ABSTRACT
All the geothermal provinces over the landmasses around the Red Sea evolved due to the dynamic tectonic, plutonic and volcanic processes that have been operating since the Precambrian. The intensity of these processes was at its peak between 31 to 25 Ma (Bosworth et al., 2005) and these activities are still continuing at present (Moufti et al., 2013, Duncan and Al-Amri, 2013, Hamlyn et al., 2014, Koulakov et al., 2014, 2015). The Arabian-Nubian Shield (ANS) was formed due to the accretion of island arcs and an oceanic plate which were generated due to plume activity (Gass, 1981). The contacts of these separated crustal blocks are represented by suture zones enclosing ophiolite assemblage of rocks. These suture zones and the ophiolites are part of the regional mega sutures representing the convergence of the East-West Gondwana during the Pan-African tectonic regime (900-550Ma) (Gass, 1981, Bakor et al., 1976, Rogers et al., 1995, Stern, 1994). This Neoproterozoic Arabian-Nubian Shield was later separated into the Arabian and Nubian shields by later tectono-magmatic events that gave rise to the formation of the Red Sea at around 31-25Ma (Cochran andMartinez, 1988). The initiation of the Red Sea rift and subsequent formation of the Red Sea was triggered by the onset of volcanism over Eritrea and Afar sea floor spreading and giving rise to the East African Rift system. Basaltic and rhyolitic magmatism dominated Djibouti and Republic of Yemen. In Egypt, volcanism is represented by the Mesozoic and Tertiary basalt flows and dikes (Siedner, 1973, Meneisy and Kreuzer, 1974). The western coast of Saudi Arabia also experienced volcanic activity due to the opening of the Red Sea, represented by dike swarms, which intruded parallel to the coast with an outpouring of lava that gave rise to volcanic centres that are known as harrats. Volcanic activity in these harrats is still continuing (Koulakov et al., 2014, 2015). The Al Madinah basalt flows in Saudi Arabia, recorded the youngest K/Ar and Ar/Ar ages of 1.7Ma (Moufti et al., 2013, Duncan and Al-Amri, 2013) and volcanic activity in this region continued till 1256 AD (Bosworth et al., 2005, D’Almeida, 2010). Volcanism is still active in all the countries around the Red Sea (Brown, 1970, Bayer, et al., 1989, Moufti et al., 2013, Chandrasekharam et al., 2014c). The initial
rifting of the Red Sea followed the Arabian-Nubian tectonic fabric initiated by plume related volcanism towards the southern part of the Red Sea and migrated north giving rise to the Red Sea. This activity initiated between 31 and 25Ma and was followed by sin-rift intrusive activity represented by dike swarms (Bosworth et al., 2005). This Red Sea tectonic activity resulted in an outpouring of basaltic lavas over the western Arabian Shield, giving rise to large volcanic fields or centres, which are known as “harrats’’. A thinning of continental crust and high heat flow values along the coast generated large volumes of granitic melts that intruded the Precambrian basement as well as the volcanic flows along the Arabian Shield. These post tectonic granitic intrusives are enriched in uranium, thorium and potassium. The entire tectono-magmatic activities around the Red Sea gave rise to several geothermal provinces over all the continents surrounding the Red Sea, represented by thermal springs with very high issuing temperatures and fumaroles in several locations in Eretria, Djibouti, Ethiopia, Republic of Yemen and Saudi Arabia (Figure 4.1).
