-depleted pattern. The rather flat HREE patterns imply the absence of garnet and /or hornblende in the source of these magmas. The absence of Eu negative anomaly in non-altered volcanic rocks explains the high-water content or oxygen fugacity and an abundance of hornblende, pyroxene, sphene, and garnet may cause a positive Eu anomaly. Discussion and Conclusion Elevated LILE, and LREE, and depleted HFSE content of volcanic rocks in the south of Mamoniyeh indicate the metasomatized asthenospheric mantle source in a subduction zone. The presence of non-equilibrium textures such as sieve texture in plagioclase and opacification of amphiboles are probably related to crustal contamination. Zr/Y>3 ratio in most samples corresponds to a continental volcanic arc rather than the oceanic arc. The available geochemical data show calc-alkaline magmatism occurred by 20 to 45% partial melting of a garnet-spinel lherzolite to spinel lherzolite. Trace elements reveal crustal contamination and magma mixing during the parent magma ascent as well as the role of fluids released from the subducting plate. The subduction-related process, including water and volatile materials released from the subducting slab, resulted in mantle wedge metasomatism and partial melting. This genetic model is consistent with other models suggested for the magmatism along the Urumieh-Dokhtar magmatic arc. Acknowledgments The authors are very grateful to the esteemed referees of Petrological Journal for their valuable suggestions for improving the scientific structure of the article. The study area lies in the south of Mamoniyeh, a part of the Zaviyeh 1:100000 geological map, which covers the middle part of the Urumieh-Dokhtar magmatic arc. The volcanic phases and the intrusive masses constitute the predominant rocks of the area which has been subjected to magmatic and tectonic activities. Thus, owing to the lack of detailed studies on the volcanic rocks of this area, we try to link the tectonic setting and the magmatic evolution of the rocks under study. In addition, magma evolution processes, such as fractional crystallization, crustal contamination, and magma mixing may play an important role in the genesis of these rocks. The present paper presents new petrological and geochemical data on these volcanic rocks, which were formed during the Eocene. The Urumieh Dokhtar Magmatic arc is characterized by a series of volcanic and plutonic rocks that formed during the Late Cretaceous to Early Miocene, approximately 95 to 20 million years ago, and extends for about 2,000 kilometers. The magmatic rocks in the Urumieh Dokhtar Magmatic Arc are lavas, pyroclastic deposits, and plutonic rocks (i.e., granites and diorites) believed to have originated in the course of subduction of the Arabian plate beneath the Eurasian plate. which gave rise to the melting of the mantle. In this area, the Eocene volcanic units have been completely disrupted due to the influx of intrusive masses and high displacement by shear-compressional faulting. Volcanic rocks in the region with over 4 km thick are composed of flows, pyroclastic layers, tuff, and ignimbrite. Regional Geology The Urumieh Dokhtar Magmatic arc is characterized by a series of volcanic and plutonic rocks formed during the Late Cretaceous to Early Miocene, approximately 20 to 95 million years ago, extending for about 2,000 kilometers. The magmatic rocks in Urumieh Dokhtar Magmatic Arc include a variety of lithologies, such as lavas, pyroclastic deposits, and plutonic rocks (i.e., granites and diorites). These rocks were formed as a result of the subduction of the Arabian plate beneath the Eurasian plate, which led to the melting of the mantle and the formation of magma. In this area, the Eocene volcanic units have been completely disrupted due to the influx of intrusive masses and high displacement by shear-compressional faulting. Research methodology Preparation of a 1:20000 geological map of the area, sampling of surface volcanic units, and drilled boreholes were carried out simultaneously. Based on lithological diversity, 50 samples of volcanic rocks were collected, and 15 of those with the least amount of alteration were analyzed by ICP-MS and XRF methods. Using GCDkit software, petrogenesis and the development of the studied volcanic rocks were investigated. Petrography The main rock-forming minerals are plagioclase, K-feldspar, quartz, amphibole, biotite, and pyroxene, with small amount of olivine, apatite, zircon, and Fe-Ti oxides. Minor minerals include opaques, quartz, carbonate, epidote, chlorite, sericite, apatite, sphene, and zircon, accompanied by rare tremolite and actinolite. Fine-grained and idiomorphic apatites as well as short prismatic zircon crystals are found as inclusions in plagioclase. and biotite. respectively. The predominant textures are clastic and porphyritic with trachytic and cryptocrystalline. Also. sieve intergranular, intersertal, hyalomicrolitic hyaloporphyritic, and microgranular are common textures. Geochemistry The amounts of SiO2 and Al2O3 vary from 47 to 73 wt% and from 11.6 to 17.8 wt%, respectively. The total amounts of alkali elements in the investigated samples range from 4.5 to 10.1 wt%. As the different charts of rare elements display the magmatic series of rocks are in the range of basalt-andesite, calc-alkaline series, and dacite-rhyodacite of the calc-alkaline series. The ratios of Nb versus Nb/Zr, Sr/Zr versus Ti/Zr, Rb versus Rb/Sr, and Rb/Sr versus Ti/Zr show the effect of crystal segregation and mixing