فهرست مطالب

نشریه پترولوژی
پیاپی 55 (پاییز 1402)

  • تاریخ انتشار: 1403/02/08
  • تعداد عناوین: 6
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  • جواد ایزدیار*، میرمحمد میری، معصومه زارع شولی صفحات 1-24

    در شمال‏ باختری سروجهان، از بالاآمدگی سلطانیه در شمال‏ باختری ایران، شیست‏ های نئوپروتروزوییک بالایی - کامبرین زیرین در آن رخداد دارند. بررسی‏ های ریزساختارها نشان می‏ دهند شیست‏ های یادشده در سه مرحله دگرریختی (D1، D2 و D3) و دو مرحله دگرگونی (M1 و M2) پدید آمده‏ اند. دگرگونی M1، همزمان با D1 رخ داده است و همتافت کانیایی گارنت + استارولیت + بیوتیت + مسکویت + کلریت + کوارتز + پلاژیوکلاز را پدید آورده است. دگرگونی M2 به‏ صورت پسرونده همزمان با فاز دگرریختی D2 روی داده است و تبلور کانی‏ های کلریت، بیوتیت، مسکوویت و کوارتز را به دنبال داشته است. فاز D3 که به‏ صورت ریزچین روی فابریک قدیمی تر (برگوارگی S2) گسترش یافته، با فاز دگرگونی همراه نبوده است. نمودارهای تعادلی فازی به دست آمده و نتایج دما-فشارسنجی نشان می‏ دهند دگرگونی M1 در بازه دمایی 550 تا 650 درجه سانتیگراد و فشارهای 5 تا 7 کیلوبار و دگرگونی M2 در دماهای کمتر از 500 درجه سانتیگراد و فشارهای کمتر از 5 کیلوبار رخ داده‏ اند. الگوی ساعت گرد مسیر فشار-دمای به دست آمده برای این شیست‏ ها نشان دهنده تحولات دگرگونی و زمین‏ ساختی در محیطی برخوردی است. همچنین، نمودارهای فازی آشکار کردند محتوای بالای آهن سنگ مادر و محتوای کم کربن‏ دی‏ اکسید در سیال دگرگونی نقش بسزایی در پایداری همتافت کانی‏ های گارنت + استارولیت + بیوتیت در این سنگ‏ ها داشته‏ اند.

    کلیدواژگان: شیست نئوپروتروزوییک بالایی، کامبرین پیشین نمودار تعادلی فازی سروجهان کمربند سلطانیه
  • منیره خیرخواه* صفحات 25-52

    دماوند آتشفشان چینه ای خاموشی در کمربند ماگمایی البرز در شمال ایران است که با مخروطی مرکب (بیش از 400 کیلومترمربع) روی پوسته نسبتا ستبر رشته کوه البرز (58-67 کیلومتر) در فلات ایران جای ‏ گرفته است و مرتفع ترین کوه (5671 متر) در خاورمیانه و جنوب آسیا به شمار می رود. تکاپوی های آتشفشان دماوند با خروج حجم های کوچک و مجزایی از روانه های مافیک (تفریت، بازانیت، تراکی بازالت و آلکالی الیوین بازالت) نزدیک به 1.8 میلیون سال پیش آغاز‏ شده است و تا 600 هزار سال پیش با فوران گدازه های حد واسط تا اسیدی (تراکی آندزیت، تراکی داسیت و تراکیت) ادامه یافته است. بر پایه تجزیه نقطه ای کانی های سازنده این گدازه ها، ترکیب پلاژیوکلاز (An31-58)، آندزین تا لابرادوریت و فلدسپار (Or32-65) سانیدین و انورتوکلاز است، میکای فلوگوپیت (Fe2+/(Fe2++Mg)<0.3)، کلینوپیروکسن اوژیت (Wo42-45 En42-47 Fs10-13) و دیوپسید (Wo46-48En43-46Fs8-10) و کانی‏ های تیره تیتانومگنتیت است. با محاسبات زمین دمافشارسنجی، تبلور فلوگوپیت ها در دمای 843 تا 819 درجه سانتیگراد و فشار 6 تا 0.63 کیلوبار و کلینوپیروکسن ها در دمای نزدیک به 1200 درجه سانتیگراد و فشار 10 تا 6 کیلو بار روی داده است‏ .

    کلیدواژگان: آتشفشان دماوند کمربند ماگمایی البرز زمین، دما فشارسنجی تراکی آندزیت
  • نگار گوانجی، زهرا طهماسبی*، محمود صادقیان، قاسم قربانی صفحات 53-90

    مجموعه سنگ‏ های آتشفشانی جنوب باختری طرود، بخشی از کمان ماگمایی سنوزوییک (ائوسن) در شمال پهنه ساختاری ایران مرکزی است. افزون بر روانه‏ های آندزیتی و بازالتی، میان لایه‏ های آهکی، آذرآواری ها (لیتیک‏ توف، کریستال لیتیک توف) و اپی کلاست‏ ها، این سنگ ها را همراهی می‏ کنند. سنگ‏ های بازالتی و آندزیتی سرشت کالک‏ آلکالن پتاسیم متوسط دارند و با غنی‏ شدگی از عنصرهای خاکی کمیاب سبک (LREE)، آنومالی منفی Nb-Ta-Ti و نسبت بالای LILE/HFSE شناخته می‏ شوند. ویژگی‏ های یادشده نشان دهنده پیدایش این سنگ‏ ها در پهنه های فرورانشی (کمان آتشفشانی حاشیه قاره ‏ ای) است. سنگ‏ های آتشفشانی بررسی شده محتوای SiO2 کم و مقدار Sr بالا دارند وبدون ناهنجاری چشمگیر Eu هستند و میزان Mg# آنها از 40 بیشتر است. این ویژگی ها نشان می دهند خاستگاه ماگمای اولیه سازنده آنها منبع گوشته‏ ای غنی شده بوده است. تغییرات Rb/Y در برابر Nb/Y نشان‏ دهنده غنی‏ شدگی به علت مولفه های فرورانش و یا نقش آلایش پوسته‏ ای در تحولات ماگمایی این سنگ‏ هاست. برپایه بررسی‏ های زمین شیمیایی، ماگمای مادر از خاستگاهی اسپینل لرزولیتی در ژرفای نزدیک به 80 تا 100 کیلومتر پدید آمده است که هنگام صعود ماگما، فرایندهای تبلور تفریقی و آلایش پوسته‏ ای آن رادچار تغییر و تحول کرده‏ اند.

