فهرست مطالب

  • پیاپی 18 (تابستان 1398)
  • تاریخ انتشار: 1398/05/10
  • تعداد عناوین: 7
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  • فاطمه سبک خیز*، عبدالله سیف، محمد رامشت، مرتضی جمالی صفحات 143-161

    دریاچه ها به عنوان بایگانی تغییرات محیطی قاره ای در آخرین دوران زمین شناسی به حساب می آیند. در این پژوهش پس از مطالعات میدانی، یک مغزه ی رسوبی از شمال غرب دریاچه مهارلو برداشت و حساسیت مغناطیسی آن اندازه گیری شد. سپس به روش تلفیقی تعداد 150 نمونه انتخاب و تحت مطالعات؛ ژیوشیمی (LOI)، PH متری، مطالعات میکروسکوپی ذرات رسوبی و بقایای گیاهی،  (SEM) بقایای جانوری، آنالیز دانه بندی قرار گرفته، با استفاده از سن سنجی ایزوتوپی δ14C سن مغزه ی رسوبی تعیین گردید. شواهد نشان داد؛ سن کف مغزه ی رسوبیBP 60±10813 بوده، وجود لس های یخبندان، عدم وجود بقایای زیستی گیاهی و جانوری، مبنی بر حاکمیت شرایط سرد و خشک در فاز پایانی یانگر دریاس (اواخر دیریخبندان) در دریاچه مهارلو است. دوران هولوسن تحتانی، BP 60±10200 سال پیش ، ابتدا سرد و خشک بوده، سپس حاکمیت محیط فلوویال و دوران گرم و خشک نمایان می شود. هولوسن میانی از  BP60±4000 سال پیش با شروع فعالیت چشمه ها ظاهر شده، دوره ی بهینه اقلیم گرم و مرطوب همراه با تناوبهای کوتاه مدت خشک شدگی بر دریاچه تسلط می یابد. هولوسن فوقانی در BP 45±2000 سال پیش، روند رو به خشکی حوضه (پلایا) را نشان میدهد. تغییرات محیطی دریاچه مهارلو در این دوران؛ مشابه با آخرین دوره یخبندان دریاچه های؛ پریشان، هشیلان و نیور و هولوسن پیشین دریاچه ارومیه و منطقه اطلس شمالی می باشد.

    کلیدواژگان: هولوسن، دریاچه مهارلو، تغییرات محیطی، یانگر دریاس
  • عباس علیان نژادی، سید رضا مهرنیا*، سلیمه کیمیاگر، حبیب رحیمی، نسرین صدرمحمدی صفحات 163-183

    در این تحقیق برای تشخیص گسل های پنهان کواترنری در رسوبات آبرفتی واقع در جنوب غربی بوستان جنگلی چیتگر (منطقه 22 تهران)، از روش های ژیوفیزیکی رادار نفوذی به زمین (GPR) و ژیوالکتریک استفاده شده است. با مطالعه  پروفیل (GPR) مناطق دارای گسل شناسایی شدند. نتایج به دست آمده از 2 پروفیل ژیوالکتریک، حاکی از وجود دو زون با مقاومت الکتریکی پایین و مقاومت الکتریکی بالا در کنار یک دیگر است. افت مقاومت الکتریکی در رسوبات منطقه می تواند در ارتباط با عواملی مانند وجود سنگ های هوازده نشده، هوا در داخل رسوبات، دانه ریز بودن رسوبات و با جنگلی بودن منطقه مورد مطالعه به علت آبیاری درختان و نفوذ آب باران در زیرزمین باشد. مقاومت الکتریکی بالا نشان دهنده خردشدگی سنگ ها در اثر فعالیت گسل ها، رسوبات دانه درشت و خشک است. نتایج حاصل از روش های مورد استفاده در این تحقیق نشان دهنده، وجود یک زون گسلی با طول تقریبی 140 متر است. با توجه به روندهای ساختاری اغلب گسل های شناسایی شده، ادامه داشتن امتداد گسل ها به سمت قسمت های بالایی بوستان چیتگر بسیار محتمل است. با توجه به پتانسیل لرزه خیزی و احتمال آسیب پذیری سازه های مسکونی بویژه در شمال و شمال غربی منطقه مورد مطالعه، نتایج این تحقیق حایز اهمیت است. استفاده از آن برای تحلیل مخاطرات زمین ساختی و ارتقای کیفی نقشه های موضوعی توصیه می گردد.

    کلیدواژگان: رادار نفوذی به زمین، زون گسلی، لندفرم، مخاطرات زمین ساختی، مقاومت الکتریکی
  • منیره خیرخواه* صفحات 185-204

    گدازه های بازیک کواترنری گریک (منتهی الیه بخش شمالی آذربایجان غربی)، در گستره ای با ضخامتی بیش از 30 متر، حاصلی از جوان ترین تکاپوهای آتشفشانی آرارات کوچک در خاور ترکیه است. این آتشفشان در فلات ایرانی ترکی و در نزدیکی مرز ایران و ترکیه و ارمنستان قرار دارد که متاثر از برخورد قاره قاره عربی اورازیایی است. شیمی همه نمونه ها با ویژگی هایی مانند نسبت های La/Nb بالا و LILE افزایش یافته تاثیر مولفه فرورانش را در ماگمای سازنده گدازه های کواترنری منطقه نشان می دهد. کلینوپیروکسن، الیوین، و پلاژیوکلاز کانی های تشکیل دهنده این گدازه ها هستند. با مطالعه شیمی کانی، مشخص شد کلینوپیروکسن (میانگین ترکیبی (Wo=0.38.5,En=0.51, Fs=12.9 ترکیب دیوپسید دارد. منطقه بندی شیمیایی عادی و نوسانی بلورهای کلینوپیروکسن بر تاثیر تحولات ماگمایی منطقه و شرایط متفاوت اکسیداسیون و فوگاسیته اکسیژن دلالت دارد. با بررسی ترموبارومتری این کانی ها، تبلور پیروکسن در گستره دمایی 1200 درجه سانتی گراد (مقدار < AlVI 02/0 اتم در ساختار کلینوپیروکسن) و فشار 8 تا 11 کیلوبار مشخص شده است. درصد اکسید آهن فریک (1/0 تا 9/4) گریزندگی اکسیژن در منشا ماگمایی گوشته لیتوسفری با سرشت نیمه آلکالن را نشان می دهد که در محیط فشارشی کلی با کشش های موضعی فوران یافته است.

