ژئوشیمی، پتروژنز و محیط زمین ساختی گرانیتوئید گیسور – شرق گناباد

نوع مقاله: مقاله پژوهشی

نویسندگان

1 دانشجوی دکترا، گروه زمین شناسی، دانشکده علوم پایه، دانشگاه لرستان، خرمآباد، ایران

2 استادیار، گروه زمینشناسی، دانشکده علوم پایه، دانشگاه لرستان، خرمآباد، ایران

3 دانشیار، گروه زمینشناسی، دانشکده علوم، دانشگاه فردوسی مشهد، مشهد، ایران

4 استادیار، گروه زمین شناسی، دانشکده علوم پایه، دانشگاه لرستان، خرمآباد، ایران

5 دانشیار، گروه زمین شناسی، دانشکده علوم پایه، دانشگاه زنجان، زنجان، ایران

چکیده

منطقه گیسور در شرق شهرستان گناباد قرار دارد و بخشی از شمال بلوک لوت محسوب می­شود. سنگ­های این منطقه شامل سنگ­های گرانیتوئیدی و مجموعه­ دگرگونی دمای بالا -  فشار پایین هستند. سنگ­های گرانیتوئیدی از سه واحد گرانودیوریت، آنکلاو (دگرگونی و آذرین) و میکروگرانیت تشکیل شده‌اند. این سنگ­ها در سری کالک­آلکالن پتاسیم­دار  متوسط تا بالا قرار می­گیرند و به­طور ضعیفی پرآلومینوس و از نوع گرانیت I دمای پایین­اند. الگوی عناصر کمیاب بهنجار شده به کندریت، غنی‌شدگی کمتر عناصر ناسازگار و آنومالی منفی منحصر به فرد نسبت به سایر عناصر در Ta, Nb, Sr, P, Ti و Ba اما غنی‌شدگی قویی را در K، Rb و Th نشان می­دهد. این الگوها در نمونه­های گرانودیوریت، آنکلاو میکروگرانولار مافیک و تا حدودی میکروگرانیت با هم هماهنگی فوق­العاده­ای نشان می­دهند. به علاوه، این نمونه­ها چنین هماهنگی را با ترکیب متوسط پوسته بالایی، میانی و گری وک­ها دارند. آنومالی مثبت در Rb، Th، Sm و آنومالی منفی در Ba به­طور برجسته­ای مشخص کننده ترکیب پوسته­ای است. بر پایه ادغام این الگوها با الگوی عناصر کمیاب پوسته بالایی و گری­وک­ها و انطباق با کارهای آزمایشگاهی انجام یافته،گرانیتوئیدهای گیسور دارای منشأ بارز پوسته­ای هستند. دمای تشکیل براساس دمای اشباع زیرکن C֯ 790- 748 برآورد شده است. آنکلاوهای میکروگرانولار مافیک با داشتن ویژگی هایی از قبیل اشکال گرد شده و تخم مرغی و هاله اختلاطی در اطراف آنها، بافت دانه­ریز، چشم­های کوارتزی و پلاژیوکلازی، دارای بیوتیت تیغه­ای و آپاتیت سوزنی، فازهای اکسیدی در بیوتیت و وجود روند سهمی شکل (هیپربولیک) بین آنکلاو و گرانودیوریت میزبان به همراه مطالعات ژئوشیمی عناصر اصلی و کمیاب، فرآیندهای اختلاط/ آمیختگی (ذوب بخشی) را برای آنها نشان می­دهد. الگوی عناصر کمیاب نشان دهنده ارتباط نمونه­های گرانیتوئیدی گیسور با سیستم فرورانش است. تجزیه و تحلیل داده­های آن براساس نسبت­های لگاریتمی، محیط برخوردی را نشان می­دهد و نمودارهای متمایزکننده تکتونیکی–  شیمیایی نیز محیط همزمان تا پس از برخورد را پیشنهاد می­دهند که در ارتباط با برخورد بلوک افغان با بلوک لوت تفسیر می­شود.