    کلیدواژگان: سنگ‏ های آتشفشانی، منبع گوشته‏ ای، آلایش، فرورانش، سنوزوییک، طرود
  • محمدحسین یوسف زاده*، مرضیه چهکندی نژاد صفحات 91-118

    منطقه آسفیچ در جنوب باختری سربیشه (خراسان جنوبی) و در مرز بلوک لوت و پهنه سیستان جای دارد. سنگ های آتشفشانی ترشیری منطقه شامل پیروکسن آندزیت، آندزیت، داسیت، ریوداسیت، ریولیت (پرلیت)، توف، برش و آگلومرا هستند که روی پریدوتیت‏ های سرپانتینی شده و میکروگابروی کرتاسه جای گرفته‏ اند. کانی های پلاژیوکلاز، سانیدین، کوارتز، هورنبلند، بیوتیت و کلینوپیروکسن از کانی‏ های اصلی و بافت‏ ‏ های پورفیریتیک با زمینه میکروگرانولار و یا میکرولیتی، گلومروپورفیریتیک، جریانی، حفره‏ ای و پرلیتی‏ از بافت های رایج این سنگ‏ ها هستند. منطقه‏ بندی شیمیایی، بافت غربالی و خوردگی خلیجی در پلاژیوکلازها نشان‏ دهنده شرایط نبود تعادل هنگام تبلور ماگما هستند. سنگ های یادشده، از سری ماگمایی کالک‏ آلکالن و در گروه سنگ‏ های با پتاسیم بالا به شمار می روند. نمودارهای بهنجارشده عنصرهای کمیاب و خاکی کمیاب این سنگ ها در برابر گوشته اولیه و کندریت وابستگی زایشی آنها با یکدیگر را نشان می دهند. تهی‏ شدگی از عنصرهای P، Ti، Ta و Nb و غنی شدگی از U، K، Sr، Zr، Rb و Th و همچنین، غنی‏ شدگی LREE نسبت به HREE گویای پیدایش این سنگ‏ ها در حاشیه فعال قاره‏ ای هستند و در پی ذوب بخشی گوه گوشته‏ ای و افزوده شدن سازنده های متاسوماتیک آزادشده از سنگ کره فرورونده و یا به دنبال نازک شدگی (لایه لایه شدگی) سنگ کره ستبر پدید آمده اند. شواهد زمین شیمیایی مانند Nb/Y در برابر Rb/Y نشان می‏ دهد آلودگی پوسته‏ ای یکی از مهم ترین پدیده ها در تحول ماگما در این منطقه است. بر پایه نمودار های Dy/Yb در برابر La/Yb و Dy/Yb در برابر Dy می‏ توان خاستگاه ماگمای سازنده این سنگ ها را ذوب بخشی گوشته اسپینل لرزولیتی در محدوده رخساره اسپینل لرزولیت فلوگوپیت دار دانست.

    کلیدواژگان: آندزیت کالک‏ آلکالن اسپینل لرزولیت آسفیچ، سربیشه بلوک لوت
  • علی قاسمی*، اکرم السادات میرلوحی، مهران فرهمندیان صفحات 119-162

    توده نفلین سینیت رزگاه در حاشیه جنوبی پهنه آتشفشانی اهر- ارسباران (بخشی از کمربند البرز- قفقاز کوچک که خود بخشی از کمربند بزرگ آلپ- هیمالیاست) رخنمون دارد. سنگ نگاری توده آذرین درونی نشان دهنده حضور سنگ های نفلین گابروی الیوین دار، نفلین مونزوسینیت، پسودولوسیت سینیت و پتاسیم فلدسپار نفلین سینیت به همراه دایک های بازیک (لامپروفیر) و مشابه توده آذرین درونی است. بر پایه مقدار عنصرهای فرعی Co و Th و نسبت های Ce/Yb، Ta/Yb و Th/Yb و مقدار کم TiO2، سرشت ماگما کالک آلکالن پتاسیم بالا (شوشونیتی) است. الگوی REE، LILE و HFSE، بی هنجاری منفی عنصرهای Nb و Ti و HFSE، بی هنجاری مثبت Pb و LILE همگی گویای رخداد فرایند متاسوماتیسم گوشته و یا آلایش پوسته قاره ای است. بررسی کانی شناسی و زمین شیمی سنگ کل توده آذرین درونی رزگاه و لامپروفیرهای همراه نشان می دهد احتمالا خاستگاه گوشته ای با ترکیب اولیه اسپینل لرزولیتی دچار 1 درصد ذوب بخشی شده و مذاب اولیه را پدید آورده است. بر پایه الگوی زمین ساختی پیشنهادی، پس از فرورانش صفحه عربی به زیر ورقه ایران و شکست تخته فرورونده و سپس رخداد رژیم کششی، ماگمای برخاسته از گوشته غنی شده و ذوب تخته فرورونده، در قاعده پوسته دچار جدایش بلوری شده است و سپس با نفوذ بخش جدایش یافته به ترازهای بالاتر پوسته، آلایش پوسته ای رخ داده است. با خروج گازها و پیدایش شکستگی های عادی در سقف آشیانه، امکان نفوذ دایک های لامپروفیری و دیگر دایک های قطع کننده توده آذرین درونی در منطقه رزگاه فراهم شده است.