    کلیدواژگان: آرارات، بازالت کواترنری، ترموبارومتری، شیمی کانی، کلینوپیروکسن، گریک
  • کیوان شیعیان*، رحیم دبیری صفحات 205-220

    سنگ های آتشفشانی بزمان با سن کواترنری، دارای ترکیب آندزیت ، بازالت آندزیت، بازالت ، تراکی بازالت، داسیت و ریوداسیت هستند. آنالیز شیمی کانی های مافیک در مورد سه نمونه از بازالت آندزیت و الیوین بازالت واحد های کواترنری انجام گردید. در شت بلور های الیوین در نمونه الیوین بازالت از نوع کریزولیت هستند. کلینو پیروکسن ها در محدوده اوژیت  و ارتو پیرکسن ها درمحدوده کلینوانستاتیت قرارمی گیرند. آمفیبول این سنگ ها ازنوع هورنبلند، هورنبلند چرماکیت، هورنبلند منیزیم دار و هورنبلند هیستینگزایت وچرماکیت است. ماگمایی تشکیل دهنده کلینو پیروکسن و ارتو پیروکسن این بازالت ها در محدوده تولییت و کالک آلکالن قرار دارد. دما و فشار تعیین شده براساس کانی الیوین حدود  c°1100و فشا ر Kbar 5.5 است. همچنین شرایط دما تشکیل ماگما  c°15± 1160 درجه سانتی گراد و فشار 1±75/5 کیلوبار بر اساس کانی پیروکسن می باشد.

    کلیدواژگان: آتشفشان بزمان، دما و فشار سنجی، کواترنری، مافیک. مکران
  • بهنام پاشازاده، داوود جهانی*، راضیه لک، حمید نظری، مهدی محمدی ویژه، میشائیلا براسمایر صفحات 221-236
  • علی محمدی*، جواد درویشی خاتونی، علی رضا صالحی پور میلانی، آمنه کاوه فیروز، راضیه لک صفحات 237-262

    دریاچه ارومیه در شمال باختر ایران به عنوان یکی از بزرگترین دریاچه های فوق اشباع نمک جهان، به دلیل عوامل انسانی و طبیعی در معرض کاهش شدید تراز آب و خشک شدن قرار دارد. کاهش شدید تراز آب در دو دهه اخیر و رخنمون یافتن بستر دریاچه به صورت پهنه های گلی، گلی-نمکی و نمکی در بخش های بزرگی از دریاچه منجر به تغییر محیط رسوبی از یک محیط دریاچه ای دایمی به یک محیط رسوبی پلایایی تحت تاثیر تغییرات فصلی شده است. ظهور و گسترش میکرولندفرم های محیط های پلایایی در بستر خشک شده دریاچه موید تغییر در محیط رسوبی دریاچه و روند رسوبگذاری است. مهم ترین میکرولندفرم های پهنه های گلی دریاچه شامل ترک های گلی، زمین های پف کرده با ساخت تی پی و دیاپیرهای گلی می باشند. میکرولندفرم ها در پهنه های نمکی گسترش و تنوع بیشتری دارند و شامل  ساخت های انحلالی نمک در مقیاس میکروسکوپی و ماکروسکوپی، رشد بلورهای هالیت و سیلویت در اشکال و اندازه های مختلف، هالیت های شعاعی، ریپل های نامتقارن نمکی، پلی گون های نمکی، قارچ های نمکی، پشته های نمکی، سواحل و سدهای نمکی، ساخت های نعل اسبی نمکی، حفره ها و غارهای نمکی، پهنه های گسیختگی نمک و فرش های جلبکی می باشند. رخنمون یافتن پهنه های نمکی در بخش های بزرگی از بستر دریاچه و نیز  برداشت نمک برای استفاده های صنعتی می تواند منجر به حمل ذرات منفصل نمک به مناطق مسکونی و کشاورزی در زمان طوفان های بادی و گرد و غبار گشته و عوارض زیست محیطی برای ساکنین اطراف دریاچه به همراه داشته باشد.

    کلیدواژگان: دریاچه ارومیه، میکرولندفرم، سواحل ماسه ای، پهنه های گلی و نمکی، تغییرات تراز آب دریاچه
  • مهران مقصودی*، حمید کامرانی دلیر، میلاد هاشمی صفحات 263-277

