دانشگاه اصفهان پترولوژی 2228-5210 16 1 2025 05 21 Geochemistry and petrogenesis of mafic and intermediate dyke swarms in eastern Tafresh (Urumieh-Dokhtar magmatic belt) زمین‌شیمی و سنگ‌زایی مجموعة دایک‌های مافیک و حد واسط در خاور تفرش (پهنة ماگمایی ارومیه- دختر) 1 22 29271 10.22108/ijp.2025.143646.1347 FA احمدرضا احمدی استادیار، گروه زمین‌شناسی، دانشگاه پیام‌نور، تهران، ایران بهناز حسینی استادیار، گروه زمین‌شناسی، دانشگاه پیام‌نور، تهران، ایران Journal Article 1403 09 21 Introduction The Urumieh-Dokhtar magmatic belt is one of the most active magmatic regions of Iran during the Cenozoic era. There are differing views regarding the tectonomagmatic setting of this magmatism; some attribute it to active continental margin magmatism, island arcs, post-collisional regions, and intra-continental rifts (Hassanzadeh, 1993; Shahabpour, 2007; Ghasemi and Talbot, 2006). The study area as the other sections of the Urumieh-Dokhtar Belt, is the area of Eocene magmatic activity. The geochemical characteristics of volcanic rocks in the northeast of Tafresh are similar to those of magmatism in active continental margin subduction zones (Nasiri Bezanjani, 2006). In the eastern part of Tafresh, numerous dikes cut through Paleozoic and older sedimentary and volcanic units. K-Ar dating of these dikes indicates an age of 15.4 million years (Ghorbani et al., 2014). Babazadeh et al. (2022) have provided a U-Pb age of 17.5 million years for the mafic dykes. This study examines the petrology and geochemistry of the Mafic and intermediate dyke bodies located in the eastern part of Tafresh and discusses their tectonomagmatic setting. Geology The study area lies in the central part of the Urumieh-Dokhtar magmatic belt. Cenozoic sedimentary-volcanic deposits unconformably overlie Upper Cretaceous marly limestones due to the Laramide orogeny, which uplifted the region. Eocene units comprise alternating marine and continental deposits of volcanic flows, pyroclastics, and sediments. Marine transgression during early Eocene introduced marl-sandstone units (E1), followed by dominant volcanic activities forming basaltic to rhyolitic flows and pyroclastics (E2). Continental red deposits and marine green layers alternate. Later, marine conditions resumed (E3), forming sedimentary layers with green tuffs, while subsequent continental volcanic phases (E4) produced dacitic flows and tuffs. Renewed marine sedimentation (E5) followed, then thick terrestrial volcanic layers of andesitic-basalts (E6). Extensive dykes, mostly basaltic-intermediate, intrude older units, with U-Pb dating indicating Miocene age (17.5 Ma). Analytical method 8 samples with the least alteration were selected for analysis of major and trace elements. The analysis of major and trace elements was carried out using the ICP-MS method (LF200 analytical system) at the ACME-Bureau Veritas Laboratory in Canada. For the study of the chemistry of clinopyroxene, plagioclase, and amphibole minerals, 15 points were analyzed using an electron microprobe at the University of Milan, Italy. Petrography and mineral chemistry Diabase: These rocks display a doleritic texture with minimal groundmass. Plagioclase crystals dominate (70 vol.%). The other primary minerals include clinopyroxene and iron-titanium oxides, while amphibole, alkali feldspar, olivine, and apatite appear as accessory minerals. Secondary minerals, such as calcite, chlorite, and epidote, form from plagioclase and clinopyroxene alteration. Basaltic andesite: These rocks comprise plagioclase (60–70 vol.