Petrogenetic and mineralogical constraints in metamorphic-plutonic complex of N-Bijar, Kordestan, Iran
IntroductionThe Sanandaj-Sirjan metamorphic-magmatic zone (SSZ) (with 1500 km in length and 150-200 km in width) along with the Urumieh-Dokhtar magmatic arc as well as the folded-thrust belt of Zagros comprise the Zagros orogeny in south west of Iran. The SSZ. based on the grade and age of metamorph...
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University of Isfahan
2025-03-01
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| author | Maryam Bafandeh Abbas Asiabanha Mohsen Nadrabady |
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| description | IntroductionThe Sanandaj-Sirjan metamorphic-magmatic zone (SSZ) (with 1500 km in length and 150-200 km in width) along with the Urumieh-Dokhtar magmatic arc as well as the folded-thrust belt of Zagros comprise the Zagros orogeny in south west of Iran. The SSZ. based on the grade and age of metamorphism, has been divided into northern and southern subzones (Ghasemi and Talbot, 2006). The southern subzone are dominated by metamorphosed and deformed lithologies belonging to middle - upper Triassic, whereas, the Jurassic and the upper Cretaceous metamorphic rocks as well as the felsic intrusions are more widespread in the northern subzone (Moazzen et al. 2004; Ghasemi and Talbot, 2006; Sepahi et al., 2014). The intrusions of SSZ range in composition from gabbro to granite and are Neoproterozoic to Miocene in age. But the granitic bodies of Jurassic (140-170 Ma) are more abundant (Hassanzadeh and Wernicke, 2016).The metamorphic-plutonic complex of northern Bijar, situated on the northern part of the Sanandaj-Sirjan zone of Iran, is important for co-existence of regional metamorphic rocks (dominated by slate and phyllite as well as inliers of green-schist) and a white garnet-bearing leucogranite. Fonoudi and Sayareh (2000) suggested that this lithology was metamorphosed during Cretaceous and were intruded by a leucogranitic intrusion in N-Bijar. Although it is not seen any contact metamorphic halo at the boundary zones of the pluton (likely because of its low heat potential) but the presence of the aplitic apophyses in the country schistose rocks and especially the occurrence of abundant xenoliths at the marginal zone of the pluton (Figures 2C and 2D) are good indications of the age of the pluton which is younger than that of the country metamorphic rocks.Mineralogically, the country rocks are the metabasites metamorphosed under amphibolite facies. and as the textural evidences show they were affected by at least two episodes of regional metamorphism followed by retrograde and dynamic metamorphism. The high temperature ductile deformation is given by the following indications: the seriate boundaries in quartz grains, the ribbon quartz, the fish-shaped amphiboles, the granoblastic and the recrystallized textures. On the other hand, the granitic pluton, as a homogenous body, is composed of more than 95 vol% of felsic minerals (i.e. quartz, plagioclase and alkali feldspars) and about less than 5 vol% other minerals (i.e. garnet, muscovite, biotite). The shallow depth emplacement of the intrusion is implied by the granophyric and perthitic textures. Also, the high temperature deformation of the rocks is shown by the seriate boundaries and dynamic recrystallizations in quartz grains as well as the abundant myrmekitic textures.Geochemistry and Mineral ChemistryThe studied pluton is poor in Fe-Mg conrent but peraluminous (A/CNK=1.05-1.11) in nature and classified as high-K calc-alkaline magmatic series. The convex downward of in REE pattern in studied samples can be due to MREEs depletion possibly produced by differentiation of ferromagnesian minerals (i.e., pyroxene, hornblende and even titanite) (Rollinson and Pease, 2021). Whereas, the metabasites have a uniform pattern of LREEs/HREEs mildly enrichment ratio (LaN/LuN » 3.01).To determine the role of minerals in the petrological evolutions, the rock-forming minerals were analyzed by EPMA (Tables 2-6). As the results show the metabasites mainly contain: Ca-amphiboles magnesio-hornblende and lesser amounts of pargasite, epidote containing of pistacite component of about 0.24-0.27, oligoclase-plagioclase. The same analyses reveal that the granite samples are composed of albite-oligoclase, orthoclase, microcline, as the major and the zoned Mn-garnet (spessartine), phengitic muscovite, as the minor minerals.Discussion and ConclusionThe metamorphic-plutonic complex of northern Bijar comprises of two distinct lithologies, namely the Cretaceous metabasites as the country rocks and the