تکوین ساختاری روند شمال‌باختری - جنوب‌خاوری در منطقه همت‌آباد - خاور ایران

نوع مقاله : مقاله پژوهشی

نویسندگان

گروه زمین‎شناسی، دانشکده علوم، دانشگاه بیرجند، بیرجند، ایران

چکیده

مقدمه: روند ساختاری شمال غربی- جنوب شرقی، یکی از روندهای ساختاری غالب در شرق ایران است. راستگرد N-S گسلی نهبندان، بین زون ساختاری سیستان و لوت قرار دارد. مدل تکتونیکی و رشد روندهای شمال غربی - جنوب شرقی در شرق ایران با تحلیل تغییر شکل در منطقه همت آباد معرفی می­شود.
مواد و روش­ها: واحدهای سنگی زیرپهنه سیستان عبارتند از: واحدهای افیولیتی و دگرگونی کرتاسه و واحدهای فلیش- آوارآلاستی. منطقه همت آباد شامل: واحدهای افیولیتی امتداد یافته در جهت شمال غربی- جنوب شرقی، سنگ­های آتشفشانی و واحدهای ماسه سنگ، شیل، آهک با دگرگونی از تخته سنگ، فیلیت تا شیست است. چین‌های فرورفته شمال‌غربی در واحدهای شیل و ماسه‌سنگ ثالث دارای قسمت جلویی شیب‌دار در سمت جنوب غربی هستند که نشان‌دهنده همگرایی زمین ساختی جنوب غربی است. تحلیل هندسی و سینماتیکی پهنه­های گسلی مذکور نشان می­دهد که محور اصلی تراکم در منطقه دارای روند متوسط N25E است. مولفه برشی در پهنه­های گسلی شمال- جنوب و مولفه فشاری در پهنه­های شمال غربی- جنوب شرقی غالب است. با توجه به تحلیل هندسی گسل‌ها و مکانیسم‌های آن‌ها، چین‌خوردگی‌ها و برون‌آمدگی واحدهای سنگی، می‌توان فعالیت گسل‌های شمال شرقی را به‌عنوان گسل‌های قدیمی‌تر (پیش‌تر) در نظر گرفت.
نتایج و بحث: براساس شواهد ژئومورفولوژیکی از قبیل رودخانه­های جابجا شده، برآمدگی­های دریچه­ای و اسکارپ­های گسلی در منطقه همت آباد، پهنه­های گسلی به سمت جنوب غربی مهاجرت می­کنند. با ارزیابی گسل­ها و چین خوردگی ها، رخنمون واحدهای سنگی و ویژگی­های مورفوتکتونیکی، می­توان مدل ساختاری زیر را ارائه داد:
مرحله اول: با مولفه NE تنش فشاری، پهنه گسلی همت آباد برخوردی NW-SE که مولفه فشار در آن غالب است، واحدهای افیولیتی در معرض دید قرار گرفت.
مرحله دوم: گسل جدیدی مانند پهنه گسلی همت آباد (NW-SE) در قسمت جنوب غربی آن با مکانیزم راست- جانبی معکوس تشکیل شده است. با ادامه تغییر شکل مذکور، چین خوردگی سنگ­های رسوبی کرتاسه و پالئوسن- ائوسن و جابجایی در رودخانه­ها رخ داد.
مرحله سوم: برآمدگی­های شاتر با تشکیل گسل­های جدید ایجاد می­شوند. در این مدل رشد سازه­ها از شمال شرق به جنوب غرب انجام شده است. مولفه NE تنش فشاری، چین‌خوردگی‌هایی با ردپای محوری شمال غربی- جنوب شرقی در منطقه ایجاد کرده است. در گسل‌های ضربه‌گیر شمال به جنوب، مولفه امتداد لغز غالب است، اما در گسل‌های ضربه‌گیر شمال غربی به جنوب شرقی (مانند پهنه گسل همت‌آباد)، مولفه معکوس غالب است. شواهد مورفوتکتونیکی حاکی از آن است که برآمدگی اسکارپ­های گسلی از شمال شرقی به جنوب غربی و انحراف رودخانه­ها از جنوب شرقی به شمال غربی در حال کاهش است. بنابراین فعالیت زمین ساختی در قسمت جنوب شرقی بیشتر از قسمت شمال غربی در این منطقه است.
نتیجه ­گیری: رشد سازه‌ها در این ناحیه با ایجاد پهنه‌های گسلی ضربه‌گیر شمال باختری- جنوب شرقی از شمال شرق به جنوب غرب ادامه می‌یابد که نشان‌دهنده رشد ساختاری در روند شمال غربی- جنوب شرقی شرق ایران است. تکوین ساختاری روند شمال‌باختری - جنوب‌خاوری در منطقه همت‌آباد - خاور ایران.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Structural evolution of northwest-southeast trend in Hemmatabad area – East Iran

