کاربرد شاخص‌های ژئوشیمیایی برای تشخیص ماگمای مولد از عقیم در محدوده قره گل، استان اردبیل با استفاده از عناصر خاکی کمیاب

نوع مقاله : مقاله پژوهشی

نویسندگان

گروه زمین‌شناسی، دانشکده علوم، دانشگاه محقق اردبیلی، اردبیل، ایران

چکیده

مقدمه: منطقه مطالعاتی قره گل در منطقه متالوژنیک اهر- ارسباران در مشگین شهر در بخش مرادلو قرار دارد. براساس مطالعات میدانی، واحدهای سنگی اصلی در معرض در منطقه شامل سنگ‌های آذرین آتشفشانی، پلوتونیک و آذرآواری است. در نواحی فرورانش، ماگمای مولد، نیمه مولد و بارور با هم یافت می­شوند که شناسایی این توده­ها از نظر اکتشاف بسیار حائز اهمیت است. ماگماهای گرانیتوئیدی بارور عموماً در شرایط فرورانش پیش از برخورد تشکیل در حالی که ماگماهای گرانیتوئیدی تولیدی در محیط تکتونیکی پس از برخورد تشکیل می­شوند. تصور می‌شود که ذوب پوسته مافیک جوان ضخیم شده یا تبلور جزئی ماگمای بازالتی آبدار عامل کلیدی در تولید انواع مختلف ماگماهای مولد است. در حالی که ذوب بخشی از پوسته پایین مافیک نازک جوان می­تواند ماگمای بارور ایجاد کند.
مواد و روش­ها: در این تحقیق 14 مقطع نازک از نمونه­های سطحی و 28 مقطع نازک از هسته­های حفاری برای مطالعه پترولوژیک در مرکز تحقیقات و فرآوری مواد معدنی تهیه شد. برای تعیین بافت و پاراژنز سنگ معدن، 30 مقطع نازک صیقل داده شده و 20 مقطع صیقل داده شده از نمونه­ها تهیه شد. 23 نمونه لیتوژئوشیمیایی سطحی توسط ICP-MS مورد مطالعه قرار گرفتند. همچنین 14 نمونه هسته توسط XRF برای اکسیدهای اصلی مورد مطالعه قرار گرفت.
نتایج و بحث: گرانیتوئیدهای مولد در UDMB مقادیر کمتری از Ni (9-31 ppm) و کروم (ppm 14-36) را نسبت به گرانیتوئیدهای بی حاصل (Ni = 11-73 ppm)؛ (کروم = ppm 21-81) نشان می­دهند. مقادیر کم نیکل (ppm 6-5/19) و کروم (ppm 2-14/30) در سنگ­های آذرین قره گل نشان می­دهد که این ماگما از ذوب نسبی منشاء می­گیرد. پوسته پایین ضخیم همچنین ماگمای مولد نسبت LREE/HREE  بالاتری نسبت به ماگمای بی حاصل دارد که در نمونه­های منطقه قره گل نیز مشاهده می­شود. در ماگماهای مولد، الگوی عناصر کمیاب نرمال شده به N-MORB با غنی شدن در Cs، Rb،Ba  و Pb و کاهش در Nb، Ta، Th، Zr،Hf  و Ti مشخص می­شود. این فرآیند نشان می‌دهد که گارنت به‌ عنوان یک فاز باقی‌مانده در محفظه ماگمایی منشأ سنگ‌ها وجود دارد و شکل‌گیری را در فشار (> 15 کیلوبار) معادل ضخامت پوسته 45-55 کیلومتر نشان می‌دهد.
نتیجه­ گیری: براساس نتایج ژئوشیمیایی، میانگین غلظت مس 21/138 ppm است. مشاهدات سنگ­شناسی و داده­های ژئوشیمیایی نشان می­دهد که گرانیتوئیدهای منطقه قره گل از نوع قلیائی کالک آلکالین نوع I مربوط به زون فرورانش است که با کانی­سازی مس پورفیری مرتبط است. نتایج نشان می­دهد که منطقه مورد مطالعه در برخورد پس از قاره قرار دارد. همچنین استفاده از نمودار La/Yb در مقابل Sm/Yb نشان می‌دهد که نمونه‌ها از ذوب جزئی پریدوتیت گارنت 10 تا 20 درصد ساخته شده‌اند. براساس نمودار Ce در مقابل Ce/Yb، عمق ذوب 100 تا 110 کیلومتر برآورد شده است. ماگمای مولد نسبت LREE/HREE بالاتری نسبت به ماگمای بی حاصل دارد که در نمونه­های منطقه قره گل مشهود است.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Application of geochemical indicators to distinguish productive magma from barren in Qarah Gol area, Ardabil province using rare earth elements