garnet-bearing leucogranite pluton. The mineral assemblages of the pluton point to the peraluminous nature of granite confirmed by the A/CNK>1. The mentioned pluton was intruded the country rocks in a shallow depth of the crust with lack of any indication of contact metamorphism. However, the observation of abundant xenoliths of metabasites at the margin zone of the pluton is a strong reason for its younger age than the metabasites.The metamorphic rocks of the studied area are the low-medium grade regional metamorphic rocks (i. e. slate, phyllite, hornblende schist and epidote schist) affected by at least two regionally followed by dynamic and retrograde metamorphisms. As the mineral paragenesis show, the protolith of these rocks are enriched in Ca, Fe and Mg (namely calc-alkaline basalts). Also, they have been originated from MORB sources with proxies of continental arcs. Moreover, the studied granitic pluton belongs to a volcanic arc and/or continental collision granite type.The thermo-barometric calculations based on different procedures yielded: T= 600±20 and P=13-15 kbar for amphiboles by the method reported by Ernst and Liu (1998), T=593-718 °C in 2 kbar and T=640-708 °C in 8 kbar by Holland and Blundy's method (1994) and finally T = 730 °C and P. 2-6.9 kbar by the method suggested by Bhadra and Bhattacharya (2007).On the other hand, by plotting the plagioclase data of leucogranite pluton on Nekvasil et al. (2000) a P = 4.5 kbar and T= 500 °C. were obtained. Thus, the lower temperatures of the granitic pluton can be explained by the lack of contact metamorphic halo in the country rocks. |
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| spelling | doaj-art-66e10cd488304d7e9dcd70786e2dbdd72025-08-20T03:53:57ZfasUniversity of Isfahanپترولوژی2228-52102322-21822025-03-01161719410.22108/ijp.2025.144343.135329459Petrogenetic and mineralogical constraints in metamorphic-plutonic complex of N-Bijar, Kordestan, IranMaryam Bafandeh0Abbas Asiabanha1Mohsen Nadrabady2M.Sc. student of petrology, Department of Geology, Faculty of Sciences, Imam Khomeini International University, Qazvin, IranAssociate Professor, Department of Geology, Faculty of Sciences, Imam Khomeini International University, Qazvin, IranAssociate Professor, Department of Geology, Faculty of Sciences, Imam Khomeini International University, Qazvin, IranIntroductionThe Sanandaj-Sirjan metamorphic-magmatic zone (SSZ) (with 1500 km in length and 150-200 km in width) along with the Urumieh-Dokhtar magmatic arc as well as the folded-thrust belt of Zagros comprise the Zagros orogeny in south west of Iran. The SSZ. based on the grade and age of metamorphism, has been divided into northern and southern subzones (Ghasemi and Talbot, 2006). The southern subzone are dominated by metamorphosed and deformed lithologies belonging to middle - upper Triassic, whereas, the Jurassic and the upper Cretaceous metamorphic rocks as well as the felsic intrusions are more widespread in the northern subzone (Moazzen et al. 2004; Ghasemi and Talbot, 2006; Sepahi et al., 2014). The intrusions of SSZ range in composition from gabbro to granite and are Neoproterozoic to Miocene in age. But the granitic bodies of Jurassic (140-170 Ma) are more abundant (Hassanzadeh and Wernicke, 2016).The metamorphic-plutonic complex of northern Bijar, situated on the northern part of the Sanandaj-Sirjan zone of Iran, is important for co-existence of regional metamorphic rocks (dominated by slate and phyllite as well as inliers of green-schist) and a white garnet-bearing leucogranite. Fonoudi and Sayareh (2000) suggested that this lithology was metamorphosed during Cretaceous and were intruded by a leucogranitic intrusion in N-Bijar. Although it is not seen any contact metamorphic halo at the boundary zones of the pluton (likely because of its low heat potential) but the presence of the aplitic apophyses in the country schistose rocks and especially the occurrence of abundant xenoliths at the marginal zone of the pluton (Figures 2C and 2D) are good indications of the age of the pluton which is younger than that of the country metamorphic rocks.Mineralogically, the country rocks are the metabasites metamorphosed under amphibolite facies. and as the textural evidences show they were affected by at least two episodes of regional metamorphism followed by retrograde and dynamic metamorphism. The high temperature ductile deformation is given by the following indications: the seriate boundaries in quartz grains, the ribbon quartz, the fish-shaped amphiboles, the granoblastic and the recrystallized textures. On the other hand, the granitic pluton, as a homogenous