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

فضل نیا, عبدالناصر; میری, میرمحمد

doi:10.22084/nfag.2024.28564.1586

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

10.22084/nfag.2024.28564.1586

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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