پتروگرافی و شیمی‌کانی گرانودیوریت های ائوسن تویره (جنوب‌ غرب جندق، استان اصفهان)

نوع مقاله : علمی- پژوهشی

نویسندگان

اصفهان

چکیده

توده نفوذی گرانیتوئیدی تویره با سن ائوسن میانی در جنوب‌غرب جندق و در حاشیه غربی خرد قاره شرق– ایران مرکزی قرار‌گرفته است. این توده نفوذی در قسمت­‌های جنوبی و شرقی، سنگ­‌های آتشفشانی ائوسن را قطع‌کرده و خود نیز توسط بازالت­‌های آلکالن الیگوسن زیرین قطع‌شده است. سنگ­‌های سازنده این توده نفوذی گرانیت و گرانودیوریت است که گرانودیوریت­‌ها از فراوانی بیشتری برخوردارند. کانی‌های اصلی و فرعی تشکیل‌دهنده واحد گرانودیوریتی شامل پلاژیوکلاز، کوارتز، ارتوکلاز، آمفیبول، بیوتیت، آپاتیت، زیرکن و اسفن است. آمفیبول­‌های گرانودیوریت­‌ها از نوع کلسیک، با Mg# (میانگین 61/0) و ترکیب مگنزیوهورنبلند تا اکتینولیت دارند. دامنه ترکیب پلاژیوکلاز­های این توده نفوذی از آلبیت تا آندزین در نوسان است و مرکز برخی از بلور­های پلاژیوکلاز ترکیب لابرادوریت دارند. بررسی شیمی‌کانی بیوتیت­‌های این توده نفوذی نشان می­‌دهد که بیوتیت­‌های آن شبیه بیوتیت­‌های متبلور‌شده از ماگما­های کالک­‌آلکالن هستند. با استفاده از دما‌– فشار‌سنجی زوج کانی هورنبلند- پلاژیوکلاز، دمای تبلور 700 – 800  درجه سانتی‌گراد و فشار 1- 15/1 کیلو­بار (معادل عمق 5/3 – 6 کیلومتر) محاسبه‌شده است دماسنجی کلریت­‌‌ها دمای دگرسانی حدود 245‌- 262 درجه سانتی‌گراد را نشان می­‌دهد. بررسی‌های پتروگرافی و شیمی‌کانی بیوتیت‌ها و آمفیبول­‌های توده نفوذی نشان‌دهنده I-Type بودن این گرانیتوئید است که از ماگمایی با منابع مختلط پوسته‌- گوشته شکل‌گرفته است. فوگاسیته بالای اکسیژن (+1< ∆FQM < +2.0) در مذاب سازنده آن شاهدی برای ارتباط آن با فرورانش است.

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