ژئوشیمی و سنگ‌زایی مجموعه‌ی افیولیتی هرسین- صحنه (شمال شرق کرمانشاه- غرب ایران) شاهدی بر زمین ساخت جنوب نئوتتیس

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چکیده

افیولیت­های موجود در کمربند کوهزایی زاگرس بخشی از افیولیت­های تتیسی هستند که به علت موقعیت جغرافیایی خود، افیولیت­های خاورمیانه و دیگر افیولیت­های آسیا (نظیر پاکستان و تبت) را به افیولیت­های مدیترانه (نظیر ترودوس، یونان و شرق اروپا) وصل می­کنند. ماهیت افیولیت­های هرسین-صحنه (کرمانشاه) سبب درک نسبی از شاخه­ی جنوبی اقیانوس مزوزوئیک نئوتتیس و بقایای سیستم افیولیتی پری- عربی فرارانده شده بر سپر عربی (گندوانا) می­شود که در اینجا مورد بررسی قرار گرفته است. شواهد سنگ­نگاری نشان می­دهند که دنباله  افیولیتی مورد بررسی متشکل از اجزای پوسته­ای و گوشته ای است. به­طور کلی سنگ­های موجود در این دنباله شامل پریدوتیت­های هارزبورژیتی و لرزولیتی، گابروهای کوموله­ای، پگماتوئیدی، میلونیتی، همبافت دایکی و پیلولاواهای بازالتی است. شیمی کانی سنگ­های مافیک هرسین حاکی از محیط جزایر قوسی برای این بخش از مجموعه بوده و ژئوشیمی سنگ­های مافیک و اولترامافیک منطقه­ی صحنه ویژگی مورب­های نوع P < span dir="RTL"> را به نمایش می­گذارند. حضور ترکیب­های بازالتی مختلف موجود در منطقه را می­توان به­عنوان اثر متقابل بین استنوسفر MORB و OIA تفسیر کرد. روابط صحرایی و شواهد ژئوشیمیایی حاکی از آنند که افیولیت­های مورد بحث بخشی از یک حوضه­ی اقیانوسی کافت شده در زون انتقال قاره – اقیانوس بوده که در جنوب اقیانوس نئوتتیس شکل گرفته است. شکسته شدن پوسته­ی نئوتتیس و فرورانش آن به زیر خود در کرتاسه پایانی، منجر به توقف فرورانش نئوتتیس به زیربلوک سنندج - سیرجان و شکل­گیری حوضه­ی قوس- پشت قوس و سنگ­های وابسته به آن در افیولیت­های کرمانشاه شده است و ماگماتیسم مورب در پاسخ به عقب کشیده شدن زبانه فرورو در حاشیه­ی قاره­ای اوراسیا صورت پذیرفته است.

کلیدواژه‌ها


عنوان مقاله [English]

Geochemistry and petrology of the Harsin-Sahneh ophiolitic complex (NE Kermanshah-West of Iran): Implication for the tectonic of Southern Neo-Tethys

چکیده [English]

Ophiolites of the Zagros orogenic belt are part of the Tethys ophiolites, because of their geographical locations and link the Middle East ophiolites and other Asian ophiolites (e.g. Pakistani and Tibetan) to the Mediterranean ophiolites (e.g. Troodos , Greek and East European). The nature of the Harsin- Sahneh ophiolite (Kermanshah) traditionally identified as one of the Mesozoic southern branch of the Neo-Tethys Ocean and remnants of the Peri- Arabic ophiolite system obducted onto Arabian shield (Gondwana) that is reinvestigated in this study. Petrographic evidence indicates that this ophiolitic sequence consists of both mantle and crustal suites. In generals lithologies in this complex include harzburgitic and lherzolitic peridotites, cumulate, pegmatoidic and mylonitic gabbros, dyke complex and basaltic pillow lavas. Mineral chemisty of Harsin mafic rocks indicating island arc setting for this part of complex and geochemistry of mafic and ultramafic rocks of Sahneh region displaying P-type MORB nature. Presence of basalts with different composition in this region can be interpreted as the interaction between MORB-type and OIA-type asthenosphere.  Field relationships and geochemical evidence indicate that involved ophiolites were part of a rifted basin at the ocean-continent transition zone, which formed in the south of the Neo-Tethyan Ocean. The break-off of Neo-Tethyan slab and subduction of this slab branch itself during Cretaceous led to cessation of Neo-Tethyan subduction branch Sanandaj-Sirjan block, and forming arc-back arc basin and related rocks in the Kermanshah ophiolite and MORB magmatism occurred in response to slab retreat in the Eurasian continental margin.

کلیدواژه‌ها [English]

  • Tethyan ophiolites
  • Arc magmatism
  • P-type MORB
  • Zagros
  • Iran
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