%), amphibole (10–20 vol.%), iron-titanium oxides (5–10 vol.%), and clinopyroxene (5–10 vol.%), with accessory alkali feldspar, olivine, and apatite. Phenocrysts make up to 40 vol.% of the total volume, primarily plagioclase and amphibole. Secondary minerals, including chlorite and epidote, are present in the groundmass. Andesite: The primary minerals in these rocks are plagioclase (70–80 vol.%), iron-titanium oxides (10–20 vol.%), and amphibole (5–10 vol.%), with minor pyroxene, alkali feldspar, and apatite in the groundmass. The matrix consists of plagioclase microlites and fine-grained oxides, with secondary minerals like calcite, epidote, and sericite. The clinopyroxene crystals are of the salite type, and the plagioclase crystals ranging in composition from labradorite to andesine. Additionally, the amphiboles are of the pargasite type. Geochemistry The continuity of trends in Harker diagrams for the studied samples suggests a common origin. Increasing Na2O+K2O and decreasing MgO, FeOt, TiO2, Al2O3, and CaO/Na2O along with increasing SiO2 indicate that the crystallization and separation of ferromagnesian minerals (especially clinopyroxene) with feldspar and Fe-Ti oxides played a significant role in the magmatic evolution of these rocks. On TAS diagram, the samples are classified as basalt, basaltic andesite, and andesite. Using immobile elements on the Zr/TiO2 versus Nb/Y diagram, the samples fall within the basaltic andesite field. All samples plot in the sub-alkaline field on the alkaline-subalkaline discrimination line. On AFM diagram, the samples lie near the boundary between tholeiitic and calc-alkaline series. Based on K2O versus SiO2, they range from medium-K calc-alkaline to low-K tholeiitic compositions. The chondrite-normalized REE patterns show enrichment in LREE relative to MREE and HREE, with flat MREE-HREE trends. The spider diagram normalized to the primitive mantle reveals LILE enrichment and HFSE depletion. Source and Tectonomagmatic Setting The gentle slope between HREEs and MREEs in the REE pattern is consistent with the magma's origin from a spinel lherzolite mantle with little or no garnet involvement. Furthermore, in the Dy/Yb versus La/Yb diagram, the studied rocks fall within the range of melts originating from a spinel lherzolite mantle, and in the Nb/La versus La/Yb diagram, they lie within the lithospheric mantle field. Based on Nb/Th ratio versus Nb and the Ba/Nb ratio versus La/Nb, the studied rocks are located in the volcanic arc-related rocks field. In the Th-Hf-Ta diagram, the samples are placed within the magmatic arc-related rocks field. Also, based on the Nb/La ratio versus La/Yb, the samples fall within the active continental margin-related rocks field. However, in the Th/Yb versus Ta/Yb diagram, the samples fall within both the island arc and active continental margin-related rocks fields. Overall, the studied rocks display some characteristics to those of Island arcs and some others to those of active continental margins. Conclusion The rare earth element patterns indicate that the magma associated with these igneous rocks originated from partial melting of the shallow lithospheric mantle in the spinel peridotite facies, with minimal or absent