    های جنوبی های باستانی در دامنه هدف اصلی این پژوهش، شناسایی عوامل محیطی موثر در پراکنش مکانی-فضایی محوطه ارتفاعات البرز و حاشیه شمالی کهن دریاچه دشت کویر در اواخر دوران کواترنری یعنی دوره هولوسن می باشد .لندفرمهای شاخص با استفاده از عکسهای هوایی، تصاویر ماهواره ای لندست و تصاویر گوگل ارث، شناسایی گردید. سپس عمق کهن  های پژوهشگران پیشین اندازه گیری و منحنی تراز آن رسم گردیده و دریاچه دشت کویر و سطح تراز تقریبی آن با توجه به یافته مرزهای دایمی در اواخر دوران کواترنری محاسبه و به بر اساس مطالعات پالیوکلیماتولوژی صورت گرفته پیشین، منحنی تراز برف لایه های اطلاعاتی افزوده گردید. در پایان، موقعیت مکانی و جغرافیایی استقرارگاه های باستانی به تفکیک دوره های تاریخی به لایه های اطلاعاتی فوق جهت تلفیق و تجزیه و تحلیل نهایی اضافه گردید. پس از تلفیق و روی هم گذاری لایه های اطلاعاتی  ای معنادار میان جابجایی و پراکنش استقرارگاه های باستانی با تغییرات متناوب اقلیمی و بدست آمده در مراحل فوق، رابطه ژیومورفولوژیکی حاکم در اواخر کواترنری در منطقه مورد مطالعه بدست آمد .نتایج این تحقیق نشان می دهند که پراکنش استقرارگاه های باستانی از یک الگوی پراکنش خطی و ارتفاعی تبعیت می کنند.

    کلیدواژگان: پالئوژئومورفولوژی، الگوی استقراری، محوطه های باستانی، زمین باستانشناسی، دریاچه پلویال
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  • Fatemeh Sabokkhiz* Pages 143-161
    Introduction

    There is a direct relationship in evaporative deposit with the changes in the depth of the lake. Therefore?, valuable information is gained regarding the causation of changes in environment over time. Evaporite minerals formation is a natural phenomenon accruing in water-bodies containing deferent mineral Since sulfate is abundant in seawater and saline lakes, it is main component in evaporative minerals (Lewis and Mc Conchie,1994). Playa lake deposits even in small precipitation rates may cause major changes in lake-level, salinity and sedimentary records (Battarbee 1999). The sediments generated in present saline lakes and playas have been studied by numerous researchers in order to determine the paleoclimate (Spencer et al. 1984; Holliday et al. 1996; Crowley and Hook 1996; Li et al. 1996; Enzel and Wells 1997; Menking et al. 1997; Lowenstein et al. 1999; Sinha et al. 2006; Chao et al. 2009).Playas are found in many parts of the world including Western US (Rosen 1991), Australia (Bowler 1986) and Iran (Krinsley 1970). In Iran, the ancient evaporites are present in sedimentary records of the Tertiary evaporites are found mainly in the Zagros Basin and in the Central Iran (Rahimpour-Bonab and Kalantarzadeh 2005, Rahimpour-Bonab et al. 2007a, b). In addition, Holocene evaporite deposits are widespread in numerous playas and lake/playas in various parts of Iran with different characteristics (e.g., Krinsley 1972; Shahrabi 1995; Farpoor and Krouse 2008; Farpoor et al. 2012). In his pioneering work, Krinsley (1970) studied morphology of surficial features of 60 playas within the interior of Iran. He determined characteristics, distribution, and development of the available playas. According to his findings, because the form and bedrock permeability of most of the Iranian basins have remained essentially stable since the late Pleistocene (Würm), subsequent hydrologic changes can be attributed to climatic changes.Rahimpour-Bonab and Abdi (2012) with study on the lake/playa Meyghan Flowing water with low percentage of ions and Na–(Ca)–(Mg)–SO4–Cl–(CO3) types evolve, into a brine with high ions concentration during the geochemical evolution and mineral deposition. The geochemical evolution yields a Na–SO4–Cl type brine.While clastic components (calcite, quartz etc.) show on increasing trend in relation to depth, evaporites abundances show opposite trends. Furthermore, the average grain size of sediments increases with depth indicating higher energy in the past. This study evaluated clastic sediments and evaporite deposits’ changes in the sedimentary core Maharlou lake by using physical and geochemical methods.1-2- Study site (Physical setting)The hypersaline Lake, Maharlou is located in SW Iran with an area of 24910 km2 and 1.5 m depth. The lake lies about 20 km east of Shiraz at 1,455 m above sea level (masl) [Fig. 1]. This lake is fed by direct precipitation and water inflow from surface run-offs, a few seasonal rivers and several karstic springs which compensate for the strong evaporation in a semi-arid climatic context (Dumas et al. 2003). The Maharlou catchment area consist of sedimentary rocks, mainly Precambrian diapiric evaporites associated with Mesozoic and Cenozoic limestone, sandstone, shale and dolomite formations. The formation of this lake goes back to the beginning of the Pleistocene because of its hydrogeological properties, past higher lake level stands and the survival of Pleistocene relict fish species (Krinsley 1970; Dumas et al. 2003).

    Materials and methods

    Lakes are accurate intercontinental ambiences to record past environmental changes. After theorical researches, vibracorer machine took 533cm core sample from the north west of the lake near Kaftarak village. Magnetic susceptibility tool measured the magnetic sensibilities. Sequences identified and analysed after cutting sedimental core. Then, 150 samples with high resolution checked to apply combination method, however only 84 items selected. SEM method and LOI analysing system used for geo-chemistry studies. After particle size analyses, sediments are studied to identify life remains of animal and plant as well as lithologic study by using polarizing and binocular microscopes.

