بررسی ژئوشیمی و ایزوتوپ های پایدار اکسیژن آگات های رضا‌آباد، جنوب‌ شرق شاهرود، ایران مرکزی: رهیافتی بر دما و فرایند تشکیل

زمین شناسی اقتصادی

مقاله 8، دوره 11، شماره 3 - شماره پیاپی 22، 1398، صفحه 525-541   

نوع مقاله: علمی- پژوهشی

شناسه دیجیتال (DOI): 10.22067/econg.v11i3.70421

نویسندگان

مهدی رضائی کهخائی^* ؛ ام البنین انصاری فر؛ حبیب الله قاسمی

دانشگاه صنعتی شاهرود

چکیده

در این پژوهش با توصیف ویژگی‌های صحرایی، ژئوشیمی و ایزوتوپ­‌های پایدار اکسیژن آگات­‌های رضا‌آباد در جنوب‌شرق شاهرود، اطلاعاتی درباره منشأ سیال­ کانی‌­ساز، دما و فرایندهای تشکیل آگات ارائه‌شده است. نتایج تجزیه ژئوشیمیایی این آگات‌ها نشان می‌دهد که آنها دارای مقادیر SiO2 از 1/97 تا 6/99 درصد وزنی با مقادیر جزئی از دیگر اکسیدها از قبیل CaO، Fe2O3، Al2O3 وNa2O هستند. نمودار توزیع عناصر خاکی کمیاب این آگات‌ها شیب منفی ملایمی را از La تا Nd و شیب نسبتاً همواری را در دیگر قسمت‌ها نشان می‌­دهد. شباهت در طرح‌های عناصر خاکی کمیاب سبک آگات‌ها و سنگ والدهای آتشفشانی آنها نشان می‌دهد که این عناصر توسط گردش سیالات در طول دگرسانی هم‌زمان و/یا پس از فعالیت آتشفشانی تحرک پیدا کرده‌اند. داده‌های ایزوتوپ اکسیژن آگات‌های رضاآباد نشان می‌دهد که مقادیر O18δ از  ‰ 8/23 تا ‰ 6/26 متغیر است و بیانگر تشکیل آنها از برهم‌کنش یک سیال هیدروترمالی دما‌پایین با سنگ‌های بازالتی است. دمای تشکیل این آگات‌ها که بر اساس مقادیر O18δ سیالات مختلف محاسبه‌شده است، نشان‌دهنده  تشکیل آنها در محدوده دمایی بین 7/35 تا 3/48 درجه سانتی‌گراد است.

کلیدواژه‌ها

آگات؛ ژئوشیمی؛ عناصر خاکی کمیاب؛ رضا آباد؛ شاهرود

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