garnet involvement. Additionally, the observed characteristics in the incompatible element patterns, such as enrichment of mobile elements over rare earth elements and depletion of immobile elements, along with analyses in various geochemical diagrams, suggest their association with subduction-related magmatism. However, the studied rocks display geochemical criteria belonging to island arc as well as active continental margin magmatism The intermediate geochemical features of island arc and active continental margin magmatism, along with other evidence including the association of these igneous rocks with a thick sequence of green tuffs and other shallow marine sediments indicate that the rocks under study originated in an intra-continental back-arc basin در خاور تفرش، مجموعه‌ای گسترده‌ای از دایک‌ها با سن میوسن در واحدهای آتشفشانی و رسوبی ائوسن نفوذ کرده‌‌اند. از دیدگاه زمین‌شیمیایی، دایک‌های مافیک و حد واسط ویژگی‌های سنگ‌های وابسته به سری کالک‌آلکالن با پتاسیم متوسط را نشان می‌دهند. در الگوهای عنصرهای خاکی کمیاب، عنصرهای LREE در مقایسه با عنصرهای MREE تا اندازه‌ای غنی شده‌اند (میانگین میزان (La/Sm)Cn نزدیک به 5/2)، درحالی‌که عنصرهای MREE نسبت به عنصرهای HREE غنی‌شدگی چندانی نشان نمی‌دهند. در الگوی عنصرهای ناسازگار، غنی‌شدگی عنصرهای LILE و تهی‌شدگی عنصرهای HFSE در مقایسه با عنصرهای LREE همانندِ الگوی سنگ‌های ماگمایی وابسته به پهنه‌های فرورانش است. با وجود این، ویژگی‌های زمین‌شیمیایی سنگ‌های یادشده همانندِ ویژگی‌های زمین‌شیمیایی سنگ‌های آذرینِ پدیدآمده در پهنة پشت‌کمان قاره‌ای[1] است. گمان می‌رود در مراحل پایانی فرورانش نئوتتیس به زیر ایران‌مرکزی و کاهش سرعت فرورانش و در پی آن افزایش شیب ورقة فرورونده، زمین‌ساخت کششی بر منطقه حاکم شده است. این زمین‌ساخت کششی به نازک‌شدگی گوشتة سنگ‌کره‌ای و پوستة قاره‌ای و هم‌زمان بالاآمدن سست‌کره انجامیده است. گوشتة سنگ‌کره‌ای که پیشتر تحت‌تأثیر سیال‌ها و گدازه‌های آزادشده از ورقة فرورونده بوده است، اکنون به‌علت ذوب‌بخشی، گدازه‌هایی با ویژگی‌های ماگماهای پهنه‌های فرورانش را پدید آورده است. گسترش شکستگی‌های کششی در واحدهای پالئوژن، فضای خوبی را برای جایگیری دایک‌ها در زمان میوسن فراهم کرده است. [1] intra-continental back-arc basin

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دانشگاه اصفهان پترولوژی 2228-5210 16 1 2025 03 21 Direklo-Mehdikhan Alkaline Basalt District, an Indication of a Quaternary Continental Within Plate Extensional Mechanism پهنة بازالت آلکالن دیرکلو- مهدی‌خان، نشانه‌ای از یک سازوکار کششی درون‌صفحه قاره‌ای کواترنری 23 50 29364 10.22108/ijp.2025.143905.1350 FA فاطمه نریمانی دانشجوی دکتری، گروه زمین‌شناسی، دانشکده علوم‌، دانشگاه اصفهان، اصفهان، ایران محمدعلی مکی زاده دانشیار، گروه زمین‌شناسی، دانشکده علوم، دانشگاه اصفهان، اصفهان، ایران مرتضی شریفی دانشیار، گروه زمین‌شناسی، دانشکده علوم، دانشگاه اصفهان، اصفهان، ایران Journal Article 2025 01 07 Introduction The Direklo-Mehdikhan volcanic district is the largest volcanic region within the Qorveh-Bijar Quaternary volcanic belt, located near Qorveh in Kurdistan province, Iran. The Qorveh-Bijar Quaternary basic volcanic belt lies between the provinces of West Azerbaijan and Kurdistan, within the Sanandaj-Sirjan zone as a segment of the Alpine-Himalayan Orogeny with a Gondwana-affinity basement. The Orogeny is strongly influenced by the Middle-Late Tertiary post-orogenic development that followed the continental collision between the Arabian and Eurasian plates. Following the collision, the SSZ continental lithosphere was thickened (Agard et al., 2005), leading to a lithospheric thickness of ~150–170 km (Priestley and McKenzie, 2006). In this district, the deposits of pyroclastic origins and scoria, which erupted from a thick lithosphere, are covered by alkaline basic lava flows (Neill et al., 2015). The primary objective of the present study is to provide evidences for the subduction of the Neotethys oceanic plate beneath the Eurasian margin and the collision of the Arabian plate. Therefore, this study focuses on the Direklo-Mehdikhan volcanic district. Petrographic observations, along with whole-rock geochemstry and clinopyroxene mineral chemistry, were carried out to enhance our understanding of the magmatic activity of the Direklo-Mehdikhan volcanic district. Research Methods The study started by fieldwork, petrographic analysis, and geochemical investigations. Field observations were conducted on the lava flow situated between the villages of Direklo and Mehdikhan. Samples were collected from various locations within the lava flow, and thin sections were prepared for petrographic examination. Additionally, geochemical data on pyroxene crystals and whole-rock samples were analyzed to explore the origin and the evolution of the lava flow body. All EMPA and whole-rock analyses were performed at the Central Laboratory of Moscow State University in Russia and the Australian Lab West, respectively. Results and Discussion The main mineral components which are defined by aphanitic to porphyritic texture, are phenocrysts mainly consist of olivine and pyroxene. The matrix includes plagioclase, opaque minerals, glass, and similar microcrystalline mineral phases. In some samples, xenoliths and quartz xenocrysts is observed. These fragments likely detached from adjacent rocks and were incorporated during magma ascending the crust. The studied samples primarily exhibit a porphyritic texture, with additional secondary textures observable in some samples, such as glomeroporphyritic, sieve, vesicular, vitrophyric, amygdaloidal, hyalomicrolitic, and microlithic porphyritic. The formation of porphyritic texture formed during a crystallization stage deep within the Earth (where phenocrysts crystallize), followed by further crystallization at or near the Earth's surface, resulting in the development of finer crystals. The presence of a glassy background and the microlithic texture is largely due to insufficient time for the remaining magma to crystallize at shallow depths or close to the surface (Shea, 2017). EPMA results of clinopyroxene indicate that the clinopyroxenes are classified within the iron-magnesium-calcium pyroxenes quadrilateral and are identified as diopside type. The Mg number (Mg#) for these minerals ranges from 0.82 to 0.92 (Figures 5A and 5B). The chemical composition of clinopyroxene demonstrate the alkaline magmatic series, as well as the extensional and intraplate tectonic environments. The crystallization process is believed to have occurred under conditions of high oxygen fugacity (Figures 5C and 5D). The calculated temperature and pressure conditions for the crystallization of clinopyroxenes indicate a pressure range of 6 to 10 kbar and a temperature range of 1160 to 1250 °C (Figure 6). The variation in crystallization pressure is attributed to existence of multiple magma chambers and the clinopyroxene crystallization during the rapid ascent of magma (Özdemir et al., 2020). Based on geochemical discrimination diagrams, the samples plot in the alkaline series and low-SiO2 basalt (Figure 7-A). Normalized rare earth elements (REEs) diagrams, along with various elemental ratios such as Nb/Pb, La/Sm, Nb/U, and La/Yb, reveal a significant enrichment of light rare earth elements compared to heavy elements. This suggests the involvement of an enriched mantle, characterized by the presence of garnet in the source and a low degree of partial melting. So, the magma originated from a garnet lherzolite source during a partial melting process with a melting percentage of less than 5% and showed some clues of crustal contamination (Figures 14 and 15). Conclusions Field studies, petrographic, and geochemical analysis of the Direklo-Mehdikhan low-SiO2 alkaline basalt reveals valuable insights into the subduction of the Neotethys Oceanic crust and post-collisional mantle-derived mafic magmatism within intracontinental extensional settings. Normalized elemental diagrams, in comparison to primitive mantle compositions, reveals an enrichment in large-ion lithophile elements (LILE) and light rare earth elements (LREE) relative to high field strength elements (HFSE). Negative anomalies are observed in niobium (Nb) and titanium (Ti). Petrographic evidence and geochemical data indicate that local extensional and depressurization activities triggered low-grade partial melting (less than 5%). The parent magma derived from enriched garnet lherzolite at the pressure varying from 6 to 10 kbar and a temperature ranging from 1160 to 1250 °C. This process engaged in magma ascending rapidly to surface with minimal contamination by crust. در شمال‌خاوری استان کردستان، شهرستان قروه، و در فاصله میان روستاهای مهدی‌خان و دیرکلو، پهنه‌ای از سنگ‌های بازالتی با ماهیت آلکالن روی رسوبات کواترنری جای گرفته‌ است. بررسی‌ مقاطع نازک تهیه شده از سنگ‌های منطقه مشخص کرده که این سنگ‌ها درشت بلورهایی از الیوین، کلینوپیروکسن و پلاژیوکلاز دارند که در زمینه‌ای از ریزبلورهای پلاژیوکلاز، پیروکسن، کانی‌های کدر و شیشه آتشفشانی قهوه‌ای رنگ جای گرفته‌اند. بافت اصلی این نمونه‌ها پورفیریتیک است و پیروکسن‌های آنها افزون‌بر بافت زونینگ ترکیبی و غربالی، بافت سری‌اِیت و گلومرول نیز دارند. چنین بافت‌هایی می‌تواند گویای رخداد آلایش ماگمایی و نبود تعادل ماگمایی باشد. افزون‌بر این، نمودارهای هارکر رخداد تبلوربخشی را نشان می‌دهند. دیگر ویژگی‌های زمین‌شیمیایی مانند آنومالی منفی در Nb، Ta و Y، غنی‌شدگی در Th/Yb، آنومالی مثبت Th، Ba و Pb، غنی‌شدگی LILE، مقدار بالای LREE، نسبت‌های Ce/Sm، Sm/Yb و نیز نسبت‌های Nb/La و La/Yb و همچنین Th/Yb و Ta/Yb نشان‌ می‌دهند خاستگاه ماگمای سازندة پهنة بازانیتی مهدی‌خان- دیرکلو ذو‌بخشی (کمتر از 5 درصدی) یک منبع گوشته‌ایِ (گارنت‌لرزولیتی) غنی‌شده با سیال‌های حاصل از تختة فرورونده بوده است. فوران این پهنة بازالتی در یک محیط کششی پس از برخورد، روی داده است.

https://ijp.ui.ac.ir/article_29364_3454fe4f0c20c163481425d44cbcc63d.pdf

دانشگاه اصفهان پترولوژی 2228-5210 16 1 2025 03 21 Geochemistry and tectonic setting of volcanic rocks in Ahovan area, northeast of Semnan (Central Iran) زمین‌شیمی و جایگاه زمین‌ساختی پیدایش سنگ‏‌های آتشفشانی منطقة آهوان، شمال‌خاوری سمنان (ایران مرکزی) 51 70 29402 10.22108/ijp.2025.144132.1351 FA سعید کامران دانش آموختة دکتری، گروه زمین‌شناسی، دانشکده علوم‌پایه، دانشگاه لرستان، خرم‌آباد، ایرانن احمد احمدی خلجی دانشیار، گروه زمین‌شناسی، دانشکده علوم‌پایه، دانشگاه لرستان، خرم‌آباد، ایران مهدی رضایی کهخائی