    کلیدواژگان: زمین شیمی، زمین ساخت، نفلین سینیت، رزگاه
  • نرگس شیردشت زاده* صفحات 163-188

    این پژوهش بر پایه سنگ نگاری و شیمی کانی های سازنده متاگرانیت آیرکان به بررسی رخداد دگرگونی دما-فشار بالا در ارتباط با بسته شدن پروتوتتیس در آغاز اردوویسین و دگرریختی دمابالا در ارتباط با بازشدن پالئوتتیس در دونین بالایی در شمال خردقاره شرق-ایران مرکزی می پردازد. دمافشارسنجی بر پایه داده های شیمی کانی ها و داده های پیشین شیمی سنگ کل این متاگرانیت نشان دهنده ضخیم شدگی پوسته قدیمی قاره ای و رخداد یک دگرگونی دما-فشار بالا و در نتیجه، آناتکسی (آب زدایی میکا) در دمای نزدیک به 817-850 درجه سانتیگراد است. این رویداد با برخورد قاره ها در شمال بلوک یزد هنگام بسته شدن اقیانوس پروتوتتیس از یونان تا ایران و هیمالیا و کوهزایی پان-آفریکن از پرکامبرین تا آغاز اردوویسین همخوانی دارد. افزون براین، ویژگی های سنگ نگاری (مانند پیدایش پرتیت شعله ای، میرمکیت و بازتبلور کوارتزها و فلدسپارها) نشان می دهند این گرانیت در یک پهنه برشی ژرف و در دمای نزدیک به 500-700 درجه سانتیگراد دچار دگرریختی دگرگونی کمابیش درجه بالا شده است. بر پایه داده های سن سنجی پیشین می توان آن را پیامد تحولات پالئوتتیس در مرز فعال قاره ای جنوب اوراسیا در دونین بالایی دانست.

    کلیدواژگان: دماسنجی، دگرریختی دگرگونی، متاگرانیت، آیرکان
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  • Javad Izadyar *, Mirmohammad Miri, Masoumeh Zare-Shooli Pages 1-24

    Mineral assemblage of metamorphic rocks forms by various factors including temperature, pressure, protolith chemical composition, and fluids. Although, P-T variation is the main factor controlling mineralogical evolution and assemblages, chemical differences of protoliths and metamorphic fluids also play an important role in the formation of final mineral assemblages (e.g. Spear, 1993). Therefore, mineral assemblages can be used in the study of thermodynamic and chemical conditions of metamorphic events. The studied area is located in the northwest of Sarve-Jahan village. For the purpose of the present paper, we investigate the metamorphic evolution of Sarve-Jahan schists (Zanjan province) and the effect of important factors on the formation of their mineral assemblages are through calculating phase diagrams. The study area is located in the northwest of Sarve-Jahan from Soltanieh structural zone and hosts Upper Neoproterozoic - Lower Cambrian schists (Fig. 1). The Soltanieh strip is a narrow and long structural strip trending northwest-southeast with a length of over 150 km and a width of 10-12 km. This belt as an uplifted tectonic bedrock lies in the structural zone of Central Iran. It comprises a complete set of thick clastic, carbonate and pyroclastic sediments (Kahar, Bayandor, Soltanieh, Barut and Lalon Formations) (Stöcklin and Eftekharnezhad, 1969) belonging to Precambrian-Paleozoic.. In the northwest of Sarve-Jahan and the vicinity of Sarve-Jahan granite, there is a metamorphic complex trending northwest-southeast, composing pelitic schists, metacarbonate (chalk schist) and sandstone (quartz schist and quartzite). The complex belongs to the Kahar Formation (Stöcklin and Eftekhar-nezhad, 1969; Babakhani and Sadeghi, 2004). In the southwest of metamorphic complex, there is a row of slates gradually replaced by phyllites and schists towards the northeast. The exposed Mesozoic deposits in the studied area include the sediments of Shemshak Formation and Lar limestones (Fig. 1) (Babakhani and Sadeghi, 2004, Stöcklin and Eftekhar-nezhad, 1969). Tertiary deposits include a sequence of detrial sediments as well as igneous and volcanic rocks (Stöcklin and Eftekhar-nezhad, 1969).

    Materials and Methods

    Seventy microscopic thin sections were studied by a polarizing microscope with transmitted light. Five samples with the highest number of phases in equilibrium were selected for microprobe analyze. The samples were analyzed in Iranian Mineral Processing Research Center using a CAMECA model SX 100 device with an electron beam acceleration voltage of 15 kv, current intensity of 3 nA and analysis time of 40 seconds for each point. Whole-rock compositions of these samples, also were determined by X-ray Fluorescence (XRF) spectroscopy method using a PHILIPS PW1480 instrument in the Kansaran Binaloud laboratory.

    Petrography:

    The studied rocks include garnet and staurolite porphyroblasts lie in a well-oriented matrix composed of biotite + muscovite + chlorite + plagioclase + quartz. Three phases of deformation (D1, D2, D3) and two phases (M1, M2) of metamorphism occurred in the metamorphic rocks. The M1, could be related to the D1 and characterized by garnet + staurolite + chlorite + biotite + muscovite + plagioclase + quartz assemblage. The M2, could occur in association with D2 and formed chlorite + biotite2 + muscovite2 + quartz. The third deformation phase (D3) caused crenulation cleavage on D2 schistosity but with no new mineral phase. Garnet and staurolite porphyroblasts formed during M1. Retrogressive metamorphism replaced these minerals with chlorite and muscovite in their rims. Whole-rock and mineral chemistry The samples studied contain high SiO2, Al2O3 and K2O corresponding to a Fe-rich shale protolith (Table 1). The biotites and white-micas have high annite and muscovite end-members, respectively. Garnets and staurolites are also Fe-rich and plagioclase are of albite to oligoclase compositions (Table 2).

    Discussion

    Thermobarometry Various thermobarometry calculations based on garnet-biotite (Bhattacharya et al., 1992), muscovite-chlorite (Vidal and Parra, 2000) and garnet-plagioclase-biotite-quartz (Hoisch, 1990) methods resulted c.a. 600 °C and 5-7 kbar for the M1 and 500°C and 6 kbar for the M2.

