شیمی کانی‌ها و زمین دما-فشارسنجی سنگ‌های بازالتی متاع (جنوب کرمان): شاخص نوع ماگما و جایگاه زمین‌ساختی

نوع مقاله : مقاله پژوهشی

نویسنده

گروه زمین‎شناسی، دانشکده علوم، دانشگاه پیام نور، تهران، ایران

چکیده

سنگ‌های آتشفشانی بازالتی با ساخت بالشی در دورترین بخش جنوب‎شرقی پهنه سنندج-سیرجان رخنمون دارند. این سنگ­ها وابسته به توالی آتشفشانی-رسوبی ژوراسیک‌پیشین با روند شمال‌غرب-جنوب‌شرق تا شمالی-جنوبی هستند. در این پژوهش، شیمی بلورهای کلینوپیروکسن و پلاژیوکلاز برای شناسایی شرایط فیزیکوشیمیایی تشکیل ماگما و محیط زمین­ساختی قدیمی آن­ها بررسی شد. بازالت‌های مورد بررسی  بافت پورفیری دارند. کلینوپیروکسن و پلاژیوکلاز کانی‎های درشت‌بلور هستند که در زمینه دانه‌ریز  با بافت بین دانه­ای تا اینترسرتال قرار دارند. نتایج تجزیه نقطه‌ای نشان داد که بلورهای پلاژیوکلاز غنی از کلسیم هستند و ترکیب بیتونیتی دارند و پیروکسن‌ها از نوع اوژیت هستند. نتایج عنصر سنجی پیروکسن‌ها از جمله مقدار بالای Al و مقدار پایین Ti و Fe3+، نقش اصلی مولفه چرماک بویژه مولفه CaAlAlSiO6 و نقش ناچیز مولفه اکمیت (NaFe3+Si2O6) را در ترکیب آن­ها نشان می‎دهد. مقدار پایین TiO2 و Na2O و مقدار بالای SiO2 بیانگر ماهیت تولئیتی آن­هاست. برپایه دما فشارسنجی، دمای تبلور درشت‌بلورهای کلینوپیروکسن حدود C˚1200-1150 و فشار تبلور آن­ها حدود 6-5 کیلوبار است که با عمق تبلور 15 تا 18کیلومتری همخوانی دارد. درشت‌بلورهای کلینوپیروکسن مورد بررسی ویژگی‌های زمین شیمیایی مشابه با پیروکسن‌ موجود در بازالت‌های حوضه پشت‎قوس را دارند.     

کلیدواژه‌ها


عنوان مقاله [English]

Mineral composition and geothermobarometry of Mata basaltic rocks (SouthKerman): An indicator of magma type and tectonic setting

نویسنده [English]

  • Zahra Badrzadeh
چکیده [English]

Basaltic volcanic rocks with pillow structures are exposed at the southeasternmost extremity of the Sanandaj-Sirjan zone.They belong to volcanic-sedimentary complexes that formed in a general northwest-southeast to north-south trend. In this research, the mineral chemistry of clinopyroxene and plagioclases are employed to study physicochemical conditions and paleo-tectonic setting during generation of basaltic rock. Basalts with plagioclase and clinopyroxene, as the major constituents, have porphyritic texture, which groundmass marked by fine grained plagioclase, clinopyroxene, apatite, opaque minerals and chloritized glass with intergranular to intersertal textures. Electron probe micro-analyzer (EMPA) data indicate most of the feldspars are calcic plagioclase with bytownite composition and clinopyroxenes are augite. High Al and low- Ti and Fe3+contents in clinopyroxenes show the major role of Tschermak’s components, specially CaAlAlSiO6 and minor presence of acmite component. Low TiO2 and Na2O and high SiO2 content indicate their tholeiitic affinity. Based on thermobarometric approaches Mata clinopyroxenes were formed at temperatures of about 1150-1200 ˚C and pressures in the range of 5–6 kbars, which approximately corresponds to a crystallization depth of 15-18 km. Clinopyroxenes have geochemical characteristics similar to ones generated in an extensional environment related to back-arc basin setting.

کلیدواژه‌ها [English]

  • clinopyroxene
  • geotermobarometry
  • basalt
  • tectonic setting
  • Mata
  • Kerman
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