پتروژنز و جایگاه تکتونوماگمایی تشکیل سنگ‌های آتش‌فشانی ائوسن خان علی دره‌سی، شمال لاهرود، شمال باختر ایران

نوع مقاله : مقاله پژوهشی

نویسندگان

گروه زمین‌شناسی، دانشکده علوم، دانشگاه محقق اردبیلی، اردبیل، ایران

چکیده

توده­های تراکی آندزیت - تراکی آندزیت بازالتی ائوسن در شمال باختر ایران، شمال لاهرود(استان اردبیل) با روند شمال غربی – جنوب شرقی برون‌زد دارند. این سنگ­ها بافت­ عمده هیالومیکرولیتی پورفیریک دارند و دارای کانی­های اصلی پلاژیوکلاز به همراه کانی‌های فرعی آمفیبول، پیروکسن و اندکی بیوتیت و کانی­های تیره و پتاسیم فلدسپار هستند. ماگمای مولد این سنگ‌ها سرشت شوشونیتی دارند. ماگمای والد این سنگ­های آتشفشانی متاثر از فرآیند تفریق بلورین بوده و مقادیرEu/Eu* ≤ 1 (83/0 تا 08/1) می­باشد. در نمودارهای عنکبوتی فروافتادگی‌های عناصر ,Ta Ti, Nb و غنی شدگی شاخص عناصر LILE و LREE وابستگی ماگمای اولیه مولد این سنگ‌ها را به محیط‌های فرورانشی نشان می‌دهد. نسبت Ba/Nb با مقادیر 45 تا 131، نسبتN (La/Sm) با مقادیر بالای 2 و نسبت Th/Ce نیز با مقادیر 13/0 تا 2/0 نشانگر ارتباط غنی شدگی با ذوب رسوبات فرورانده شده طی فرورانش می­باشد. همچنین نسبت پایین Ba/Rb از 0/10 تا 2/15 و نسبت Rb/Sr از 07/0 تا 1/0 نشانگر ذوب منشأ فلوگوپیت دار با ماهیت شوشونیتی است. ماگمای اولیه این توده­ها از ذوب بخشی 5 تا 10 درصدی منشأ اسپینل لرزولیت فلوگوپیت دار ایجاد شده است که منشأ توسط ذوب رسوبات حین فرورانش متاسوماتیزه شده است. این سنگ­ها در محیط قاره­ای پس از برخورد ایجاد شده‌اند.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Petrology, geochemistry and petrogenesis of Eocene volcanic rocks from Khan Ali Darasi North of Lahrod city, Northwest of Iran

نویسندگان [English]

  • gholamreza ahmadzadeh
  • Mohammad Mobashergermi
  • Alireza Ravankhah
Department of geology, Faculty of Science, University of Mohaghegh Ardabili, Ardabil, Iran
چکیده [English]

Introduction
According to the outcrops of volcanic and intrusive rocks with different compositions and ages in the northwest of Iran, the magmatism of the northwest of Iran has been introduced under the titles of Talash and Arsbaran tectonomagmatic zone (Berberian, 1981; Aghazadeh et al, 2010, 2011; Castro et al, 2013). The Talash zone in the east of the Western Alborz-Azerbaijan zone, like the rest of Azerbaijan and Urmia-Dakhtar magmatism, has experienced the peak of magmatism in the Eocene to Oligomiocene (Vincent et al, 2005; Shafaii Moghadam and Shahbazi Shiran, 2010). Volcanic rocks in the northeast of Lahrud are andesitic, basaltic eruptive outcrops and plutonic internal alkaline, calc-alkaline and Shoshonitic masses (Vincent et al, 2005), which continue to spread significantly beyond the borders of the country. Eocene volcanic rocks are seen in the 1:100,000 maps of Lahrud with a northwest-southeast trend. In this research, the lithological, geochemical and petrogenesis characteristics of volcanic rocks in the north of Lahrood in the Khanali Daresi section have been evaluated.
Materials and methods
Volcanic rock outcrops in the study area were first evaluated in the field and 45 samples were taken from different parts and then 20 thin sections were prepared from the samples for petrographically studies by using an Olympus type polarizing microscope. Then 11 fresh samples were sent to MS Analytical Laboratory in Canada by Zaminriz Kavan company for chemical analysis and determining the main oxides of whole rock.
Results and discussion
Eocene- trachy-andesite and trachy andesy basaltic rocks in northwestern Iran, north of Lahroud (Ardabil province), Extruded with northwest-southeast trend. These rocks have hyalomicrolith porphyritic textures and have plagioclase as major minerals with minor amphibole, pyroxene, biotite and opaque minerals and alkali feldspar minerals. The productive magmas of these rocks are of potassic and shoshonitic nature of Roman type. The parent magma of these volcanic rocks is affected by the fractional crystallization process and Eu / Eu * ≤ values (0.83 to 1.08) indicate plagioclase separation in the magmatic reservoir. Negative anomaly of Ta Ti, Nb in the spider diagrams and enrichment of the LILE and LREE index indicate the effect of subduction environments component in generation of g these rocks. Ba / Nb ratios of 45 to 131, La / Sm ratios of N above 2 and Th / Ce ratios of 0.13 to 0.2 indicate enrichment correlations with melting of subducted sediments during subduction. Also, low Ba / Rb ratios from 0.10 to 15.2 and Rb / Sr ratios from 0.07 to 0.1 indicate melting of phlogopitic bearing source with shoshonitic nature in genesis of these rocks. primary magmas of these rocks form from partial melting of less than 10% matosomatized phlegopolite bearing spinel- lherzolite source and melting of magmatic subduction sediments during subduction in the post-Collisional setting.
 
Conclusion
The geochemical characteristics of the studied samples indicate their enrichment and formation in connection with the subduction environment. This indicates a continental volcanic arc in the experimental diagrams of determining the tectonic environment. The primary magma of volcanic rocks consists of the melting of less than 10% of spinel-phlogopite mantle and metasomatized with subduction factors and associated sediments.

کلیدواژه‌ها [English]

  • Trachy andesite
  • Post-collision
  • Khan Ali Darasi
  • Volcanic rocks
  • Subduction
  • Lahrod
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