Document Details
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Document Type |
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Thesis |
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Document Title |
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TECTONIC STYLES OF HANABIC, AJJAJ AND QAZAZ SHEAR ZONES: IMPLICATION OF OBLIQUE TRANSPRESSION IN THE ARABIAN SHIELD, SAUDI ARABIA الوضع التكتوني لنطاقات القص حنبق وعجاج وقزاز: آثار تصادم لوحي مائل في الدرع العربي. المملكة العربية السعودية |
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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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The study area is located in the southern part of the Midyan Terrane in the northwestern part of the Arabian Shield. It composes of Neoproterozoic rock assemblages comprising an elongated ridge of ophiolitic rocks, arc-metavolcanics, and contemporary arc-related Intrusions. They are unconformably overlained by the post-amalgamation molasses-type Sediments, and finally intruded by Late- to Post-tectonic Intrusions. The arc-related volcano-sedimentary association and related intrusions had suffered polyphase deformation and metamorphism at greenschist facies condition and locally reached an amphibolite facies. They developed during the propagation of the NW-trending transpressional Najd Fault System. They constitute what is known as Qazaz-Ajjaj-Hanabiq shear zone strands. Integration of the remote sensing technique of the ASTER Landsat images and the field observation allows to delineate the alteration zones, gossans, and quartz vein, which are commonly hosted-ore mineralization. The processed images are also used to discriminate and construct a structural and a geological map.
The study area characterized by several primary structures, formed during the solidification of volcanic flows and the deposition of the sedimentary rocks. Secondary structures, commonly related to the deformation of the NW-trending Najd Fault System; they are ductile to semi-ductile associated with the deformation along the Qazaz-Ajjaj-Hanabiq shear zones. They include foliation, mineral stretching lineation, pencil structures, intersection foliations, boudinage and rod structures in addition to folds of different shape and style. Folding in the area represented by three phases (F1-F3), coinciding with the three deformational phases (D1-D3) of the Pan-African Orogeny in the Arabian Shield.
Structural analysis of the structural parameters, from the microscopic- to map-scale, of the shear sense indicators imply that both Qazaz and Ajjaj shear zones display top-to-NW and top-to-WNW sinistral transpressional regime; however, the shear-sense indicators along Hanabiq shear zone show top-to-NNE and top-to-E dextral strike-slip movement. Geometric analyses of planar and linear structures including foliations and lineations along the Qazaz-Ajjaj-Hanabiq shear strands, in addition to the constructed strike-form-line map display a sub-horizontal tight large-scale fold; its fold axis trends 4.4° towards S30°E. This mega-scale fold comprising three sets of fold attitudes coinciding with the ductile deformational phases of the Pan-African Orogeny. The finite strain analysis indicate that the amount of strain is commonly similar across the three shear zone strands, where they increase in the deflection and the conjunction's areas. The increasing strain values attributed to the mechanical resistance between the shear zone and the exhumed gneissic core complex, which was controlled the deflection of the shear orientations and the sense of movements. The resulted finite strain ellipses exhibit commonly flattening strain symmetry with a significant component of a mean of approximately 88% pure shear. The maximum stretching direction of the strain ellipses are commonly oriented parallel to the shear trends: NW- to WNW-directions for the Ajjaj and Qazaz shear zone strain ellipsoids, and NNE-direction for the Hanabiq shear zone. The flattening strain symmetry comprise both horizontal flattening across the shear zones, where the foliation planes are sub-vertical to vertical; however, in the gneisses domes and away from the shear zones, the flattening strain symmetry is defined as vertical flattening regime.
This study concludes that the three anastomosing shear strands known as Qazaz-Ajjaj-Hanabiq shear zones were developed during the D3 deformational phase. However, inconsistency in their shear-sense and their orientations were caused by the exhumation of the high-grade gneisses, which deviate the shear trend to the north in Hanabiq shear zone and Baladiyah Complex, and E-W trend in the northwestern part of Ajjaj shear zone. Furthermore, switching of shear sense movements to be sinistral in Ajjaj-Qazaz shear zones, and being of dextral sense in the Hanabiq shear zone, relate to the exhumation of the gneissic core complex and the oblique transpression. Structural features in the studied Al-Wajh area are related to the D3 deformational phase. They are accompanied with the Najd Fault System-related anastomosing shear zone strands. On the other hand, the oldest two deformational phases in the Arabian Shield; the Hijaz and the Nabitah are expressed by F1 and F2 folding phases, respectively. The brittle deformation attributed to the D4 deformational phase and probably extended to the Red Sea rifting. |
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Supervisor |
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PROF. DR. MOHAMED K. EL-SHAFEI |
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Thesis Type |
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Doctorate Thesis |
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Publishing Year |
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1439 AH
2017 AD |
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Added Date |
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Wednesday, November 1, 2017 |
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Researchers
| وديع أحمد القشقري | ALKASHGHARI, WADEE Ahmed | Researcher | Doctorate | |
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