سنگ‌نگاری، زمین‌شیمی، جایگاه زمین‌ساختی و سنگ‌زایی مخروط های آتشفشانی دشت مختاران (جنوب غرب بیرجند - شرق ایران)

نویسندگان

استادیار گروه زمین‌شناسی، دانشگاه پیام‌نور، تهران، ایران

چکیده

مخروط­های آتشفشانی دشت مختاران بصورت قلل متمایز و پراکنده در بخش شمالی پهنه جوش‌خورده سیستان و در جنوب باختری بیرجند قرار گرفته‌اند. این مجموعه با طیف ترکیبی آندزیت بازالتی، آندزیت و تراکی­آندزیت بروی نهشته‌های فیلیشی پالئوژن به صورت مخروط­های منفرد دیده می‌شوند. مجموعه کانی‌های اصلی این سنگ­ها را پلاژیوکلاز همراه با پیروکسن و کمتر هورنبلند به صورت فنوکریستال­های درشت تشکیل می‌دهند. بافت غالب در این سنگ­ها پورفیریتیک، میکرولیتیک پورفیری، هیالومیکرولیتیک پورفیری و گلومروپورفیریتیک و مزوستاز آن­ها عموماً شیشه‌ای تا ریزبلور می‎باشد. بیوتیت، الیوین و اپاک نیز به عنوان فاز فرعی حضور دارند. ‌بررسی‌های ژئوشیمیایی دال بر ماهیت کالک­آلکالن این سنگ­ها می‌باشد که در یک محیط زمین‌ساختی قوس آتشفشانی پس از برخورد تشکیل شده‌اند. الگوی پراکندگی عناصر نادر خاکی نشان از غنی‌شدگی از عناصر نادر خاکی سبک و تهی‌شدگی از عناصر نادر خاکی سنگین داشته و ویژگی شاخص آن­ها آنومالی منفی Nb و انومالی مثبت Pb می‌باشد. در نمودار تعیین موقعیت تکتونیکی، نمونه‌های دشت مختاران با موقعیت کمان­های آتشفشانی پس از برخورد مربوط به زون فرورانش حاشیه فعال قاره‌ای تطابق دارد.

کلیدواژه‌ها


عنوان مقاله [English]

Petrography, geochemistry, tectonic setting and petrogenesis of Mokhtaran plain volcanic cones (Southwest of Birjand - East of Iran)

نویسندگان [English]

  • E. Elahpour
  • M. Ahankoub
Assist. Prof., Dept., of Geology, Payame Noor University, Tehran, Iran
چکیده [English]

Mokhtaran Volcanic cones are located in the northern part of the Sistan suture zone - southwest of Birjand, as several distinct and scattered structures. The complex includes some individual cones with the composition of basaltic andesite, andesite, and trachyandesite located on Paleogene flysch deposits of the plain. The main phenocrysts of these rocks are plagioclase, pyroxene, and hornblende in lower amounts and porphyritic and glomeroporphyritic as their common textures. Their mesostasis is generally glassy to microcrystalline and biotite, olivine, and opaque are secondary phases. Geochemical investigations indicate the calc-alkaline nature of these rocks, which were formed in a post-collision volcanic arc tectonic setting. The distribution pattern of REE indicates the enrichment and depletion for LREE and HREE respectively, and their main characteristic feature is the negative anomaly of Nb and positive for Pb. Based on tectonic setting diagrams, Mokhtaran Plain samples belong to the post-collision volcanic arcs related to the active continental margins concerning subduction.

کلیدواژه‌ها [English]

  • Andesite
  • Volcanic arc
  • Active continental margin
  • Mokhtaran plain
  • Southwest of Birjand
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