    Equilibrium phase diagram:

    The equilibrium phase diagrams were calculated using GeoPs software (version 3.3) and Bi(w), Chl(W), Crd(W), Ctd(W), St(W), Gt(W), Mica(W), Opx(W), melt(W) and Fsp(C1) (Holland and Powell, 2003; White et al, 2014) solid solution models for average composition of the studied samples. The P-T pseudosection diagram (Fig. 5) shows that the M1 assemblage garnet + staurolite + biotite + muscovite + chlorite + quartz + plagioclase is stable in 550 – 650 °C and 5 – 7.2 kbar, while the assemblage biotite2 + muscovite2 + chlorite2 + quartz + plagioclase corresponding to M2, is stable in T<550 °C and P<5 kbar. The calculated isopleths for pyrope in garnet and phlogopite in biotite intersect at the stable filed of M1 assemblage (Fig. 6) confirming the thermobarometry results.

    Protolith composition:

    The Mg# [Mg# = (MgO/MgO+FeO)] versus T variations phase diagram (Fig. 7) shows that the stability of garnet and staurolite is affected by Mg and Fe contents of the protolith. They leave the system with increasing Mg# at constant T. In other words, the high FeO contents of the Sarve-Jahan schist protolith had a significant role in the formation and the stability of the peak metamorphism mineral assemblage.

    Fluid composition:

    The CO2 contents of metamorphic fluids is important in the stability of minerals (e.g. Miri et al., 2023). A T-XCO2 phase diagram was calculated for the sample assuming a H2O-CO2 fluid to investigate the role of CO2 in the metamorphic of the samples (Fig. 8). The diagram indicates that the M1 mineral assemblages was stable at XCO2 < 0.3, but the M2 was stable only in the presence of pure H2O fluid.

    Conclusion

    Microstructures show that the deformation phases (D1, D2, and D3) and the two metamorphic phases (M1 and M2) occurred in the area. The M1 and M2 were contemporaneous with D1 and D2, respectively, while D2 was not in association with a metamorphic phase.The mineral assemblage garnet + staurolite + chlorite + biotite + muscovite + plagioclase + quartz formed in M1 and peak of metamorphism (amphibolite facies) and biotite2 + muscovite2 + chlorite2 + quartz + plagioclase formed in the retrogressive metamorphism M2 phase (greenschist facies).The traditional (mineral pairs) and modern (phase diagram) thermobarometry calculations show obtain 550 – 650 °C and 5 –7 kbar for M1 and < 500 °C and < 5kbar for M2. On this basis, a clockwise P-T-t path can be considered for metamorphism of the Sarve-Jahan schists. Which could have occurred in a subduction-collision tectonic site.The calculated T-Mg# and T-XCO2 phase diagrams show that the composition of the protolith and the metamorphic fluid played a significant role in the minerals assemblage event occurring during peak metamorphic conditions.

    Keywords: Upper Neoproterozoic, Lower Cambrian schists Phase Equilibrium Diagrams Sarve Jahan Soltanieh Belt
  • Monireh Kheirkhah * Pages 25-52

    Damavand stratovolcano is in Alborz Magmatic Belt (AMB), in the north of Iran, and the Iranian plateau. This large dormant volcano was constructed with a composite large cone (more than 400 km2). Damavand is known as the highest mountain (elevation ~5671 m) in the Middle East and South Asia. The youngest known eruptions of Damavand volcano (7.3 Ka), which mostly erupted on the western side of the summit, are composed of trachyandesite, and trachyte lavas with pyroclastic while the older eruptions (1.8-0.6 Ma) consisting of alkali olivine basalts, tephrite basanite, and trachyandesite, emplaced at the base of the volcano. The current Damavand cone is located above the old and eroded building and periodically includes trachyandesite- trachyte lavas with small eruptions of mafic lavas and pyroclastic rock. These lavas formed in the youngest geological period (Quaternary) covered Mesozoic deposits (Shemshak and Lar Formations). The intensity of Alborz volcanic activities extended into the Tertiary, but was not uniform, as its maximum occurred in the late Eocene and Oligocene, and after a period, volcanic activities re-intensified in the Pliocene.

    Regional Geology:

    Damavand volcano is in the center of Alborz Mountain Belt, in the Iranian plateau. The stratigraphic evidence indicates that the volcanism occurred in the two phases the older (old Damavand) and the younger sequences (younger Damavand)

    Analytical Methods

    After initial petrographic studies, suitable samples were analyzed for whole-rock composition determined by XRF and ICP-MS analyses at the Geological Survey of Iran. Mineral composition determined by EPMA (Electron Probe Micro-Analyser) at Iran Mineral Processing Research Center. The analysis was performed at this center by the electronic microprocessor model CAMECA-SX 100 made by the French company Cameca. This device is equipped with a spectrometer with an electron diode receiver and works automatically based on a high accuracy of 1% and the simultaneous operation of several diode detectors and electron beam stability with a carbon coating. Petrography, Minerals, and Whole Rocks Chemistry The analyzed samples roughly cluster in the two zones, mafic alkaline rocks (tephrite-basanite) and intermediate-felsic rocks (trachyandesite- trachyte). The main purpose of this study is the mineral chemistry of the Ziar-Lasen trachyandesites, with a SiO2 content of 57wt%. The predominant mineral assemblages of these rocks are plagioclases (andesine-Labradorite), k-feldspar (sanidine-anorthoclase), clinopyroxene (augite-diopside), mica (phlogopite, biotite), apatite, and Ti-magnetite and the dominant textures are porphyry and microlithic porphyry textures with main phenocrysts. Feldspars show signs of disequilibrium and sieve textures in their cores and rim and desorption and skeletal. These phenocrysts, which are sometimes as glomerocrysts, show zoning Some mafic enclaves with variable textures and mineralogy are seen in the matrix of the trachyandesitic rocks.