processes during magma ascent, and the presence of large plagioclase and clinopyroxene crystals also support the hypophysis. In the spider diagram (primitive mantle-normalized multi-element spider) samples show enrichment in large ion lithophile elements (LILE), especially Rb, Ba, K, and Cs and depleted in high field strength elements (HFSE) (i.e., Ti, Yb, and Zr). The positive Pb and K anomaly can be caused by crustal involvement in magmatic processes. On the chondrite-normalized REE diagram, samples show an LREE-enriched and HREE-depleted pattern. The rather flat HREE patterns imply the absence of garnet and /or hornblende in the source of these magmas. The absence of Eu negative anomaly in non-altered volcanic rocks explains the high-water content or oxygen fugacity and an abundance of hornblende, pyroxene, sphene, and garnet may cause a positive Eu anomaly. Discussion and Conclusion Elevated LILE, and LREE, and depleted HFSE content of volcanic rocks in the south of Mamoniyeh indicate the metasomatized asthenospheric mantle source in a subduction zone. The presence of non-equilibrium textures such as sieve texture in plagioclase and opacification of amphiboles are probably related to crustal contamination. Zr/Y>3 ratio in most samples corresponds to a continental volcanic arc rather than the oceanic arc. The available geochemical data show calc-alkaline magmatism occurred by 20 to 45% partial melting of a garnet-spinel lherzolite to spinel lherzolite. Trace elements reveal crustal contamination and magma mixing during the parent magma ascent as well as the role of fluids released from the subducting plate. The subduction-related process, including water and volatile materials released from the subducting slab, resulted in mantle wedge metasomatism and partial melting. This genetic model is consistent with other models suggested for the magmatism along the Urumieh-Dokhtar magmatic arc. Acknowledgments The authors are very grateful to the esteemed referees of Petrological Journal for their valuable suggestions for improving the scientific structure of the article.

https://ijp.ui.ac.ir/article_28257_b90cb9425176f8f19fe355a52c4623d2.pdf

University of Isfahan Petrological Journal 2228-5210 15 1 2024 04 20 Relationship between deformation structure and partial melting in pelitic migmatites of Hamaden region, Sanandaj-Sirjan Zone Relationship between deformation structure and partial melting in pelitic migmatites of Hamaden region, Sanandaj-Sirjan Zone 117 138 28461 10.22108/ijp.2024.140789.1323 FA Seyedeh Razieh Jafari Assistant Professor, Assistant Professor, Department of Geology, Faculty of Sciences, Payam Noor University, Tehran, Iran, Leyli Izadi Kian Assistant Professor, Department of Geology, Faculty of Basic Sciences, Bu-Ali Sina University, Hamadan, Iran, Journal Article 2024 02 22 The present paper describes some field characteristics of deformation in a high-strain and high temperature zone in migmatitic rocks, with several kilometers wide occurring in Hamedan and Toyserkan regions, NW of the Sanandaj- Sirjan Zone. A number of workers believe deformation and metamorphism are closely related. We tried to establish relationships between deformation evidence and rheological contrasts in different parts of migmatites during the migmatization process. In recent years, several studies have been carried out regarding the deformation and tectonic events of the various rocks of Hamedan region. However, this work is the first attempt to establish the relationship between deformation structure and partial melting in the migmatitic rocks of the study region. The obtained data can be used to interpret probable relationship between deformation and metamorphism and to determine the role of rheology of the various rocks in the region. Regional Geology The Sanandaj-Sirjan Zone (SSZ) comprises a metamorphic belt of low- to high-grade regional and contact metamorphic rocks intruded by mafic, intermediate and felsic plutonic bodies. Plutonic rocks of the Alvand complex in the Hamedan region, belonging to middle Jurassic (Shahbazi et al., 2010; Mahmoudi et al., 2011; Chiu et al., 2013), consisting of gabbro-diorite-tonalite association, granite-granodiorite porphyroid, and hololeucocratic granitoids (Sepahi et al., 2019). Major metamorphic rocks events in the SSZ occurred 160-170 Ma (e.g., Sepahi et al., 2019). The metamorphic rocks of the area with different composition and metamorphic grade, are mainly pelites with small bodies of psammites, quartzites, meta-basites, calc-pelites and calc-silicates. During partial melting, some minerals such as cordierite, aluminosilicate (andalusite, sillimanite) and garnet porphyroblasts, in spite of floated, partly remained stable and when the partial melt reached its critical moving threshold, they were re-distributed in the viscous mush (Sepahi et al., 2009). Analytical methods Description of rock units, structural analyses, accurate measurements of parameters (i.e. lineation, boudins, folds, veins) were carried out during field observation. 