بررسی رخداد آنالسیم در تفریت‌های رشته کوه بزقوش، شمال میانه، شمال غرب ایران

نوع مقاله : علمی -پژوهشی

نویسندگان

1 دانشجوی دکتری زمین شناسی، دانشکده علوم زمین، دانشگاه شهید بهشتی

2 دانشیار دانشکده علوم زمین، دانشگاه شهید بهشتی

3 دانشیار سازمان زمین شناسی و اکتشافات معدنی کشور

چکیده

سنگ­های آتشفشانی با ترکیب تفریتی و فونوتفریتی با سن ائوسن بالایی در رشته کوه بزقوش، شمال غرب ایران گسترش قابل ملاحظه­ای دارند. این سنگ­های آتشفشانی هم به صورت گدازه­هایی با حجم زیاد که عمدتاً در قسمت شمالی رشته کوه بزقوش قرار گرفته­اند و با یک روند شرقی-غربی بر روی آندزیت­های مگاپورفیری ائوسن میانی قرار گرفته اند، دیده می­شوند و هم به صورت لنزهایی کوچک در بین سنگ­های ولکانی کلاستیکی جای گرفته­اند. بافت این سنگ­ها پورفیری بوده و کانی­های تشکیل دهنده شامل کلینوپیروکسن، پلاژیوکلاز، آلکالی فلدسپار، آنالسیم، الیوین و کمی لوسیت در یک زمینه شیشه­ای تا دانه­ریز می­باشند. آنالسیم در این سنگ­ها عمدتاً ایزوتروپ بوده و به صورت اجزای ریز کمتر از یک میلی­متر تا درشت بلورهایی به اندازه 1 سانتی­متر دیده می­شود. غنی شدگی سنگ­های آنالسیم­دار منطقه در Sr، عدم حضور کانی­های آبدار مثل آمفیبول و بیوتیت در سنگ­های مورد مطالعه، فقدان پیروکسن­های سدیم­دار، ترکیب هموژن بلورهای آنالسیم و وجود ترک­های نامنظم در سطح و اطراف بلور آنالسیم بیانگر این است که آنالسیم­های موجود در سنگ­های آتشفشانی رشته کوه بزقوش از تبادل یونی لوسیت­های اولیه در حین سرد شدن ماگما و یا در زمان انجماد ماگما به وجود آمده ­اند. AbstractVolcanic rocks of upper Eocene age with tephritic to phono-tephritic composition are widespread in the Bozghush Mountains, NW of Iran.These volcanic rocks are occur both as lava flowd above a megaporphyritic andesite (middle Eocene age?) as well as small lenses within the volcaniclastic rocks. The rocks are porphyritic in texture and consist of phenocrysts of pyroxene, plagioclase, alkali feldspar, analcime, olivin, apatite and minor leucite in a fine-grained and glassy matrix. The analcime in these rocks occurs as an isotropic mineral 0.5 mm to 1 cm in diameter. Enrichment of the studied rocks in Sr, the absence of hydrous primary igneous minerals such as amphibole or biotite, lack of Na-pyroxene, the homogenous nature of the analcime and irregular cracks in the analcime indicate that the analcime crystals in volcanic rocks of the Bozghush Mountains formed by ion-exchange pseudomorphous replacement of primary leucite either during cooling and crystallization, or shortly afterwards. Keywords: Eocene, Analcime, Azerbaijan, Bozghush, Tephrite. 

کلیدواژه‌ها

عنوان مقاله [English]

On the occurrence of analcime in the tephritic rocks in the Bozghush Mountains, north of Miyaneh, northwest of Iran

چکیده [English]

Volcanic rocks of upper Eocene age with tephritic to phono-tephritic composition are widespread in the Bozghush Mountains, NW of Iran.These volcanic rocks are occur both as lava flowd above a megaporphyritic andesite (middle Eocene age?) as well as small lenses within the volcaniclastic rocks. The rocks are porphyritic in texture and consist of phenocrysts of pyroxene, plagioclase, alkali feldspar, analcime, olivin, apatite and minor leucite in a fine-grained and glassy matrix. The analcime in these rocks occurs as an isotropic mineral 0.5 mm to 1 cm in diameter. Enrichment of the studied rocks in Sr, the absence of hydrous primary igneous minerals such as amphibole or biotite, lack of Na-pyroxene, the homogenous nature of the analcime and irregular cracks in the analcime indicate that the analcime crystals in volcanic rocks of the Bozghush Mountains formed by ion-exchange pseudomorphous replacement of primary leucite either during cooling and crystallization, or shortly afterwards.

کلیدواژه‌ها [English]

  • Eocene
  • Analcime
  • Azerbaijan
  • Bozghush
  • Tephrite

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