    Result and Discussion

    Volcanic activities in the middle part of Central Alborz Mountain initiated about 2 million years ago with the eruption of mafic to intermediate-acidic lavas and pyroclastic rocks. The most common minerals of the trachyandesits from the south of Damavand (Polour to Ziar-Lasem) are felspar, pyroxene, mica, apatite, and opaque minerals., whereas the intermediate lavas are characterized by the presence of plagioclases (An31-58, andesine), alkali feldspars (Or32-65, sanidine to anorthoclase), pyroxene, mostly augite (Wo42-45 En42-47Fs10-13) rare diopside (Wo46-48 En43-46 Fs8-10), mica phlogopite (Fe2+/(Fe2++Mg) <0.3) as well as high Mg # (67-76) and Ti-magnetite.Chemically, the clinopyroxenes are characterized by high Mg # (97-76) and phlogopites by Fe # <0.33, high Ti (70-79), and high Mg # (76-67) and so, the nature of host magma is sub-alkaline.On the base of thermobarometer data, the clinopyroxene and phlogopite phenocrysts from Ziar-Lasem trachyandesites crystallized at a wide range of temperature and pressure.The crystallization temperature for clinopyroxenes, ranges from 1180 to 1250 °C, at 6-10 kbars pressure (equi. to 22-36.5 km depth), and for mica varies from 819 to 843°C, at 0.1-1.14 kbars pressure (equal to 4-0.65 km depth.). Base on clinopyroxenes compositions (Mg#>80) the crystallization of these minerals was re-equilibrated with high Mg# melts (50–54) (Eskandari et al., 2018). The similarity of these values with those of basalts indicate their deep crystallization from more mafic magma (Lanzafame et al., 2013). It is suggested that the clinopyroxenes of the intermediate volcanic products of Ziar-Lasen were crystallized at 22-36.5 km depth, approximately equivalent to lower crust (28–33 km), and evolved by assimilation, fractionation, and contamination when their parent magma erupted from deep depth to the surface or crystallized at shallow chambers within a thick crust.

    Keywords: Damavand volcano, Alborz Magmatic Belt, geothermobarometric, Trachyandesite
  • Negar Gavanji, Zahra Tahmasbi *, Mahmoud Sadeghian, Ghasem Ghorbani Pages 53-90

    The study area is located in the south of Damghan, 160 km south of Shahrood, and 17 to 30 km south of Torud village. The area geologically, lies in the Cenozoic magmatic belt, a part of the Alpine-Himalayan belt, in the north of the structural zone of Central Iran (Aghanabati, 2004). The Cenozoic magmatic belt has been studied by many researchers (e.g., Ghorbani, 2005; Khajehzadeh, 2009; Mardani-Beldaji, 2011; Tayefi, 2014; Yousefi, 2017). The volcanic rocks in the southern part of the Torud area have not been comprehensively studied. Therefore, it requires a detailed study. So, for the purpose of this study attempt has been made to investigate and to study the nature of magma, tectonic setting, and the petrogenesis of the volcanic rocks using the geochemical data of the whole rock. Also, the results of this study have been compared with some areas belonging to the Cenozoic Era located in the north of the structural zone of Central Iran.

    Regional Geology:

    The area under study in the Torud-Moalleman magmatic belt belongs to the Chah-Shirin-Sabzevar-Khaf magmatic complex, located in the western part of this magmatic complex. In this magmatic belt, the Eocene volcanic rocks, including the main volume of igneous rocks are basic to acidic in composition. The predominant rocks are basaltic to intermediate rocks. The Torud-Moalleman magmatic belt is mainly composed of volcanic rocks with a lithological composition consisting of olivine-basalt, basalt, andesite, and dacite rocks and their pyroclastic equivalents, as well as plastic and limestone interlayers.

    Analytical methods

    During field surveying, 50 samples of the volcanic rocks with the least alteration were collected. From these samples, 30 thin sections were prepared for microscopic studies and 11 samples were selected for ICP-MS geochemical analyses for minor elements and XRF for major elements and were sent to ACME Laboratory in Vancouver (Canada). GCDkit, Excel, and Corel Draw software were used to check the results obtained from the whole rock chemistry analyses and drawing diagrams.

    Petrography:

    The study rocks include volcanic rocks ranging from andesite to basalt. The basalts are dark gray to black in color with glomeroporphyritic, microlithic, sieve, and trachytic textures containing plagioclase and clinopyroxene as the main minerals. These minerals along with olivine and magnetite can also be seen in the form of microcrystals in the background of the rock, and their accumulation have created the glomeroporphyritic texture in these rocks. Secondary minerals are chlorite, iron oxide, zeolite (natrolite and analcime), calcite, and gypsum, filling the holes.The andesites are light gray to slightly dark with porphyritic and glomeroporphyritic textures and are dominated by amphibole (green and brown hornblende), plagioclase, and clinopyroxene as the main, biotite, iron oxide, sphene, and zircon. as the minor, as well as sericite, chlorite, calcite, and epidote as the secondary minerals.

    Whole Rocks Chemistry :

    The data obtained from the whole rock geochemical analyses display that the volcanic samples of the Torud area are classified as the andesite and basalt, placed mostly in the range of calc-alkaline series (medium potassium). LREE and LILE enrichment, HREE and HFSE depletion and Nb, Ta, and Ti negative anomalies of these rocks point to their formation in subduction zones. Also, as the tectonic diagrams display the rocks belong to the active continental margin. The rocks under study have mostly mantle origin and are derived from an enriched lithospheric mantle. The flat HREE patterns also show that melting occurred in the mantle, above the stability field of garnet. Therefore, the parent magmas were formed by the melting of spinel lherzolite at a depth of 80 to 100 km and evolved due to fractional crystallization as well as contamination caused by subducted sediments and the continental crust.

