Ahmed M. Hegazi Department of Structural Geology and Remote Sensing, Faculty of Earth Sciences, King Abdul Aziz University Jeddah 21589, P.O.B. 80206, Saudi Arabia

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The Sa'al Belt comprises a variety of Late Proterozoic island-arc assemblages of metasediments and metavolcanics. The metavolcanics are calc-alkaline to sub-alkaline rocks with minor tholeiitic tendency, whereas the metasediments are originally sediments that were shed from active volcanic islands. The belt is polydeformed and regionally metamorphosed up to the greenschist facies, with late and post-tectonic granitoid intrusions. Tectonically the Sa'al Belt evolved through multiple phases of ductile and brittle deformation. The ductile deformation is manifested in three folding generations and shear zones whereas the brittle deformation is represented by thrusting and faulting. The first folding generation (F1) is represented by intrafolial and drag folds that are apparently coeval with thrusting, and show vergence more or less parallel to that of thrusts. Thrusting took place in a convergent environment within and along the contact between different metavolcanics and metasediments. The highest principal stress is horizontal, oriented N50°W, and the relative transport direction is to SE toward the foreland. A second fold generation (F2) overprinted the first folding with widely-spread kink folds and kink bands. All criteria indicate the prevalence of a NW-SE-oriented simple shear regime that was associated with slip essentially parallel to banding. The third folding generation (F3) has a slip nature and has overprinted both F1 and F2, producing sub-vertical NW-SE-trending S3-surfaces, meaning that the highest principal stress orientation rotated towards NE-SW. Dynamic analysis of the fabrics within the extensive subvertical E-W-trending ductile shear zones indicates that they are produced by a subhorizontal highest principal stress oriented S47°E. Moreover, shear sense indicators display a simple shear with dextral sense of movement. Two conjugate shear planes are the main elements of the brittle deformation. The first is a left-lateral strike-slip fault set trending N to NNE, and the second a right-lateral strike-slip fault set trending NW. These conjugate shear planes were formed with subhorizontal highest principal stress oriented N25°W.

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Acta Geologica Hungarica
Language English
Year of
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Founder Magyar Tudományos Akadémia  
H-1051 Budapest, Hungary, Széchenyi István tér 9.
Publisher Akadémiai Kiadó
H-1117 Budapest, Hungary 1516 Budapest, PO Box 245.
Chief Executive Officer, Akadémiai Kiadó
ISSN 0236-5278 (Print)
ISSN 1588-2594 (Online)

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