متاپلیتهای گرمی¬چای، شمالغرب ایران: شیمی سنگ کل، زادگاه رسوبی و شرایط دگرگونی

چکیده مقاله :

بمنظور بررسی زادگاه رسوبی و شرایط دگرگونی متاپلیتهای گرمی چای واقع در شمال شهرستان میانه (شمالغرب ایران) شیمی شنگ کل این مجموعه مورد بررسی قرار گرفته است. بررسیهای پتروفابریک حاکی از شکلگیری همزمان با تکتونیک پورفیروبلاستهای کردیریت (دگرگونی ناحیه ای) در این سنگهاست. همچنین ساختارهای برشی C' ویژگی بارز بافتی می باشد. دو فاز دگرگونی ناحیه ای (RMP1 و RMP2)، یک فاز دگرگونی مجاورتی (CM) و دو فاز دگرشکلی (D1 و D2) شناسایی شده اند. ژئوشیمی عناصر اصلی حاکی از سنگ مادر شیلی و گری وکی برای متاپلیتهاست. بر اساس عناصر اصلی، واسطه و کمیاب (K2O، TiO2، Zr، Ni و Ti) سنگ آذرین مولد این رسوبات دارای سرشت آندزیتی و داسیتی/ریوداسیتی بوده است. درجه دگرسانی شیمیایی (CIA و CIW) سنگ آذرین اولیه متوسط بوده است. همچنین برمبنای اکسید عناصر اصلی محیط تکتونیکی تشکیل رسوب حاشیه فعال قاره ای شناسایی شده است. متاپلیتهای گرمی چای در مقایسه با PAAS و UCC غنی از Cs، La و Ce، تهی از Sr، Nb و Ta می باشند. نمونه های معرف در نمودارهای سازگاری در داخل مثلثهای پاراژنتیک قرار می گیرند که حاکی از تعادلی بودن آنهاست. بر اساس مقاطع ترکیبی استاندارد برای متاپلیتها بازه دمایی و فشاری تشکیل درجه بالاترین پاراژنز بترتیب 535 تا 635 درجه سانتی گراد و 1-3 کیلوبار بوده است.

چکیده انگلیسی :

In order to study the provenance and metamorphic conditions of the Garmichay metapelites located in Northern Miyaneh, NW Iran the whole rock chemistry of this assemblage is investigated. Petrofabric scrutinizes have revealed the syn-tectonic nature of cordierite porphyroblasts (regional metamorphism) in the metapelites. Besides, C' shear band structures are observed. Two regional metamorphic (RMP1, RMP2), one contact metamorphic (CMP) and two deformation (D1, D2) phases are identified. The major oxide geochemistry implies two sedimentary progenitors: shale and greywacke. Based on major, rare earth and trace elements (Ti, Ni, TiO2, Zr and K2O) the igneous source rock has had andesite to dacite/rhyodacite nature. The chemical index of alteration and weathering indexes (CIA, CIW) imply a medium degree of alteration in the igneous progenitor. The Garmichay metapelites, in comparison with the PAAS and UCC, are enriched in Cs, La and Ce and depleted in Sr, Nb and Ta. The representative samples in the compatibility diagrams lie inside the paragenetic triangles that imply their stable conditions. Finally, based on the standard pseudosections the temperature and pressure range of the highest degree paragenesis has been 535-635 °C and 1-3 kb, respectively.

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