کلیدواژه‌ها


عنوان مقاله [English]

Geochemistry, petrogenesis and tectonic setting of Geysour granitoid, East Gonabad

نویسندگان [English]

  • Abdolsamad pourmohammad 1
  • Ahmad Ahmadi khalaji 2
  • Masoud Homam 3
  • Zahra Tahmasbi 4
  • Mohammad Ebrahimi 5
1 Ph.D. Student, Department of Geology, Faculty of Sciences, Lorestan University, Khorramabad, Iran
2 Assistant Professor, Department of Geology, Faculty of Sciences, Lorestan University, Khorramabad, Iran
3 Associate Professor, Department of Geology, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, Iran
4 Assistant Professor, Department of Geology, Faculty of Sciences, Lorestan University, Khorramabad, Iran
5 Associate Professor, Department of Geology, Faculty of Sciences, University of Zanjan, Zanjan, Iran
چکیده [English]

Geysour area is located in the east of Gonabad city and is part of the north of the Lut Block. The rocks in this area include granitoid rocks and high temperature – low pressure metamorphic rocks. Granitoid rocks are composed of granodiorite, enclave (metamorphic and igneous) and microgranites. These rocks belong to medium to high potassium calc-alkaline series, low temperature I type granite and are poorly peraluminous. The Chondrite-normalized REE patterns show that the rocks are enriched incompatible elements, with negative anomalies in Nb, Ta, Sr, P, Ti and Ba and strong enrichment in Rb, K and Th. These patterns are in perfect harmony in granodiorite, microgranular enclave (MME) and microgranite specimens. This harmony also has in upper, middle continental crust and greywackes. Positive anomalies in Rb, Th, Sm and negative anomalies in Ba are prominent in the composition of the crust. Based on the integration of these patterns with the pattern of upper continental crust (UCC) elements and greywackes and adaptation to laboratory work, the Geysour granitoid originated from crustal materials and a little mantle component. The temperature of granitoid formation was estimated based on the Zircon saturation temperature of 748-790 ֯C. Microgranular enclaves have rounded and oval shapes, mixed areole around them, fine grained texture, quartz and plagioclase eyes, bladed biotite, needled apatite, oxide phases in biotite, and the presence of a simple mixed – hyperbolic curve between MME and granodiorite. Field, petrography and geochemistry of the major and rare earth elements data suggest mixing/ mingling (partial melting) processes for the origin of enclaves and the rare earth elements patterns indicates the relationship between Geysour granitoid with the subduction system. Analysing its data, based on logarithmic ratios, show collision tectonic environment. Also, the tectonic-chemical distinctive diagrams suggest a syn-collision to post-collision tectonic type that is interpreted in connection with the collision of the Afghan Block with the Lut Block.

کلیدواژه‌ها [English]

  • Granodiorites
  • micro-granite
  • Enclave
  • crustal origin
  • Geysour
کتابنگاری
فوله، ا.، 1383- نقشه زمین‌شناسی1:250000 گناباد، سازمان زمین‌شناسی و اکتشافات معدنی کشور.
قائمی، ف.، 1389- نقشه زمین‌شناسی1:100000 نوده، سازمان زمین‌شناسی و اکتشافات معدنی کشور.
کریم‎پور، م. ح. و مرادی، م.، 1388- پترولوژی گرانودیوریت و مونزونیت­های شرق نجم‌آباد ) گناباد(، هفدهمین همایش انجمن بلورشناسی و کانی شناسی ایران، دانشگاه بو علی سینا همدان.
هامونی، س. ج.، کریم‏پور، م. ح.، ملک‎زاده شفارودی، آ. و حاجی میرزاجان، ح.، 1392- زمین شناسی، کانی­سازی، ژئوشیمی و پترولوژی توده­های نفوذی منطقه اکتشافی رودگز جنوب شرق گناباد، مجله پترولوژی، سال چهارم، شماره پانزدهم، صص77تا 96.
 
 
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