44 thin sections parallel to lineation and perpendicular to foliation were prepared at the section preparation laboratory of Bu-Ali Sina University, and then their petrography and microstructures were examined and analyzed. The samples are taken from metatexite dominated migmatites as well as diatexite. Mineral abbreviations are taken from Whitney and Evans (2010). Petrography Following pelites the most abundant rocks of the area, slate, phyllite, pelitic schist/migmatite and hornfels are common rocks of the region under study. The migmatite rocks evolved from the hornfelses (metatexite) and schists (diatexite) of the region. The mesosome of schistic migmatites with similar mineralogy with that of the schists, crosscut by abundant granitic pegmatites, aplites, as well as quartz veins. This zone is associated with partial melting and development of granitic leucosomes in migmatites. Plagioclase-bearing leucosomes are predominant, but some contain K-feldspar as well. Melanosomes are less developed and resemble the mesosomes in their mineralogy and texture, except for greater amounts of mafic minerals (i.e. biotite), and smaller amounts of felsic minerals. Partial melting fronts were initiated around various porphyroblasts, especially Al2SiO5 minerals and cordierite, and migrated to other parts of the rocks. During diatexis, garnet and aluminosilicate (andalusite, sillimanite) porphyroblasts remained partly stable but floated and were re-distributed in the viscous mush when the partial melt reached its critical moving threshold. Discussion and Conclusion The essential processes of migmatites formation, are partial melting, metamorphic differentiation and injection of granitic magma. Leucosome layers appear following the peak of metamorphism and partial melting process. In the course of anatexis, with increasing melt fraction, migmatite strength progressively decreases. The boudinage of high temperature metamorphic rocks is significantly controlled by the evolving rheological contrasts between the leucosome (melt) and mesosome of migmatites. The deformation observed in migmatites, occurred on a large scale in the form of folded leucosome and Boudinage, and on a microscale in the form of intracrystalline (undulose extinction, deformation twinning) and intercrystalline deformation (grain boundary migration, protrusion...). Therefore, the folded and boudinated leucosome represent the activity of tectonic forces in the conditions of the peak transformation of the region. The simultaneous adaptation of tectonic processes with the peak of metamorphism created synmigmatites and probably occurred in the catazone segment. While the performance of tectonic processes after cooling and creating post-tectonic fabrics, possibly happened in the mesozone to epizone. Syn to post-tectonic structures have recorded the relationship between the different phases of the involved melt and deformation in the solid state in the area. Synmigmatites can be seen in different parts of Hamedan, such as Simin, Toyserkan, Cheshme Ghasaban and Morad-Beik valley. Deformation occurred following the melt crystallization in the investigated migmatites. According to the structures of boudin, folds and veins, which played an important role in development of dynamic state of migmatites, the rheological evolution of Hamedan migmatites (Simin and Toyserkan regions) can be divided into three stages: (1) deformation during melting, (2) solid state deformation immediately after crystallization, and (3) subsequent solid-state deformation. The present paper describes some field characteristics of deformation in a high-strain and high temperature zone in migmatitic rocks, with several kilometers wide occurring in Hamedan and Toyserkan regions, NW of the Sanandaj- Sirjan Zone. A number of workers believe deformation and metamorphism are closely related. We tried to establish relationships between deformation evidence and rheological contrasts in different parts of migmatites during the migmatization process. In recent years, several studies have been carried out regarding the deformation and tectonic events of the various rocks of Hamedan region. However, this work is the first attempt to establish the relationship between deformation structure and partial melting in the migmatitic rocks of the study region. The obtained data can be used to interpret probable relationship between deformation and metamorphism and to determine the role of rheology of the various rocks in the region. Regional Geology The Sanandaj-Sirjan Zone (SSZ) comprises a metamorphic belt of low- to high-grade regional and contact metamorphic rocks intruded by mafic, intermediate and felsic plutonic bodies. Plutonic rocks of the Alvand complex in the Hamedan region, belonging to middle Jurassic (Shahbazi et al., 2010; Mahmoudi et al., 2011; Chiu et al., 2013), consisting of gabbro-diorite-tonalite association, granite-granodiorite porphyroid, and hololeucocratic granitoids (Sepahi et al., 2019). Major metamorphic rocks events in the SSZ occurred 160-170 Ma (e.g., Sepahi et al., 2019). The metamorphic rocks of the area with different composition and metamorphic grade, are mainly pelites with small bodies of psammites, quartzites, meta-basites, calc-pelites and calc-silicates. During partial melting, some minerals such as cordierite, aluminosilicate (andalusite, sillimanite) and garnet porphyroblasts, in spite of floated, partly remained stable and when the partial melt reached its critical moving threshold, they were re-distributed in the viscous mush (Sepahi et al., 2009). Analytical methods Description of rock units, structural analyses, accurate measurements of parameters (i.e. lineation, boudins, folds, veins) were carried out during field observation. 