شیمی و مکانیسم تشکیل گارنت‌ها در متاپلیت‌ها و متابازیت‌های کمپلکس دگرگونی گل گوهر، استان کرمان

نویسنده

گروه زمین‌شناسی، دانشکده علوم، دانشگاه شهید باهنر کرمان، کرمان

چکیده

شواهد بافتی ثبت شـده در گارنت­های موجود در متاپلیت­ها و متابازیت­های کـمپلکس دگرگونی گـل­گـوهـر در جـنوب­شـرق زون سنندج-سیرجان، نشانه­های رشد همزمان با شیستوزیته S1، بعد از شیستوزیته S1، همزمان با شیستوزیته S2 و بعد از شیستوزیته S2 را نـشان می­دهند و وجود دو نسل از گارنت (GrtIa, GrtIb) در یک نمـونه واکنش GrtIa+BtI=BtII+GrtIb+Qz+H2O را بـرای آن­ها پیـشنهاد می­کند. پروفیل­های ترکیبی بلورهای گارنت در متاپلیت­ها و متابازیت­های گل­گوهر کاهش سازنده­های اسپسارتین و XFe و افزایش سازنده­های پیروپ و آلماندن را از مرکز به سمت حاشیه بلورها نشان می­دهند و حاکی از تبلور آن­ها در طی دگرگونی پیشرونده می­باشند. افزایش Mn در هسته گارنت­ها حاکی از رشد بلوری و تفریق عناصر مرتبط با فرآیندهای دگرگونی می­باشد. از طرفی عدم منطقه­بندی مشخص عناصر Ca و Al از هسته به حاشیه گارنت­ها و تغییرات ناچیز عنصر Fe از مرکز به سمت حاشیه می­تواند به دلیل بسته بودن سیستم دگرگونی و عدم اکسیداسیون Fe2+/Fe3+ باشد و نشانگر آن است که رشد گارنت­ها در اثر پدیده رشد بلوری و تفریق عناصر در طی دگرگونی رخ داده است. در فیلونیت­های گاربن­شیفر افزایش منیزیم و آهن از مرکز به سمت حاشیه گارنت­ها همراه با افزایش Ca در هورنبلندها و کاهش Ca و آنورتیت از مرکز به سمت حاشیه پلاژیوکلازها پیشنهاد می­کند که گارنت­ها، احتمالاً در اثر واکنش بین آمفیبول و پلاژیوکلاز، طبق واکنشHornblende + Anorthite = Garnet + Quartz + H2O  بـوجود آمـده باشند. درشت­شدگی و رشد سریع پورفیروبلاست­های فراوان هورنبلند همراه با بوجود آمدن بلورهای گارنت، باعث کاهش H2O و افزایش CO2سیال شده که بلورهای کلسیت تشکیل شده در زمینه سنگ، این موضوع را نشان می­دهند.

کلیدواژه‌ها


عنوان مقاله [English]

Chemistry and formation mechanism of garnet in the metapelites amd metabasites from the Gol-e-Gohar metamorphic complex, Kerman province

نویسنده [English]

  • hossein fatehi
Department of Geology, Faculty of Sciences, Shahid Bahonar University of Kerman, Kerman, Iran.
چکیده [English]

The recorded textural evidences of garnets included in the metapelites and metabasites from the Gol-e-Gohar complex in southeastern Sanandaj-Sirjan zone highlight evidences of syn-S1 growth, post S1 schistosity, syn-S2 and after S2 schistosity. The presence of two generations of garnet (GrtIa, GrtIb) in metapelites suggest dehydration continuous reaction GrtIa+BtI=BtII+GrtIb+Qz+H2O. Compositional profiles of garnet crystals in the metapelites and metabasites show decreasing spessartine and XFe proportions and increase of pyrope and almandine from the center to the rim. All garnets belong to the pyralspite series (Spessartine-Almandine-Pyrope) and are almandine-rich. Increasing Mn in the garnet core is indicative of differentiation and crystalline growth associated with metamorphic processes. On the other hand, the lack of clear zoning of Ca and Al from the center to the rim of garnets and the minor changes of Fe element from the center to the rim could be an indicative of a closed system and Fe2+/Fe3+ non-oxidation during metamorphism indicating growth of garnets occurred due to crystalline growth and differentiation of elements during metamorphism. Also, increasing Mg and Fe from the center to the garnet rim along with increasing Ca contents in hornblendes and decreasing Ca and An contents in plagioclase from their centers to the margins suggest that the garnets probably formed by reaction between hornblende and plagioclase as the reaction Hornblende + Anorthite = Garnet + Quartz + H2O. The coarsening and rapid growth of garnet and hornblende porphyroblasts removed H2O from the fluids and resulted in a gradual increase in the CO2 contents of the fluids. Sporadic calcites in the matrix testifies this issue.

کلیدواژه‌ها [English]

  • Metapelite
  • Metabasite
  • Garnet
  • Gol-e-Gohar complex
  • Sanandaj-Sirjan zone
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