سنگ‌ شناسی، زمین‌ شیمی و جایگاه زمین‌ ساختی بازالت‌ های بوژان، شمال‌ شرق نیشابور

نوع مقاله : مقاله پژوهشی

نویسندگان

1 کارشناسی ارشد، گروه زمین‌شناسی، دانشکده علوم، دانشگاه فردوسی مشهد، مشهد، ایران

2 دانشیار، گروه زمین‌شناسی، دانشکده علوم، دانشگاه فردوسی مشهد، مشهد، ایران

چکیده

منطقه بوژان در شمال‌شرق ایران و در 22 کیلومتری شمال‌شرق نیشابور واقع‌شده است. این محدوده شامل برون‌زدهایی از واحدهای رسوبی پالئوزوئیک (سیلت، کنگلومرا، آهک ماسه‌ای) و سنگ‌های آتشفشانی بازالت، آندزیتی بازالتی، آندزیت، تراکیت و آذرآواری (سیلورین) است. بافت غالب واحدهای آتشفشانی پورفیری، گلومروپورفیری و جریانی بوده و شامل کانی‌های اصلی پلاژیوکلاز، پیروکسن و به مقدار کم الیوین و کانی فرعی آپاتیت هستند. بازالت‌های بوژان سرشت آلکالن با گرایش سدیک دارند. این سنگ‌ها دارای ویژگی‌های بازالت‌های درون صفحه‌ای (مانند نبود آنومالی منفی عناصر Nb، P و Ti و دارا بودن روند کاهشی در نمودار چند عنصری بهنجار‌شده به ترکیب گوشته اولیه) هستند. همچنین بر اساس نمودارهای گوناگون برای محیط زمین‌ساختی، در محدوده بازالت‌های درون صفحه‌ای قرار می‌گیرند. ماگمای اولیه بر اساس نسبت‌های Nb/Zr، Ce/Zr، La/Zr و Rb/Zr شواهدی از آغشتگی پوسته‌ای نشان نمی‌دهد. سنگ‌های بوژان در طول چرخه‌ای از کافت درون قاره در هنگام باز شدگی پالئوتتیس در اردویسین تا سیلورین شکل گرفته‌اند.

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