44 thin sections parallel to lineation and perpendicular to foliation were prepared at the section preparation laboratory of Bu-Ali Sina University, and then their petrography and microstructures were examined and analyzed. The samples are taken from metatexite dominated migmatites as well as diatexite. Mineral abbreviations are taken from Whitney and Evans (2010). Petrography Following pelites the most abundant rocks of the area, slate, phyllite, pelitic schist/migmatite and hornfels are common rocks of the region under study. The migmatite rocks evolved from the hornfelses (metatexite) and schists (diatexite) of the region. The mesosome of schistic migmatites with similar mineralogy with that of the schists, crosscut by abundant granitic pegmatites, aplites, as well as quartz veins. This zone is associated with partial melting and development of granitic leucosomes in migmatites. Plagioclase-bearing leucosomes are predominant, but some contain K-feldspar as well. Melanosomes are less developed and resemble the mesosomes in their mineralogy and texture, except for greater amounts of mafic minerals (i.e. biotite), and smaller amounts of felsic minerals. Partial melting fronts were initiated around various porphyroblasts, especially Al2SiO5 minerals and cordierite, and migrated to other parts of the rocks. During diatexis, garnet and aluminosilicate (andalusite, sillimanite) porphyroblasts remained partly stable but floated and were re-distributed in the viscous mush when the partial melt reached its critical moving threshold. Discussion and Conclusion The essential processes of migmatites formation, are partial melting, metamorphic differentiation and injection of granitic magma. Leucosome layers appear following the peak of metamorphism and partial melting process. In the course of anatexis, with increasing melt fraction, migmatite strength progressively decreases. The boudinage of high temperature metamorphic rocks is significantly controlled by the evolving rheological contrasts between the leucosome (melt) and mesosome of migmatites. The deformation observed in migmatites, occurred on a large scale in the form of folded leucosome and Boudinage, and on a microscale in the form of intracrystalline (undulose extinction, deformation twinning) and intercrystalline deformation (grain boundary migration, protrusion...). Therefore, the folded and boudinated leucosome represent the activity of tectonic forces in the conditions of the peak transformation of the region. The simultaneous adaptation of tectonic processes with the peak of metamorphism created synmigmatites and probably occurred in the catazone segment. While the performance of tectonic processes after cooling and creating post-tectonic fabrics, possibly happened in the mesozone to epizone. Syn to post-tectonic structures have recorded the relationship between the different phases of the involved melt and deformation in the solid state in the area. Synmigmatites can be seen in different parts of Hamedan, such as Simin, Toyserkan, Cheshme Ghasaban and Morad-Beik valley. Deformation occurred following the melt crystallization in the investigated migmatites. According to the structures of boudin, folds and veins, which played an important role in development of dynamic state of migmatites, the rheological evolution of Hamedan migmatites (Simin and Toyserkan regions) can be divided into three stages: (1) deformation during melting, (2) solid state deformation immediately after crystallization, and (3) subsequent solid-state deformation.

https://ijp.ui.ac.ir/article_28461_01bfd7ba2325664b4bd49f48aae2df81.pdf

University of Isfahan Petrological Journal 2228-5210 15 1 2024 04 20 Mineral chemistry and geochemistry of Kabbarik syenite stock, North of Zanjan Mineral chemistry and geochemistry of Kabbarik syenite stock, North of Zanjan 139 158 28762 10.22108/ijp.2023.136589.1292 FA Alireza Ravankhah Assistant Professor, Department of Geology, Faculty of Sciences, University of Mohaghegh Ardabili, Ardabil, Iran, Mohsen Moayyed Professor, Earth Science Department, Natural Sciences Faculty, University of Tabriz, Tabriz, Iran, Mohammadali Shirinzadeh M.Sc. in Exploration Mining Engineering, Arak University, Arak, Iran, Journal Article 2023 01 29 The study area, Tarom, is situated in northwestern Iran, within the Zanjan province. Geologically, it falls within the western Alborz zone, a volcanic-plutonic belt, oriented northwest-southeast. This region, extending from Qazvin (west of Taleghan) to the north-northwest of Miane and north of the Manjil embayment, is bounded by the Abhar-Zanjan-Miane axis to the south (Ghorbani, 2009). Within this mountain range, numerous intrusive masses, primarily granodiorite, have intruded into the Eocene volcanic rocks. These masses, including the Bakhtar Takhestan, Khorasanlu, Zaker, and Chal masses, follow a northwest-southeast trend, aligning with the overall orientation of the Tarom mountains. They are arranged in two parallel rows, cutting through the older volcanic formations. Geology of the area The most important rock units in the Tarom Mountains consist of Eocene pyroclastic rocks, including andesite, rhyolite, basalt, andesite basalt, and rhyodacite, as well as shear tuff and andesite tuff. The region's main elevations are composed of Eocene volcanic and volcano-clastic rocks, along with Oligocene intrusive masses, which form the bulk of the mountain unit. Oligocene trachytic deposits, which are deposited on the Eocene units at an angle of approximately 23 degrees, are exposed in the northern part of the Kabbarik syenitic porphyroid stock. The syenitic porphyroid stock has intruded into the Eocene volcanic and volcano-clastic rocks. This study is grounded in field surveys, sampling of the slightly intrusive mass, and