    Discussion

    The rare elements pattern of the study rocks in spider diagrams show the cogenesis of these rocks and the role of differential crystallization as the main mechanism of their formation. Based on geochemical data, the study samples and compared volcanic rocks share similar characteristics. Therefore, the normalized REE patterns with chondrite (Nakamura, 1974) NMORB (Sun and McDonough, 1989) and MORB (Pearce, 1983), indicate the enrichment of LREEs (such as La, Ce) and LILEs (e.g., Ba, K, U, Pb, Cs) compared to HREEs and HFSEs (i.e. Nb, Ta, Ti, P) indicating that the rocks under study were formed in the active continental arc margin. The samples have no negative anomaly of Eu. Volcanic rocks with the age of late Eocene and Oligo-Miocene and basaltic to trachy-basaltic composition range from alkaline to sub-alkaline rocks and volcanic rocks with the age of middle Eocene with andesite to trachy-andesite composition have the nature of calc-alkaline.

    Conclusions

    The volcanic rocks in the south of Torud, with calc-alkaline and medium potassium nature, are mainly composed of basalt and andesite characterized by LREE enrichment, negative Nb-Ta-Ti anomaly, and the high ratio of LILE/HFSE. These characteristics point to the formation of these rocks in the subduction zones.The rocks under investigation have low SiO2 content, high amounts of Sr, no significant Eu anomaly, and Mg# content greater than 40. These geochemical features indicate a mantle source for the studied volcanic rocks. The changes of Rb/Y versus Nb/Y show the enrichment by subduction components or crustal contamination in the magmatic evolution of these rocks. Based on the geochemical investigations, the productive magma originated from a spinel lherzolitic source at a depth of about 80 to 100 km; during the ascent of magma, as a result of fractional crystallization and contamination, the magma derived from the mantle has been enriched and gave rise to lithological diversity.

    Keywords: volcanic rocks, mantle source, Contamination, Subduction, Cenozoic, Torud
  • MohammadHossein Yousefzadeh *, Marzieh Chahkandinezhad Pages 91-118

    The magmatic activities of Lut block started from the middle of Jurassic (165-162 Ma) with the intrusion of Kalate Ahani, Shahkoh and Sorkh kooh intrusive masses and reached its peak in the Tertiary. Tertiary volcanic and semi-volcanic rocks cover more than half of the Lot block with a thickness of about 2000 meters, which were formed as a result of subduction before the collision of the Arabian and Asian plates (Camp; Griffis, 1982; Tirrul et al., 1983; Berberian et al., 1982). The studied area with geographic coordinates 59º31′14″ - 59º36′05″ east longitude, 32º32′28″ -32º34′29″ north latitude, is located 40 km southwest of Sarbisheh and includes a thick succession of Tertiary volcanic and pyroclastic rocks that are covered by young Quaternary sediments in some places. This area is located in the 1:100,000 Sarbisheh geological map prepared by Nazari and Salamati (1999). According to the map prepared by Pang et al. (2012) for parts of Sistan zone and Lut block, the studied area is located on the eastern edge of Lut block and on the border of two structural states of Lut block and Sistan zone (Figure 1). Since the Tertiary volcanic rocks in the mentioned region, despite their wide expansion and having large reserves of perlite and clay minerals, have not been subjected to detailed lithology and geochemistry studies, they have been selected as the subject of this research.

    Regional Geology:

    In this area, there are extensive outcrops of Tertiary volcanic rocks, including pyroxene-andesite, andesite-trachyandesite, dacite, rhyodacite, rhyolite (perlite) and related pyroclastic rocks such as tuff, ignimbrite, and agglomerate, which are on serpentinized peridotites in the east of Fal village to the south of Asfich, and gabbro belongs to the Cretaceous ophiolites of southeast Birjand. In terms of age, the ophiolitic units are related to the late Cretaceous. Tertiary volcanic units are related to the Eocene and Oligocene (Pang et al., 2013).

    Research method

    In order to carry out this research, first of all, library studies including the collection and review of geological and topographical maps and previous studies have been carried out. In the next step, during 10 days, field investigations, separation of different rock units and sampling were done, and then 90 thin sections of the rocks of the area were prepared and their mineralogical and textural characteristics were examined by a Leitz type polarized microscope. In the next step, according to the diversity and geographical spread of different rock units, 9 unaltered or less altered samples were selected and coded (LF200) for chemical analysis by ICP-ES for major elements and ICP-MS for trace elements. Acme laboratory in Canada and 2 samples have been sent to Kansaran Binaloud laboratory. Finally, GCDKit, Excel (@2007), Corel and Minpet software were used to draw diagrams. In order to obtain Fe2O3 and FeO values that are closer to the real values, Minpet software was used according to the Irvine and Baragar method (Irvine and Baragar, 1971).

    Petrography:

    Tertiary volcanic rocks of the region include pyroxene andesite, andesite, dacite, rhyodacite, rhyolite (perlite), tuff, breccia and agglomerate. The common texture of these rocks is porphyritic with microgranular or microlithic, glomeroporphyritic, flow and cavity texture. Pearlites have a pearlitic texture. Euhedral and subhedral phenocrysts of plagioclase with oligoclase-andesine composition are the main constituents of these rocks and have rounded or bay sides. Some plagioclase phenocrysts show a sieve texture. Plagioclase microlites are the main component of the matrix. Clinopyroxene (augite) and hornblende are present in small amounts. In addition, bay-sided phenocrysts of sanidine and quartz are observed in rhyolites.

    Geochemistry:

    The results of chemical analysis of volcanic rocks of Asfich area are presented in Table 1. In the diagram of total alkali versus silica, presented by Cox et al. (1979), the samples are in the range of andesite, dacite and rhyolite (Figure 8A). Due to the presence of variation in some samples, charts based on immobile elements have been used for the geochemical nomenclature of rocks. In this regard, in the Nb/Y vs. Zr/TiO2 diagram presented by Winchester and Floyd (1977), the samples are in the range of andesite, trachyandesite, dacite, rhyodacite and rhyolite and show a subalkaline nature (Figure 8B). In the Na2O+K2O-MgO-FeO* triangle diagram (AFM diagram), which is used to identify magmatic series and their transformations, and subalkaline series is divided into two separate tholeiitic and calc-alkaline series and presented by Irvine and Baragar (1971), the samples are in the calc-alkaline range (Figure 8C).

