سنگ‌نگاری و زمین‌دمافشارسنجی لرزولیت‌های چاه‌لقه (افیولیت عشین)

نوع مقاله: مقاله پژوهشی

نویسندگان

1 دکترا، گروه زمین‌شناسی،‌ دانشکده علوم، دانشگاه اصفهان، اصفهان، ایران

2 استاد، گروه زمین‌شناسی،‌ دانشکده علوم، دانشگاه اصفهان، اصفهان، ایران

چکیده

در این پژوهش گروهی از لرزولیت‌های گوشته‌ای افیولیت عشین بررسی شده‌اند که شواهد رویداد دگرگونی-زمین‌ساختی هنگام بالاآمدگی (exhumation) و فرارانش روی پوستة قاره‌ای پس از بسته‌شدن اقیانوس نئوتتیس در آنها دیده می‌شود. برپایة سنگ‌نگاری، ارتوپیروکسن، کلینوپیروکسن، الیوین و کرم‌اسپینل از کانی‌های سازندة اولیة این سنگ‌ها هستند. برپایة کانی‌شناسی و زمین‌دمافشارسنجی، این لرزولیت‌های چهارفازی در گوشتة سنگ‌کُره‌ای (در فشار ~6/21 -6/8 کیلوبار) و در پی واکنش‌های مذاب/سنگ‌دیواره (در دمای 1012-1183 درجة‌سانتیگراد) پدید آمده‌اند.پس از تشکیل، این سنگ‌ها در راستای پهنة گسلی این منطقه روی پوستة‌قاره‌ای جایگیری و فرارانش کرده‌ و دگرریخت شده‌اند. نخستین رویداد دگرریختی انعطاف‌پذیر و در بخش‌های ژرف‌تر سنگ‌کره موجب میلونیتی‌شدن دمابالای این سنگ‌ها (دمای بیشتر از 600 -800~ درجة‌سانتیگراد) شده است. ویژگی‌های کانی‌شناسی نشان‌دهندة کاهش فشار در این مرحله و واکنش ساب‌سولیدوس پیروکسن‌ها و اسپینل‌ها با هم و پیدایش الیوین و پلاژیوکلاز به‌جای آنهاست. ازاین‌رو، داده‌های سنگ‌نگاری و دمافشارسنجی‌ نشان‌دهندة رخسارة لرزولیت‌های گوشته‌ای اسپینل‌دار تا پلاژیوکلازدار برای این سنگ‌ها هستند. سرانجام، درپی فرایند بالاآمدن و بیرون‌آمدن، این سنگ‌ها تا اندازه‌ای دچار خردشدگی و دگرریختی شکنا و کاتاکلاستیک در دمای کمتر از 600 ~ درجة سانتیگراد و فشار و ژرفای کمتر شده‌اند. در پی فرایندهای دگرسانی، بیشتر پلاژیوکلازها با کانی‌های پرهنیت، پومپله‌ایت، کلریت، هیدروگروسولر و زنوتلیت جایگزین شده‌اند.

کلیدواژه‌ها


عنوان مقاله [English]

Petrography and geothermobarometry of lherzolites in Chah-Loqeh (Ashin Ophiolite)

نویسندگان [English]

  • Nargess Shirdashtzadeh 1
  • Ghodrat Torabi 2
1 Ph.D., Department of Geology, Faculty of Science, University of Isfahan, Isfahan, Iran
2 Professor, Department of Geology, Faculty of Science, University of Isfahan, Isfahan, Iran
چکیده [English]

In this study, some mantle lherzolites of Ashin ophiolite are investigated which contain evidence of a geotectonic/metamorphism during exhumation and obduction of oceanic lithosphere on the continental crust, after closure of Neo-Tethys Ocean. Based on petrography, their primary rock-forming minerals are orthopyroxene, clinopyroxene, olivine, and chromian spinel. Mineralogy and geothermobarometry indicate that these 4-phase lherzolites were formed in the lithospheric mantle (at pressures ~ 21.6 to 8.6 kbar) by melt/wall rock reactions (at temperatures ~ 1012-1183 °C). Then, they were emplaced and obducted on the continental crust along the fault zone of this region, and consequently deformed. The first ductile deformation event occurred in the depth of lithosphere and resulted in high-temperature mylonitization at temperatures higher than 600 to 800 °C. Mineralogical features confirm pressure decreasing of this stage by subsolidus reaction of pyroxene and spinel and substitution of plagioclase and olivine. Therefore, petrography and thermobarometry data are indicative of the spinel to plagioclase lherzolite facies for these rocks. Finally, they partially underwent brittle and cataclastic deformation at temperatures below 600°C and lower pressures and depth during exhumation. However, most of plagioclases were replaced by with prehnite, pumpellyite, chlorite, hydrogrossular and xonotlite minerals by further alterations.

کلیدواژه‌ها [English]

  • Petrography
  • Geothermobarometry
  • exhumation
  • Lherzolite
  • Ashin ophiolite
کتابنگاری
ترابی، ق.، 1383- پترولوژی افیولیت‌های منطقه انارک (شمال شرق استان اصفهان). رساله دکترای پترولوژی، دانشگاه تربیت مدرس، 240 ص (http://www.irandoc.ac.ir).
شیردشت‌زاده، ن.، 1393- پترولوژی گدازه‌های بالشی و آمفیبولیت‌ها و دگرگونی در پریدوتیت‌های گوشته افیولیت‌های نایین و عشین، پایان نامه دکترا پترولوژی گروه زمین­شناسی دانشگاه اصفهان، اصفهان، 345 ص (http://www.irandoc.ac.ir).
 
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