ویژگی های ژئوشیمیایی و ایزوتوپی پروتولیت اکلوژیت های شمال شهرکرد: شاهدی بر تکوین حوضه پشت‌ کمان نئوپروتروزوئیک در پهنه سنندج-سیرجان

زمین شناسی اقتصادی

مقاله 4، دوره 11، شماره 3 - شماره پیاپی 22، 1398، صفحه 439-456   

نوع مقاله: علمی- پژوهشی

شناسه دیجیتال (DOI): 10.22067/econg.v11i3.68644

نویسندگان

فروغ ملک محمودی¹؛ علیرضا داودیان دهکردی^{* 1}؛ ناهید شبانیان بروجنی¹؛ حسین عزیزی²

¹دانشگاه شهرکرد

²دانشگاه کردستان

چکیده

اکلوژیت­‌های مورد بررسی بخشی از کمپلکس دگرگونی شمال شهرکرد هستند که به پهنه­ ساختاری سنندج-سیرجان تعلق دارند. این اکلوژیت­‌ها با ترکیب کانی شناسی غالب آمفیبول، گارنت، زوئیزیت و پیروکسن (امفاسیت) به‌صورت عدسی­‌هایی همراه پاراگنایس­‌های نئوپروتروزوئیک مشاهده می­‌شوند. مجموعه کانیایی این سنگ­ها نشان‌دهنده دگرگونی آنها در فشار بالا‌ست. با در‌نظر‌گرفتن سیستم نسبتاً بسته در تعادلات شیمیایی این سنگ‌ها در طی فرایندهای دگرگونی می‌­توان محیط تشکیل سنگ مادر این سنگ­‌ها را مورد بررسی قرار داد. نمودار عناصر نادر خاکی بهنجار‌شده به کندریت، غنی­‌شدگی جزئی از عناصر نادر خاکی سبک نسبت به عناصر نادر خاکی سنگین را نشان می­‌دهد و نسبت La/Yb)cn) در این نمونه‌ها بین 7/1 تا 7/2 متغیر است. نمودار عناصر نادر بهنجار‌شده به گوشته­ اولیه آنومالی منفی Ti ،Nb ،P و Y را نشان می­‌دهد. نمودارهای ژئوشیمیایی نشان‌دهنده تمایل زیاد این سنگ‌ها با بازالت­‌های تولئیتی است که در محیط­‌های کششی پشت‌کمان شکل گرفته‌­اند. بررسی‌های ایزوتوپی Sr-Nd نشان‌دهنده­ ماگمای اولیه این سنگ‌ها با ترکیب گوشته­ غنی‌­شده  بالای زون فرورانش است. با توجه به الگوی پراگندگی عناصر و نسبت‌­های ایزوتوپی اولیه می­‌توان تشکیل سنگ مادر اکلوژیت‌های منطقه را ناشی از کشش­‌های پشت‌کمان در پهنه سنندج-سیرجان در اواخر پروتروزوئیک پایانی (ادیاکاران) دانست.

کلیدواژه‌ها

: اکلوژیت؛ گوشته‌ی غنی شده؛ نسبت‌های ایزوتوپی Nd-Sr؛ شمال شهرکرد؛ پهنه‌ی سنندج-سیرجان

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