مطالعات زمین شناسی مجموعه افیولیت اللهیارلو، شمال غرب ایران

نوع مقاله: مقاله پژوهشی

نویسندگان

1 گروه زمین‌شناسی، دانشگاه پیام‌نور، ایران

2 گروه مهندسی معدن، دانشگاه بین‌المللی امام خمینی (ره)، قزوین

10.22084/nfag.2019.2761

چکیده

سنگ‌های اصلی این مجموعه از توالی گابرو و سنگ­هایی نفوذی الترابازیکی و پریدوتیتی تشکیل شده‌اند و هم­چنین شامل پلاژیوگرانیت‌ها بوده و از بازالت­های بالشی بزرگی که بصورت بین لایه‌ای با سنگ‌های رسوبی پلاژیک همراه با چرت‌های رادیولردار تشکیل شده‌اند. داده‌های عناصر ناسازگار بهنجار شده نسبت به گوشته اولیه و کندریت نشان می‌دهند که افیولیت اللهیارلو از بازالت‌هایی با منشأ گوشته‌ای حاصل آمده است. براساس داده‌های عناصر نادر خاکی (REE)، تمام سنگ‌های افیولیت اللهیارلو، سنگ‌های همزاد و حاصل تفریق ماگمایی با منشأ بازالت‌های پشته‌های میان اقیانوسی از نوع آرایه گوشته­ای مورب غنی شده (E-MORB) هستند. سنگ‌های گابرو، بازالت، پلاژیوگرانیت و متاگابرو همگی خصوصیات کالک­آلکالن از خود نشان می‌دهند. سنگ‌های افیولیتی اولترامافیک و بازالت‌های  بالشی به ترتیب در طول پالئوزوئیک پسین تا تریاس پسین تشکیل شده‌اند. بازسازی صفحات تکتونیکی نشان می‌دهد که سنگ‌های این مجموعه تقریباً همزمان با افیولیت‌های نواحی مشهد و رشت تشکیل شده‌اند و سن تبلور آن‌ها حدوداً 380 میلیون سال است. مجموعه سنگ‌های افیولیت اللهیارلو نشان­دهنده موقعیت شمالی پوسته اقیانوسی پالئوتتیس بوده و پوسته پالتوتتیس در این زمین درز افیولیتی از پالئوزوئیک فوقانی تا تریاس پسین حفظ شده است. این مجموعه هم­چنین شامل کربنات‌های پلاژیک و بازالت‌ها به عنوان لایه‌های میانی یا قطعات بیگانه هستند. نتایج مطالعات چینه­شناسی، شواهد بیواستراتیگرافی مربوط به دوران پالئوزوئیک را نشان می‌دهد. شواهد بدست آمده حاکی از آن است که اگرچه ریفت اولیه و متبلور شدن پوسته اقیانوسیِ افیولیتِ اللهیارلو در کربونیفر آغاز شده، اما فعالیت‌های آتشفشانی همچنان تا تریاس پسین ادامه داشته است.

کلیدواژه‌ها


عنوان مقاله [English]

Geological Studies of Ophiolite Collection Allahyarlu, Northwest of Iran

نویسندگان [English]

  • Sh. Hassanpour 1
  • S. Senemari 2
چکیده [English]

The principal rock units are a gabbro sequence, late intrusive rocks that consist largely of the plagiogranite and volcanic rocks, which are largely pillow basalts interbedded with pelagic sedimentary rocks, including radiolarian cherts. Chondrite- and primitive mantle-normalized incompatible trace element data indicate that the Lahroud ophiolite was derived from a within plate basalt-like mantle source. All rocks are cogenetic geochemically and were derived by fractionation from melts with a composition similar to average E-MORB with calc-alkaline signatures. Plate reconstructions suggest that the rocks appear to be approximately contemporaneous with the Mashhad ophiolites and Rasht ophiolite, which has a crystallization age of ~380 Ma. Rocks from the Lahroud ophiolite complex represent northern Paleo-Tethyan ocean crust that was formed distinctly earlier than crust preserved in the Ma Paleo-Tethys suture zone ophiolite from upper Paleozoic to Later Teriassic. The results from microfossil studies show the presence of Paleozoic biostratigraphy (e.g., Paleotextularia, Nodosinella cf. concinna, Pseudokahlerina, Cylindrica, Earlandia, Endothyra baileyi, pachyphloia, Fusulinella Stafella and Bivalve, Paratikhine). The data suggest that although the initial rifting and crystallization of the oceanic crust of the Lahroud ophiolite began in the Carboniferous, with volcanic activities continuing through to the late Triassic.

کلیدواژه‌ها [English]

  • Ophiolite
  • Paleo-Tethys
  • Allahyarlou
  • Lahroud
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