Deformed dike swarms as an implication of transpression deformation in Western Arabian shield, Wadi Fatima, Saudi Arabia
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ORIGINAL PAPER
Deformed dike swarms as an implication of transpression deformation in Western Arabian shield, Wadi Fatima, Saudi Arabia Mohamed I. Matsah 1 & Haitham M. Baggazi 1
&
Abdelhamid El Fakharani 1,2 & Mohamed K. El-Shafei 1,3
Received: 26 February 2018 / Accepted: 19 November 2018 / Published online: 26 November 2018 # Saudi Society for Geosciences 2018
Abstract Utilization of satellite images and field observations of dike swarms in pre-Fatima basement show that these dikes are older than the overlaying Fatima Formation. Dikes digitization and orientation analysis on satellite images show that the prevailing trend of the dikes is ENE-WSW. The granitic rocks of pre-Fatima basement and its hosted dikes expose evidences of completely a different deformation regime from the overlaying Fatima Formation. These evidences include shearing, dextral shear indicators, isoclinal folds, deflection and rotation of crystals, mineral elongation, and mylonitic and gneissose textures. Strain analysis results of using Fry method on quartz and feldspar grains support the presence of deformation in these ENE-WSW dikes. These results gave a strain ratio of 2.1:1.3:1, which suggest an amount of 40% stretching in the ENE-WSW direction parallel to the dike walls, and an amount of 30% shortening in the NNW-SSE direction. Mesoscopic and microscopic scale structures confirm the existence of dextral ductile-brittle shearing followed the emplacement of the dikes and before the pure shear deformation that caused the thrusting and folding of Fatima Formation. This ductile-brittle deformation is correlated with the dextral transpression that formed the Fatima Shear Zone (FSZ). Keywords Strain analyses . Folded dikes . Pre-Fatima basement . Tectonics of Arabian-Nubian shield . Simple shear . Transpressional deformation . Fatima shear zone
Introduction The Arabian-Nubian Shield (ANS) formed as a result of island arcs and continental fragments amalgamation during the closing of the Mozambique Ocean about 870–630 Ma (Stern 1994; Johnson et al. 2011; Abd-Allah et al. 2014). The amalgamation resulted in shortening that caused thickening and shearing of the ANS crust (Johnson et al. 2011; Abd-Allah et al. 2014), and was followed by N-S and/or NW-SE BIntra-
* Haitham M. Baggazi [email protected] 1
Department of Structural Geology and Remote Sensing, Faculty of Earth Sciences, King Abdulaziz University, P.O. Box 80206, Jeddah 21589, Saudi Arabia
2
Geology Department, Faculty of Science, Aswan University, Aswan, Egypt
3
Geology Department, Faculty of Science, Suez Canal University, Ismailia, Egypt
continental extension.^ Results of the extension include crustal thinning of the ANS, magmatism, and intrusion of generally subvertical dike swarms (Genna et al. 2002; Johnson et al. 2011; Abd-Allah et al. 2014). The dike swarms occur in linear and curved shapes and show variations in thickness and length (Genna et al. 2002). Subvertical NW-SE transform faults, Najd Faults System (NFS), controlled the magmatism (Brooijmans 1999; Genna et a