body, is composed of more than 95 vol% of felsic minerals (i.e. quartz, plagioclase and alkali feldspars) and about less than 5 vol% other minerals (i.e. garnet, muscovite, biotite). The shallow depth emplacement of the intrusion is implied by the granophyric and perthitic textures. Also, the high temperature deformation of the rocks is shown by the seriate boundaries and dynamic recrystallizations in quartz grains as well as the abundant myrmekitic textures.Geochemistry and Mineral ChemistryThe studied pluton is poor in Fe-Mg conrent but peraluminous (A/CNK=1.05-1.11) in nature and classified as high-K calc-alkaline magmatic series. The convex downward of in REE pattern in studied samples can be due to MREEs depletion possibly produced by differentiation of ferromagnesian minerals (i.e., pyroxene, hornblende and even titanite) (Rollinson and Pease, 2021). Whereas, the metabasites have a uniform pattern of LREEs/HREEs mildly enrichment ratio (LaN/LuN » 3.01).To determine the role of minerals in the petrological evolutions, the rock-forming minerals were analyzed by EPMA (Tables 2-6). As the results show the metabasites mainly contain: Ca-amphiboles magnesio-hornblende and lesser amounts of pargasite, epidote containing of pistacite component of about 0.24-0.27, oligoclase-plagioclase. The same analyses reveal that the granite samples are composed of albite-oligoclase, orthoclase, microcline, as the major and the zoned Mn-garnet (spessartine), phengitic muscovite, as the minor minerals.Discussion and ConclusionThe metamorphic-plutonic complex of northern Bijar comprises of two distinct lithologies, namely the Cretaceous metabasites as the country rocks and the garnet-bearing leucogranite pluton. The mineral assemblages of the pluton point to the peraluminous nature of granite confirmed by the A/CNK>1. The mentioned pluton was intruded the country rocks in a shallow depth of the crust with lack of any indication of contact metamorphism. However, the observation of abundant xenoliths of metabasites at the margin zone of the pluton is a strong reason for its younger age than the metabasites.The metamorphic rocks of the studied area are the low-medium grade regional metamorphic rocks (i. e. slate, phyllite, hornblende schist and epidote schist) affected by at least two regionally followed by dynamic and retrograde metamorphisms. As the mineral paragenesis show, the protolith of these rocks are enriched in Ca, Fe and Mg (namely calc-alkaline basalts). Also, they have been originated from MORB sources with proxies of continental arcs. Moreover, the studied granitic pluton belongs to a volcanic arc and/or continental collision granite type.The thermo-barometric calculations based on different procedures yielded: T= 600±20 and P=13-15 kbar for amphiboles by the method reported by Ernst and Liu (1998), T=593-718 °C in 2 kbar and T=640-708 °C in 8 kbar by Holland and Blundy's method (1994) and finally T = 730 °C and P. 2-6.9 kbar by the method suggested by Bhadra and Bhattacharya (2007).On the other hand, by plotting the plagioclase data of leucogranite pluton on Nekvasil et al. (2000) a P = 4.5 kbar and T= 500 °C. were obtained. Thus, the lower temperatures of the granitic pluton can be explained by the lack of contact metamorphic halo in the country rocks.https://ijp.ui.ac.ir/article_29459_1106c4d4be08904e70700c4bb89ec85b.pdfpetrogenesismagmatic processesgeochemistryzircon chemistrysangan magmatism |
| spellingShingle | Maryam Bafandeh Abbas Asiabanha Mohsen Nadrabady Petrogenetic and mineralogical constraints in metamorphic-plutonic complex of N-Bijar, Kordestan, Iran پترولوژی petrogenesis magmatic processes geochemistry zircon chemistry sangan magmatism |
| title | Petrogenetic and mineralogical constraints in metamorphic-plutonic complex of N-Bijar, Kordestan, Iran |
| title_full | Petrogenetic and mineralogical constraints in metamorphic-plutonic complex of N-Bijar, Kordestan, Iran |
| title_fullStr | Petrogenetic and mineralogical constraints in metamorphic-plutonic complex of N-Bijar, Kordestan, Iran |
| title_full_unstemmed | Petrogenetic and mineralogical constraints in metamorphic-plutonic complex of N-Bijar, Kordestan, Iran |
| title_short | Petrogenetic and mineralogical constraints in metamorphic-plutonic complex of N-Bijar, Kordestan, Iran |
| title_sort | petrogenetic and mineralogical constraints in metamorphic plutonic complex of n bijar kordestan iran |
| topic | petrogenesis magmatic processes geochemistry zircon chemistry sangan magmatism |
| url | https://ijp.ui.ac.ir/article_29459_1106c4d4be08904e70700c4bb89ec85b.pdf |
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