NDLI: Synoblique convergent and extensional deformation and metamorphism in the Neoproterozoic rocks along Wadi Fatira shear zone, Northern Eastern Desert, Egypt

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Synoblique convergent and extensional deformation and metamorphism in the Neoproterozoic rocks along Wadi Fatira shear zone, Northern Eastern Desert, Egypt

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Arabian Journal of Geosciences : Volume 1

Synoblique convergent and extensional deformation and metamorphism in the Neoproterozoic rocks along Wadi Fatira shear zone, Northern Eastern Desert, Egypt

Content Provider	Springer Nature Link
Author	Abd El Wahed, Mohamed Abu Anbar, Mohamed
Copyright Year	2008
Abstract	The Wadi Fatira area occurs at the southern margin of the Northern Eastern Desert (NED) of Egypt and is occupied by highly sheared metavolcanics tectonically alternated with banded iron formations and intruded by Barud tonalite–granodiorite, post-tectonic gabbroic and granitic intrusions. Detailed structural investigation showed that the schists and migmatitic amphibolites are formed by shearing in metavolcanics and syntectonic Barud tonalite–granodiorite due to movement along the Wadi Fatira shear zone (WFSZ). This shear zone starts as a NW–SE striking fault along Wadi Barud Al Azraq and the Eastern part of Wadi Fatira and turns to a E–W trending fault to the north of Wadi Fatira. Microstructural shear sense indicators such as asymmetric geometry of porphyroclasts such as σ-type and asymmetric folds deforming fine-grained bands which are frequently found around porphyroclasts indicate sinistral sense of shearing along the WFSZ. This shear zone is characterized by transitions from local convergence to local extension along their E–W and NW–SE trending parts, respectively. The NW–SE part of the WFSZ is of about 200 m in width and characterized by synmagmatic extensional features such as intrusion of synkinematic tonalite, creation of NE–SE trending normal faults, and formation of migmatitic amphibolites and schlieric tonalites. This part of the shear zone is metamorphosed under synthermal peak metamorphic conditions (725°C at 2–4 kbar). The E–W compressional part of the WFSZ is up to 3 km in width and composed of hornblende, chlorite, actinolite, and biotite schists together with sheared intermediate and acidic metatuffs. Contractional and transpressional structures in this part of the WFSZ include E–W trending major asymmetrical anticline and syncline, nearly vertical foliation and steeply pitching stretching lineations, NNE dipping minor thrusts, and minor intrafolial folds with their hinges parallel to the stretching lineation. P–T estimates using mineral analyses of plagioclase and hornblende from schists and foliated metavolcanics indicate prograde metamorphism under medium-grade amphibolite facies (500–600°C at 3–7 kbar) retrogressed to low-grade greenschist facies (227–317°C). The foliation in Barud tonalite–granodiorite close to the E–W part of the WFSZ runs parallel to the plane of shearing and the tonalite show numerous magmatic flow structures overprinted by folding and ductile shearing. The WFSZ is similar to structures resulted from combined simple shear and orthogonal shortening of oblique transpressive shear zones and their sense of movement is comparable with the characteristics of the Najd Fault System.