    Results and discussion

    Lakes are accurate intercontinental ambiences to record past environmental changes. After theorical researches, vibracorer machine took 533cm core sample from the north west of the lake near Kaftarak village. Magnetic susceptibility tool measured the magnetic sensibilities. Sequences identified and analysed after cutting sedimental core. Then, 150 samples with high resolution checked to apply combination method, however only 84 items selected. SEM method and LOI analysing system used for geo-chemistry studies (Sabokkhiz et all 2015). After particle size analyses, sediments are studied to identify life remains of animal and plant as well as lithologic study by using polarizing and binocular microscopes (Sabokkhiz et al 2014). Finally, the age of the core measured by δ14c ageing technique and calculation methods. The age of the sedimental core bottom is 10813 ±60 years BP that presents the time period before Holocene. Existence of los like and lack of biological matters in 521 cm depth show the dominance of the last part the Younger drays (late Glacial). This event has the horizon of the fine grain sediments without life remains. Therefore younger dryas phase of the lake Maharlou is cold and dry. Early Holocene ages, 10200±60 years BP were cold and dry. There were evaporates with fine grains and without biological matters. Afterwards evaporate and siliciclastic particles increased, calcium carbonates decreased and fluvial environment dominance appeared followed by warm and dry age. Middle Holocene ages, 4000±60 years BP came to light by the activity of the springs when pleasant warm and wet weather controlled lakes. There were some fluctuating dry weather conditions until late Holocene age. A Hiatus and detached surface appeared in 3062±45 years BP that showed water offgoing from the lake along with surface weathering. Late Holocene starts from 2000±45 years BP. First demonstrated dry fluctuations then raining increase and then core surface which indicated drying trend of playa basin.

     Conclusion

    4-1- The age of the sedimental core bottom is 10813 ±60 years BP 4-2- Therefore younger dryas phase of the lake Maharlou is cold and dry.  Early Holocene ages, 10200±60 years BP were cold and dry weather and fluvial environment dominance appeared followed by warm and dry age. 4-3- Middle Holocene ages, 4000±60 years BP came to light by warm and wet weather controlled lakes. There were some fluctuating dry weather conditions until late Holocene age 3062±45 years BP that showed water offgoing from the lake along with surface weathering.4-4- Late Holocene starts from 2000±45 years BP. First demonstrated dry fluctuations then raining increase and then core surface which indicated drying trend of playa basin.4-5- These changes are similar to other studies for different lakes in North-West of Zagros mountains such as Parishan lake, Hashilan wetland, Neuor lake in Alborz mountains in late glacial. Recent researches about the time of the early Holocene on Oroumiyeh lake and north Atlantic sea showed lowering in monsoon currents and increase of extreme dryness in middle east, which have similar conclusions to our research on Maharlou lake.

    Keywords: lake Maharlou, Holocene, invironmental changes, Younger drays
  • Abbas Aliyannezhadi, Seyyed Reza Mehrnia*, Salimeh Kimiagar, Habib Rahimi, Nasrin Sadrmohammadi Pages 163-183

    In this research, Geophysical methods Ground Penetration Radar (GPR) and Geoelectric have been used to detect hidden Quaternary faults in alluvial sediments located southwest of Chitgar Forest Park (District 22 of Tehran). The study of profiles (GPR) identified areas such as fault. The results obtained from two Geoelectric profiles indicate that there are two zones with low electrical resistance and high electrical resistance. Reduce the electrical resistance in the sediments of the area can be related to factors such as the existence of non-weathered rocks, the air inside the sediments, fine-grained sediments and being a forest of the study area, due to irrigation of trees and rainwater penetration underground. High electrical resistivity indicates crushing of rocks by fault activity, coarse-grained and dry sediment. The results of the methods used in this research indicates that there is a fault zone with an approximate length of 140 m. Considering the structural trends of most of the faults identified, it is very likely that the faults will continue along the upper part of the Chitgar Park. Due to the seismic potential and vulnerability of residential structures, especially in the north and northwest of the study area, the results of this research are important. Its use is recommended for analyzing tectonic hazards and improving the quality of thematic maps.

    Keywords: Electrical resistivity, Fault zone, Ground Penetrating Radar, Landform, tectonic hazards
  • Monireh Kheirkhah* Pages 185-204
    Introduction

    North western Iran are neighboring of the largest Turkey volcanic centers (e.g. Ararat, Nemrut, Tendürek and Süphan volcanoes), within the Turkish-Iranian orogenic plateau. Quaternary basaltic lavas from NW Azerbaijan are related to the on-going Arabia-Eurasia collision zone, and inherited by subduction of the Neo-Tethyan Ocean at a Late Eocene age (~ 35 Ma). The Quaternary lava flows in north of Gerik are originated from the Little Ararat volcano (Agri Dag) and covered a large area in the end member of north western Azerbaijan. This youngest lavas(0.4Ma) are derived from little Ararat and cropped in northern part (NNW) of Iran.The Quaternary basic lavas show alkali to subalcaline trend. The volcanic rocks have basic composition( olivine basalts, hawaiites and mugearites) and show mainly hyaloporphyritic,intergranular, microlitic and hyalin textures . These alkali basaltes show Hawaian and Strombolian type eruptions. According to geochemical and mineralogical composition, these basaltic rocks are relative comparable with Ararat lava flow in Turkey. By geochemical studies, it is suggested that the volcanites evolved by fractional crystallization, low degree of partial melting and crustal contaminations. Geodynamic reaserch and tectonic setting  show, that these rocks  are related to Quaternary extensional tectonic regime and have erupted along the shear zone in pull-apart local  basin zone.

    Materials and methods

    Samples were collected from basic lava flows which have travelled much further than 100 km from Little Ararat, and producing narrow ribbons of lava to the valley floors in north of Gerik with typically thickness of 5 – 30 m. plagioclase+ clinopyroxene+ Olivine forms the essential mineral assemblage of these basalts. Accessory minerals include magnetite and apatite. Small biotite grains are occasionally present. Textures are hyaloporphyritic, with plagioclase, pyroxene and olivine phenocrysts. This section focused on the mineral chemistry of clinopyroxenes present in the basic lavas.Approximately 5 representative crystals (comprising pyroxenes) were selected for electron microprobe analysis in Hubland Institute at Wuerzburg University in Germany. The analyses were performed with a JEOL JXA 8200 microprobe analyzer, with peak counting times of 20 s (except 40 s for Na) and a background time of 10 s (20 s for Na). Acceleration voltage was set to 15 kV and a beam current of 20 nA was used for all analyses.

