TERTIARY EXTENSIONAL FAULTING AND STRATIGRAPHY IN THE HAMD-JIZIL HALF-GRABEN ALONG THE CENTRAL RED SEA RIFT SYSTEM IN SAUDI ARABIA

Many fundamental processes that govern continental rifting and that ultimately lead to rupturing of continental lithosphere and the birth of an ocean remain poorly understood. The Tertiary Red Sea-Gulf of Suez rift system is one of the best-exposed and studied examples of continental rifting and has significantly contributed to our understanding of rupturing modes and mechanisms of continental lithosphere. Significant progress has been made in understanding the plate tectonic framework and modern strain field of this region, as well as the transition from distributed continental extension to sea-floor spreading. However, limited knowledge exists on how extensional strain is spatially and temporally distributed on the adjacent continental margins. This study focuses on the development of extensional structures, syn-extensional sedimentary deposits, and rift-related Tertiary basaltic volcanism along the central flank of the rift system in Saudi Arabia. Initial work has focused on a series of structurally-controlled extensional basins inboard from the coastal escarpment that parallel the trend of the main Red Sea rift and demonstrate extensional faulting well inboard from the modern rift margin. The most prominent extensional basin is the NW-trending Hamd-Jizil basin located north of Medinah (~130 km inland), measuring ~200 km along strike and up to 20 km in width. The Hamd-Jizil basin is structurally characterized by two half-grabens exposing a series of syn-rift sedimentary sections below Tertiary basalts; the half-grabens are kinematically linked by soft accommodation zones that exploit basement anisotropies. These Hamd-Jizil basin sediments consist of numerous sandstone and conglomerate successions that rest unconformably on saprolitized metavolcanic and granitic Neo-Proterozoic basement rocks. The siliciclastic strata thicken to the NE where they are juxtaposed against basement along NW-striking normal faults. The basin fill is unconformably overlain by coarse Tertiary gravels and voluminous and regionally extensive flood basalts that are cut by normal faulting as well. Thermochronometric efforts to elucidate the cooling history of exhumed footwall and hanging wall blocks on either side of the Hamd-Jizil basin and geochronological analyses of flood basalts are currently in progress.