دانشگاه اصفهان پترولوژی 2228-5210 16 2 2025 06 22 Petrography, Petrology, and Geochemistry of Subvolcanic Bodies in Dogan Porphyry Copper-Molybdenum Deposit (Toroud-Chah Shirin Belt) سنگ‌نگاری، سنگ‌شناسی و زمین‌شیمی توده‌های نیمه‌آتشفشانی در کانسار مس- مولیبدن پورفیری دوگان (کمربند ترود- چاه‌شیرین) 1 22 29573 10.22108/ijp.2025.144992.1357 FA شادی ستاری دانشجوی دکتری، گروه علوم زمین، دانشکده علوم طبیعی، دانشگاه تبریز، تبریز، ایران محمدرضا حسین زاده استاد، گروه زمین‌شناسی، دانشکده علوم طبیعی، دانشگاه تبریز، تبریز، ایران محسن موید استاد، گروه زمین‌شناسی، دانشکده علوم طبیعی، دانشگاه تبریز، تبریز، ایران Journal Article 2025 04 20 Introduction Dogan mining area is located on the northern edge of Iran's central desert plain and northwest of Toroud village. Structurally, the area is a part of Central Alborz, Eastern Alborz, and Central Iran zones, which gave rise to the formation of deposits and a diverse metallogenic environment. Geologically, this area is a part of Toroud‐Chah Shirin (TCS) belt, a Tertiary base metal and gold-silver mineral region in northern Iran. The TCS belt consists mainly of Eocene volcanic and pyroclastic rocks, equivalent to subvolcanic and intrusive bodies, although there are scattered outcrops of metamorphosed Paleozoic and Mesozoic rocks. Structural patterns are controlled by two principal strike-slip faults, Anjilow in the north and Toroud in the south, both trending NE. So far, no detail study has been carried out on the study area in terms of separation and investigation of intrusive bodies, and only one subvolcanic microdiorite body has been introduced in the previous studies in this area. While, the overall data obtained from detailed field surveys, drilling core as well as petrographic studies indicate that at least three subvolcanic bodies have been identified injected in the area in a telescopic form, and all three are the carriers of copper mineralization as disseminated and vein-veined forms. Therefore, the petrographic and geochemical characteristics of, these bodies are the purpose of the present study. Regional Geology The main volume of rock units in the study area, based on 1:1000 geological map of Dogan area, includes andesitic lavas, pyroclastic tuffs, and various subvolcanic bodies. The subvolcanic bodies are relatively diverse in composition, and the greatest areal extent of these bodies is in the northeastern, central, and southeastern parts of the region. The nature of these subvolcanic bodies are as follows: Porphyritic quartz monzonite to quartz monzodiorite (Qmz): A large part of the central part of the study area is surrounded by porphyritic body, which is older than the other bodies and is injected into Eocene units. Porphyritic diorite to microdiorite (Dr): This unit lies in the central part of the area with a less extensive distribution than that of the Porphyritic quartz monzonite body. This body in the central part cuts the Porphyritic quartz monzonite body and is, therefore, younger in age, but its cutting by the dykes of the porphyritic quartz diorite body indicating it is older than this body. Porphyric quartz diorite to granodiorite (Qdr): As the youngest body as well as less extensive area than that of the existing bodies, is exposed in the central part of the area. Analytical methods In this study, after field investigations and sampling of drill cores, about 200 thin sections were prepared from the collected samples for petrographic studies and about 60 polished sections for mineralogy studies. After microscopic studies and separation of intrusive units, 15 samples with minimal alteration were analyzed in the laboratory of Zar Azma Company to measure the main oxides and determine the abundance of trace and rare earth elements by XRF and ICP-MS methods. Petrography Porphyritic quartz monzonite to quartz monzodiorite (Qmz): Microscopically, this porphyry body ranges from quartz monzonite to quartz monzodiorite, exhibiting a porphyritic texture with a fine-grained matrix. Main minerals include plagioclase, K-feldspar, and quartz, with accessory amphibole, biotite, apatite, zircon, and opaque minerals. Plagioclase and K-feldspar phenocrysts are pseudomorphed by sericite and carbonate, while