    Results and discussion

    This paper presents basaltic lava flows by focused on mineral chemichemistry of pyroxenes in the northwest Iran, within the Turkish-Iranian plateau (eastern Anatolia); These lavas were generated from Ararat and were covered a big amounts of basaltic materials in eastern Turkey to N-Gerik) during a short time in the Quaternary. By Microprobe analyses, the compositional range of clinopyroxenes is (WO=0.38.5, En=0.51, Fs=12.9) and show that clinopyroxenes are diopside. According to geotermobarometrical studies, clinopyroxenes in the studied basalts were formed about 1205-1275°C temperature with 7.9- 11.2 Kbar pressure and the clinopyroxenes are situated above the line of Fe3+ show high oxygen fugacity

    Conclusion

    Basaltic Quaternary lavas of N Gerik in NW Iran are generated from the Little Ararat volcano in eastern Turkey and these lava flows have travelled further than about 100 km to NW Iran. The main minerals in these these rocks, are Olivine + plagioclase ± clinopyroxene. Clinopyroxenes crystals represent normal and reverse zoning with sieve texture and diopside in composition. By chemistry studies of this mineral, it is indicated that, the clinopyroxenes were crystallized from the primary magmas at high temperature1205-1275°C, pressure of 7.9- 11.2 Kbar and depth average 35Km with high oxygen fugacity in their magmatic arc setting.

    Keywords: Ararat, Basaltic lavas, Clinoppyroxene, Gerik, Termobarometry
  • Keyvan Shiaian*, Rahim Dabiri Pages 205-220
    Introduction

    Bazman volcano is located on Chgay - Makran magmatic arc. This magmatic arc with east-west trend is 500 km long and 150 km wide and extends from southeastern Iran to southwestern Pakistan. Early evolution of the Makran zone from the upper Oligocene to the upper Miocene is characterized by turbidite sediments deposited on the oceanic crust. There are several quaternary volcanoes such as Bazman, Taftan, Shahsavaran and Soltan (southern Pakistan) which situated along northward of Makran subduction zone as continental arc magmatism. Bazman volcano as an astratovolcano have been explosive and non-explosive eruptions in Quaternary. The purpose of this paper is to investigation of mafic minerals chemistry and thermobarometry of Bazman Quaternary volcanic rocks.

    Materials and Methods

    Based on field studies, its volcanic rocks are classified into two groups Quaternary and Neogene volcanic rocks. Petrographic studies were conducted with the preparation of thin sections of rock and were named rocks. Three samples Quaternary units (Qa1, Qa2, Qa3) were selected for microprobe analysis.  Mineral analyses were conducted at Iran Minerals Processing Research Center Electron Microprobe Laboratory using a Cameca SX100 electron probe microanalyzer outfitted with combined WDS and EDS systems. The analyses were conducted at an accelerating voltage of 15 kV and a beam current of 10 nA.

    Results and discussion

     According to Petrographic studies, unit Qa1 was formed of  andesite, andesitic basalt, basaltic andesite and andesite lithic crystal tuff, unit Qa2, andesite to trachyte andesite and basaltic andesite, unit Qa3,andesitic basalt, olivine basalt and basaltic andesite. 3 sample basaltic andesite and olivine basalt Quaternary units were selected for mafic mineral microprobe analysis. Olivine phenocrysts of olivine basalt are chrysolite mineral. Clinopyroxenes are augite and orthopryoxene are clinoenstatite. Amphibole minerals are hornblende, magnesio-hornblende, hastingsite hornblende, tschermakite hornblende and tschermakite. Pyroxene composition in igneous rock depends on the chemical composition and tectonic setting of the host lava which can be used widely to determine the series of magmatic and physicochemical conditions such as pressure, temperature, oxygen fugacity. Ca+Na vs Ti diagram define that the pyroxenes occur in the range of tholeiitic calc-alkaline. Al2O3 vs TiO2 diagram was drawn to identify the nature of magma. This diagram  shows orthopyroxene of both the Quaternary units and clinopyroxene unit Qa1 calc-alkaline ranges and clinopyroxene unit Qa2 tholeiitic tendency. The chemical composition of the samples pyroxenes evaluates the physicochemical conditions of magma such as pressure, temperature, oxygen fugacity.Using Al IV + Na vs Al IV + 2Ti + Cr diagram which depend on the amount of 3-valent iron in pyroxenes, we can get oxygen fugacity. The diagram is set based on the aluminum balance in the tetrahedral position and Cr3+in the octahedral position. The Fe3+ in pyroxenes can be displaced 3-valence elements such as AlVI, Ti and Cr in the octahedral position. In the other hand, Fe3+in pyroxenes depends on the amount of AlVI which means that it depends on the aluminum balance in tetrahedral and octahedral position. The pyroxenes which crystallized at high oxygen fugacity, has been situated above the line of Fe3+. Furthermore, Papike and Cameron (1976) have mentioned the distances of the samples from the Fe3+ line and noted that further distances of the samples from this line were indicating more oxygen frugalities in their geological setting. In this diagram samples are located above the line of Fe3+. In order to study thermodynamic conditions pyroxene crystallization is used methods Soesoo (1997) and Patrikia (2008). By Soesoo (1997)  clinopyroxene samples operating temperature range 1200c°-1300c° and comprised approximately at 1250 c°. Orthopyroxene samples are composed at temperatures from 1150c°-1200 c°. Accordingly, the pressure range of clinopyroxenes is 6-10 kbar and Orthopyroxenes 2-5 kbar. By Patrkia (2008) orthopyroxenes crystallization temperature  Qa1 unit is 1124c° and clinopyroxene and  1145c°  and the setting pressure at the orthopyroxene is 5 Kbar and clinopyroxene 8 Kbar. Orthopyroxenes crystallization temperature  Qa2 unit is 1068 c° and clinopyroxene and  1100 c°  and the setting pressure at the orthopyroxene is 2.2 Kbar and clinopyroxene 4.3 Kbar. According to both methods clinopyroxene crystallization, temperature is higher than orthopyroxene in  Quaternary units. Temperature and pressure of the magmatic Qa1 little more than Qa2. Reduce pressure and temperature conditions of crystallization orthopyroxene can be attributed to an increase in the amount of iron in the crystal lattice orthopyroxene. The temperature and pressure determined on the basis of the mineral olivine  in olivine basalt rock (Qa3 unit) are about 1100 °C and 5.5 Kbar.