دانشیار، گروه پترولوژی و زمین‏‌شناسی اقتصادی، دانشکده علوم‌زمین، دانشگاه صنعتی شاهرود، شاهرود، ایران پیمان اسکندرنیا دانشجوی دکتری، گروه زمین‌شناسی، دانشکده علوم‌پایه، دانشگاه لرستان، خرم‌آباد، ایران زهرا طهماسبی دانشیار، گروه زمین‌شناسی، دانشکده علوم‌پایه، دانشگاه لرستان، خرم‌آباد، ایران Journal Article 2025 01 24 Introduction Volcanic rocks widely extended throughout the Earth's continental crust (Brilhante et al., 2024). Among the different tectonic setting, a group of igneous rocks is related to volcanic arc; these rocks, according to Tang et al. (2022), include a range of mafic-intermediate rocks with SiO2 (47.34-60 wt%), Fe2O3 (11.63-73.4 wt%) and Mg coefficient (26-66 wt%), remarkable chemical criteria are related to calc-alkaline series with medium to high potassium and LILE enrichment. Moreover, the Ce negative anomaly in these rocks is consistent with the subduction zone. In this paper, based on whole-rock chemistry data, the geochemical properties of volcanic rocks of the Ahovan area in northeast of Semnan (Central Iran) are investigated. The main purpose of the present paper is the study of tectonic setting as well as the tectonomagmatism of these rocks. Analytical Methods During the field studies, 80 samples were collected from the volcanic rocks for petrographic observations. Following the preparation of thin sections, their mineralogy and textural relationships were carefully considered, and 10 of them with least alteration were sent to the ALS-CHEMEX laboratory in Canada for identification of major elements by ICP-OES and trace and rare earth elements by ICP-MS (Table 1). Furthermore, 11 samples of the Khalatbari-Jafari and Etesami (2018) were used in this study for comparison The measurement accuracy for all major elements was 0.01%w.t, the maximum measurement accuracy in the trace elements for Cr, Li, and Tl was 10 ppm and for Cs, Ho, Lu, Tb, and Tm was 0.01 ppm. Petrography According to field studies, the Eocene volcanic units, trending east-west, are much more widespread than the intrusive rocks of Ahovan area. These units have a mixed spectrum of basalt, trachyte and andesite-trachyandesite, which the latter rocks cover a large volume. The basaltic rocks, with gray and black in color, are dominated by the presence of plagioclase and clinopyroxene as the main minerals. The white and grayish white andesite-trachyandesite are characterized by the occurrence of plagioclase, clinopyroxene, amphibole and biotite as well as porphyry and microlithic porphyry textures. Trachyte rocks are white and grayish white in hand spacemen. Plagioclase and sanidine as phenocrysts and microlites constitute the main minerals of the trachyte rocks. Amphibole and biotite are small amounts in these rocks (10 vol.%). Iron oxides, calcite, chlorite and epidote are the alteration products of these minerals. Dolerite dykes, trending N-S and a maximum thickness of 2 m crosscut all the volcanic rocks. under study. Geochemistry The overall petrographic and geochemical data point to the nature of calc-alkaline to high-potassium calc-alkaline of the rocks studied, which are originated by the low-pressure melting of spinel lherzolite and developed at a depth less than the garnet stability field. In the Y versus Zr diagram, the study rocks are in the volcanic arc setting. The REE pattern of the study rocks normalized to chondrite follow the sloping