ژئوشیمی و خاستگاه زمین‌ساختی سنگ‌های بازالتی پلیو-کواترنری جنوب شرق نهبندان، خاور ایران

نویسندگان

دانشگاه سیستان و بلوچستان

چکیده

فوران­های آتشفشانی با سن پلیو کواترنری در جنوب شرق نهبندان در بردارنده­ی سنگ­های بازی هستند، که روی نهشته­های فلیشی کرتاسه پسین و ته نشست­های آبرفتی جوان قرار گرفته­اند. از نظر سنگ­نگاشتی این سنگ­ها بازالت، آندزیت بازالت و آندزیت هستند. این گدازه­ها دارای بافت­های پورفیری، ریز بلوری-پورفیری، تراکیتی و پورفیری خوشه­ای هستند. این سنگ­ها دارای درشت بلورهای پلاژیوکلاز، کلینوپیروکسن (اوژیت)، اولیوین و آمفیبول (هورنبلند) و نیز پلاژیوکلاز-کلینوپیروکسن­های ریز بلور در خمیره هستند. از نظر ژئوشیمیایی این سنگ­ها آهکی- قلیایی و دارای 8/47 تا 57 درصد وزنی SiO2  و در حدود 17 درصد وزنی Al2O3 هستند. در نمودار عناصر نادر خاکی بهنجار شده نسبت به کندریت، این سنگ­ها نشانی از غنی­شدگی در عناصر نادر خاکی سبک (LREE) و تهی­شدگی در عناصر نادر خاکی سنگین (HREE) دارند. این سنگ­ها در نمودار عناصر کمیاب بهنجار شده نسبت به گوشته­ی اولیه، عناصرNb ، P < /span>، Ti و Zr دارای بی­هنجاری منفی ولی عناصرPb ،K ، Ba و Srبی­هنجاری مثبت نشان می­دهند. این ویژگی­های شیمیایی گدازه­های پلیو کواترنری نهبندان همراه با بالا بودن نسبت­های LILE/HFSE و LREE/HREE نشان می­دهد که در یک محیط فرورانش حاصل شده­اند. نسبتY / Zrدر این سنگ­ها مشابه گدازه­های قوس قاره­ای است. بر اساس نمودارهای جدایشی زمین ساختی- ماگمایی گدازه­های پلیو کواترنری نهبندان در یک محیط حاشیه­ی فعال قاره­ای شکل گرفته­اند.

کلیدواژه‌ها


عنوان مقاله [English]

Geochemistry and tectonic setting of Plio-Quaternary basaltic rocks in SE of Nehbandan, eastern Iran

چکیده [English]

Plio-Quaternary volcanic eruptions in southeast of Nehbandan are composed of basic rocks, overlying the Late Cretaceous flysch-type and younger alluvium deposits. Petrographically, these rocks are basalt, basaltic andesite and andesite. These lavas are characterized by porphyritic, microlitic-porphyry, trachytic and glomeropophyritic textures. They contain plagioclase, clinopyroxene (augite), olivine and amphibole (hornblende) phenocrysts and fine-grained plagioclase-clinopyroxene microlite in groundmass. Geochemically, these rocks are calc-alkaline and represented by 47.8 - 57 wt. %. SiO2 and about 17 wt. % Al2O3. In chondrite-normalized REE diagram, these rocks show enrichment in LREEs and depletion in HREEs. In primitive-mantle normalized trace elements diagram, they are characterized by Nb (and P, Ti, Zr) negative anomalies and positive anomalies in Pb, K, Ba and Sr. These chemical characteristics of Nehbandan Plio-Quaternary lavas associated with high LILE/HFSE and LREE/HREE ratios are consistent with derivation from a subduction environment. Y/Zr ratio of these rocks is similar to that of continental arc lavas. Discrimination tectono-magmatic diagrams suggest an active continental margin for the formation of Nehbandan Plio-Quaternary lavas.

کلیدواژه‌ها [English]

  • Geochemistry
  • nehbandan
  • subduction
  • basaltic lavas
  • Iran
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