the examination of thin sections. Additionally, chemical analyses were conducted on ten samples from Zarazma Company to determine major, minor, and trace elements using inductively coupled plasma mass spectrometry (ICP-MS). Two samples were also analyzed using electron microscopy. To analyze the mineral composition of Kabbarik rocks for major elements, a JEOL JXA-8100 Superprobe electron microprobe (EMP) equipped with an Oxford Instruments INCA EDS system was employed at the Institute of Geology and Geophysics, Chinese Academy of Science. A 5-micron spot size, a 20 nA beam current, and a 15 keV accelerating voltage were utilized during these analyses. Petrography The intrusive Kabbarik stock exhibits a porphyritic texture, characterized by euhedral to subhedral phenocrysts of alkali feldspar. Its primary mineral composition includes alkali feldspar (Orthoclase) constituting 65-70 Vol.%, followed by 10-15 Vol.% clinopyroxene (diopside), 5-7 Vol.% anorthoclase, and 3-5 Vol.% secondary minerals such as olivine, altered to iddingsite. Minor amounts of apatite, zircon, and dark minerals are also present. Orthoclase phenocrysts often display Carlsbad and polysynthetic twinning. Megacrysts of Orthoclase may contain tiny inclusions of olivine and clinopyroxene, exhibiting a poikilitic texture. Some crystals exhibit a sieve texture, and in certain cases, overgrowth on plagioclase results in a Rapakivi texture. Clinopyroxene (diopside) crystals are generally euhedral to subhedral, with some containing small dark mineral inclusions distributed along their edges and conforming to their shape. Subhedral crystals of iddingsitized olivine are scattered throughout the rock matrix in small quantities. The overall texture of the microlithic rock remains porphyritic. Mineral Chemistry The chemical composition of clinopyroxene and alkali feldspar minerals from the syenitic stock was analyzed using a JEOL JXA-8200 electron microscope at the Department of Geology and Geophysics, Chinese Academy of Sciences. Based on relevant diagrams, the clinopyroxenes were classified as diopside-type (Eby et al., 1998; Morimoto, 1988). The chemical composition of the pyroxenes indicates a sub-alkaline, volcanic arc magmatic setting. EPMA analysis of the alkali feldspars revealed an anorthoclase composition (Deer et al., 1991). Whole Rock Geochemistry The chemical analysis of significant, rare, and rare earth elements (ICP-MS) reveals a calc-alkaline composition for the intrusive mass of the syenite zone and its parent magma. Normalized spider diagrams compared to chondrite demonstrate a clear enrichment of light rare earth elements (LREE) and incompatible elements relative to heavy rare earth elements (HREE) in the examined rocks. Based on tectonic environment diagrams, the studied samples are classified as post-collisional. Results The predominant rock formations in the Tarom Mountains consist of Eocene volcanic and volcaniclastic rocks, which constitute the bulk of the mountain range. The investigated syenitic stock, intruding into the overlying rocks, dates back to the Oligocene epoch. Based on spider diagrams, the absence of significant heavy rare earth element (HREE) depletion suggests a mantle that has been metasomatized by subduction-related fluids. Studies indicate that the analyzed samples originated in a setting associated with an arc and a post-collisional environment. The study area, Tarom, is situated in northwestern Iran, within the Zanjan province. Geologically, it falls within the western Alborz zone, a volcanic-plutonic belt, oriented northwest-southeast. This region, extending from Qazvin (west of Taleghan) to the north-northwest of Miane and north of the Manjil embayment, is bounded by the Abhar-Zanjan-Miane axis to the south (Ghorbani, 2009). Within this mountain range, numerous intrusive masses, primarily granodiorite, have intruded into the Eocene volcanic rocks. These masses, including the Bakhtar Takhestan, Khorasanlu, Zaker, and Chal masses, follow a northwest-southeast trend, aligning with the overall orientation of the Tarom mountains. They are arranged in two parallel rows, cutting through the older volcanic formations. Geology of the area The most important rock units in the Tarom Mountains consist of Eocene pyroclastic rocks, including andesite, rhyolite, basalt, andesite basalt, and rhyodacite, as well as shear tuff and andesite tuff. The region's main elevations are composed of Eocene volcanic and volcano-clastic rocks, along with Oligocene intrusive masses, which form the bulk of the mountain unit. Oligocene trachytic deposits, which are deposited on the Eocene units at an angle of approximately 23 degrees, are exposed in the northern part of the Kabbarik syenitic porphyroid stock. The syenitic porphyroid stock has intruded into the Eocene volcanic and volcano-clastic rocks. This study is grounded in field surveys, sampling of the slightly intrusive mass, and the examination of thin sections. Additionally, chemical analyses were conducted on ten samples from Zarazma Company to determine major, minor, and trace elements using inductively coupled plasma mass spectrometry (ICP-MS). Two samples were also analyzed using electron microscopy. To analyze the mineral composition of Kabbarik rocks for major elements, a JEOL JXA-8100 Superprobe electron microprobe (EMP) equipped with an Oxford Instruments INCA EDS system was employed at the Institute of Geology and Geophysics, Chinese Academy of Science. A 5-micron spot size, a 20 nA beam current, and a 15 keV accelerating voltage were utilized during these analyses. Petrography The intrusive Kabbarik stock exhibits a porphyritic texture, characterized by euhedral to subhedral phenocrysts of alkali feldspar. Its primary mineral composition includes alkali feldspar (Orthoclase) constituting 65-70 Vol.