نویسندگان [English]

  • ebrahim gholami
  • mohammadmahdi khatib
  • Mohsen Karimidehkordi
Department of Geology, Faculty of Sciences, University of Birjand, Birjand, Iran
چکیده [English]

Introduction: Northwest-southeast structural trend, is one of the dominant structural trends in the east of Iran. Dextral N-S striking Nehbandan fault system, is located between Sistan and Lut structural zones. The tectonic model and growth of northwest-southeast trends in the east of Iran will be introduced by deformation analysis in Hematabad region.
Materials and methods: The rock units of the Sistan subzone include: Cretaceous ophiolitic and metamorphic units and flysch-pyroclastic units. Hematabad region includes: ophiolitic units extending in the northwest-southeast direction, volcanic rocks, and sandstone, shale, limestone units with metamorphism ranging from slate, phyllite to schist.
The northwest plunging folds in the tertiary’s shale and sandstone units have steep forelimb on the southwest side, which indicates the southwest tectonic vergence. Geometric and kinematic analysis of mentioned fault zones, indicates the main axis of compression in the region has an average trend of N25E. The shear component is dominant in the north-south fault zones and the compressive component is dominant in the northwest-southeast ones. According to the geometrical analysis of the faults and their mechanisms, folds and the rock units outcrop, the activity of the faults in the northeastern part can be considered as older (earlier) faults.
Results and Discussion: Based on geomorphological evidences such as displaced rivers, shutter ridges and fault scarps in Hematabad region, fault zones migrate to the southwest. By asessement of the fault and folds, outcrop of the rock units and the morphotectonic features, the following structural model can be presented:
The first stage: by NE component of compressive stress, the NW-SE striking Hematabad fault zone in which the pressure component is dominant, ophiolitic units was exposed.
The second stage: a new fault the same as Hemmatabad fault zone (NW-SE) has been formed in its southwestern part with a reverse right-lateral mechanism. With the continuation of mentioned deformation, folding of Cretaceous and Paleocene-Eocene sedimentary rocks and displacement in rivers occurred.
Third stage: Shutter ridges develop with the formation of new faults. In this model, the growth of the structures has been done from the northeast to the southwest.
NE component of compressive stress, has caused folds with a northwest-southeast axial trace in the region. In north-south striking faults, the strike-slip component is dominant, but in northwest-southeast striking faults (such as Hematabad fault zone), the reverse component is dominant.
The morphotectonic evidences indicate that the uplift of fault scarps is decreasing from the northeast to the southwest, and the deflection of rivers is decreasing from the southeast to the northwest. Therefore, the tectonic activity in the southeastern part is more than the northwestern part in this region.
Conclusion: The growth of structures in this area continues with the creation of NW-SE striking fault zones from the northeast to the southwest, which indicates the structural growth in the northwest-southeast trends in the east of Iran.

کلیدواژه‌ها [English]

  • Nehbandan fault zone
  • Hemmat abad fault zone
  • East Iran
  • Structural growth
  • Right-lateral fault

مراجع

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