Red Sea related history of extension and magmatism in the Jizan area (Southwest Saudi Arabia): indication for simple-shear during early Red Sea rifting

Abstract

The tectonic and magmatic history of the Jizan coastal plain of the Red Sea (Tihama Asir) in Southwest Saudi Arabia is dominated by SW-NE extension. This extension manifests itself by a basic dike swarm and several generations of normal faults that trend roughly NW-SE. The oldest synrift deposits are non-marine clastics and bimodal volcanics of the Jizan Group, which were intruded by basic dikes, gabbros and granophyres of the Tihama Asir Magmatic Complex (TAMC). Radiometric ages for the TAMC-rocks range from 26 to 18 Ma. Rifting in the southern part of the Red Sea System therefore is certainly older than 26 Ma. Between 26 and 20 Ma the southwestern Arabian margin was affected by a monoclinal downwarp (flexure). The oldest extensional features in the Jizan area are N-S to NNW-SSE striking dikes and normal faults which were overprinted by other NW-SE striking extension structures. An array of en-echelon extensionzones is linked by complex patterns of transfer faults, mainly WNW-ESE striking dextral strike slip or oblique-slip faults. The observed superposition of dikes and normal faults of different orientations was not necessarily caused by a counterclockwise rotation of the regional stress-field, but more likely reflects the clockwise rotation of individual faultbounded blocks between the two phases of extension. Uplift of the graben shoulder east of the Jizan coastal plain is probably younger than 14 Ma and its development coincides with a major rearrangement of the kinematics along the Red Sea. This new kinematic pattern probably led to the onset of strike-slip movement along the Aqaba-Levant transform. At the same time extension and volcanism ceased in the Jizan area or shifted further to the west. After a long hiatus of about 10 Ma renewed extension facilitated extrusion of alkali-olivine-basalts since 2 Ma ago.