ferromagnesian minerals (amphibole, biotite) are altered to chlorite and magnetite. Secondary minerals including sericite, chlorite, carbonate, and iron oxides result from alteration. Porphyritic diorite to microdiorite (Dr): These rocks dominated by the presence of plagioclase and amphibole and small volume of quartz, apatite, zircon, and opaque minerals. They display a microlithic porphyritic texture, with subhedral plagioclase phenocrysts (showing mixed zoning) in a microlithic matrix of plagioclase and quartz. Plagioclase is altered to sericite and clay minerals, while amphibole phenocrysts are pseudomorphed by chlorite and iron oxides. Secondary biotite, actinolite, and ore accumulations occur, alongside potassic alteration. Porphyritic quartz diorite to granodiorite (Qdr): The essential minerals of this body’ are plagioclase, K-feldspar, and quartz, with accessory zircon and apatite as well as porphyritic texture with a fine-grained matrix. Plagioclase exhibits mixed zoning; amphibole is partly altered to chlorite. Biotite appears as primary (magmatic, altered to chlorite and iron oxides) and thesecondary (hydrothermal, flaky, brown). Chloritization and iron oxide precipitation are common. Discussion As the SiO2 versus Zr/TiO2 diagram display the subvolcanic bodies in the Dogan mining area are dominated by granodiorite, tonalite, and diorite/. These I-type granitoids are calc-alkaline to high-K calc-alkaline and metaluminous to peraluminous nature formed in a continental arc setting. Geochemical data show depletion in Sm, Nd, Ti, and Y and enrichment in LILEs (Ba, Rb, Cs, K), consistent with subduction-related magmatism. The REE patterns display LREE enrichment over HREE, further supporting a subduction origin. Low Th/Nb and Ba/Th ratios point out to subduction zone fluids/melts and crustal contamination. The elevated Y/Rb ratios may reflect subduction enrichment or crustal input. The parental magma likely originated from a metasomatized mantle wedge, influenced by fluids from subducting oceanic lithosphere, and underwent fractionation and crustal contamination during ascent. On Y versus Sr/Y and Ybn versus (La/Yb)n diagrams, the rocks show adakite-like signatures. Given the association of high Sr/Y magmas with porphyry systems, these subvolcanic rocks may be linked to porphyry mineralization. Acknowledgments This article is part of the studies carried out for the first author’s Ph.D. thesis, which is being conducted at the University of Tabriz, and part of its costs were covered by the University of Tabriz and the Shahid Arefi Complex. Therefore, I would like to express my deepest gratitude and appreciation to the respected management of the Graduate Studies Department of the University of Tabriz and the management of the Shahid Arefi Complex. محدودة معدنی دوگان در حاشیة شمالی دشت کویر مرکزی ایران و در شمال‌باختری روستای ترود از توابع شهرستان شاهرود جای دارد. واحدهای سنگیِ منطقه شامل سه تودة مجزای نیمه‌آتشفشانی و به‌ترتیب سنی از قدیم به جدید شامل کوارتزمونزونیت تا مونزودیوریت پورفیری، دیوریت تا میکرودیوریت پورفیری، کوارتزدیوریت تا گرانودیوریت پورفیری و سنگ‌های درونگیر آتشفشانی و آذرآواری ائوسن هستند. بیشترین گسترش این تودهها در بخشهای شمالخاوری، مرکز و جنوب‌خاوری محدوده است و تودة کوارتزمونزونیت تا مونزودیوریت پورفیری نسبت به دیگر تودهها گسترش بیشتری دارد. میزان SiO2 این توده‌ها برابر با 15/52 تا 85/66 درصدوزنی است. بر پایة شواهد زمین‌شیمیایی، این تودهها سرشت متاآلومین تا پرآلومین و کالک‌آلکالن تا کالک‌آلکالن با پتاسیم بالا دارند. در نمودار بهنجارشده به ترکیب گوشتة اولیه و کندریت کمابیش همة نمونه‌ها، از عنصرهای خاکی کمیاب سبک (LREE) نسبت به عنصرهای خاکی کمیاب سنگین (HREE) غنی‌شدگی نشان می‌دهند. در این نمونهها مقدار (La/Ybn) برابر با 83/1 تا 02/20 است. غنیشدگی از عنصرهای لیتوفیل با یون بزرگ (LILE) مانند Rb، Cs و K در همة نمونههای نیمه‌آتشفشانی منطقه، ویژگی‌های زمین‌شیمیایی یک محیط ژئودینامیکی مرتبط با فرورانش را نشان می‌دهد. با توجه به نمودارY در برابر Sr/Y و و Ybn در برابر (La/Yb)n، بیشتر نمونه‌های نیمه‌آتشفشانی منطقه شاخص شبه‌آداکیتی دارند. نسبت Sr/Y در تودة کوارتزمونزونیت تا مونزودیوریت پورفیری برابر با 13/14-28/50، در تودة دیوریت تا میکرودیوریت پورفیری برابر با 77/47 -49/74 و در تودة کوارتزدیوریت تا گرانودیوریت پورفیری برابر با 51/58- 03/137 است.

