Document Details
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Document Type |
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Thesis |
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Document Title |
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TECTONIC EVOLUTION OF WADI FATIMA FOLD-THRUST BELT, WEST-CENTRAL PART OF THE ARABIAN SHIELD, SAUDI ARABIA التَّطور التِكْتُونِي لحزام الطي والدَّسر بوادي فاطمة، الجزء الأوسط الغربي من الدِّرع العربي، المملكة العربية السُّعُوديَّة |
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Subject |
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Faculty of Earth Sciences - Structural Geology and Remote Sensing |
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Document Language |
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Arabic |
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Abstract |
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Wadi Fatima fold-thrust (FAT) belt is a distinctive foreland FAT belt involving unmetamorphosed to slightly metamorphosed sedimentary sequence of Fatima Group, whose thickness decreases towards the foreland, deposited over a metamorphic/igneous basement, comprising gneisses, ortho-amphibolites, ortho- and para-schists (with chaotic unmappable blocks of marbles, hornblendite and metagabbros), older granite (77316 Ma) and younger granite. The basement displays structural fabrics, such as attenuated tight isoclinal folds, sheared-out hinges, NE-SW penetrative foliation and subhorizontal stretched and mineral lineations, related to an oldest prominent dextral shearing phase affected the main Wadi Fatima during the Neoproterozoic. In Wadi Fatima FAT belt, the style of deformation encompasses flexural-slip folding forming mesoscopic- and map-scales NE to ENE plunging overturned antiforms and synforms, and a thrust duplex system bounded by floor thrust and sole thrust (basal detachment) dipping gently towards the hinterland (SE to SSE direction) and rises stratigraphically upwards towards the foreland. Such style is affiliated to thin-skinned deformation, for the reason that thrusting involves only Fatima Group, whereas the underlying basement remains unaffected by thrusting, opposing to thick-skinned style of basement-involved belts in which both the sedimentary cover and the basement are deformed due to shortening or contraction and affected by the same thrust system and history of deformation.
Several lines of evidence, for instance geometry of interacting outcrop- and map-scale folds and thrusts, patterns of thrust displacement variations and indications for hinge migration during fold growth, strongly suggest that folding and thrusting in Wadi Fatima FAT belt are geometrically and kinematically linked and that thrusting initiated as a consequence of folding (fold-first kinematics). Although, the question of whether deformation was progressive or two-phase in character, or in other word whether folding and thrusting were formed during one phase or two distinct phases of deformation, remains unanswered, the data presented in this thesis attested a progressive deformation model.
Thrusts frequently show flat-ramp-flat geometry, and every so often give an impression that they were formed during two main sub-stages; an older sub-stage during which bedding sub-parallel thrusts were formed, and a younger sub-stage which generated younger ramps oblique to bedding. Moreover, close to the basement, thrusts seem to develop under ductile to brittle conditions and those located away from the contact were deformed under brittle conditions, and thrust sheets themselves may be transported by brittle translation. Thrust ramps with SE to SSE dipping regularly show sequential decrease in dip or inclination (due to piggy-back imbrication) into their transport direction which is proposed to be towards NW to NNW. Evidence indicating this transport direction of Wadi Fatima FAT belt embrace NW to NNW oriented stretching lineations recorded along thrust planes, NW to NNW folding vergence, and diminishing of the intensity of deformation and thrust stacking and imbrication from SE or SSE to NW or NNW; i.e. from hinterland to foreland. The tectonic transport vector is in congruent with the mean orientation of slickenline striae formed by layer-parallel slipping along folded bedding planes, which is found to be N25OW–S25OE. Overprinting of the widespread NW to NNW stretching lineations to the infrequent WSW stretching lineations reveals that Wadi Fatima FAT belt underwent a WSW transportation pre-dating the main transportation towards the NW to NNW direction.
Two tectonic models or scenarios are proposed to elucidate the structural history of the study area and to illustrate the tectonic evolution of Wadi Fatima FAT belt which represents one of interesting foreland FAT belts recorded worldwide. In the first model, the area was evolved from dextral shearing during the early convergence and amalgamation between East and West Gondwana, to emplacement of the older granite during a period of crustal cessation and relaxation, NNW-SSE extension and extrusion of dyke swarms, emplacement of younger granite, deposition of Fatima Group over an ancient peneplain, layer parallel shortening, folding and fold tightening and overturning, thrusting, NE-SW (to NNE-SSW) shortening, and eventually NE tilting accompanied with Red Sea rifting (?). The second model suggests the presence of basement ramps (pre-existing normal faults), with NW to NNW dipping, have a strong effect on overlying Fatima Group which was evolved throughout gravitational, soft-sediment slumping and deformation. |
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Supervisor |
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dr.. Zakaria Hamimi |
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Thesis Type |
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Master Thesis |
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Publishing Year |
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1433 AH
2012 AD |
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Co-Supervisor |
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Dr. Mohammed Ibrahim Matsah. |
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Added Date |
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Sunday, June 24, 2012 |
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Researchers
| ماجد مُحَمَّد الجَبَلِي | Al-Gabali, Majid Mohammed | Researcher | Master | |
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