تقع منطقة وادى فطيرة على الحافة الجنوبية للجزء الشمالي من الصحراء الشرقية المصرية، والمنطقة يتواجد بها صخور البركانيات المتحولة يصاحبها رقائق من تكوينات الحديد ويتداخل فى هذه الصخور جرانيت وادى بارود المصاحب للحركة التكتونية وكذلك بعض من متداخلات مابعد الحركة التكتونية من الجرانيت والجابرو. الدراسة التركيبية التفصيلية للمنطقة أثبتت ان الشيست والأمفيبولايت الميجماتى تكونا نتيجة التشوة والتحول اللذان حدثا للصخور البركانية وتوناليت-جرانودايورايت وادى بارود وذلك كنتيجة للحركة على نطاق تشوه وادى فطيرة وأثناء تداخل جرانيت وادى بارود. نطاق تشوه وادى فطيرة بدأ كصدع يتجة شمال غربى-جنوب شرقى عبر وادى بارود الأزرق والجزء الشرقى من وادى فطيرة ثم تغير مساره الى صدع يتجه شرق-غرب وذلك الى الشمال من وادى فطيرة. أدلة الحركة مثل تواجد البروفيروبلاست فى شكل سيجما، تواجد الطيات الدقيقة الغير متماثلة والتى تشوه الأشرطة الدقيقة الموجودة حول البروفيروبلاست، هذه الأدلة أكدت أن الحركة يسارية عبر نطاق تشوه وادى فطيرة. يتميز نطاق تشوه وادى فطيرة بالانتقال من مرحلة التشوة المصاحب للتقارب المائل الى التشوه المصاحب للبسط والإطالة. يتكون نطاق بتر وادى فطيرة من جزأين، الجزء الأول يتجه شمال غرب – جنوب شرق وهذا اتساعه حوالى 200 متر ويتميز بتواجد الظواهر المصاحبة لتشوه البسط والصخور فى الحالة المجماتية، ومن أمثلة هذا الظواهر تداخل جرانيت وادى بارود، الصدوع التى تتجة شمال شرق-جنوب غرب، وتكوين الأمفيبولايت الميجماتى والتونالايت ذو الأشرطة. وجد أن ظروف التحول فى هذا الجزء من نطاق التشوه وصلت الى قمة الحرارة حيث تم تسجيل حرارة تصل الى 725 درجة مئوية وضغط يتراوح بين 2 الى 4 كليوبار. أما الجزء الثانى من نطاق تشوه وادى فطيرة فإنه يتجه شرق-غرب واتساعه حوالى 3 كيلومتر ويتكون من أنواع مختلفة من صخر الشيست بالإضافة الى صخور بركانية متوسطة التشوه. ويميز هذا الجزء من نطاق تشوه وادى فطيرة التراكيب المصاحبة للتضاغط والتقارب والتى تشمل التحدبات والتقعرات الغير متماثلة والتى تتجه شرق-غرب، التورق الشبة رأسى واستطالة المعادن شديدة الغطس، الدسور المائلة فى اتجاه شمال الشمال الشرقى، والطيات الصغيرة التى تتوازى اتجاهات محاورها مع الاتجاهات التى تميز استطالة المعادن. وجد ان الصخور فى هذا الجزء من نطاق التشوة تحولت تحت ظروف من الضغط ودرجة الحرارة تتوافق مع سحنة الأمفيبولايت (500-600 درجة مئوية، 3-7 كيلوبار) ثم حدث تراجع حتى وصلت الى سحنة الشيست الأخضر (227-317 درجة مئوية). التورق الذى يميز صخور التوناليت والجرانودايورايت فى متداخل جرانيت وادى بارود يتوازى مع مستوى التشوه فى هذا الجزء من نطاق تشوه وادى فطيرة. أخيرا، ان نطاق تشوه وادى فطيرة يشبه التراكيب التى تنتج من تأثير simple shear والتقصير المتعامد المصاحب لنطاقات التشوة والعقص المائلة هذا يجعله مشابه لنطاقات التشوه التى تميز نظام صدوع النجد. للمراسلة: د/ محمد احمد عبد الواحد
Starting Page	29
Ending Page	52
Page Count	24
File Format	PDF
ISSN	18667511
Journal	Arabian Journal of Geosciences
Volume Number	2
Issue Number	1
e-ISSN	18667538
Language	Arabic
Publisher	Springer-Verlag
Publisher Date	2008-12-16
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Northern Eastern Desert Fatira shear zone Oblique convergent Transpression Extension Najd Fault System Earth Sciences
Content Type	Text
Resource Type	Article
Subject	Earth and Planetary Sciences Environmental Science

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