بررسی فرایندهای میگماتیت زایی و گرانیت های لوکوکرات در منطقه تویسرکان، همدان

نوع مقاله : علمی- پژوهشی

نویسندگان

1 دانشگاه لرستان

2 دانشگاه شهید چمران اهواز

چکیده

در مجاورت توده پلوتونیکی الوند، انواع سنگ­ های دگرگونی ناحیه ­ای و مجاورتی درجه پایین تا بالا وجود دارد. نفوذ توده مافیک باتولیت الوند در سنگ‌ های رسی دگرگون‌شده (شیست­ ها) سبب ایجاد هورنفلس­ های رسی و میگماتیت­ های آناتکسی در هاله دگرگونی خود شده است. پدیده ذوب‌بخشی در هاله همبری الوند فقط در سنگ­ های با ترکیب رسی رخ‌داده است. مشاهده­ های صحرایی، بررسی­ های میکروسکوپی و داده­ های ژئوشیمیایی نشان می­ دهد که در منطقه مورد بررسی میگماتیت­ ها از ذوب‌بخشی هورنفلس­ ها حاصل شده‌اند. اختلاف قابل‌توجه در مقادیر عناصر نادر خاکی و الگوی REE گرانیت­ های لوکوکرات و لوکوسوم ­های میگماتیت نشان می‌دهد که ارتباط ژنتیکی بین میگماتیت­ ها و گرانیت­ های هم‌جوار وجود ندارد و نفوذ گرانیت­ های لوکوکرات بعد از حادثه میگماتیتی‌شدن رخ‌داده است. این نشان‌دهنده آن است که آناتکسی و ذوب‌بخشی به‌دلیل حرارت ناشی از توده­ های گرانیتی نیست؛ بلکه گرمای حاصل از توده­ های مافیک قدیمی­ تر (گابرودیویت­ ها) عامل اصلی پدیده ذوب‌بخشی و میگماتیتی‌شدن در منطقه است. این یافته­ ها با داده ­های سن‌سنجی توده پلوتونیکی الوند و سنگ­ های میگماتیتی پیرامون آنها همخوانی دارد.

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