    Tectonic setting and origin:

    It is possible that the Th/Yb ratio for the samples is higher than the mantle, and this compositional change is attributed to subduction-related processes (Helvaci et al., 2009). Arc magmas are mainly formed as a result of partial melting in the subduction-related mantle wedge, due to the addition of metasomatic components released from the subducting oceanic lithosphere. Metasomatic fluids may include hydrous fluid (supercritical) or primary melts from sediments or basaltic crust subducted into the mantle wedge, which causes the mantle solidus to decrease and magma production (Figure 11) (Harangi et al, 2007; Hoang et al, 2001). Depletion in elements P, Ti, Ta and Nb and enrichment in U, K, Sr, Zr, Rb and Th and enrichment of LREE compared to HREE indicate the formation of these rocks in the active continental margin regime. which are mainly formed as a result of partial melting in the mantle wedge, due to the addition of metasomatic components released from the subducting lithosphere. Geochemical evidence such as Nb/Y versus Rb/Y shows that contamination is one of the most important phenomena in magma evolution in the area. According to the diagram of Dy/Yb versus La/Yb and Dy/Yb versus Dy, it is possible to imagine the origin of partial melting of lherzolite spinel mantle and the range of phlogopite-bearing spinel lherzolite facies for the magma that forms the rocks of the region.

    Keywords: andesite, Calcalkaline, Spinel lherzolite, Asfich Sarbisheh, Lut block
  • Ali Ghasemi *, Akramosadat Mirlohi, Mehran Farahmandian Pages 119-162

    Razgah, Kalibar, and Bozghosh intrusive rocks, located in East Azarbaijan province, are among the most important alkaline nepheline syenite rocks known in Iran. Several theories reported regarding the geochemical characteristics as well as the geotectonic environment of the Tertiary igneous rocks exposed in the Ahar-Arasbaran belt (Jamali et al., 2012). Some workers have considered the magmatism of this belt as an important extensional phase of the late Cretaceous, while, some others believe it is related to subduction zones. Although the mineralogy, petrology, geochemistry, and petrogenesis of these rocks have been studied by several people (i.e., Esmaeili, 1997; Ameri, 2004; Ashrafi, 2009), in none of them the origin and geotectonic setting of the area has been discussed in detail. Thus, for the present study, mineralogical, petrological, and geochemical studies are applied to understand the origin, the petrogenesis, and the geotectonic setting of the intrusive rocks from the nepheline syenite exploration areas, particularly the Razgah intrusive rocks.

     Regional Geology:

    The Razgah intrusive. a part of the Western Alborz-Azarbaijan zone lies on the southern edge of the Ahar-Arasbaran volcanic belt. Geologically, the Eocene volcanic rocks cover the Jurassic-Cretaceous flysch is intruded by the Oligo-Miocene plutonic rocks (Mahdavi and Fazli, 2008). The Razgah nepheline syenite intrusive intruded the sediments of evaporate basins including gypsum marl, limestone marl, sandstone, and the Miocene conglomerates. Their contact with previous rocks has vanished due to weathering and erosion of itself and the Quaternary sediments surrounding it. Copper mineralization (malachite and azurite) can be identified in the western part of Razgah intrusive. In addition, a number of dykes are distributed especially in the western and northwestern parts. Also, numerous silica veins were observed in different parts, mainly along, in parallel, and in contact with dykes, more widespread in the western part.

    Materials and methods

    Following the sampling (150 rock pieces) and preparation of 70 thin sections for petrographic and mineralogical investigations, trace and REE were determined on 93 samples using the ICP-MS method.

    Petrography:

    The Razgah intrusive rocks are dominated by olivine-bearing nepheline gabbro, nepheline monzosyenite, pseudolucite syenite, and K-feldspar nepheline syenite. Also, basic dykes (lamprophyre), similar to their host (altered syenite nepheline), syenite and microsyenite dykes and finally altered dykes with siliceous and mineralized veins are present. Nepheline, pseudolucite, potassium feldspar, plagioclase, clinopyroxene, and olivine are among the most important major minerals. Apatite, zircon, and iron-oxide are the minor while chlorite, calcite, adularia, and hematite along with sericite, epidote, kaolinite, and biotite present as secondary minerals. Granular and porphyroid textures, as well as poikilitics, graphics, and replacements (causing pseudomorphous forms), are the common textures of the rocks under study. Lamprophyre dykes with porphyry texture and olivine, pyroxene, and Kaersutite (brown amphibole) are present. The other dykes, to some extent, have similar mineralogical characteristics as nepheline syenites, in which clay minerals occur.

    Discussion and Conclusion

    The Co and Th contents, the amount of Ce/Yb, Ta/Yb, and Th/Yb ratios along with low TiO2 content point to the nature of the parent magma as a high potassium calc-alkaline type (shoshonite). The pattern of REE, LILE, and HFSE, the negative Nb, Ti, and HFSE anomalies as well as Pb and LILE positive anomalies, indicate the mantle metasomatism process or continental crust contamination occurrence (Rollinson, 1993; Soesoo, 2000). In addition, the decrease in P solubility with the high level of K and REE gave rise to the separation of apatite from the parent melt (Green and Adam, 2002). The similarity of REE patterns indicates the same magmatic processes involved in the generation of the rocks under study. The mineralogical and geochemical data on Razgah intrusive rocks and the associated lamprophyres point to 1% partial melting of a spinel lherzolite source. Based on the presented tectonic model, following the Arabian plate subduction beneath the Iranian plate, several processes including the slab breakoff, extensile regime, magma formation from the enriched mantle, and subducted slab melting took place which followed by crystal fractionation and contamination at the base of the crust and finally differentiated melts intruded the high levels. As the gases release, the lamprophyre dykes injected into the fractured roof and the other dykes crosscut the Razgah intrusive rocks.

