ژئوشیمی و پترولوژی سنگ های خروجی مافیک جنوب گنبد، شمال غرب ارومیه

نویسندگان

1 استاد، گروه زمین شناسی، دانشگاه ارومیه، ارومیه، ایران

2 استادیار گروه زمین‌شناسی، دانشکده علوم‌زمین، دانشگاه شهید چمران اهواز، اهواز، ایران

چکیده

سنگ­های خروجی مافیک جنوب گنبد، شمال­غرب ارومیه، به سن پلئیستوسن بر روی رسوبات دشت سیلابی قدیمی در پهنه سنندج-سیرجان رخنمون دارند. این سنگ­ها به صورت منشوری و اسکوری گسترش یافته­اند. مطالعات پتروگرافی و ژئوشیمی نشان داد که سنگ­های این منطقه، لامپروفیر کامپتونیتی با مشخصاتی شبیه به آلکالی بازالت و تراکی­بازالت بوده، ماهیت آلکالن دارند و به صورت یک روانه گدازه­ای در بین روانه­های بازالتی- تراکی­بازالتی رخنمون دارند. عمده کانی­های تشکیل دهنده این سنگ­ها، کلینوپیروکسن همراه با کانی­های فرعی آمفیبول می­باشند. همه نمونه­های سنگی دارای بافت پورفیری، گلومروپورفیری و آمیگدالوئیدال هستند. سنگ­های آتشفشانی منطقه گنبد در عناصر Ba، Th، U و LREE غنی­شدگی و در عناصر Ta، Nb، Hf و Rb فقیرشدگی نشان می­دهند که با جایگاه زمین­ساختی حاشیه قاره­ای سازگار است. پس از پایان فرورانش نئوتتیس به زیر ایران مرکزی، شکست در بقایای پوسته اقیانوسی در زیر پهنه برخوردی صفحه­های عربی و اوراسیا تحت شرایط درون صفحه­ای اتفاق افتاد. فشار ناشی از همگرایی مایل صفحه­های عربی و اوراسیا و گسترش عملکرد گسل­های امتداد لغز راستگرد که با شکست بقایای پوسته اقیانوسی توسعه یافته­اند، باعث افزایش دما، کاهش فشار و در نتیجه ذوب در گوشته بالایی شد. مذاب­های گوشته­ای مافیک که از راه این سامانه گسل­ها بالا آمدند، پیش از فوران با مواد پهنه فرورانشی قاره­ای آلوده شدند.

کلیدواژه‌ها


عنوان مقاله [English]

Geochemistry and petrology of the South Gonbad mafic volcanic rocks from the Northwest Urmia

نویسندگان [English]

  • A. Falnia 1
  • M. M. Miri 2
1 Prof., Dept., of Geology, Faculty of Sciences, Urmia University, Urmia, Iran
2 Assist. Prof., Dept., of Geology, Faculty of Earth Sciences, Shahid Chamran University of Ahvaz, Ahvaz, Iran
چکیده [English]

The Gonbad Pleistocene mafic volcanic rocks from the Northwest Urmia occur on the old floodplain deposits of the Sanandaj-Sirjan zone. The rocks crop out with prismatic and scoria structures. Petrographic and geochemical studies show that the rocks of this region are mostly comptonitic lamprophyre with characteristics comparable to alkali basalts and trachybasalt, with alkaline nature and occur as a lava flow among the basaltic-trachybasalt flows. The lamprophyres are mainly composed of clinopyroxene and some amphibole. ­­­­­­­All of the rocksshow porphyritic, glomeroporphyritic, and amygdaloidal textures. The Gonbad mafic volcanic rocks are enriched in the Ba, Th, U, and LREE and depleted in the Ta, Nb, Hf, and Rb that are consistent with continental subduction zone settings. After subduction of the Neo-Tethys beneath the Central Iran, a slab break-off occurred in the remnants of Neotethys oceanic crust, just in the collision zone of Arabian-Eurasian plates. Pressure due to oblique direction convergence of the Arabian and Eurasian plates and activity of right-lateral strike-slip fault, resulted from the slab break-off in the Neotethys remnants, and caused thermal uplift, decrease of lithostatic pressure in the mantle and decompression melting in the upper mantle. The mafic mantle released melts ascend through that fault system and contaminated by the continental subduction zone materials before eruption.

کلیدواژه‌ها [English]

  • Lamprophyre
  • Comptonite
  • Alkaline
  • Subduction
  • Neo-Tethys
  • Gonbad
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