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دانشگاه اصفهان پترولوژی 2228-5210 16 2 2025 06 22 Chromian spinel geochemistry as a petrogenetic indicator in the chromitites and peridotites of the Bajgan Complex, Western Makran زمین‏‌شیمی کروم-اسپینل به‏‌عنوان شاخص پتروژنتیک در کرومیتیت‌ها و پریدوتیت‌های مجموعة بجگان، باختر مکران 23 44 29577 10.22108/ijp.2025.144914.1355 FA لیلا واحدی دانشجوی دکتری، گروه زمین‏‌شیمی، دانشکده علوم زمین، دانشگاه خوارزمی، تهران، ایران مرتضی دلاوری دانشیار، گروه زمین‏‌شیمی، دانشکده علوم زمین، دانشگاه خوارزمی، تهران، ایران امیلیو ساکانی استاد، بخش فیزیک و علوم زمین، دانشگاه فرارا، فرارا، ایتالیا Journal Article 2025 04 13 Introduction Economic chromite deposits are very common in ophiolite belts. These deposits usually occur in the uppermost horizons of the ophiolite mantle sequence or within the ultramafic cumulitic rocks at the base of the crustal sequence (González-Jiménez et al., 2014a; González-Jiménez et al., 2014b; Uysal et al., 2018; Arai, 2021). The largest chromite deposit in Iran lies within the Sorkhband Ultramafic Complex (Faryab chromite mine). In addition, numerous peridotite masses are exposed within the Bajgan Complex and the Colored-mélange Complex, as well as around Rudan, which are host for minor chromite deposits. In this study, chromite masses from different areas of the Bajgan Complex and the Colored-mélange Complex in western Makran were sampled and their field characteristics, petrography and chemical composition were studied. These data were applied to identify the nature of the rocks, the petrological changes and the tectono-magmatic setting as well. Field Evidence and Petrography The study area located in the south of Kerman Province and the western part of the Makran Zone. The peridotite outcrops occurred within the Bajgan metamorphic complex and around Kahnuj, Kuhshah, Kuh-e-Sefid, and Rudan. These rocks mainly contain minor chromite reserves. These peridotite masses occur as relatively small to large blocks ranging in size from a few meters to several kilometers, often in fault contact with metamorphic units of the Bajgan Complex. The southwestern Kahnuj peridotite outcrop with a dunite composition covers an area of ov 10 square kilometers. The Kuhshah peridotite masses cover an area of over 50 square kilometers consisting mainly of dunite and to a lesser extent harzburgite, pyroxenite and wehrlite. Dunites exhibit a variety of textures, including porphyroclastic, granoblastic, and mylonitic, reflecting varying degrees of deformation and recrystallization. Harzburgites consist mainly of olivine (80-85 %Vol), orthopyroxene (10-15 %Vol), clinopyroxene (less than 2-3 %Vol) and spinel (1-3 %Vol). Harzburgites often have a porphyroclastic texture, and the effects of plastic deformation in olivine and orthopyroxene crystals are visible as wave extinction and kink bands. Chromitites often occur as irregular lenses or masses within dunite units. These rocks are mostly massive to semi-massive and disseminated in texture. Analytical Methods Following the mineralogical studies using Polarized light microscopy, polished thin sections were prepared from a number of mantle peridotite and chromitite samples. In order to determine the chemical composition of chromite minerals, point analysis of minerals was carried out in the Experimental Laboratory of Geophysics and Volcanology, Department of Seismology and Tectonophysics, INGV, Rome (Italy). In this method, the main elemental composition of the minerals was obtained by Jeol JXA 8200 electron microprobe (EMP). The analysis conditions included an accelerating voltage of 15 keV, a sample current of about 7.5 nA, a counting time of 10s and 5s on the peaks and background, respectively, and a beam size of 2-3 mm. Geochemistry In the dunites, the Al2O3 content of the chromian spinels varies from 21.89 to 25.26 wt.% and Mg# [Mg/ (Mg + Fe2+)] varies from 0.19 to 0.63 (Table 1), while in the harzburgite chromian spinels, the Al2O3 and Mg# contents are higher (Al2O3: 43.01 to 48.28 wt.%; Mg#:0.71 to 0.76). The value of Cr# [Cr/ (Cr + Al)] in the dunites and harzburgites, varies from 0.50 to 0.75 and 0.24 to 0.30, respectively. In chromitites, the Cr# content has a relatively wide range, based on which they are classified into two groups: high-Cr and high-Al chromitites. The Kutak chromitite has relatively high amounts of Al2O3 (20.52 to 23.63 wt%), while the Al2O3 content in the Kuhshah, Faryab and colored-mélange chromitites varies between 2.45 and 10.47 wt.