بررسی ژئوشیمیایی، کانی شناسی و سنگ‌زایی سنگ‌های آداکیتی جنوب شرق جلفا (شمال‌غرب ایران)

نویسندگان

1 دانشگاه شهید بهشتی تهران

2 دانشگاه تهران

چکیده

گنبد نیمه ژرف کیامکی در فاصله­ی 25 کیلومتری جنوب شرقی شهرستان جلفا (استان آذربایجان شرقی) واقع شده است. سنگ‌های این گنبد ترکیب چیره داسیتی داشته ولی با فاصله از کیامکی، در کمان معروف به قلنج بافت و ترکیب گرانودیوریتی نشان می دهند. مقادیر SiO2 آن­ها برابر  73-64 درصد وزنی و عدد منیزیم آن­ها در بازه­ی 57-27 تغییر می‌کند. بر پایه­ی ویژگی­های ژئوشیمیایی، این سنگ‌ها از نوع آداکیت‌های پرسیلیس رده بندی می شوند. در نمودارهای هارکر روندهای جدایشی عناصر مختلف نسبت به SiO2 نمود داشته و در عین حال روند عمومی خطی سنگ­های مورد بررسی می­تواند نشانگر خاستگاه یکسان آن­ها باشد. در نمودارهای عنکبوتی چند عنصری، سنگ­های منطقه به مانند سنگ­های وابسته­به فرورانش حاشیه فعال قاره ای، به صورت مشخص از عناصر لیتوفیل با شعاع یونی بزرگ (LILE) غنی شدگی و از Nb و HFSE تهی شدگی نشان می دهند. بر اساس سرشتی­های ژئوشیمیایی؛ مثل مقادیر Th و نسبت­های Th/Sm، Th/Ce، Th/Yb و ایزوتوپی Sr و Nd، محیط تشکیل این گنبد پسا برخورد بوده و با مدل زایشی ناشی از ذوب بخشی سنگ‌های مافیک پوسته­ی قاره‌ای ضخیم شده، سازگارتر است. با توجه به مدل زایشی و محیط تشکیل این سنگ‌ها، سن میوسن پایانی گنبد مورد بررسی و سن بسته‌شدن میوسن تحتانی و قبل از آن برای نئوتیتس، نمی‌توان پیدایش این سنگ‌ها را به طور مستقیم در ارتباط با فرایندهای ژئودینامیکی نئوتتیس در ارتباط دانست.

کلیدواژه‌ها


عنوان مقاله [English]

Geochemistry and petrogenesis of Adakitic rocks from the Kiyamaki magmatic dome, southeast Jolfa (NW Iran)

چکیده [English]

Composition of the Kiyamaki dome has mostly dacite and granodiorite in rims, with SiO2 contents ranging from 64 to 73 wt% and Mg# values ranging from 27 to 57. These rocks are high-Si adakite. Geochemical characteristics and Sr and Nd isotopic rates indicate that the rocks of Kiyamaki dome are a post-collisional adakite. Combined geochemical and Sr–Nd isotope data suggest that the Kiyamaki adakitic magma derived from partial melting of mafic rocks in the lower part of a thickened crust. So, with attention to tectonic setting and source of derived adakitic magma, age of Eocene to Miocene for generation and closing time of Neo-Tethys (Middle Miocene), it is not possible that generation of Kiyamaki adakites be directly related to geodynamical evolution of Neo-Tethys. Here, with suppose of age information  for generation of Kiyamaki dome and closing of Neo-Tethys,formation of domes in the northern part of Tabriz fault can be related to the collision of Sanandaj-Sirjan micro-continual with Alborz-Azarbaijan block in Paleogene that was happened due to subduction of oceanic crust of Khoy-Zanjan basin toward beneath of Alborz-Azarbaijan block.

کلیدواژه‌ها [English]

  • Kiyamaki
  • adakite
  • Post-collisional
  • Partial melting of the lower part of a thickened crust
  • Oceanic basin of Khoy-Zanjan
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