پراکندگی اندازه و شکل بلورهای پلاژیوکلاز در آندزیت‌های ‌بازالتی‌ شمال گاوخونی

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشگاه یزد

2 دانشگاه شهرکرد

چکیده

پلاژیوکلاز فراوانترین کانی سازنده‌ی آندزیت‌های بازالتی‌ شمال گاوخونی است که بصورت ریزسنگ و درشت­بلور و با شکل­های سه‌بعدی دوکی تا تیغه‌ای دیده می‌شود. اولیوین و پیروکسن از دیگر کانی‌های سازنده‌ی این سنگ‌ها هستند. بلورهای پلاژیوکلاز گاهی بافت غباری، منطقه‌بندی نوسانی و رشد سینوسی از خود نشان می‌دهند. براساس نتایج بررسی پراکندگی اندازه بلور، سرعت هسته‌بندی برای بلورهای پلاژیوکلاز 8- 10*77/2 تا mm-3s-1  8- 10×07/3 و مدت زمان سرد شدن 77/17-08/71 سال برآورد شد که نشانه‌ی نرخ هسته‌بندی بالا، سردشدن سریع و مدت زمان نسبتاً کوتاه اقامت بلور در آشیانه ماگمایی است. نمودارهای پراکندگی اندازه بلور نشانگر فراوانی بلورهای کوچک­تر و در ادامه رشد نسبی بلورهای متوسط بخرج آنها و همچنین وجود جمعیت بلوری دوگانه هستند. وجود جمعیت‌های بلوری متغیر می‌تواند ناشی از ورود مذاب جدید با مجموعه بلوری جدید به آشیانه‌ی ماگمایی باشد. این رخداد می‌تواند باعث افزایش حجم اتاق ماگمایی و کمک به خروج سریع‌تر ماگما شود.     

کلیدواژه‌ها

عنوان مقاله [English]

Crystal size and shape distribution of plagioclase in the basaltic andesites, North of Gavkhouni

نویسندگان [English]

  • mahnaz Khodami 1
  • Behnaz Bakhtiari 2
1 Yazd University
2 Shahrekord University
چکیده [English]

Plagioclase is the most abundant mineral in basaltic andesites in the north Gavkhouni. Olivine and pyroxene are the other rock forming mineral there. In their 3-dimensional shapes, they are unequal and varies between bladed to prolate. Plagioclase sometimes exhibit dusty texture, oscillatory zoning and sinusoid growth. Based on crystal size distribution data, the rate of crystal nucleation of plagioclase varies between 2.77*10-8-3.07*10-8 mm-3s-1 in 71.78 - 17.77 years. The results indicate the higher nucleation rate, rapid cooling and a short crystal residence time in the magma chamber. The crystal size distribution diagrams show the high frequency of smaller crystals and the coarsening of the average crystals. However, the presence of two populations of plagioclase indicates the interfering of new magma with the same chemical composition and new crystal population into the magma chamber. This event can increase the volume of the magma chamber pressure and eruption of the magma.

کلیدواژه‌ها [English]

  • Basaltic andesite
  • crystal size distribution
  • crystal residence time
  • plagioclase

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  • تاریخ دریافت: 01 آبان 1397
  • تاریخ بازنگری: 07 دی 1397
  • تاریخ پذیرش: 02 بهمن 1397

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