%. Similarly, the Cr2O3 content in the Kutak chromitites varies between 45.96 and 52.26, while it is higher in other chromitites in the region, it has a higher value and varies between 60 and 70.93 wt.%. Therefore, Kutak chromitite with Cr# between 0.57 and 0.63 are in the high-Al chromitites range, and Kuhshah, Faryab and colored-mélange chromitites (Cr# between 0.80 and 0.95) are in the high-Cr chromitites group. Discussion The chemical composition of chromian spinel is widely used to determine the origin of magma and also to determine the tectonic setting of peridotites (Dick and Bullen, 1984; Kamenetsky et al., 2001). The chromian spinel in the ophiolitic peridotites and chromitites studied in the western Makran region shows a relatively wide range in terms of Cr# content. The high Mg# and low Cr# content in the chromian spinels of harzburgite rocks indicate the remnants of a relatively depleted mantle melt. The Cr# content of the chromian spinels in dunites and high-Al chromitites can often be explained by melt-rock reaction and chemical equilibrium with similar MORB melts, while the Cr# content in high-Cr chromitites points to the effective role of Mg-rich magmas or boninitic melts in the melt-rock reaction. The chemical compositions of chromite as well as the chemistry of the parental magma calculated using the Al2O3 content and the FeO/MgO ratio indicate that the genesis of the mantle peridotites of the Bajgan complex evolved in a supra-subduction environment (SSZ). As the obtained data of this study display the chemical diversity of chromites indicates a complex history of chemical and tectonic evolution, which is related to the heterogeneity of the mantle origin, different degrees of partial melting of the host rock, the compositional diversity of the reacting melts (MORB-like melts to boninitic melts), the evolution of the tectonic setting during the initial stages of subduction, and the development of the fore-arc tectonic environment. Conclusion The study of chromite deposits in the Bajgan complex and colored-mélange complex in western Makran reveals significant variations in chromian spinel chemistry, reflecting diverse magmatic and tectonic processes. High-Al chromitites (e.g., Kutak) suggest melt-rock reactions with MORB-like melts, while high-Cr chromitites (e.g., Kuhshah, Faryab) indicate interaction with boninitic melts in a supra-subduction zone (SSZ) setting. The chemical diversity of chromites points to a complex mantle evolution involving heterogeneous sources, varying degrees of partial melting, and changing tectonic conditions during subduction initiation and fore-arc development. These findings enhance understanding of ophiolite formation and chromite genesis in the Makran zone. Acknowledgment Authors gratefully thanks Dr. Manuela Nazzari (HPHT Lab., INGV-Roma, Italy) and Prof. Federico Lucci (DISTEGEO, University of Bari, Italy) for providing the original EMP raw chemical analyses and the related calculated stoichiometry presented in this manuscript. رخنمون‌های الترامافیک مجموعة بجگان (باختر مکران) دربردارندۀ واحدهای گوناگونِ دونیت، پیروکسنیت و هارزبورگیت هستند. توده‌های کرومیتی از نوع کرومیت‌های نوع آلپی هستند و بیشتر به‌صورت لنزها یا عدسی‌هایی نمایان شده‌اند که نیام‌های دونیتی و هارزبورگیت میزبان آنها را فراگرفته‌اند. بافت کرومیت‌ها به‌صورت توده‌ای، نیمه‌توده‌ای و پراکنده (افشان) است. مقدار Cr# در سنگ‌های هارزبورگیتی در محدودۀ 24/0 تا 30/0 و مقدار Mg# در محدودۀ 71/0 تا 76/0 تغییر می‌کند. مقدار Cr# در دونیت‌ها از 50/0 تا 75/0 و مقدار Mg# از 19/0 تا 63/0 متغیر است. مقدار Cr# در کرومیتیت‌ها نیز گسترۀ بالایی از نزدیک به 57/0 تا 63/0 (کرومیت‌های Al-بالا) تا مقدار 80/0 تا 95/0 (کرومیت‌های Cr-بالا) دارد. مقدار بالای Mg# و مقدار کم Cr# در کروم-اسپینل‌های سنگ‌های هارزبورگیتی نشان‌دهندۀ بازمانده‌های ذوب‌بخشی یک گوشته کمابیش تهی‌شده است. از سوی دیگر، میزان Cr# کروم-اسپینل‌های درون دونیت‌ها و کرومیت‌های Al-بالا بیشتر با واکنش گدازه- سنگ و تعامل با گدازه‌های همانند MORB توجیه‌شدنی است؛ اما مقدار Cr# در کرومیت‌های Cr-بالا نشان‌دهندۀ نقش مؤثر ماگماهای سرشار از Mg و یا گدازه‌های بونینیتی در واکنش گدازه- سنگ و تحولات شیمیایی سنگ است. ترکیبات شیمیایی کرومیت و شیمی ماگمای مادر آنها نشان‌دهندۀ تحول پریدوتیت‌های گوشته‌ای مجموعة بجگان در یک محیط فرافرورانش[1] است. بر پایۀ یافته‌های این پژوهش، تنوع شیمیایی کرومیت‌ها گویای تاریخچة پیچیده تحولات شیمیایی و زمین‌ساختی است که با ناهمگنی خاستگاه گوشته‌ای، درجات مختلف ذوب‌بخشی سنگ میزبان، تنوع ترکیبی گدازه‌های واکنش‌دهنده (گدازه‌های شبه MORB تا گدازه‌های بونینیتی)، تحولات جایگاه زمین‌ساختی در مراحل آغاز فرورانش و توسعه محیط زمین‌ساختی پیش کمانی پیوستگی دارد. [1] Suprasubduction zone (SSZ)