%, followed by 10-15 Vol.% clinopyroxene (diopside), 5-7 Vol.% anorthoclase, and 3-5 Vol.% secondary minerals such as olivine, altered to iddingsite. Minor amounts of apatite, zircon, and dark minerals are also present. Orthoclase phenocrysts often display Carlsbad and polysynthetic twinning. Megacrysts of Orthoclase may contain tiny inclusions of olivine and clinopyroxene, exhibiting a poikilitic texture. Some crystals exhibit a sieve texture, and in certain cases, overgrowth on plagioclase results in a Rapakivi texture. Clinopyroxene (diopside) crystals are generally euhedral to subhedral, with some containing small dark mineral inclusions distributed along their edges and conforming to their shape. Subhedral crystals of iddingsitized olivine are scattered throughout the rock matrix in small quantities. The overall texture of the microlithic rock remains porphyritic. Mineral Chemistry The chemical composition of clinopyroxene and alkali feldspar minerals from the syenitic stock was analyzed using a JEOL JXA-8200 electron microscope at the Department of Geology and Geophysics, Chinese Academy of Sciences. Based on relevant diagrams, the clinopyroxenes were classified as diopside-type (Eby et al., 1998; Morimoto, 1988). The chemical composition of the pyroxenes indicates a sub-alkaline, volcanic arc magmatic setting. EPMA analysis of the alkali feldspars revealed an anorthoclase composition (Deer et al., 1991). Whole Rock Geochemistry The chemical analysis of significant, rare, and rare earth elements (ICP-MS) reveals a calc-alkaline composition for the intrusive mass of the syenite zone and its parent magma. Normalized spider diagrams compared to chondrite demonstrate a clear enrichment of light rare earth elements (LREE) and incompatible elements relative to heavy rare earth elements (HREE) in the examined rocks. Based on tectonic environment diagrams, the studied samples are classified as post-collisional. Results The predominant rock formations in the Tarom Mountains consist of Eocene volcanic and volcaniclastic rocks, which constitute the bulk of the mountain range. The investigated syenitic stock, intruding into the overlying rocks, dates back to the Oligocene epoch. Based on spider diagrams, the absence of significant heavy rare earth element (HREE) depletion suggests a mantle that has been metasomatized by subduction-related fluids. Studies indicate that the analyzed samples originated in a setting associated with an arc and a post-collisional environment.

https://ijp.ui.ac.ir/article_28762_5be189f3e99afb1aef518e597b425052.pdf

University of Isfahan Petrological Journal 2228-5210 15 1 2024 04 20 Mineralogy, geochemistry and gemology of fluorite in carbonate rocks of the Pinavand deposit (Central Iran Zone) Mineralogy, geochemistry and gemology of fluorite in carbonate rocks of the Pinavand deposit (Central Iran Zone) 159 184 28537 10.22108/ijp.2024.141098.1330 FA Farimah Ayati Associate Professor, Department of Geology, Faculty of Sciences, University of Payame Noor, Tehran, Iran, Mohammad Ali Mackizade Associate Professor, Department of Geology, Faculty of Sciences, University of Isfahan, Isfahan, Iran, Roghaye Heidari M.Sc., Department of Geology, Faculty of Sciences, University of Payame Noor, Tehran, Iran; Ministry of Education, Shahrekord, Iran, Journal Article 2024 04 02 Fluorite deposits in Iran are widely located in dolomites and dolomitic limestones (Triassic-Cretaceous age) (Darvishzadeh, 1991) in Alborz and the Central Iran zone (Rajabi et al., 2013). Qishlaqi (2002) investigated the geochemistry and genesis of the Pinavand fluorite mines. Shafahizadeh (2011) investigated the mineralogy and fluids involved in fluorite and barite mineralization in the Pinavand region. Heidari et al. (2021) investigated the paragenetic relationships of minerals in the alteration zone of the Pinavand deposit. In the present paper, the semi-precious gem fluorine in the limestones of the Pinavand deposit is investigated from the point of view of geochemistry and gemology. Also, the connection of the host rock with the minerals of this area and the reaction of the ore-forming fluid with them will be determined. Materials and Methods Following field studies, several thin sections (about 25) and polished sections were prepared for petrographic studies. The fluorine mineral of the studied deposit was subjected to SEM analysis (at the Isfahan University of Technology) and gemological investigations (at Isfahan University). Also, the results of geochemical analyses of fluorites (ICP-MS) (Shafahizadeh, 2011) were applied. Results and Discussion Mineralization of fluorite and barite occurred in scattered, massive, veined, breccia and lens-shaped in the Lower Cretaceous limestone and dolomitic host rocks. Major alterations observed in the region including silicification and to a lesser extent dolomitization. The main minerals are quartz, calcite, dolomite, fluorite, and barite scattered in the limestone. The fluorite decomposed into carbonate along fractures, which indicates the continuous influx of hydrothermal solutions. A final silicification process has occurred following fluorine formation. It seems that the Mississippi Valley deposit type is one of the proposed