منشاء و ژئودینامیک دلریت‌های گنبد نمکی کوهرنگ

نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه مهندسی طبیعت، دانشکده منابع طبیعی و علوم زمین، دانشگاه شهرکرد، شهرکرد، ایران

2 گروه مهندسی معدن، دانشکده مهندسی، دانشگاه کردستان، سنندج، ایران

چکیده

در این مقاله به بررسی خصوصیات سنگ­شناسی و ژئوشیمیایی سنگ­های مافیک ناحیه کوهرنگ به عنوان بخشی از پهنه ساختاری زاگرس در استان چهارمحال و بختیاری پرداخته می­شود. سنگ­های آذرین گنبد نمکی کوهرنگ دارای بافت اینترگرانولار و گاهی افتیک با کانی­شناسی پلاژیوکلاز، پیروکسن، آمفیبول، تیتانیت و لوکوکسن می­باشند. این سنگ­ها حاوی 10/48 -02/47 درصد وزنی سیلیس بوده و از نظر ترکیبی در محدوده سنگ­های آذرین بازیک قرار می­گیرند. این سنگ­ها میزان K2O متغیر (34/1-28/4 درصد وزنی)، Na2O متوسط (11/1–37/2 درصد وزنی)، MgO (21/5–29/6 درصد وزنی) و *Fe2O3 (93/3- 60/4 درصد وزنی) را نشان می­دهند. میزان TiO2 در آنها نسبتا بالاست. در نمودار به هنجار شده به کندریت غنی­شدگی از LREES نسبت به عناصر HREES مشاهده می­شود که بیانگر ماهیت E-MORB برای ماگمای منشا این سنگ­هاست. نمودارهای ژئوشیمیایی، شکل­گیری سنگ­های منطقه در محیط درون صفحه و ریفت قاره­ای را نشان می­دهد که دارای منشا مانتوی آستنوسفری بوده و آلایش پوسته­ایی چندانی را متحمل نشده است. نسبت CaO/Al2O3 برابر 66/00-48/0 به همراه الگوی تخت در HREE موید یک منشا مانتویی اسپینل­دار است.

کلیدواژه‌ها

عنوان مقاله [English]

Source and geodynamics of dolerites of Kuhrang salt dome

نویسندگان [English]

  • Pardis Jafari 1
  • Nahid Shabanian Boroujeni 1
  • Alireza Davoudian Dehkordi 1
  • Hossein Azizi 2
1 Department of Natural Engineering, Faculty of Natural Resources and Earth Sciences, Shahrekord University, Shahrekord, Iran
2 Department of Mining Engineering, Faculty of Engineering, University of Kurdistan, Sanandaj, Iran
چکیده [English]

Introduction
Formation and rocks of Kuhrang salt dome in Zagros zone, Chaharmahal Va Bakhtiari province, are equivalent to the same units in the Hormuz Formation of Persian Gulf. Evaporate basins of Late Precambrian – Early Cambrian resulted in the deposition of Hormuz and similar series (Arian and Noroozpour, 2015; Motiei, 2001). The basins were formed due to the extensional tectonic phase, as a continental rift, in the continental crust of Iran and neighboring countries occurred during Infracambrian (Nabavi, 1976; Stöcklin, 1968; Berberian and King, 1981). Acidic and mostly alkaline magmatism is dominated in the rifts resulting from the extensional phase (Berberian and King, 1981).
Magmas of the continental rifts mainly have alkaline nature and they are rich volatile material (e.g. halogens and CO2) and LILE (Lithophile large ion elements), indicating they are driven from enriched sources of the mantle (Wilson, 1989; Bailey, 1983). In the continental rift regions, the lavas mostly form during the fractional crystallization of basaltic magmas which are contaminated by the variant degree of crustal sources (Wilson, 1989).
The aim of the paper is the determination of geochemical characters, tectonic setting and source of the doleritic rocks of Kuhrang salt dome by using whole-rock analyses.
Materials and Methods
After field sampling and microscopic studies, 8 fresh samples were analyzed for whole-rock geochemical determination by ICP-ES and ICP-MS methods in ACME lab (Vancouver, Canada).
Results and Discussion
The igneous rocks of Kuhrang salt dome display the including textures (intergranular and sometimes ophitic). Their mineralogy consists of plagioclase, pyroxene, amphibole, titanite and leucoxene. Compositionally, the rocks have 47.02-48.10 %wt. of SiO2. Therefore they plot in field of basic igneous rocks. The rocks display variable contents of K2O (3.34-4.28 wt.%), medium values of Na2O (1.11-2.37 wt.%), MgO (5.21-6.29 wt.%) and Fe2O3*(3.93-4.60 wt.%).
In the Zr/TiO2-Nb/Y diagram (Winchester and Floyd, 1977), the studied rocks are plotted in basalt field and have sub-alkaline nature. Also, the samples display tholeiitic nature on the Ce/Yb-Ta/Yb diagram (Pearce, 1982).
The chondrite normalized REE patterns show low enrichment in the LREEs relative to HREEs, which confirm E-MORB nature for their origin. Geochemical diagrams (e.g. Zr/Y-Zr (Pearce and Norry, 1979); Zr/4-Y-2 Nb (Meschede, 1986); Zr/117-Th- Nb/16 (Wood, 1980); Ti-Zr (Pearce, 1982)) show that the rocks have occurred in tectonic setting of intracontinental rift. TiO2 concentrations (2.38-2.48 wt.%) are relatively high in the rocks suggesting asthenospheric mantle (enrichment mantle) as their source. Moreover, flat patterns in HREEs (TbN/YbN= 1.58-1.74) and CaO/Al2O3 ratios (0.48-0.66) demonstrate spinel-mantle sources rather than garnet ones. Enrichment of Ba, Rb, K and K2O>Na2O and Rb/Sr-Ba/Rb diagram (Furman and Graham, 1999) reveal a mantle source involvement of phlogopite (Rosenthal et al, 2009).
Conclusion
Basic magma of Kuhrang salt dome doleritic rocks, show sub-alkaline nature (tholeiite) with various K2O contents. It has been formed in tectonic setting of intra- continental rift due to low partial melting of phlogopite spinel lherzolite of asthenospheric mantle.

کلیدواژه‌ها [English]

  • Intra continental rifts
  • Dolerite
  • Salt dome
  • Zagros

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