نویسندگان [English]

  • shadi zia
  • Seyedeh Narges Sadati
  • gholamreza ahmadzadeh
Department of Geology, Faculty of science, University of Mohaghegh Ardabili, Ardabil, Iran
چکیده [English]

Introduction: Qarah Gol study area is located in Ahar- Arasbaran metallogenic zone in Meshginshahr city in Moradloo section. According to field studies, the main exposed rock units in the region include volcanic, plutonic and pyroclastic igneous rocks. In the subduction zones, productive, semi-productive and fertile magma are found together, and the identification of these masses is very important from the point of view of exploration. Fertile granitoid magmas are generally formed in pre-collisional subduction setting. While productive granitoid magmas are formed in post-collision tectonic setting. It is thought that the melting of young thickened mafic lower crust or the partial crystallization of hydrous basaltic magma is the key factor in the production of various types of productive magmas, while partial melting of the young thin mafic lower crust is considered that can produce fertile magmas.
Materials and methods: In this research, 14 thin sections of surface samples and 28 thin sections of drilling cores were prepared for the petrologic study at Mineral Research and Processing Center. To determine the texture and paragenesis of ores, 30 polished thin sections and 20 polished sections of the samples were prepared. The 23 surface lithogeochemical samples were studied by ICP-MS. Also 14 core samples were studied by XRF for main oxides.
Results and discussion: Productive granitoids in the UDMB display lower values of Ni (9–31 ppm) and Cr (14–36 ppm) than barren granitoids (Ni = 11–73 ppm; Cr = 21–81 ppm). The low values of Ni (5–19.6 ppm) and Cr (14–30.2 ppm) in the igneous rocks of the Qarah Gol indicate that this magma originates from partial melting of the thick lower crust. Also, the productive magma has a higher LREE/HREE ratio than the barren magma, which is also seen in the samples of Qarah Gol area. In productive magmas, pattern of trace elements normalized to N-MORB is characterized by enrichment in Cs, Rb, Ba and Pb and depletion in Nb, Ta, Th, Zr, Hf and Ti. This process shows that garnet is present as a residual phase in the magma chamber of origin of the rocks and indicates the formation at a pressure (>15kbar) equivalent to a crustal thickness of 45-55 km (Palin et al, 2016).
Conclusion: According to geochemical results, the average concentration of copper is 138.21 ppm. Petrological observations and geochemical data show that the graniteoids of Qarah Gol area are calc alkalines type I related to subduction zone which is linked to porphyry copper mineralization. These results show that the study area is located in post-continental collision. Also, the use of La / Yb versus Sm / Yb diagram shows that the samples were made from partial melting of 10 to 20% garnet peridotite. Based on Ce against Ce / Yb diagram, the melting depth of 100 to 110 km is estimated. Productive magma has a higher LREE / HREE ratio than barren magma, which is evident in samples of the Qarah Gol area.

کلیدواژه‌ها [English]

  • Ardabil
  • Rare earth elements
  • Barren
  • Qarah Gol
  • Copper
  • Productive

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