models for the formation of Pinavand mineral region. Dolomitization and silicification processes are the characteristics of the Mississippi Valley-type deposits (Pirajno, 2009). However, in the Mississippi Valley-type deposits, unlike epithermal mineralization, dolomitization process occurs with a weak silicification. The mineralogy in Pinavand deposit includes pyrite, chalcopyrite, chalcocite, galena, goethite, fluorite, barite, quartz, calcite and dolomite. No proximity with evaporite rocks is observed. A low extent of dolomitization with a larger scale of silicification can be an indication of epithermal type alterations. As optical and gemological characteristics display the fluorine crystals with glassy and transparent feature and specific weight of 3.18 vary from colorless to green to pale blue in color. They are without any birefringence and their refractive index is 1.43. The presence of rare elements such as Sc, Sr and Zr can affect the color of this mineral. Yellow and transparent fluorites have a higher Yb/La ratio than blue and purple fluorites (Palmer and Williams-Jones, 1996). It seems that various of color in fluorite crystals are related to the amount of Y and ∑REE (e.g., Dill et al., 2011). The concentration of REE in the Pinavand fluorites is generally low, and LREEs are more enriched than heavy earth elements (HREE). The low REE in fluorites can be attributed to the high fluid-to-rock ratio (Sánchez et al., 2010). The low level of rare earth elements can be attributed to the high pH of the fluids and the reaction of the fluids with the carbonate host rock as well as the high ratio of fluid/rock. On the other hand, the low values of rare earth elements can indicate the mixing of magmatic fluids and atmospheric waters (Valenza et al., 2000). According to Moller et al. (1986) the fluorites formed in the early or middle stages of crystallization are enriched with LREE, the amount of La element is high and the amount of Tb is low, but the fluorites related to the final stage of crystallization are enriched with HREE. So, the Pinavand fluorites created in the early stages of crystallization. The examined fluorites have a small positive anomaly in europium, indicating the substitution of Eu2+ for Ca2+ and the deposit formation temperature is less than 250°C (Schwin and Markl, 2005). The negative anomaly of cerium points to its removal from the environment as a consequence of fluid reaction with calcareous wall rock giving rise to increment to oxygen fugacity. Fluorites are divided into three sedimentary, hydrothermal and pegmatitic environments (Constantopoulos, 1988). The studied fluorites are classified as sedimentary type with some features of primary crystallization and fluid's reaction with calcareous host rocks. Conclusions Pinavand deposit is a fluorite-barite deposit consisting both of the non-metallic and metallic minerals. The latter minerals were formed under the influence of hydrothermal alteration. The negative anomaly of cerium in the fluorites suggests that it has been removed from the environment as a result of the fluid's reaction with the limestone wall rock, which in turn increased the oxygen fugacity. This process highlights the significant role of fluid-rock interactions in the removal and redistribution of certain elements within the depositional environment. Mineralization of the fluorite and barite formed as veins, veinlets, lenticular and breccia shapes have occurred mainly in the Lower Cretaceous limestone units. The main minerals of this deposit include quartz, calcite, saddle dolomite, fluorite and barite, scattered in the limestone background. The major changes in the region include silicification and, to a lesser extent, dolomitization processes. Fluorite can observe as coarse-grained or fine-grained in size, and its gemological characteristics are as follows: transparent to semi-transparent crystals, pale blue colors, green and violet, hardness 4, specific gravity 3.18, vitreous luster, without birefringence and having a refractive index of 1.43. Based on the geochemical studies, the concentration of LREE in the Pinavand deposit indicates the formation of fluorites in the early to middle stages of crystallization. The Mineralogy in the Pinavand deposit is simple like in the Mississippi Valley deposit. Based on the type of minerals as well as alteration type, the Pinavand mineralization shows some characteristics of MVT deposits, and due to the huge of silicification process, it also shows similarity to the alteration of epithermal deposits. Fluorite deposits in Iran are widely located in dolomites and dolomitic limestones (Triassic-Cretaceous age) (Darvishzadeh, 1991) in Alborz and the Central Iran zone (Rajabi et al., 2013). Qishlaqi (2002) investigated the geochemistry and genesis of the Pinavand fluorite mines. Shafahizadeh (2011) investigated the mineralogy and fluids involved in fluorite and barite mineralization in the Pinavand region. Heidari et al. (2021) investigated the paragenetic relationships of minerals in the alteration zone of the Pinavand deposit. In the present paper, the semi-precious gem fluorine in the limestones of the Pinavand deposit is investigated from the point of view of geochemistry and gemology. Also, the connection of the host rock with the minerals of this area and the reaction of the ore-forming fluid with them will be determined. Materials and Methods Following field studies, several thin sections (about 25) and polished sections were prepared for petrographic studies. The