https://ijp.ui.ac.ir/article_29577_0c8176bc9ea656621b0724d191f83c96.pdf

دانشگاه اصفهان پترولوژی 2228-5210 16 2 2025 06 22 Mantle heterogeneity beneath the oceanic crust of forearc basin of Nain ophiolite based on the composition of pyroxenes in harzburgites ناهمگنی گوشتة زیر پوستة اقیانوسی در پهنة پیش‌کمانی افیولیت نایین بر پایة ترکیب پیروکسن‌های درون هارزبورگیت‌ها 45 72 29681 10.22108/ijp.2025.145418.1364 FA الهه صفدری دانشجوی کارشناسی‌ارشد، گروه پترولوژی، دانشکده علوم‌پایه، دانشگاه تربیت مدرس، تهران، ایران نرگس شیردشت‌زاده استادیار، گروه پترولوژی، دانشکده علوم‌پایه، دانشگاه تربیت مدرس، تهران، ایران Journal Article 2025 06 07 Introduction The Nain ophiolite in Central Iran has been the subject of numerous petrological investigations, particularly focusing on its ultramafic rocks. The present study examines the crystal chemistry of pyroxenes in harzburgite massifs from the southern Separab area in order to compare with those of the central (near Sucheh village) and eastern parts of the Nain ophiolite (Darreh Deh region). Understanding mantle heterogeneity is crucial for interpreting the tectonomagmatic conditions of forearc oceanic lithosphere (Ishii et al., 2019a; Zheng, 2019a). This study examines the oceanic lithosphere remnants of Nain ophiolite in the northwest of Central East Iranian Microcontinent (CEIM), where mantle peridotites record suprasubduction zone (SSZ) processes (Mehdipour et al., 2010; Pirnia et al., 2013; Shirdashtzadeh et al., 2014). Previous work documented a lherzolite-harzburgite-dunite transition (Pirnia, 2007; Shirdashtzadeh, 2014) formed by melt-rock interactions in a suprasubduction setting (Pirnia et al., 2010, 2018). While peridotites from the central and southern sections have been studied (e.g., Mehdipour et al., 2010; Pirnia et al., 2013), the western exposures near Separab (or Separo) village remain poorly characterized. A preliminary study by Safdari and Shirdashtzadeh (2024) have shown compositional heterogeneity for the olivines in the various harzburgite massifs of the aforementioned ophiolite. Chemical analysis of constituent minerals in these rock units provides critical insights into the origin and the nature of the oceanic lithospheric mantle sequence. Among these, pyroxenes - particularly clinopyroxene - serve as important petrogenetic indicators due to their refractory nature and high chemical/physical resistance, especially against alteration processes. As demonstrated in numerous studies (e.g., Aldanmaz, 2012; Mohamed et al., 2013; Nishio et al., 2022; Ghorbani et al., 2024), their chemistry has been extensively used to determine the nature and the origin of host rocks. Therefore, this study conducts detailed petrographic and chemical analyses of clinopyroxene and orthopyroxene in harzburgite outcrops south of Separab village to investigate the nature and the evolution of the mantle beneath the Neotethyan oceanic lithosphere. The obtained results are then compared with previously studied harzburgite samples from other sections of this ophiolite by various researchers. Geological Background The Nain ophiolite, located in central Iran, is a part of the larger Central Iranian tectonic zone representing the remnants of the Neotethyan oceanic lithosphere. The ophiolitic sequence includes harzburgites, which are key to understanding mantle processes during subduction initiation. The studied harzburgites from Separab, Suché, and Darreh Deh exhibit variations in mineralogy and geochemistry, suggesting different tectonic settings. The Separab harzburgites are dominated by olivine, orthopyroxene, and minor clinopyroxene (<5 vol%) and spinel, whereas the Sucheh and Darreh Deh harzburgites show greater evidence of subduction-related metasomatism. These differences imply that the Separab harzburgites may represent an earlier stage of forearc mantle evolution, while the Sucheh and Darreh Deh harzburgites reflect a more mature SSZ environment. Analytical Methods Field sampling was conducted to collect fresh, least-altered samples. Thin sections were prepared using resin mounts (without coverslips) and examined under an Olympus BH-2 polarizing microscope at Tarbiat Modares University. Selected polished thin sections were analyzed for major elements compositions of