Geochemistry of metapelitic rocks from the Garmichay Area, East Azerbaijan, NW Iran; protolith nature and whole rock control on metamorphic mineral assemblages

Document Type: Research Paper

Authors

1 Department of Earth Sciences, University of Tabriz, 51664, Tabriz

2 Department of Earth Sciences, University of Tabriz

3 Geoscience Department, University Brunei Darussalam, Tunkgu Link, Gadong BE 1410, Brunei Darussalam

4 Department of Geology, University of Gorgan

Abstract

The protoliths of metamorphosed argillaceous rocks from the Garmichay area in the East Azerbaijan province of NW Iran were clay-rich sediments of reworked nature, originating most likely from an andesite to andesite-basalt source and deposited in an active continental margin tectonic setting. The protoliths of the Garmichay metapelites experienced low to moderate chemical weathering. Andalusite, cordierite, biotite, and muscovite are produced due to metamorphism under low-pressure and medium-temperature conditions. Cordierite throughout the whole assemblages is altered to the pseudomorphs pinite. Some rock samples contain both andalusite and altered cordierite as porphyroblasts, whereas others contain only andalusite or altered cordierite. Pressure and temperature estimates indicate that pressure for metamorphism was in the range 1-2.5 kbar with temperature between 500-600°C. Major oxides abundance show similar values in all analyzed samples, while concentration of some minor elements, especially zinc, show meaningful differences in rocks with different metamorphic mineral assemblages. The variations in the abundance of these minor elements may have played important role in the control of the mineral assemblages present.

Keywords


Article Title [Persian]

زمین شیمی سنگهای رسی دگرگون در منطقه گرمی چای، آذربایجان شرقی، شمال غرب ایران- ماهیت سنگ مادر اولیه و کنترل شیمی سنگ کل بر مجموعه کانیهای دگرگونی

Authors [Persian]

  • محسن موذن 1
  • مهدی قادری 2
  • هادی عمرانی 4
2 گروه علوم زمین - دانشگاه تبریز
4 گروه زمین شناسی دانشگاه گرگان
Abstract [Persian]

سنگ مادر سنگها دگرگونی رسی منطقه گرمی چای در آذربایجان شرقی در شمال غرب ایران رسوبات غنی از رس با ماهیت فرسایش یافته بوده است که به احتمال زیاد از یک سنگ اولیه آندزیت تا آندزیت بازالت منشا گرفته و در یک محیط  تکتونیکی حاشیه فعال قاره ای رسوب کرده اند. سنگ مادر سنگهای دگرگونی گرمی چای قبل از دگرگونی هوازدگی شیمیایی ضعیف تا متوسطی را تحمل کردند. آندالوزیت، کردیریت، بیوتیت و موسکویت حاصل دگرگونی در شرایط فشار پایین و دمای متوسط  هستند. کردیریت در تمامی این سنگها به سودومورف پنیت تجزیه شده اند. برخی از نمونه های سنگی دارای هر دو کانی آندالوزیت و کردیریت هوازده به صورت درشت بلور هستند در حالیکه نمونه های دیگر حاوی تنها آندالوزیت و یا تنها کردیریت هوازده هستند. دما و فشار محاسبه شده برای دگرگونی نشان می دهد که محدوده فشاری 1 تا 5/2 کیلوبار و دما بین 500 تا 600 درجه سانتیگراد بوده است.  فراوانی اکسیدهای اصلی در تمامی نمونه های تجزیه شده مقادیر مشبهی نشان می دهند در حالیکه مقادیر برخی عناصر فرعی به ویژه روی تفاوت معنی داری بین نمونه ها ی با مجموعه کانی شناسی متفاوت نشان می دهند. تفادت مقادیر این عناصر فرعی می تواند نقش مهمی در مجموعه کانی شناسی سنگها ایفا کند.

Keywords [Persian]

  • سنگ رسی دگرگون
  • سنگ مادر
  • هوازدگی شیمیایی
  • دگرگونی
  • مجموعه کانی
  • شمال غرب ایران
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