fluorine mineral of the studied deposit was subjected to SEM analysis (at the Isfahan University of Technology) and gemological investigations (at Isfahan University). Also, the results of geochemical analyses of fluorites (ICP-MS) (Shafahizadeh, 2011) were applied. Results and Discussion Mineralization of fluorite and barite occurred in scattered, massive, veined, breccia and lens-shaped in the Lower Cretaceous limestone and dolomitic host rocks. Major alterations observed in the region including silicification and to a lesser extent dolomitization. The main minerals are quartz, calcite, dolomite, fluorite, and barite scattered in the limestone. The fluorite decomposed into carbonate along fractures, which indicates the continuous influx of hydrothermal solutions. A final silicification process has occurred following fluorine formation. It seems that the Mississippi Valley deposit type is one of the proposed models for the formation of Pinavand mineral region. Dolomitization and silicification processes are the characteristics of the Mississippi Valley-type deposits (Pirajno, 2009). However, in the Mississippi Valley-type deposits, unlike epithermal mineralization, dolomitization process occurs with a weak silicification. The mineralogy in Pinavand deposit includes pyrite, chalcopyrite, chalcocite, galena, goethite, fluorite, barite, quartz, calcite and dolomite. No proximity with evaporite rocks is observed. A low extent of dolomitization with a larger scale of silicification can be an indication of epithermal type alterations. As optical and gemological characteristics display the fluorine crystals with glassy and transparent feature and specific weight of 3.18 vary from colorless to green to pale blue in color. They are without any birefringence and their refractive index is 1.43. The presence of rare elements such as Sc, Sr and Zr can affect the color of this mineral. Yellow and transparent fluorites have a higher Yb/La ratio than blue and purple fluorites (Palmer and Williams-Jones, 1996). It seems that various of color in fluorite crystals are related to the amount of Y and ∑REE (e.g., Dill et al., 2011). The concentration of REE in the Pinavand fluorites is generally low, and LREEs are more enriched than heavy earth elements (HREE). The low REE in fluorites can be attributed to the high fluid-to-rock ratio (Sánchez et al., 2010). The low level of rare earth elements can be attributed to the high pH of the fluids and the reaction of the fluids with the carbonate host rock as well as the high ratio of fluid/rock. On the other hand, the low values of rare earth elements can indicate the mixing of magmatic fluids and atmospheric waters (Valenza et al., 2000). According to Moller et al. (1986) the fluorites formed in the early or middle stages of crystallization are enriched with LREE, the amount of La element is high and the amount of Tb is low, but the fluorites related to the final stage of crystallization are enriched with HREE. So, the Pinavand fluorites created in the early stages of crystallization. The examined fluorites have a small positive anomaly in europium, indicating the substitution of Eu2+ for Ca2+ and the deposit formation temperature is less than 250°C (Schwin and Markl, 2005). The negative anomaly of cerium points to its removal from the environment as a consequence of fluid reaction with calcareous wall rock giving rise to increment to oxygen fugacity. Fluorites are divided into three sedimentary, hydrothermal and pegmatitic environments (Constantopoulos, 1988). The studied fluorites are classified as sedimentary type with some features of primary crystallization and fluid's reaction with calcareous host rocks. Conclusions Pinavand deposit is a fluorite-barite deposit consisting both of the non-metallic and metallic minerals. The latter minerals were formed under the influence of hydrothermal alteration. The negative anomaly of cerium in the fluorites suggests that it has been removed from the environment as a result of the fluid's reaction with the limestone wall rock, which in turn increased the oxygen fugacity. This process highlights the significant role of fluid-rock interactions in the removal and redistribution of certain elements within the depositional environment. Mineralization of the fluorite and barite formed as veins, veinlets, lenticular and breccia shapes have occurred mainly in the Lower Cretaceous limestone units. The main minerals of this deposit include quartz, calcite, saddle dolomite, fluorite and barite, scattered in the limestone background. The major changes in the region include silicification and, to a lesser extent, dolomitization processes. Fluorite can observe as coarse-grained or fine-grained in size, and its gemological characteristics are as follows: transparent to semi-transparent crystals, pale blue colors, green and violet, hardness 4, specific gravity 3.18, vitreous luster, without birefringence and having a refractive index of 1.43. Based on the geochemical studies, the concentration of LREE in the Pinavand deposit indicates the formation of fluorites in the early to middle stages of crystallization. The Mineralogy in the Pinavand deposit is simple like in the Mississippi Valley deposit. Based on the type of minerals as well as alteration type, the Pinavand mineralization shows some characteristics of MVT deposits, and due to the huge of silicification process, it also shows similarity to the alteration of epithermal deposits.

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