clinopyroxene and orthopyroxene using a JEOL JXA8800R electron microprobe (accelerating voltage: 15 kV; beam current: 15 nA; spot size: 3 µm) at Kanazawa University, Japan. Structural formulas and end-member components of pyroxenes were calculated based on 6 oxygen atoms per formula unit using Excel spreadsheets. Mineral abbreviations follow Warr (2021). Discussion The geochemical differences between the Separab harzburgites and those from Sucheh and Darreh Deh suggest two possible models for their formation: Two-Stage Formation Model: The Separab harzburgites may be older, originating in a Jurassic mid-ocean ridge (MOR) setting, while the Sucheh and Darreh Deh harzburgites formed later in a Late Cretaceous SSZ-like forearc environment above the subducting Neotethyan slab. Given that the pyroxene chemistry in all the studied harzburgites resembles that of the harzburgites from subduction-related zones (though the subduction-related chemical indicators are less pronounced in the Separab area compared to other regions), this model may not be valid for the formation of these harzburgites. Therefore, the harzburgites in the southern Separab were likely not formed in an ancient mid-ocean rift environment during the Jurassic period. Single-Stage Formation with Progressive Subduction Influence: The Separab harzburgites formed in a young forearc rift (MOR-like FAB) during the initial stages of subduction, where the mantle wedge was less affected by slab-derived fluids. In contrast, the Sucheh and Darreh Deh harzburgites formed later in the same Late Cretaceous period but under greater subduction influence (SSZ-like FAB), as the mantle wedge became more metasomatized by slab-derived fluids. The chemical composition of pyroxenes (Figs. 5-10), lower oxygen fugacity, higher temperatures (1456–1487°C) recorded in Separab pyroxenes suggest lower mantle partial melting with minimal influence of subduction-related fluids, whereas the Sucheh and Darreh Deh pyroxenes reflect more hydrated conditions of mantle wedge (e.g., chemistry of pyroxenes (Figs. 5–10), higher oxygen fugacity, lower melting temperatures) that is typical characteristics of SSZ settings. Various compositional plots for pyroxenes (Figs. 5–10) clearly distinguish the initial MOR-like FAB nature of Separab harzburgites from the SSZ-like nature of Sucheh and Darreh Deh harzburgites, supporting the interpretation of a heterogeneous mantle wedge beneath the oceanic lithosphere in this forearc basin. Conclusion The Nain ophiolite, situated north of Nain city in the Central Iranian zone, contains harzburgite units exposed in various sections, including the northwestern area near Separab village. This harzburgite consists mainly of olivine and orthopyroxene, with minor clinopyroxene (<5 vol%) and spinel. Geochemical analyses reveal that the Separab harzburgite pyroxenes (Cr#>0.3, Na₂O >0.1 wt%) formed at higher temperatures (1456–1487°C) and lower oxygen fugacity (higher AlVI/AlIV), indicating lower degrees of mantle wedge partial melting. These features suggest an initial forearc setting resembling mid-ocean ridge-like forearc basalt (MOR-like FAB). In contrast, harzburgites from the eastern (Darreh-Deh) and southern (Sucheh) sections developed under lower temperatures and higher oxygen fugacity, reflecting a mature forearc setting with subduction-related signatures (SSZ-like FAB). These compositional differences highlight temporal heterogeneities in the sub-arc mantle, driven by the advancing stages of slab subduction. The Nain ophiolite thus, records a transition from early, MOR-like forearc magmatism to later, SSZ-dominated conditions, documenting the evolution of the subduction system. افیولیت نایین یکی از افیولیت‌های پیش‌کمانیِ (FAB[1]) مزوزوییک ایران مرکزی در امتداد گسل نایین-بافت و در حاشیة شمال‌باختری خردقارة شرق-ایران مرکزی (CEIM[2]) در استان اصفهان است. در این پژوهش، شیمی عنصرهای اصلی اورتو- و کلینوپیروکسن‌ها در هارزبورگیت‌های شمال‌باختری این افیولیت (جنوب سپرآب) با بخش‌های میانی (نزدیک روستای سوچه) و خاوریِ (منطقة دره‌ده) آن مقایسه و بررسی شدند. با توجه به ‌ترکیب شیمیایی متفاوت پیروکسن‌ها در هارزبورگیت‌های سپرآب (مانند: میزان Cr#>3/0 و Na2O >1/0 درصدوزنی، AlVI/AlIV بیشتر) و تأثیر کمتر سیالات آزادشده از تختة فرورونده (و در پی آن، دمای ذوب بالاتر پیروکسن‌ها (1456 و 1487 درجة سانتیگراد)، فوگاسیتة اکسیژن کمتر، درجة ذوب‌بخشی کمتر در گوشته) نسبت به دو منطقه دیگر، می‌توان گفت هارزبورگیت‌های سپرآب در یک جایگاه پیش‌کمانی اولیه با شباهت بیشتر به کافت