pattern of calc-alkane rocks related to island arcs. In spider diagram of incompatible elements normalized to N-MORBs, the study rocks show LILE enrichment and HFSE depletion indicating the crustal contamination process involved in the formation of these rocks. The depletion of Nb, Ti and Ta show characteristics of arc islands. Moreover, LILE's enrichment such as K and Sr indicate that the rocks under study originated from the mantle metasomatism resulting from hydrous fluids penetrated from the subducting crust into the mantle wedge at different depths. Conclusion The volcanic rocks of Ahovan area are dominated by the presence of basalt, andesite-trachyandesite and trachyte belonging to Middle-Late Eocene. A series of trachybasalt and basalt-trachyandesite dykes, trending north-south, and a maximum thickness of 2 meters, crosscut the rocks of the area. The essential minerals of basalts are plagioclase and clinopyroxene and those of andesite-trachyandesite are plagioclase, clinopyroxene, amphibole and biotite. Plagioclase and sanidine are the dominant minerals of trachytes. In magmatic series diagram, all the rocks studied are in the range of calc-alkaline to high-potassium calc-alkaline series, originated from a relatively low-pressure melting of spinel lherzolite at a depth of lower than the garnet melting stability field. The Chondrite-normalized rare earth element (REE) patterns are similar to calc-alkaline rocks from island arc. Also, in the spider diagram of incompatible elements normalized to N-MORB, these rocks show enrichment in LILE and depletion in HFSE indicating the involvement of the crustal contamination process in formation of these rocks. The LILE enrichment (i.e., K and Sr) points to mantle alteration resulting from aqueous fluids penetrated from the subducting crust of the Neotethys ocean into the mantle wedge at different depths played a role in the formation of these rocks. In tectonic setting diagrams, the rocks under investigation are in the range of calc-alkaline basalts related to volcanic arcs. منطقة گردنة آهوان در حاشیة شمالی پهنة ایران مرکزی جای گرفته است. سنگ‏‌های آتشفشانی این منطقه شامل بازالت، آندزیت، تراکی‌آندزیت و تراکیت به سن ائوسن میانی- پسین هستند. این سنگ‌های آتشفشانی را دایک‏‌هایی با روند شمالی- جنوبی و ستبرای حداکثر 2 متر و ترکیب تراکی‏‌بازالت و تراکی‏‌آندزیت بازالتی قطع کرده‌اند. کانی‏‌های اصلی بازالت‏‌ها را پلاژیوکلاز و کلینوپیروکسن تشکیل می‏‌دهد.کانی‏‌های اصلی آندزیت – تراکی‏‌آندزیت شامل پلاژیوکلاز، کلینوپیروکسن، آمفیبول و بیوتیت هستند و پلاژیوکلاز و سانیدین از کانی‏‌های اصلی سازندة تراکیت‏‌ها به‌شمار می‌روند. نمودارهای زمین‌شیمیایی نشان می‏‌دهند نمونه‏‌های منطقة آهوان در محدودة کالک‌آلکالن تا کالک‌آلکالن پتاسیم بالا هستند و حاصل ذوب‏‌بخشی (2 تا 10 درصد) کم فشار اسپینل لرزولیت (ژرفای کمتر از میدان پایداری گارنت) پدید آمده‌اند. الگوی عنصرهای خاکی کمیاب بهنجارشده به ترکیب کندریت شیب‌دار است و همانند سنگ‏‌های کالک‌آلکالنِ جزیره‏‌های کمانی است. همچنین، در نمودار عنکبوتی عنصرهای ناسازگار بهنجارشده به ترکیب بازالت‏‌های میان اقیانوسی (N-MORB)، نمونه‌ها از LILE غنی‏‌شدگی و از HFSE تهی‏‌شدگی نشان می‏‌دهند. این ویژگی گویای مشـارکت فراینـد آغشتگی پوسته‏‌ای در پیدایش این سنگ‌هاست. غنی‌شدگی از عنصرهای LILE مانند K و Sr نیز نشان می‏‌دهد دگرسانی گوشته‏‌ای حاصل از سیالات آبداری که از پوستة فرورندة اقیانوس نئوتتیس درون گوۀ گوشته‏‌ای در ژرفاهای گوناگون نفوذ کرده است، در پیدایش این بازالت‏‌های کمانی نقش داشته است.