    Conclusion

    3 sample Quaternary units were selected for microprobe analysis. According to the pyroxenes chemical composition in basaltic andesite rock, orthopyroxene of both the Quaternary units and clinopyroxene unit Qa1 are calc-alkaline ranges and clinopyroxene unit Qa2 is tholeiitic tendency. The pyroxenes which crystallized at high oxygen fugacity. Clinopyroxene crystallization temperature is higher than orthopyroxene in  Quaternary units. Temperature and pressure of the magmatic Qa1 little more than Qa2. Reduce pressure and temperature conditions of crystallization orthopyroxene can be attributed to an increase in the amount of iron in the crystal lattice orthopyroxene. It could be related to tholeiite conditions magma before crustal contamination. The average pressure and temperature of the Quaternary magma chamber based on mafic minerals can be estimated at 1141 °C and 5.5 Kbar.

    Keywords: Bezman Volcano, Temperature, Pressure Measurement, Quaternary, Mafik. Makran
  • Behnam Pashazadeh, Davood Jahani*, Razyeh Lak, Hamid Nazary, Mehdi Mohammadi Vizhe, Michaelela Berensmeier Pages 221-236

    Alluvial fan are one of the most dynamic Quaternary landforms in arid areas.An alluvial fan in the southeast of the city Yazd was identified based on satellite images; in this research, the primary objective of this study is to investigate the surface and subsurface sedimentology of alluvial fan flasks. Twenty soil samples were taken for sedimentological studies. The result indicate that, three main sediment types/ lithologies were recognized: gravelly mud, gravelly sand and gravelly-muddy sand leading to three differentiated facies types. The sediment of this alluvial fan haves a high viscosity. The distribution of sediment particles and the causes of changing faces types - were interpreted. Direct current (DC) geoelctric method utilizing Wenner-Schlumberrgerarray was used for subsurface investigations. DC geoelectric surveys were carried out along two crossing profiles with the lengths of 2050m and 270 m, respectively. However more resistivity was observed in the longitudinal profile and the initial sections of the alluvial fan, compared to the last parts, and a sedimentary model was drawn finally.

    Introduction

    Quaternary alluvial fans are important depositional environments evidencing erosional topography and indirectly palaeoclimatic events. Surface runoffs formed along mountains outskirts mainly cause these deposits. Heavy rainfall and rapid (global) warming during the warm time of the Quaternary period have played a significant role in the formation of alluvial fans. Surface runoffs gradually lose energy, speed and a significant part of their solid burden after passing through the mountainous slopes of the valleys and canyons, entering the plain of the mountains. In general, the thickness of the alluvial fan decreases and its extent increases coming from the mountain to the plain. The opening section is characterized by a canal that draws the sediment from the highest point of the mountain to the plain. The alluvial fan is forming a canal from mountain to plain. The longitudinal profile line can be described concave and the transverse sections as convex. River cuts in the surface are observed. Alluvial fans , can be classified to three groups regarding size and expansion: small scale (several square kilometers), medium scale (several dozen square kilometers) and large scale (several hundred to several thousand square kilometers).Initially, the surface of the alluvial sediments has been analyzed. Therefore, common outcrops were studied and traced along the alluvial fan, through depth information is based on the interpretations of indirect information by (geoelectric measurements) and modeling with software. The purpose of this research is to investigate the sedimentology of the alluvial fans, identify subsurface units and provide a suitable sediment model for them.Initial studies of the Quaternary alluvial fan in the southeast of Yazd city, based on analysis of aerial photos and satellite imagery from the last 20 years. Sediment units were generally identified and classified. The overall geological structure of the study area and the impact of geological units on the alluvial fans have been investigated. Firstly, the alluvial fan was completely identified regarding the geologic position its dimensions.The studied alluvial fan in can be described as blade and disk in shape in its proximal and medial part. The grain kurtosis is moderate, while rounding is angled to half-angled. The poor sorting of this alluvial fan is remarkable, because the gravel size particles are present in proximal and distant facies. The results of granulation analyses and field studies revealed high viscosity of the sediments and observed debris flows moving downstream. The debris deposits consist of eroded Eocene rock units These deposits are tenon-shaped. Several factors influence the formation of the tenon-shaped alluvial fan. Rocky clay is one of the most essential components and the conditions for clay formation in this area have been provided due to the type of rock unit and weathering and erosion. Due to the high slope and the lack of vegetation and severe rain in the Pleistocene period, conditions for the formation of the alluvial fans with high viscosity deposits have been provided.Positive skewness is caused by the presence of large amounts of suspended matter in the river water, such as silt and clay, which can be deposited in parts. The statistical analysis revealed to a positive skewness value of the grain sizes within the proximal sediments. This indicates clay existence in the upstream of the alluvial fan.

