شیمی کانی و دما- فشار سنجی سنگهای رسی موجود در هسته دگرگون در دما بالا- فشار متوسط شاهنیدژ (SMC) شمال غرب ایران

نویسندگان

دانشگاه تبریز

چکیده

با توجه به مطالعات ریزبافتی، مشخص شده است که متاپلیتهای هسته دگرگون شرق شاهیندژ (SMC) دستخوش چند دگرگونی شده و حداقل دو فاز دگرگونی ناحیه­ای (RM1, RM2) و یک فاز دگرگونی مجاورتی (CM) را تجربه کرده­اند. طی فاز دگرگونی ناحیه­ای نهایی (RM2) پورفیروبلاستهای شکل­دار کیانیت، آندالوزیت، استارولیت، کردیریت، گارنت، و رشته­های فیبرولیت در میکاشیستها به وجود آمده­اند. دما- فشار سنجی این فاز با استفاده از روشهای مختلف تعیین دما و فشار برای سنگهای رسی انجام شده است. دماسنج کاتیونی گارنت - بیوتیت و گارنت - کلریت دمای بیشینه  oC 700-650 را برای دگرگونی این سنگها نشان می­دهد. همچنین با استفاده از دما -فشار سنجی از طریق قطع واکنشهای چندگانه تعادلی با استفاده از برنامه THERMOCALC، میانگین دما و فشار دگرگونی برای شیستهای کیانیت - استارولیت – کردیریت­دار oC 50 ± 650 و 5/1 ± 7- 5 کیلوبار محاسبه شد. چنین دما و فشاری نشان دهنده شیب زمین گرمایی oC 40 در هر کیلومتر است که از سرشتهای محیطهای برخورد قاره – قاره­ای است.

کلیدواژه‌ها


عنوان مقاله [English]

HT-MP metamorphism at the Shahindezh Metamorphic Core (SMC) –NW Iran; Mineral chemistry and thermobarometry of metapelites

چکیده [English]

On the basis of microstructural evidence it is clear that SMC metapelites have experienced at least two regional (RM1, RM2) and one contact metamorphism (CM). During RM2, several porphyroblasts including kyanite, andalusite, staurolite, cordierite, garnet and fibrous sillimanite have grown in the mica - schists. In order to estimate the PT condition of metamorphism of metapelites, we used cation exchange and multi-equilibrium methods. Temperature of RM2 estimated using, Grt - Bt and Grt - Chl thermometry 650 - 700 °C. Also PT conditions are calculated by THERMOCALC computer program which is based on multi-equilibrium reactions. Kyanite - staurolite - cordierite - bearing mica - schists are metamorphosed at pressure ~5 - 7 kbar and temperature ~650  ±50 °C. Thermal gradient at the SMC is considered to be ~ 40 °C/km. This thermal gradient is similar to those from continent-continent collision settings.

کلیدواژه‌ها [English]

  • metapelites
  • HT/MP Metamorphism
  • Mineral chemistry
  • Thermobarometry
  • Shahindezh Metamorphic Core (SMC)
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