بررسی شیمی کانی و زمین- دمافشارسنجی هارزبورگیت های گوشته ای کمپلکس دگرگونی شرقی افیولیت خوی- شمال غرب ایران

نوع مقاله : علمی- پژوهشی

نویسنده

صنعتی سهند

چکیده

پریدوتیت های گوشت های بخش مهم کمپلکس دگرگونی شرقی افیولیت خوی هستند. این سنگها محدوده سنی از اوایل ژوراسیک تا اواخر کرتاسه دارند و کم و‌ بیش سرپانتینی شده‌اند. بر اساس بررسیهای شیمی‌کانی بر روی هارزبورگیت‌ها، ترکیب اولیوین‌ها بین Fo89.46 Fa10.37 تا Fo89.86 Fa10.0 در نوسان بوده و عدد منیزیم (Mg# = Mg/(Mg+Fe2+)) تمامی نقاط آنالیز شده، برابر 90/0 و ترکیب اولیوین‌ها از نوع فورستریت است. ترکیب اعضای نهایی ارتوپیروکسن‌ها بین En86.022 Wo2.491 Fs9.368 تا En87.314 Wo6.719 Fs10.474 در نوسان است. عدد منیزیم (Mg# = Mg/(Mg+Fe2+)) این کانیها 90/0 و ترکیب آنها از نوع انستاتیت است. ترکیب اعضای نهایی کلینوپیروکسن ها بینEn44.159 Wo46.910 Fs4.323 Ac1.459 تا En46.803 Wo49.589 Fs4.786 Ac2.081 در نوسان است. عدد منیزیم (Mg# = Mg/(Mg+Fe2+)) این کانیها 91/0 است. کلینوپیروکسن‌های مورد بررسی بسیار غنی از کروم (21/1-87/0Cr2O3=) و از نوع دیوپسید هستند. غنی بودن ارتوپیروکسن‌ها و کلینوپیروکسن‌ها از کروم، نشان‌دهنده ذوب‌بخشی محدود پریدوتیت‌هاست. بررسیهای مینرال‌شیمی، ارتباط این هارزبورگیت‌ها را با محیط اقیانوسی نشان می‌دهند. همچنین اعداد منیزیم بالا در کانیهای بالا و درصد فوستریت بالا در اولیوین‌ها نشان‌دهنده منشأ زمین‌ساختی این سنگهاست. بررسیهای دما و فشارسنجی برای تخمین شرایط فشار- دمای تشکیل هارزبورگیت‌های مورد بررسی انجام شد. برای دماسنجی از روشهای ارتوپیروکسن (تک پیروکسن)، کلینوپیروکسن- اولیوین و ارتوپیروکسن- کلینوپیروکسن استفاده شد و دمای کلی حدود100 ±1100 درجه سانتی‌گراد به‌دست آمد. برای تخمین فشار از فشارسنج محتوای کروم درکلینوپیروکسن استفاده شد و فشار 4/2 ± 22 کیلو بار برآورد شد.

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