کانی‌شناسی و دما- فشارسنجی شیست‌های آبی مجموعه‌ی دگرگون سلطان‌آباد (شمال‌شرق سبزوار)

نویسندگان

1 دانشگاه بین المللی امام خمینی قزوین

2 دانشگاه علوم رم

3 دانشگاه خوارزمی

4 دانشگاه تربیت مدرس تهران

چکیده

مجموعه­ی دگرگونی سلطان­آباد در شمال­شرق افیولیت­های سبزوار رخنمون دارد. در این مجموعه شیست­های آبی به صورت آمیزه­ی زمین­ساختی در یک زمینه­ی سرپانتینیتی دارای برونزدهای گسترده­ای هستند. بررسی­های صحرایی، سنگ­نگاری و محاسبات دما - فشارسنجی نشان داد که این سنگ­ها دستخوش دو فاز دگرگونی شده­اند. پاراژنز فاز اول دگرگونی شامل آمفیبول سدیک (گلوکوفان و ریه­بکیت)، اپیدوت، فنژیت­های جهت­یافته و گارنت­های نسل اول است که طی تدفین و فرورانش حاصل شده­ و شرایط فشار و دمای آن به ترتیب 11 تا 14 کیلوبار و 350 تا 420 درجه­ی سانتیگراد بوده است. دومین فاز دگرگونی که حاصل تزریق توده­های ترونجمیتی است سبب تبلور پورفیروبلاست­های درشت آلبیت، گارنت و اپیدوت نسل دوم و نیز تبلور آمفیبول­های کلسیک - سدیک در اطراف آمفیبول­های سدیک شده است. شرایط دگرگونی در این مرحله فشار 4 تا 7 کیلوبار و دمای 500 تا 580 درجه سانتیگراد به­دست آمده است. بنظر می­رسد برخورد صفحه عربستان با خرده قاره­ی ایران مرکزی و حرکت این خرده قاره به سمت شمال­شرقی، منجر به فرورانش حوضه­ی اقیانوسی سبزوار و ذوب­بخشی و نیز تشکیل توده­های ترونجمیتی در پالئوسن میانی شده باشد. همچنین در نتیجه تزریق این توده­ها، شیست­های آبی موجود در منشورهای بهم­افزوده، دستخوش دگرگونی برگشتی شده­­اند.

کلیدواژه‌ها


عنوان مقاله [English]

Mineralogy and thermobarometery of blueschists from Soltan Abad metamorphic complex (NE Sabzevar)

چکیده [English]

Soltan Abad metamorphic complex cropped out at NE of the Sabzevar ophiolites. There are extensive exposures of bluschist facies rocks inside a serpentinitic groundmass as tectonic mélange in this metamorphic complex. Field investigations, petrography and thermobarometry indicate that these rocks have experienced two metamorphic phases.  Paragenesis of the first metamorphic phase consists of oriented Na-amphibole, epidote and phengite and the first generation of garnets that have formed during burial and subduction. Pressure and temperature conditions of the first metamorphic phase have been 11 to 14 Kb and 350 to 420°C respectively. The second metamorphic phase, due to injection of trondhjemitic plutons, resulted in crystallization of coarse porphyroblasts of albite, second generations of garnet and epidote as well as crystallization of Ca-Na amphiboles around Na-amphiboles. Metamorphic conditions of this stage have obtained as P= 4-7 Kb and T=500-580°C. It seems that the collision of Arabian plate with Central Iranian microcontinent and movment of this microcontinet toward the north east, led to subduction of Sabzevar oceanic basin and partial melting and generation of trondhjemite during Middle Paleocene. As a consequence of intrusion, bluschists of the accretionary prisms have undergone retrograde metamorphism.

کلیدواژه‌ها [English]

  • blueschist
  • Soltan Abad metamorphic complex
  • Sabzevar Ophiolites
  • NE Iran
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