ژئوشیمی و پتروژنز توده‌های نفوذی منطقه مهرآباد، شرق اردستان

نوع مقاله : علمی -پژوهشی

نویسندگان

1 استاد دانشکده زمین شناسی، پردیس علوم، دانشگاه تهران

2 کارشناسی ارشد دانشکده علوم زمین، پردیس علوم، دانشگاه تهران

3 استادیار گروه زمین شناسی، دانشکده علوم، دانشگاه کردستان

4 استادیار گروه زمین شناسی، دانشگاه پیام نور

چکیده

توده‌های نفوذی مهرآباد واقع در جنوب شرق اردستان، با سن تقریبی الیگوسن- میوسن، در بخش میانی کمربند ماگمایی ارومیه - دختر جای گرفته‌اند. این توده‌ها با ترکیب سنگ‌شناسی گرانیت، گرانودیوریت، تونالیت و کوارتز مونزودیوریت، در سنگ‌های آتشفشانی ائوسن منطقه تزریق شده‌اند. توده‌های نفوذی مورد مطالعه‌ با ماهیت کالک آلکالن و متا آلومین تا جزئی پرآلومین، جزو سنگ‌های گرانیتوئیدی نوع I محسوب می‌شوند. الگوی تغییرات عناصر کمیاب و کمیاب خاکی بهنجار شده به کندریت و گوشته اولیه بیانگر غنی‌شدگی این سنگ‌ها ازLREE  و  LILE نسبت به HREE و HFSE و وجود آنومالی منفیEu ، Nb،  Tiو P در نمونه‌های مورد مطالعه است. این امر در کنار موقعیت نمونه‌ها بر روی نمودارهای مختلف تمایز محیط تکتونیکی، حاکی از شکل‌گیری سنگ‌های مورد مطالعه در محیطی مرتبط با فرورانش در حاشیه فعال قاره‌ای است. شواهد ژئوشیمیایی مانند مقادیر بالای SiO2، مقادیر کم Mg# و عناصر انتقالی و همچنین میانگین نسبت‌های Nb/La، Nb/Ta، Ti/Zr، Nb/Ce و (La/Sm)n و نمودارهای تفکیک کننده خاستگاه ماگمایی، گویای آن است که پوسته زیرین با ترکیب متابازالتی، متاتونالیتی و آمفیبولیتی نقش مهمی در تشکیل توده گرانیتی مهرآباد بازی کرده است که در اثر گرمای ایجاد شده ناشی از ذوب بخشی گوشته در زون فرورانش، حاصل شده‌اند. AbstractMehrabad intrusive rocks, with probably Oligocene- Miocene age, located in the southeast of Ardestan, at the middle part of the Urumieh-Dokhtar magmatic belt. These rocks consist of granite, granodiorite, tonalite and quartz-monzodiorite that injected in the Eocene volcanic rocks of the area. Based on geochemical data, these intrusive bodies are calc-alkaline, meta-aluminium and I-type granitoid.  Primitive mantel-normalized and condrite-normalized of trace elements and rare elements patterns indicate enrichment in the LREE and LILE compared with HREE and HFSE and pronounced negative anomalies in Eu, Nb, Ti and P in the studied samples. Such geochemical characteristics along with position of samples on the various tectonic discrimination diagrams indicate that formation of these rocks are related to the subduction zone in the active continental margin. Geochemical evidences such as high SiO2, low Mg# and transitional elements, also Nb/La, Nb/Ta, Ti/Zr, Nb/Ce and (La/Sm)n average ratios and magmatic evolution discriminantion diagrams show that lower crust with meta-basalatic, meta-tonalitic and amphibolitic composition had played an important role in the formation of the granitic bodies of the Mehrabad region that generated by heat from partial melting of mantle at subduction zone. Keywords: Urumieh-Dokhtar, Geochemistry, Subduction, Continental crust, Mehrabad.

کلیدواژه‌ها


عنوان مقاله [English]

Geochemistry and Petrogenesis of the Intrusive Rocks, Mehrabad area, East Ardestan

چکیده [English]

Mehrabad intrusive rocks, with probably Oligocene- Miocene age, located in the southeast of Ardestan, at the middle part of the Urumieh-Dokhtar magmatic belt. These rocks consist of granite, granodiorite, tonalite and quartz-monzodiorite that injected in the Eocene volcanic rocks of the area. Based on geochemical data, these intrusive bodies are calc-alkaline, meta-aluminium and I-type granitoid.  Primitive mantel-normalized and condrite-normalized of trace elements and rare elements patterns indicate enrichment in the LREE and LILE compared with HREE and HFSE and pronounced negative anomalies in Eu, Nb, Ti and P in the studied samples. Such geochemical characteristics along with position of samples on the various tectonic discrimination diagrams indicate that formation of these rocks are related to the subduction zone in the active continental margin. Geochemical evidences such as high SiO2, low Mg# and transitional elements, also Nb/La, Nb/Ta, Ti/Zr, Nb/Ce and (La/Sm)naverage ratios and magmatic evolution discriminantion diagrams show that lower crust with meta-basalatic, meta-tonalitic and amphibolitic composition had played an important role in the formation of the granitic bodies of the Mehrabad region that generated by heat from partial melting of mantle at subduction zone.

کلیدواژه‌ها [English]

  • Urumieh-Dokhtar
  • Geochemistry
  • Subduction
  • Continental crust
  • Mehrabad
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