میان ‌اقیانوسی (MOR[3]-like FAB) پدید آمده‌اند؛ اما پیدایش هارزبورگیت‌های سوچه و دره‌ده در مراحل پیشرفته‌تر فرورانش پوستة اقیانوسی و در پی تکامل و بلوغ محیط پیش‌کمانی روی داده است که در پی آن، سیالات رهاشده از تختة اقیانوسی فرورونده دمای ذوب گوة گوشته‌ای را کاسته‌اند و ذوب‌بخشی گوة گوشته‌ای را افزوده‌اند و از‌این‌رو، همانندی بیشتری به هارزبورگیت‌های پهنه‌های فرورانش (SSZ[4]-like FAB) پیدا کرده‌اند. بر پایة این دسته‌بندی، چه‌بسا هارزبورگیت‌های جنوب سپرآب در مراحل آغازین و نخستینِ پیدایش این پهنة پیش‌کمانی پدید آمده‌اند و از هارزبورگیت‌های بخش‌های میانی و خاوری این افیولیت قدیمی‌تر هستند. این ویژگی‌ها تحولات و یا ناهمگنی‌های ترکیبی گوشته‌ای در زیر پوستة اقیانوسی پیش‌کمانی در حال بلوغ را در ارتباط با میزان پیشروی تختة فروروندة اقیانوسی در گوشته در طول زمان به‌خوبی نشان می‌دهد. [1] Forarc Basin [2] Central East Iranian Microcontinent [3] Mid-Oceanic Ridge [4] Suprasubduction Zone

https://ijp.ui.ac.ir/article_29681_4cf72fd92d3844ac838de40ab974df35.pdf

دانشگاه اصفهان پترولوژی 2228-5210 16 2 2025 06 22 Petrogenesis and tectonic setting of Bagh Pain granitoid body, Shahin Dezh, West Azerbaijan Province; using chemical minerals سنگ‌زایی و جایگاه زمین‌ساختی تودة گرانیتوییدی باغ‌پایین، شاهین‌دژ‌، استان آذربایجان‌ غربی؛ با کمک از شیمی‌کانی‌ها 73 96 29720 10.22108/ijp.2025.145465.1362 FA اکرم نیازی دانشجوی دکتری، گروه زمین‏‌شناسی، دانشکده علوم، دانشگاه لرستان، لرستان، ایران رضا زارعی سهامیه استاد، گروه زمین‏‌شناسی دانشکده علوم دانشگاه لرستان، لرستان، ایران رسول اسمعیلی دکتری، موسسه ژئوفیزیک، دانشگاه تهران، تهران، ایران زهرا طهماسبی دانشیار، گروه زمین‏‌شناسی، دانشکده علوم، دانشگاه لرستان، لرستان، ایران میرمحمد میری استادیار، گروه زمین‏‌شناسی، دانشکده علوم زمین، دانشگاه شهید چمران اهواز، اهواز، ایران Journal Article 2025 06 07 Introduction Granitoids represent the primary components of orogenic belts with a wide range of compositional variations (Kaygusuz et al., 2008). Therefore, analyzing the composition of granitoids contributes significantly to the understanding of continental crust formation and evolution (Barbarin, 1999). Mineral compositions provide insights into the pressure-temperature conditions and the nature of the magma during granite emplacement, and estimating these parameters for a magmatic body is crucial for interpreting petrogenesis and regional tectonic settings (Abdel-Rahman, 1994; Moazzen and Droop, 2005; Gomes and Neiva, 2005; Zhang et al., 2006; Mazhari et al., 2008; Shabani et al., 2010; Sahin et al., 2010). Mineral composition reflects the pressure, temperature, and magmatic characteristics during granite emplacement, and determining these physical and chemical conditions is essential for accurately interpreting petrogenetic processes and understanding the broader tectonic framework of a region (Mazhari et al., 2008; Shabani et al., 2010; Sahin et al., 2010). The mineral assemblage and its chemical composition within igneous rocks are significantly influenced by the original magma composition and the prevailing physicochemical conditions during the crystallization process. The minerals analyzed in this study—namely plagioclase, biotite, and amphibole—exhibit geochemical signatures that offer valuable insights into magmatic crystallization dynamics and melt evolution. The purpose of this study is to investigate the chemistry of plagioclase, biotite, and amphibole minerals and to determine the magmatic origin on the base of chemical composition of aforementioned minerals. Geological Setting The Bagh pain granitoids are located between the geographical longitudes of 46'35°6'E and 46'33°46'E and the geographical latitudes of 36'25°36'N and 36'26°36'N, 50 km south of Shahin dej County and 50 km north of Takab City in the Sanandaj-Sirjan Zone. Based on geological maps and uranium-lead dating studies, the granitoid rocks of the region belonging to Late Cretaceous, were probably generated under the influence of the Late Laramide and Cimmerian orogenic phases. The rocks under study are classified as volcanic arc type and I-type granite. Materials and Methods In this study, a total of 120 samples were collected from all intrusive units during a field visit to the area, and the most intact specimens were selected based on minimal weathering. Subsequently, 40 thin sections were prepared at Bu-Ali Sina University in Hamedan, where petrological investigations were carried out using a polarizing microscope. In addition, 9 representative samples, carefully selected from over one hundred analyzed