کانی‌شناسی، زمین‌شیمی و محیط زمین‌ساختی سنگ‌های گابرویی گنبد نمکی دشتک، چهارمحال و بختیاری، ایران

نوع مقاله : پژوهشی

نویسندگان

دانشکده منابع طبیعی و علوم زمین، دانشگاه شهرکرد، شهرکرد، ایران

چکیده

گنبدنمکی دشتک در استان چهارمحال و بختیاری و در شهرستان اردل واقع شده است. سنگ­های ماگمایی این گنبد نمکی در ارتباط با مجموعه هرمز هستند و به صورت قطعه­های پراکنده یافت می­شوند و شامل سنگ­های آذرین درونی (ریزگابرو) و بیرونی (بازالت و آندزیت) هستند. در بررسی­های سنگ­نگاری، بافت­های دانه­ای، بین دانه­ای، بادامکی، پورفیری و انبوهه پورفیری در این سنگ­ها دیده می­شود. الیوین­های جایگزین شده با کلریت (شبه ریخت)، کلینوپیروکسن و پلاژیوکلاز به عنوان کانی­های اولیه، بیوتیت و آمفیبول­های سبز ـ آبی به عنوان کانی­های تاخیری و کلریت، آپاتیت، اپیدوت، اکسیدهای آهن و تیتان به عنوان کانی­های ثانویه در مقاطع حضور دارند. این سنگ­ها دارای مقدار SiO2 بین54/54 تا 77/56  درصد وزنی و مقدار MgO از 56/5 تا 52/13 درصد و FeOt از 46/13 تا 80/7 درصد وزنی هستند که از نظر ترکیبی در گستره­ی سنگ­های آذرین مافیک رده­بندی می­شوند. همچنین، مقدار عدد منیزیومی (63/45 تا 45/72) گویای جدایش ماگماست. حضور گسترده­ی کانی­های دارای تیتانیوم­ (اسفن/تیتانیت) و تیتانواوژیت، غنی شدگی عناصر سنگ دوست درشت یون (LILEs) نسبت به عناصر با شدت میدان بالا (HFSE) در نمودار بهنجار شده به کندریت به همراه نتایج برآمده از نمودارهای زمین شیمیایی بیانگر ماهیت قلیایی برای نمونه­های مورد بررسی است. افزون بر این در نمودارهای زمین شیمیایی، سنگ­های مورد بررسی در یک محیط درون صفحه­ی قاره­ای و از یک خاستگاه گوشته­ای غنی شده در مرز انتقالی گارنت ـ اسپینل با میزان آلودگی پوسته­ای کم تشکیل شده­اند. 

کلیدواژه‌ها


عنوان مقاله [English]

Mineralogy, geochemistry, and tectonic setting of the gabbroic rocks in the Dashtak Salt Dome, Chaharmahal and Bakhtiari Province, Iran

نویسندگان [English]

  • Masoumeh Najafi
  • Nahid Shabanian
  • Alireza Davoudian Dehkordi
Faculty of Natural Resources and Earth Sciences, Shahrekord University
چکیده [English]

The Dashtak salt dome is located in the Ardal County, Chaharmahal and Bakhtiari Province, southwestern Iran. The magmatic rocks associated with this salt dome are genetically linked to the Hormuz Series and present as scattered outcrops, comprising both intrusive (microgabbros) and extrusive (basalts and andesites) rocks. Petrographic investigations reveal diverse textural features, including granular, intergranular, amygdaloidal, porphyritic, and glomeroporphyritic textures. Primary minerals identified in thin sections consist of clinopyroxene, plagioclase, and olivine pseudomorphed by chlorite, while biotite and greenish-blue amphiboles are considered late-stage minerals. Secondary phases include chlorite, apatite, epidote, and iron–titanium oxides. The studied rocks exhibit SiO₂ contents ranging from 54.54 to 56.77 wt. %, MgO ranging from 5.56 to 13.52 wt. %, and total iron (FeOt) contents between 7.80 and 13.46 wt.%, collectively classifying them as mafic igneous rocks. Furthermore, the relatively wide variation in magnesium number (Mg# = 45.63–72.45) suggests notable magmatic differentiation. The widespread occurrence of titanium-rich minerals (sphene/titanite), enrichment of large-ion lithophile elements (LILEs) relative to high field strength elements (HFSEs) in chondrite-normalized multi-element diagrams, along with geochemical discriminant plots, all support an alkaline affinity for these samples. Moreover, geochemical diagrams indicate that the rocks formed in an intraplate continental setting, derived from an enriched mantle source near the garnet–spinel transition zone with minor crustal contamination.

کلیدواژه‌ها [English]

  • Geochemistry
  • intra-plate magmatism
  • Zagros zone
  • Dashtak salt dome
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