    Keywords: Geochemistry, Geotectonic, Nepheline syenite, Razgah
  • Nargess Shirdashtzadeh * Pages 163-188

    Granites are one of the most abundant rock groups formed the continental crust, and are considered for investigating the temperature conditions of their formation and metamorphism. Thus, they are a unique window to magmatism and tectonic evolution of the earth. The S-type granites are considered to be the result of crustal shearing in collision zones in the course of orogenic processes and high degrees of metamorphism (von Huene and Scholl, 1991; Brown, 2013; Hu et al., 2018). The granite might be affected and change into metagranite by further metamorphic deformations in the orogenic zones during or following the magma crystallization and emplacement of granitic melts in the continental crust. The mineralogical and textural characteristics of metagranites have a key role in understanding tectonic events and metamorphic temperature conditions and provide valuable information regarding the geological processes and Paleozoic tectonic events in the northern part of the Central-East Iranian microcontinent (CEIM).The main goal of the present paper is to investigate the high temperature-pressure metamorphism and deformation related to the of closure the Proto-Tethys oceanic crust and the opening of Paleo-Tethys oceanic crust in the north of the Central-EastIranian microcontinent, based on the petrography and mineral chemistry of Airakan metagranite. 

    Geological Background

    In late Ediacaran, the Proto-Tethys Ocean between Proto-Gandwana and Proto-Laurasia opened (Raumer et al., 2015; Rossetti et al., 2015). Following several metamorphic events, the Proto-Tethys Ocean closure occurred at late Ordovician to early Carboniferous, and led the Precambrian terrains of Iran to collide and re-joint to form the Gondwana supercontinent (Raumer et al., 2015; Rossetti et al., 2015; Moghadam et al., 2017).Iran is a part of the western lands of the Gondwana supercontinent, moved to Eurasia in the early Permian-Triassic and following the Cimmerian orogeny, and then, with the Alpine-Himalayan orogeny event, until now, it has undergone several complex metamorphic, igneous, and tectonic processes, and various structural and geological zones have emerged in the land of Iran.Central-East Iranian microcontinent is composed of four main Pan-African continental plates, including (from east to west) Lut block, Tabas block, Posht-Badam block, and Yazd block. Airakan granite is a deformed and fractured Ordovician granite,exposed among the Miocene Upper Red Formation to the north of the Khor area in Yazd block (Northeastern Isfahan Province, Central Iran) (Shirdashtzadeh et al., 2018). The overall textural and mineralogical characteristics of the study granite point to its deformed/metamorphosed following the post magmatic metamorphic processes at sub-solidus temperatures (Bagheri and Stampfli, 2008; Shirdashtzadeh et al., 2018). U-Pb zircon dating (Shirdashtzadeh et al., 2018), revealed the Ordovician age (487.6 Ma) for the Airakan granite. The occurrence of Ordovician magmatism has also been reported in the other parts of the Gondwanan continental crust of Iran, Pakistan, and Tibet (e.g., Hu et al., 2015; Moghadam and Stern 2015; Naeem et al., 2016; Moghadam et al., 2018; Khodami et al., 2022; Samadi et al., 2022).

    Analytical Methods

    Following the microscopic observations, the selected thin sections were used for electron microprobe analysis of minerals using a JEOL JXA8800R device at an accelerating voltage of 15 kV and a current beam of 15 nanoamperes at Kanazawa University, Japan.

    Discussion

    A) High P-T Metamorphism related to Proto-Tethys Ocean closure Thermobarometry data based on the mineral chemistry (and the whole rock composition) indicate that the Airakan S-type granite was a result of greywacke anatectic melting, due to an Ordovician HPT metamorphism. This HPT metamorphism has occurred during the closure of Proto-Tethys ocean. Consequently, collision between the Gondwana and Eurasia supercontinents has resulted in the continental crust thickening and anatectic melting. Similarly, several Ordovician anatectic S-type granites are reported from China (Hu et al., 2015), Pakistan (Naeem et al., 2016), and Central Iran (e.g., Moghadam et al., 2018; Khodami et al., 2022; Samadi et al., 2022). B) Metamorphic deformation related to Paleo-Tethys Ocean Opening A metamorphic deformation caused by the opennig of Paleo-Tethys Ocean in late Ordovician to early Devonian-Carboniferous (Bagheri and Stampfli 2008) has recorded in the Airakan metagranite in the north of CEIM. According to mica crystals orientation, metamorphic deformations of quartz (GBM recrystallization, subgrains formation and elongation, as well as preferential orientation or SSPO of quartz), and feldspars (formation of flame perthite parallel to the maximum stress (σ1), myrmekitization, tartan texture and BLG recrystallization around feldspars), in 382 Ma, the Airakan granite has undergone a metamorphic deformation at ~500 to 700 °C in a shear zone.

    Conclusions

    Geothermobarometry results based on the mineral chemistry as well as the whole rock composition of Airakan metagranite indicate that a high temperature-pressure metamorphism has resulted in an anatexis event (dehydration of mica) at temperature of ~817-850℃. This event is consistent with the continental collision and of ancient continental crust thickening in the north of Yazd block during the closure of the Proto-Tethys Ocean starting from Greece to Iran and the Himalayas and, the Pan-African orogeny, from the Precambrian to the beginning of Ordovician.In addition, petrographic features (e.g., the flame perthite, myrmekite, and recrystallization of quartz and feldspars) show that Airakan granite has undergone an approximately high-grade metamorphic deformation in a deep shear zone at ~ 500-700 ℃. Based on previous geochronological data (382 Ma), it was a consequence of Paleo-Tethys evolution in the active continental margin of the southern Eurasia in Upper Devonian.

    Keywords: Thermobarometry, Metamorphic deformation, metagranite, Airakan