    Discussion

    Surface studies include the sampling,identification and classification of Quaternary sediment. The main reason for the study of rock units is the association of these units with weathering and erosion and the direct effect of these factors on the formation of quaternary units.The third unit, has a direct impact on the alluvial fan of the area, The geometric shape of the studied alluvial fan can be described as blade type due to its highest thickness (proximal part) at the mountain ridge indicating the elevation of the Eocene rock units before the formation of the alluvial fan. According to the detailed studies of the rock units of the area, it was determined that each different lithological material and lithological changes due to weathering could affect the nature and type of the alluvial fans in the area and produce alluvial fans with different length, width and sediment type. For this reason, depending on the type of origin, it is possible to differentiate the alluvial fans of the area. The grain analysis revealed different statistical parameters and three different sediment types. All sections of the alluvial fan were identified and separated in ArcGIS software. Statistical parameters such as mean sorting, skewness, and kurtosis are sensitive to flow energy variations and are controlled by factors of erosion, transport, and rate of deposition. Therefore, the study of the particle size dispersion is one of the basic principles for the study of the conditions for the sedimentation and sediment transport The matter can be discussed with the governing energy and erosion of the alluvial fan of the area by considering the statical parameters and the type of these sediments.

    Conclusion

    According to sub-surface studies (geophysics), a fault was identified between the stone unit of the Cretaceous and alluvial deposits, as indicated in.

    Keywords: Sedimentology, Geophysics, Alluvial Fan, Sedimentary Model, Yazd
  • Pages 237-262
    Introduction

    Urmia Lake is one of the word-scale large hypersaline lakes with about 5500 square kilometers in the Turkish-Iranian Plateau (NW Iran). The lake surrounded by mountains with a mean elevation of about 2000 meters and the highest peak of 4811 meters. The lake charge with 28 permanent and ephemeral rivers. As a result of anthropogenic and natural reasons, the lake exposed to the rapid water level fall and fades. The Urmia Lake experienced rapid water level fall with over 6 meters in the last two decades, which lead to the exposure of the large part of the lake. Consequently, this event changed the permanent hypersaline lake sedimentary environment to the sessional changes depended temporary (playa) sedimentary environment. In the last 20 years, the lake floor exposed in the form of Sandy beach, muddy, muddy-salty and salty plains. The appearance of the micro-landforms of playa environments in the exposed lake floor is in concordance with changes in the sedimentary environment.

    Materials and methods

    This study was done based on several field studies on Urmia Lake during 2010, 2011, 2014, 2015, 2018 and 2019. Filed works are done in the different parts of the lake during different seasons, different lake water levels, and different weather conditions. The effect of different weather conditions including temperature, evaporation, wind speed and direction, and amount of freshwater discharge by rivers on dissolution and deposition of the evaporate minerals and forming of the different micro-landforms on the lake floor were considered.

    Results and discussion

    The sandy beaches mostly exposed in the lake coasts around the “Zanbil and Eslami” volcanic complexes. The main micro-landform on the sandy beaches of the lakes is asymmetric ripple marks. In the sandy beaches, the sand grains are mostly coated grains with clastic minerals dominantly pyroxene and volcanic glasses in the core and chemical-biochemical aragonite and halite in the rim. The muddy plains are mostly exposed between the sandy beaches and the salt plains. The mud plains in the rivers deltas have seen in the form of the swamp with everglade vegetation. The main micro-landforms on the muddy plains are mud cracks, teepee structures, and mud diapers. Mud cracks with polygonal shapes are ranging between a few centimeters up to a meter in size. The tee/pee and mud diapers are common structures in the muddy-salty plains and mostly forms due to the hypersaline water capillary. Compare to the sandy and muddy plains, the micro-landforms on the salty plains are more variable in type and shape. The most common micro-landforms in the salty plains are micro and macro scale salt dissolution structures, deposition of evaporate minerals such as sylvite and halite minerals in different size, shape and crystallography, radial halite cylinders, asymmetric salt ripple marks, salt polygons, salt mushroom, salt mounds, salty beach and barrier, small scale salty pores and caves, salt rapture, organic matters, and algal mats. The landforms of salt plains generally classify into dissolution and depositional structures. These landforms are the most sensitive structures of the Urmia Lake and rapidly reorganized with slight changes in the lake water condition. The salt dissolution structures form due to salt dissolution by fresh meteoric and river waters. These structures show channel shape in the contact place of salt plain and freshwater river. Irregular polygons and groove shapes form due to meteoric water dissolution. The evaporate minerals mostly deposit in cubic and cauliflower shapes in the Urmia Lake floor and hopper and sheet shapes on the water surface which is later falling down on the lake floor. Sylvite minerals are bigger than halite minerals and forms slowly in the dissolution holes where the lake brine has been trapped. Both halite and sylvite are the common evaporate minerals in the Urmia Lake. The radial halite is forming inside the cylindrical dissolution holes in the salt plain where the halite minerals growing from the rim to the core of the holes and forming the radial halite structure. Salt mounds build up in meter to several meters in size with an oval and rounded shape and mostly they grow in dominant wind direction. The high of the mounds from the lake floor is ranging from few centimeters to a few meters. Salty beaches normally are in elongated and Horseshoe structure shape and build up between salty-muddy plain and salty plain where the waves are broken down. The small-scale salt caves with Stalactite, stalagmite and salt column are mostly located in the cliffy costs of lake islands. Ruptured salt zone on the western coast of the northern part of the lake is a special phenomenon that probably formed due to salt viscosity or even activity of fault in the lake. Algal mat and microbial organic materials are two different types of autogenic organic matter in the lake. In addition, some organic materials such as different types of insects carried into the lake by the wind from the agriculture lands around the lake. Shahid Kalantary High way as a man-made dike separated lake into the northern and the southern parts. Due to the huge weight of the used materials in the highway, the lake green color muddy-marly unconsolidated viscous sediment scapes out in both northern and southern margins of the highway and made the synusic-wave shape. In addition, some water saltwater spring formed along the high way.

