نشریه علوم زمین خوارزمی

نشریه علوم زمین خوارزمی

بررسی پتروفابریکی دگرشکلی در جنوب شرق پهنه دگرگونی سنندج-سیرجان با تکیه برگسترش ساختارها و ریزساختارها

نویسنده
سعیده کشاورز
دانشگاه خلیج فارس
10.22034/KJES.2025.11.1.108121
چکیده
هدف از انجام پژوهش بررسی دگرشکلی در مجموعه دگرگونی چای کور، واقع در کمربند سنندج-سیرجان، با استفاده از تحلیل‌های ساختاری، ریزساختاری می‎‌باشد. شواهد صحرایی نشان می‎‌دهد که این منطقه تحت تأثیر یک سیستم دگرشکلی پیچیده حاصل از تعامل سه فاز تغییر شکل قرار داشته است. مطالعات ساختاری و ریزساختاری انجام شده، شواهد واضحی از فعالیت یک سیستم ترافشارش در این منطقه ارائه می‌دهند. وجود ساختارهای متنوع از جمله چین‌های نامتقارن، چین‌های غلافی و بودین‌های نامتقارن گویای رخداد تغییر شکل ناهمگن در محدوده مورد مطالعه است. در مقیاس میکروسکوپی، بررسی پورفیروکلاست‌های نوع سیگما و دلتا، ساختارهای S/C و میکاهای ماهی‌گون نه تنها جهت برش راست‌گرد (Top-to-the-SE) را تأیید می‌کنند، بلکه اطلاعات ارزشمندی درباره شرایط دما-فشار حاکم بر منطقه ارائه می‌دهند. تحلیل‌های کمی کرنش با استفاده از روش‌های فرای و نمودار فلین نشان داد که بیضوی کرنش در این منطقه تمایل واضحی به حالت تخت‌شدگی تا صفحه‎‌ای دارد. مقادیر K بین 51/ تا 1/18 و مقادیر D بین 1/1 تا 2/22 حاکی از ناهمگنی قابل توجه در توزیع کرنش در منطقه است. محاسبه عدد تاوایی به روش RXZ/θ (83/-75/) نشان داد که جریان دگرشکلی در منطقه عمدتاً غیرهم‌محور (non-coaxial) بوده و مؤلفه برش ساده نقش غالب‌تری نسبت به برش محض ایفا کرده است. بررسی سازوکار بازبلورش در کانی‎های کوارتز و فلدسپار، از جمله بازبلورش مهاجرت مرز دانه‌ای ( GBM)و بازبلورش چرخش ریزدانه ( SGR) محدوده دمایی ۴۰۰ تا ۶۵۰ درجه سانتی‌گراد را برای دگرشکلی اصلی نشان می‌دهد که با رخساره آمفیبولیت مطابقت دارد. همچنین حضور ساختارهای شکننده مانند قفسه‌کتابی در فلدسپارها نشان‌دهنده رخداد مراحل پایانی تغییر شکل در شرایط دمایی پایین‌تر است. یافته‎های این پژوهش با سایر مطالعات ساختاری و ریزساختاری در چارچوب همگرایی مایل بین صفحات اوراسیا و عربی تطابق دارد.

کلیدواژه‌ها
میلونیت
جزءبندی کرنش
زون برشی
پهنه دگرگونی سنندج-سیرجان
ترافشارش

عنوان مقاله English

A petrofabric study of deformation in the southeastern Sanandaj-Sirjan metamorphic zone: Constraints from structures and microstructures

نویسنده English

Saeede Keshavarz
Persian Gulf University
چکیده English

This study investigates deformation in the Chai-Kour metamorphic complex, located in the Sanandaj-Sirjan metamorphic belt, using structural, microstructural, and strain analyses. Field observations show that this area has been affected by a complex deformation system resulting from the interaction of three deformation phases. The structural and microstructural analyses conducted provide evidence for the activity of a transperssion in this region. Presence of diverse structures, including asymmetric folds, sheath folds, and asymmetric boudins, all indicative of intense and heterogeneous deformation conditions. At the microscopic scale, the identification of sigma and delta porphyroclasts, S/C fabrics, and fish-shaped micas not only confirms a dextral shear sense (top-to-the-SE) but also provides valuable insights into the temperature conditions prevailing in the region. Quantitative strain analyses using the Fry methods and Flinn diagram demonstrated that the strain ellipsoid in this area exhibits a clear tendency toward plane-flattening strain. K values (0.51-1.18) and D values (1.1-2.22) indicate significant heterogeneity in strain distribution across the region. The calculated vorticity number (0.75–0.83) revealed that the deformation flow in the region was predominantly non-coaxial, with a simple shear component playing a more dominant role than pure shear. Examination of quartz and feldspar microstructures, including subgrain rotation (SGR) and grain boundary migration (GBM) recrystallization, suggests a temperature range of 400–650 °C for the main deformation event, consistent with amphibolite facies conditions. Additionally, the presence of quartz BLG recrystallization and brittle structures like book-shelf in feldspars indicates the occurrence of late-stage deformation under lower temperature conditions. These findings are in complete agreement with the region's tectonic setting within the framework of oblique convergence between the Eurasian and Arabian plates.

کلیدواژه‌ها English

mylonite
strain partitioning
Shear Zone
Sanandaj-Sirjan metamorphic belt
transpression
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