نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه پژوهشی اکتشاف ذخایر معدنی خاور ایران، دانشگاه فردوسی مشهد، مشهد، ایران گروه زمین‌شناسی دانشگاه کلرادو، بولدر، امریکا

2 گروه زمین‌شناسی دانشگاه کلرادو، بولدر، امریکا

چکیده

بیوتیت مسکوویت لیکوگرانیت و پگماتیت­های همراه در متاافیولیت و متافلیش­ها (بقایای پوسته اقیانوسی پالئوتتیس) همزمان با برخورد صفحه ایران با صفحه توران نفوذ نموده­اند. چهار نوع دایک پگماتیتی که بیوتیت مسکوویت لیکوگرانیت­ها را قطعه کرده‌­اند، شناسایی شدند. با استفاده از روشU-Pb  سن زیرکن، بیوتیت مسکوویت لیکوگرانیت 205.9 ± 4.1 Ma  تعیین شد (راتین، تریاس بالایی). بیوتیت مسکوویت لیکوگرانیت و آپلیت گرانیت از نظر شیمیایی، فوق آلومینیم و گرانیت نوع S است. عدد پذیرفتاری مغناطیسی بیوتیت مسکوویت لیکوگرانیت و آپلیت گرانیت میان  SI 5-10 * 5 تا 11 و نسبتFe2O3/FeO  کمتر از 35/0 است، بنابراین مربوط به سری ایلمینیت (نوع کاهیده) هستند. مجموع عناصر کمیاب خاکی بیوتیت مسکوویت لیکوگرانیت میان 130 تا 176 و آپلیت گرانیت میان 50 تا 79 است. Eu ناهنجاری منفی جزئی (Eu/Eu* برابر 52/0تا 76/0) نشان می‌دهد. نسبت ایزوتوپ اولیه (87Sr/86Sr)i و i(143Nd/144Nd) اولیه با توجه به سن 205 میلیون سال محاسبه شد. نسبت ایزوتوپ اولیه (87Sr/86Sr)i در بیوتیت مسکوویت لیکوگرانیت و آپلیت گرانیت به ترتیب 708161/0 و 709853/0 بوده است. نسبت (143Nd/144Nd)i اولیه در بیوتیت مسکوویت لیکوگرانیت  512214/0 و در دایک آپلیت گرانیت 512024/0 بـوده اسـت. میـزان ایزوتوپ اولیه ε Nd در بیوتیت مسکوویت لیکوگرانیت 48/6- و در دایک آپلیت گرانیت 83/6- است. بر اساس داده­های ایزوتوپی ماگمای اولیه از پوسته قاره­ای منشأ گرفته است. به توجه به نسبت‌های Rb/Sr برابر 1 تا 3/1 وCaO/Na2O  کم و بیش 3/0 در بیوتیت مسکویت لیکوگرانیت  ترکیب سنگ منشأ بین متاپلیت و متا پسامیت بوده است.
 

کلیدواژه‌ها

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