بررسی تغییرات میدان تنش و نقش آن در دگرشکلی ساختار فراقان در زاگرس خاوری

نوع مقاله: مقاله پژوهشی

نویسندگان

1 دانشجوی دکترا، گروه زمین شناسی، دانشگاه تربیت مدرس، تهران، ایران

2 دانشیار، گروه زمین شناسی، دانشگاه تربیت مدرس، تهران، ایران

3 استادیار، گروه زمین شناسی، دانشگاه تحصیلات تکمیلی علوم پایه زنجان، زنجان، ایران

چکیده

تاقدیس فراقان در شمال خاور کمان فارس قرار دارد و در این محل پوشش رسوبی به ستبرای 10 کیلومتر روی سری هرمز دگرشکل شده­ است. این تاقدیس توسط گسل زاگرس مرتفع بریده شده است. با توجه به کم بودن مطالعات تنش دیرینه و تحلیل جنبشی ساختارها در شمال خاور کمان فارس در این نوشتار به تاریخچه تغییرات میدان تنش و نقش آن در تکامل ساختار فراقان پرداخته شده است. برای تعیین متغیرهای تنسور تنش کاهش یافته و تفکیک گسل­های مربوط به هر فازدگرشکلی شکننده، از روش وارون‎سازی؛ برای تعیین امتداد محور کوتاه‎شدگی بیشینه از استیلولیت­ها و برای تعیین موقعیت تنش کمینه از رگه‌های کششی استفاده شده است. به منظور بررسی جهت­های تنش اصلی زمان حاضر داده‌های سازوکار کانونی زمین‌لرزه‌ها نیز به روش برگشتی تحلیل شده­اند. مطابق این بررسی، پیش از  چین‎خوردگی در میوسن پسین سوی تنش اصلی حداکثر N27°-29°E بوده و ترک‌های کششی در این زمان شکل گرفته‌اند. در اواخر میوسن میانی پوشش رسوبی تحت رژیم زمین‎ساختی فشاری (Compressional) و با سوی تنش اصلی بیشینه N19°E به‎صورت چین­های جدایشی (Detachment fold) و مرتبط با گسل (Fault related fold) دگرشکل شده ­است. در اواخر میوسن پسین و اوایل پلیوسن، پی‌سنگ در محدوده فراقان شروع به کوتاه‎شدگی کرده است که در این زمان رژیم زمین‎ساختی امتدادلغز و سوی تنش اصلی بیشینه N4°E است. در این زمان گسل زاگرس مرتفع فعال شده و ستون رسوبی و ساختارهای موجود را به‎طور کامل برش داده است. در پلیوسن تحت رژیم زمین‎ساختی امتدادلغز سوی تنش اصلی بیشینه به‎طور موقت به N25°W تغییر یافته و گسل­های امتدادلغز و واژگون موجود با سازوکار جدید فعال شده­اند. بررسی داده‌های سازوکار کانونی زمین‎لرزه‌ها گویای این مطلب است که در زمان حاضر سوی تنش اصلی دوباره شمالی- جنوبی ‌است.

کلیدواژه‌ها


عنوان مقاله [English]

Study on changing of stress Field and it,s role on deformation of Faraghan Structure in Eastern Zagros

نویسندگان [English]

  • S. A. Atapourfard 1
  • A. Yassaghi 2
  • M. Rezaian 3
  • E. Shabanian 3
1 Ph.D. Student, Department of Geology, Tarbiat Modares University, Tehran, Iran
2 Associate Professor, Department of Geology, Tarbiat Modares University, Tehran, Iran
3 Assistant Professor, Department of Geology, Zanjan Advance Studies in Basic Science, Zanjan, Iran
چکیده [English]

In the east of high Zagros – in Faraghan Anticline- sedimentary cover with more than 10 km thickness has decoupled from basement above the Hormuz salt and has deformed. Mention anticline is cut by High Zagros Fault. By attention to lack of paleostress study and kinematic interpretation on north east of Fars Arc structures, in this paper we reconstructed stress field and interoperated its role in evolution of Faraghan Anticline. Inversion method used for determination of reduced stress tensor parameters and discrimination faults of every brittle tectonic phase. Maximum shortening axis determined by using Stylolite's and attitude of Minimum main stress determined by using veins. The present stress field was calculated by inversion of earthquake focal mechanism data. According to our data and the deduced results,  some of veins developed with an N27° - 29°E direction of σ1 stress axis before late of middle Miocene (before folding and faulting). During the late Miocene, sedimentary cover deformed as detachment and faults related folds in a general compressional stress regime with an N27° - 29°E direction of σ1. The basement faults were reactivated during late Miocene- early Pliocene in a general strike slip regime with an N4°E direction of σ1 stress axis. The High Zagros Fault was reactivated at that time and cross- cuts the entire cover section and its associated structures. In the late Pliocene, direction of σ1 stress axis temporally changed to N025°W in strike slip tectonic regime. Strike- slip and reverse faults were reactived in new stress field. Earthquakes Focal mechanism data analysis indicate that direction of σ1 stress axis is N-S now.

کلیدواژه‌ها [English]

  • Faraghan Anticline
  • Inversion method of fault- slip data
  • Tension gashes
  • Stylolite
  • Focal mechanism data

کتابنگاری

ملک‌زاده، ز.، عباسی، م.ر.، بلیه، ا.، اوته مه یو، ک. و شبانیان بروجنی، ا.، 1387- الگوی دگرشکلی در زاگرس مرتفع باختری، علوم زمین، شماره 69.

 

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