زمین‌شیمی و سنگ‌شناسی توالی گوشته‌ای در افیولیت‌های نائین

نوع مقاله: مقاله پژوهشی

نویسندگان

1 دانشکده علوم زمین، دانشگاه شهید بهشتی، تهران، ایران

2 دانشکده علوم زمین، دانشگاه علوم پایه دامغان، دامغان، ایران

چکیده

توالی گوشته‌ای مجموعه افیولیتی نائین علاوه بر پریدوتیت‌ها (هارزبورژیت‌های Cpxدار،  لرزولیت‌ها و به طور محلی ورلیت‌ها و دونیت‌ها) از گابروهای پگماتیتی، لکه‌‌های گابرویی، دایک‌های گابرویی- دیابازی، پیروکسنیتی و وبستریتی تشکیل شده است. مطالعات سنگ‌شناسی و زمین‌شیمیایی، بیشتر پریدوتیت‌های این منطقه را هارزبورژیت‌های Cpxدار معرفی کرده است که دارای اسپینل‌های غنی از آلومینیم، با عدد کروم 55/41-12/16 = Cr# است که در دمای حدود ˚C 1000 به تعادل رسیده‌اند. گابروهای پگماتیتی به صورت انبان‌های کوچک درون پریدوتیت‌ها دیده شده که دارای  Cpx و پلاژیوکلاز دگرشکل شده هستند. دایک‌های گابرویی و دیابازی به طور عموم رودنگیتی شده‌اند و درون پریدوتیت‌ها بدون حاشیه سرد نفوذ کرده‌اند. این دایک‌ها از نظر زمین‌شیمیایی با گدازه‌های بالشی (پیلولاواها) و میکروگابروهای توالی پوسته‌ای هم منشأ بوده اما درصدهای متفاوت ذوب بخشی را نشان می‌دهند. همچنین بر اساس زمین‌شیمی سنگ‌های مافیک و پریدوتیت‌ها، می‌توان افیولیت نائین را مرتبط به گسترش یک حوضه پشت کمان دانست.

کلیدواژه‌ها


عنوان مقاله [English]

The Geochemistry and Petrology of Mantle Sequence in the Nain Ophiolite

نویسندگان [English]

  • M. Rahgoshay 1
  • J. Mehdipour Ghazi 1
  • H. Shafaii Moghadam 2
1 Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran
2 School of Earth Sciences, Damghan University of Basic Sciences, Damghan, Iran
چکیده [English]

Peridotites (Cpx-bearing harzburgites, lherzolites, wherlites and dunites) associated with pegmatite gabbros, gabbro impregnations, gabbroic-diabasic dikes, pyroxenites and websterites are the main constituents of the mantle sequence in the Nain ophioliote assemblage. Petrographic and geochemical studies indicate that peridotites in the Nain ophiolites are Cpx-bearing harzburgites with Al-rich spinels (Cr#=16.12-41.55) equilibrated at about 1000˚C. Pegmatite gabbros are found as small pockets within peridotites showing deformed clinopyroxenes and plagioclases. Gabbro-diabase dikes, mostly rodingitized, injected into the peridotites without chilled margins. These dikes are geochemically co-genetic with pillow lavas and micro-gabbros of the crustal sequence, but display variable degrees of partial melting. Based on the geochemistry of the mafic rocks and the peridotites, we suggest that Nain ophiolites were developed in a back arc spreading basin.
 

کلیدواژه‌ها [English]

  • Mantle sequence
  • Peridotite
  • Partial Melting
  • Back arc basin
  • Nain ophiolite

 

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