نوع مقاله : مقاله پژوهشی

نویسندگان

دانشگاه

چکیده

مخروط­های آتشفشانی کوه بوبک و سیخ­کوه در جنوب خاوری استان خراسان جنوبی و در شمال و جنوب باختری  شهرستان نهبندان واقع شده اند. از دیدگاه تقسیم بندی زمین شناسی ساختاری ایران آنها متعلق به پهنه لوت می باشند. این مخروط­ها عمدتاً از سنگهای آذرین خروجی تراکی بازالت، و تراکی آندزیت تشکیل شده­ و دارای  بافت غالب پورفیریتیک هستند. کانی­های اصلی سازنده آنها پلاژیوکلاز، پیروکسن، الیوین، هورنبلند و بیوتیت و کانی ­های فرعی و ثانویه آنها کوارتز، سریسیت، اپیدوت، زئولیت و کلسیت  می­باشد. تعداد 12 نمونه ازسنگ های سالم منطقه جهت انجام تجزیه های شیمیایی  عناصر اصلی و فرعی به ترتیب با روش های XRF  و ICP  انتخاب و به آزمایشگاه زرآزمای ماهان ارسال و مورد تجزیه قرار گرفتند. مشخصات ژئوشیمیایی این سنگها نشان می­دهد که که ماگمای اولیه این سنگ ها تحول ازکلسیمی- قلیایی تا قلیایی دارد. در نمودارهای عنکبوتی، غنی شدگی از عناصر LREE  و تهی شدگی از HREE با الگوی موازی و مشابه دیده می شود که حاکی از منشا یکسان آنها می­باشد. علاوه بر این، غنی شدگی در  LILE و Pb نسبت های عناصری Nb/ U‌ و   Ce/Pb نیز نشان دهنده ی آلودگی پوسته ای ماگمای سازنده سنگ های منطقه است. از طرفی نمودارهای ژئوشیمیایی، نسبت هایLa/Yb  در مقابل La و TiO2 در مقابل Zr نشان­دهنده روند تبلور تفریقی در نمونه ها است. همچنین این نمودارها نشان می دهند که ماگمای اولیه این سنگ ها، با منشا گوشته ای، دچار فرآیند تفریق و آلودگی پوسته ای شده است.  نمودارهای تکتونوماگمایی، آنومالی منفی Nb وTi   و مشخصات ژئوشیمیایی در این سنگها حاکی از شکل گیری این آتشفشان ها در محیط فرورانشی است.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Petrology and Geochemistry of Bubak and Sikh- kuh Plio - Quaternary volcanic cones, West of Nehbandan, East of Lut block

نویسندگان [English]

  • Habib Biyaban gard
  • Omol banin Shahraki
  • Mohammad Boumeri

چکیده [English]

Abstarct: Kuh-Bubak and Sikh-kuh volcanic cones are located in Southeast of South Khorasan province, north and Southwest Nehbandan city. Based on structural geology classification of Iran, these volcanos are belonging to Lut zone. These cones are composed mainly of Thrachybasalte and Thrachyandesite composition rocks and they are dominant porphyric texture. These rocks have plagioclase, pyroxene, olivine, hornblende and biotite as main minerals and quartze, sericite, epidote, zeolite and calcite is secondary minerals. Twelve fresh rock samples are selected for chemical analysis and then send to the Zrazmay Mahan laboratory were analyzed major and trace elements with XRF and ICP methods respectively. Geochemical characteristics of these rocks show that the primary magma formed these rocks have changes from Calk-alkaline to alkaline. In spider diagrams observed that LREE enrichment and HREE depletion, similar pattern can be seen in parallel and indicated their origin is the same. In addition, enrichment in LILE, and Pb, ratio elements of Nb/U and Ce/Pb indicates that they are contamination with crustal rocks. On the other hand, geochemical diagrams La/Yb versus La and Zr versus TiO2 indicating fractional crystallization process are happen in these rocks. Geochemical various diagrams show that fractionation and crustal contamination has affected on the primary magma. Nb and Ti negative anomalies and geochemical properties indicating that these volcanoes are belonging to subduction zone.
 
The study area is located in 55 Km and 45 Km northwest and south-west Nehbandan. Based on geologically classification it was located in the east of the Lut block. Kuh-Bubak and Sikh-kuh volcanic cones are composed mainly of thrachybasalte and thrachyandesite and they are dominant porphyric texture. Plagioclase, pyroxene, olivine, hornblende and biotite as main minerals and quartze, sericite, epidote, zeolite and calcite are secondary minerals.
 
Method and Material
Field prospect and sample collection are done all of outcrops, than prepared thin section and studied. Twelve fresh rock samples are selected for chemical analysis and then send to the Zrazmay Mahan laboratory were analyzed major and trace elements with XRF and ICP methods respectively.
Results and Discussion
 
 
Geochemical characteristics of these rocks show that the primary magma of these rocks has changes from Calk-alkaline to alkaline. In spider diagrams observed that LREE enrichment and HREE depletion, similar pattern can be seen in parallel and indicated their origin is the same. In addition, enrichment in LILE, and Pb, ratio elements of Nb/U and Ce/Pb indicates that they are contamination with crustal rocks. On the other hand, geochemical diagrams La/Yb versus La and Zr versus TiO2 indicating fractional crystallization process are happen in these rocks. Geochemical various diagrams show that fractionation and crustal contamination has affected on the primary magma. Nb and Ti negative anomalies and geochemical properties indicating that these volcanoes are belonging to subduction zone. According to petrographic studies and based on distribution of REE elements and incompatible elements were shows these rocks have make of crystal differntation. Geochemical studies revealed evidence of contamination in the rocks. Ratios elements such as Nb / U and Ce / Pb are also confirmed. Based on the tectonomagmatic and multi-element diagrams normalized to Chondrite and Primitive mantle rocks revealed that Bubak and Sikh-kuh volcanic rocks originated from a mantle source and make of fractionation and contamination during the ascent .
Conclusion:
1- Bubak and Sikh-kuh volcanic rocks are composed mainly of thrachybasalte and thrachyandesite with dominant porphyric texture and have maily plagioclase, pyroxene, olivine, hornblende and biotite.
1- Bubak and Sikh-kuh volcanic cones are belonging to active continental margin.
2- Bubak and Sikh-kuh volcanic rocks belonging to Calk-alkaline magma series.
3- Bubak and Sikh-kuh volcanic rocks originated from a mantle source and make of fractionation and contamination during the ascent.

کلیدواژه‌ها [English]

  • Crustal contamination
  • Tectono-magmatic
  • Subduction
  • Calk-alkaline
  • Nehbandan