    Conclusion

    Rapid water level fall of Urmia Lake leads to exposure of a large area of the lake floor as sandy beaches, muddy, muddy-salty and salty plains with a variety of dissolution and depositional micro-landforms in different shape and size. In the Urmia Lake, the micro-landforms are unstable structures and reorganizing under seasonal variation of physico-chemical conditions of the lake.

    Keywords: Urmia Lake, Micro-landform, Sandy beaches, Muddy, salty plains, Lake water level fluctuation
  • Mehran Maghsoudi* Pages 263-277
    Introduction

    Site selection of human habitats in pre-historic times, unlike the current periods, has been strongly influenced by natural factors. Studies may be focused on three areas including paleoclimate, paleogeomorphology and archeology in order to identify environmental factors affecting primary habitats. Based on studies, most of the ancient lakes in central Iran were formed during the Quaternary and were covered by sediments resulted from erosion of their adjacent heights. The research method was based on the methods of statistical analysis and spatial dispersion analysis of the aforementioned works and evidences and their comparisons in software environments with the capability of integrating information layers called Geographic Information System (GIS) and its compliance with field evidences.After integrating the layers of information, a significant relationship was found between the displacement and distribution of ancient settlements with the alternating climatic and geomorphologic changes of the late Quaternary in the study area. The results of this study show that the distribution of ancient settlements follows a linear distribution pattern and specific elevation levels.

    Objectives

    The main purpose of this study is to identify the environmental factors affecting the spatial distribution of ancient archaeological sites in the southern slopes of Alborz Mountains as well as the northern margin of the ancient lake, Kavir desert in late Quaternary, namely Holocene (Mesolithic and Neolithic, nearly 11000 years ago). Therefore, we tried to identify mentioned factors making use of paleontological evidences in four fields including epistemology, geomorphology, climatology and archeology.

    Methodology

    Research methodology is based on statistical and spatial distribution analysis of the above-mentioned evidences and their correlation in software capable to compile information layers in Geographic Information System (GIS) as well as their accordance with field evidences. Firstly, coastal landforms were identified making use of ETM+ Landsat images and Google Earth imagery and information layers were inserted to ArcMap environment. For this purpose, physical and conceptual tools such as 1: 100000 and 1: 250000 geological maps, 1: 50000 topographic maps, and 1: 55000 aerial photographs of 1335 were used in the study area. The archaeological site location data sheet (GPS) was prepared by the Archaeological Institute. Conceptual tools, such as ArcGIS software, for analyzing data and output maps, Excel software, for numerical and statistical computation and charting and charting required, Google Earth software, for using satellite imagery of the study area and digitizing some effects And geographical phenomena were applied in the study area.Depth and approximate water table of assumed ancient lakes were calculated according to the findings published in previous studies and its contour lines was drawn and added to existing information layers.

     Discussion

    Based on previous paleoclimatological studies in this basin, snow lines for permanent boundary were identified in late Quaternary period and added to the existed information layers. Finally, the geographical coordination (GPS points) of ancient habitats was added to the above-mentioned information layers for integration and final analysis, separately based on historical periods (Middle and upper paleolithic). Compiling and overlaying obtained information layers, meaningful relationship was found between the displacement and distribution of ancient habits with periodic climatic and geomorphological changes in late Quaternary in the study area.Works and evidence in the study area show that the formation and development of the desert desert was dependent on the alternation of glacial and interglacial periods. The current pits' rims and evidences show complete synergy between the expansion of the Ice Age and the high level of lake water (Crinsley 1970). Lake Urmia also developed more during the Pleistocene during cold climatic conditions due to reduced evaporation (due to a decrease of about five average annual temperatures) (Bobek 1937). On this basis, it can be concluded that the sea levels of the Southwest Asian lakes, such as the Caspian lakes, Urmia, Fars, Van, have been declining and some of them have generally dried up.Past climatic evidence can be used to determine permanent snow boundaries and the extent of glacier expansion, as well as to study soil conditions over that period's climate. For example, Schweitzer now defines permanent snow altitude in the Alborz region of about 4,400 meters (Eivazi 1347: 74). There are different views on the boundaries of glacial expansion and the height of snow boundaries in central Alborz. According to Bobek and Schweitzer, the height of the snow in the Pleistocene cold period was about 800 to 1000 m lower than it is today (Eivazi 1374: 74 and 5), in central Alborz it was between 3200 to 3700 or between 3000 and 3500 meters. Ehlers (1960) considers the permanent snow boundary in the Pleistocene 200 meters below what Bobek and Schweitzer stated (Ehlers 1372: 107), namely between 3000 and 3500 or between 2800 and 3300 meters. Pedramia defines the boundary of permanent snow in recent Wurm in central Alborz about 2200 meters.

    Results

    The results of this study indicate that distribution of ancient habits follows a linear distribution pattern in specific elevation levels. Southern parts of Alborz consisted of several through during Quaternary that have been occasionally submerged by shallow and deep lakes during Quaternary. On the other hand, climatic changes have caused movement of permanent snow line in the Alborz Mountains. Location of habitats was constantly changing proportional to climatic conditions as well as surface topography such as slope and elevation from sea level. Therefore, early humans were migrating during different climatic periods (i.e. migrating to the summer and winter habitats). It seems that by restoring ancient lakes in the area, it may be possible to find more biological remnants from human habitats

    Keywords: Paleogeomorphology, the pattern of distribution of ancient settlements, the level of the ancient lake level, the analysis, integration of information layers