https://ijp.ui.ac.ir/article_29402_c61168c936f8b071d23c89fba70c7633.pdf

دانشگاه اصفهان پترولوژی 2228-5210 16 1 2025 03 21 Petrogenetic and mineralogical constraints in metamorphic-plutonic complex of N-Bijar, Kordestan, Iran بررسی سنگ‌زایی و کانی‌شناسی مجموعة دگرگونی-آذرین درونی شمال بیجار، کردستان، ایران 71 94 29459 10.22108/ijp.2025.144343.1353 FA مریم بافنده کارشناسی ارشد پترولوژی، گروه زمین‏‌شناسی، دانشکده علوم پایه، دانشگاه بین‌المللی امام خمینی (ره)، قزوین، ایران عباس آسیابانها دانشیار گروه زمین‏‌شناسی، دانشکده علوم پایه، دانشگاه بین‌المللی امام خمینی (ره)، قزوین، ایران، 0000-0002-4652-960X محسن نصرآبادی دانشیار گروه زمین‏‌شناسی، دانشکده علوم پایه، دانشگاه بین المللی امام خمینی (ره)، قزوین، ایران Journal Article 2025 02 12 Introduction The 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 Chemistry The 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 Conclusion The 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. مجموعة دگرگونی- آذرین درونی شمال بیجار بخشی از پهنة ساختاری سنندج-سیرجان است. تودة گرانیتی منطقه از نظر سنگ‏‌شناسی ترکیب یکنواخت لویکومونزوگرانیتی دارد و با زنولیت‏‌هایی از سنگ‏‌های دگرگونی در بر‏‌گیرنده و دایک‏‌های آپلیتی همراه است. حضور بافت‏‌های گرانوفیری و پرتیتی گویای ژرفای کم این توده است. شواهدی مانند مرزهای مضرس و بازتبلور دینامیکی در کوارتزها و حضور فراوان بافت میرمکیتی، دگرریختی دمای بالا در این سنگ‏‌ها را نشان می‏‌دهند. گرانیت شمال بیجار به شدت پرآلومین و متعلق به سری کالک‏‌آلکالن پتاسیم بالاست و از گرانیت‏‌های مایل به نوع S به‌شمار می‌رود که با شواهد کانی‏‌شناسی نیز هماهنگی دارد؛ زیرا کانی‏‌های سازندة آن سرشار از آلومینیم هستند (مانند: آلبیت- الیگوکلاز، ارتوکلاز، مسکوویت و گارنت منگنزدار (اسپسارتین)). از دیگر سو، الگوی عنصرهای کمیاب خاکی آنها نیز نوعی تهی‏‌شدگی از MREEs نشان می‏‌دهد که محصول جدایش کانی‏‌های فرومنیزیم مانند کلینوپیروکسن، هورنبلند و تیتانیت است. نتایج دماسنجی پلاژیوکلازهای لویکوگرانیت‏‌ها گویای دمای تبلور 500 تا 700 درجة سانتیگراد است. افزون‌بر این، تودة یادشده از شمار گرانیتوئیدهای کمان آتشفشانی و یا برخورد قاره‏‌ای است که احتمالاً در پی فرورانش سنگ‌کرة اقیانوسی نئوتتیس به زیر پهنة سنندج-سیرجان پدید آمده است. سنگ‏‌های دگرگونی میزبان تودة گرانیتی متابازیت و متعلق به کرتاسه هستند که تودة آذرین درونی گرانیتی درون آنها تزریق شده است. درجة دگرگونی در این سنگ‏‌ها در حد رخسارة آمفیبولیت است. مرزهای مضرسی بلورهای کوارتز، کوارتزهای روبانی، آمفیبول‏‌های ماهی‏‌گون، پیدایش بافت گرانوبلاستیک و تبلور دوباره در بلورهای کوارتز از نشانه‌های دگرریختی شکل‏‌پذیر دما بالا در آنهاست. ترکیب شیمیایی کانی آمفیبول در متابازیت‏‌ها از نوع مگنزیوهورنبلند و پارگازیت است و پلاژیوکلاز نیز از نوع الیگوکلاز است. نتایج دما- فشارسنجیِ سنگ‏‌های دگرگونی به روش‏‌های گوناگون دمای 580 تا 718 درجة سانتیگراد و فشار 2/6 تا 15 کیلوبار را نشان می‏‌دهند. سنگ مادر این متابازیت‏‌ها غالباً از نوع بازالت‏‌های ساب‌آلکالن (توله‌ایتی) در کافت‏‌های قاره‏‌ای (با غنی‏‌شدگی متوسط LREEs نسبت به HREEs) است که پس از فرورانش حوضة اقیانوسی نئوتتیس به زیر پهنة سنندج-سیرجان دستخوش دگرگونی شده‏‌اند. بالاخره، دمای کمتر تودة گرانیتی با نبود هالة دگرگونی در سنگ‏‌های دربرگیرندة متابازیتی تأیید می‏‌شود.

https://ijp.ui.ac.ir/article_29459_4aa25884e4f1086fceff57dcc30dc2f8.pdf