points, were sent to the University of Vienna, Austria, for detailed microprobe analysis. These samples were subsequently examined using high-resolution electron microscopy and backscattered electron (BSE) imaging techniques. After carbon coating, they underwent rapid semi-quantitative elemental analysis using a CAMECA SX Five Electron Microprobe equipped with a field emission cathode and an energy-dispersive X-ray (EDX) system, operating at an accelerating voltage of 20 keV, a probe current of 25 nanoamperes, and a beam diameter of 60 μm, in the Lithosphere Research Group laboratory at the University of Vienna. Discussion Abdel-Rahman (1994) through the analysis of MgO, Al₂O₃, and FeO oxides in biotite minerals, proposed several geochemical classification diagrams to categorize granitoid rocks into three distinct magma series, which correspond to three tectonic zones. These classifications are derived from the type and relative concentrations of iron, magnesium, and aluminum present within the mineral structure. Zone A corresponds to alkaline, non-orogenic igneous rocks. The C range encompasses calc-alkaline magmas typically generated in subduction-related orogenic settings and is representative of I-type granites, whereas the P range includes peraluminous magmas formed in collisional orogenic environments, which are characteristic of S-type granites. Based on the geochemical discrimination diagrams utilized in this study, all analyzed samples plot within the C range, thereby indicating that the biotites in the investigated area are genetically linked to subduction-related calc-alkaline magmatic systems. Considering the relative concentrations of Na₂O and Al₂O₃ compared to TiO₂, it is inferred that the amphiboles exhibit alkaline and pseudo-alkaline characteristics. Pseudo-alkaline amphiboles typically contain lower levels of Ti, Na, and Al than alkaline types. Accordingly, the amphiboles present in the regional granitoid rocks exhibit a pseudo-alkaline character, which is consistent with the whole-rock geochemical data. Moreover, the TiO₂ versus Al₂O₃ discrimination diagram clearly demonstrates the involvement of both mantle-derived magmatic input and crustal contributions in the genesis and subsequent evolution of these granitoid formations. Conclusion The Bagh-Pain granitoid body comprises granite, granodiorite, diorite, and aplite units, containing quartz, plagioclase, alkali feldspar, amphibole, and biotite as major minerals, along with zircon and apatite as accessory mineral phases. Detailed chemical analyses of biotite and plagioclase indicate that the plagioclases are oligoclase and andesine, while the biotites are magnesium-rich and re-equilibrated. This mineralogical composition corresponds with the green coloration of biotites in the region, their weak pleochroism, and the association of their source rocks with subduction-related tectonic settings. Additionally, the amphiboles are identified as calcium-rich edenite and pargasite types. Based on mineral chemistry data, these rocks are closely linked to calc-alkaline magmatism and are interpreted to have originated from mantle-derived magma that was subsequently modified by crustal contamination. تودة گرانیتوییدی باغ‌پایین که در ۵۰ کیلومتری جنوب شهر شاهین‌دژ، در استان آذربایجان‌ غربی و در پهنة سنندج- سیرجان جای دارد و از دیدگاه سنگ‏‌نگاری شامل واحدهای گرانیتی، گرانودیوریتی تا تونالیتی، دیوریتی و آپلیتی است. از مهم‌ترین بافت‌ها می‌توان بافت‌های پرتیتی، میرمکیتی، پویی‌کیلیتیک، پورفیری وگرانوفیری را نام برد. کوارتز، آلکالی‏‌فلدسپار (میکروکلین)، پلاژیوکلاز، بیوتیت، مسکوویت، آمفیبول از کانی‌های اصلی و تیتانیت و زیرکن از کانی‌های فرعیِ سازندة واحد گرانیتی هستند. همچنین، (پلاژیوکلاز، کوارتز،ارتوز، بیوتیت و آمفیبول (بیشتر از نوع هورنبلند) از کانی‌های سازندة واحد گرانوادیوریتی و پلاژیوکلاز، کوارتز به مقدار کم، ارتوز، بیوتیت و آمفیبول از کانی‌های واحد دیوریتی به‌شمار می‌روند. کوارتز، آلکالی‏‌فلدسپار (میکروکلین)، پلاژیوکلاز، بیوتیت، مسکوویت، آمفیبول از کانی‌های اصلی سازندة واحد آپلیتی هستند. همچنین، تیتانیت، زیرکن و تورمالین و ... از کانی‌های فرعی در همة این واحدهای سنگی هستند. محیط زمین‏‌ساختی این سنگ‌ها وابسته به کمان آتشفشانی و محیط‌های فرورانشی است. بر پایة بررسی‌های شیمی‌‌کانی‌ها، پلاژیوکلازهای این سنگ‌ها دامنة ترکیبی از الیگوکلاز تا آندزین دارند و بیوتیت‌ها از نوع بیوتیت‌های منیزیم‌دار و بازتعادل‌یافته هستند، همچنین، آمفیبول‌های این توده سنگی از نوع ادنیت و پارگازیت هستند.

https://ijp.ui.ac.ir/article_29720_13090f3ba8a43e93306583fa70fa4326.pdf