تعیین منشأ پریدوتیت‌های میزبان کانسارهای کرومیت بر اساس داده‌های کانی‌شناسی در افیولیت نیریز، منطقه آباده‌طشک، استان فارس

نوع مقاله: مقاله پژوهشی

نویسندگان

1 استادیار بخش علوم زمین دانشگاه شیراز

2 دانشجوی کارشناسی ارشد زمین شناسی اقتصادی بخش علوم زمین دانشگاه شیراز

چکیده

    افیولیت نیریز در منطقه آباده­طشک عمدتاً از سنگ­های اولترامافیک (لرزولیت، هارزبورژیت و دونیت) باقیمانده از ذوب­بخشی گوشته فوقانی تشکیل شده است. افزایش درجه ذوب­بخشی به ترتیب از سنگ لرزولیت به سمت هارزبورژیت و سپس دونیت به وسیله ترکیب مودال کانی­شناسی این سنگ­ها نشان داده می­شود. تغییرات در مودال کانی­شناسی سنگ­های میزبان کانسارهای کرومیت با تغییر در ترکیب شیمیایی کانی­های اولیوین و اسپینل در سنگ­های میزبان متناسب می­باشد. میزان Fo اولیوین از لرزولیت (79/90-5/91) به سمت هارزبورژیت (23/91-56/91) و دونیت (75/91-68/94) افزایش می­یابد. این تغییر شیمیایی به موازات افزایش میزان Cr# (از 34/56 در لرزولیت به 36/79 در دونیت) و کاهش Mg# (از 05/41 در لرزولیت به 56/32 در دونیت) در اسپینل­های همان سنگ­ها است. مقادیر Cr#، Mg#، Al2O3 و TiO2 در ترکیب کانی­های اسپینل­کروم­دار سنگ­های پریدوتیتی نشانگر تشکیل مجموعه افیولیتی در یک حوضه پیش­کمانی (Forearc) بر روی منطقه فرورانش (supra-subduction zone) می­باشد.

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