Document Details
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Document Type |
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Thesis |
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Document Title |
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STRUCTURAL EVOLUTION OF WADI YIBA AREA, SOUTHERN ARABIAN SHIELD, SAUDI ARABIA التَّطَوُّر البِنَائِي لمنطقةِ وادي يِبَا، جنوب الدِّرْع العَرَبِي، المملكة العربيَّة السُّعُودِيَّة |
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Subject |
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Faculty of Earth Sciences |
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Document Language |
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Arabic |
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Abstract |
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Detailed field-structural mapping of the Pan-African basement rocks exposed at Wadi Yiba area, Southwestern Arabian Shield, Saudi Arabia, revealed the presence of four main units; metavolcanics, Ablah Group (metaclastic and marble units) and syn- and post-tectonic granitoids. The exposed rocks are tectonically evolved during the Neoproterozoic throughout, at least, three phases of deformation (D1, D2 and D3). D1 led to the formation of tight to isoclinal and intrafolial folds (F1), axial plane foliation (S1), and mineral and stretching lineations (L1). This phase resulted from an early E-W (to ENE-WSW) shortening accompanied with the early convergence between East and West Gondwana. D2 deformation phase progressively overprinted D1 structures and was dominated by mostly a transpressional tectonic regime and top-to-the-W (to WSW) thrusting under a compressive environment. Stretching lineation trajectories, S-C foliations, asymmetric shear fabrics and related mylonitic foliation, and flat-ramp and duplex geometries are main evidence supporting the proposed Pan-African transport direction. The N- to NNW-orientation of both "in-sequence piggy-back thrusts" and axial planes of minor and major F2 thrust-related overturned folds is rather solid evidence indicating the same stress trajectories of compressional regime during the D2 phase. The W- (to WSW-) propagation of Pan-African thrusting in the study area is consistent with results obtained elsewhere in the Arabian-Nubian Shield (ANS) and being in complete harmony with contraction and shortening associated with terrane amalgamation when ANS squeezed between East and West Gondwana.
Wadi Yiba Shear Zone (WYSZ) is a conspicuous structural fabric related to D2 phase, and could easily be traced on Landsat images. WYSZ is affiliated to the N-S trending brittle-ductile Late Neoproterozoic Shear Zones in the ANS. Shear sense indicators reveal that shearing during the D2 regional-scale transpression was dextral (right-handed). Dextral shearing sense is in complete harmony with the mega-scale sigmoidal pattern clearly recognizable on Landsat image; i.e. this structural pattern is penetrative allover the mapped area and environs. The shearing led to the formation of the main shear zone and the associated F2 shear zone-related folds, as well as the other unmappable shear zones in the deformed rocks. Moreover, emplacement of the syn-tectonic granitoids is likely to have occurred during the D2 transpressional phase rather than in an extensional tectonic environment. This conclusion is evidenced by: 1) absence of F1 folds and at the same time presence of F3 crenulation lineations and kink bands in syn-tectonic granitoids, 2) off-shooting of these granitoids into the enveloping rocks, and 3) intensive degree of shearing and mylonitization. Emplacement of syn-tectonic granitoid took place to accommodate space resulted from thrust propagation.
D1 and D2 structures are overprinted by mesoscopic to macroscopic-scale D3 structures (F3 folds, L3 crenulation lineations and kink bands). F3 folds are frequently open and have steep to subvertical axial planes and axes moderately to steeply plunging towards the E, ENE and ESE directions. The deformational history of Wadi Yiba area is in agreement with the general evolutionary model proposed for the ANS which represents the northern extension of the East African Orogen (EAO) or East African-Antarctic Orogen (EAAO). |
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Supervisor |
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Prof. Zakaria A. Hamimi |
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Thesis Type |
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Master Thesis |
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Publishing Year |
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1432 AH
2011 AD |
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Co-Supervisor |
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Dr. Mohamed K. El Shafei |
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Added Date |
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Friday, June 17, 2011 |
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Researchers
| غازي علي كتو | KATTU, GHAZI ALI | Researcher | Master | |
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