Ductile shear zones in the northern Red Sea Hills, Sudan and their implication for crustal collision

Abstract

In the northern Red Sea Hills. of Sudan, deformation is largely concentrated into a network of shear zones. Several of these zones strike north-south. hut the important Nakasih and Sol Hamid zones are northeast-trending, and there are also minor shear zones which strike east-west. We distinguish between massive shear zones, such as that of Nakasih. and more diffuse braided shear zones. typified by the Oko zonc. The massive type owes its character to an origin a s a reactivated oceanic suture. whereas the braided type was characterized by strikc-slip shearing from its inception. Most of thc shear zone rocks are mylonites formed under greenschkt facies conditions. but early shearing along the Oko zone took place at higher temperature and resulted in gneissose mylonites with amphiholitc facics mineralogy. The northeast-trending. Nakasib shearing appears to have preceded a phase of batholithic intrusion, whereas north-south shearing in the Oko and Abirkitib zones is younger than the batholithic intrusions and is i n turn post-dated by emplacement o f bimodal granite-gabbro complexes. Thcsc cvcnts cannot be dated precisely as yet, but took place between 95 Ma and 700 Ma. and probably towards the end of that interval. The pattern of shear and suturc zoncs in northeast Sudan suggests that the northeast-trending Hijaz and Asir arcs. recognized in Saudi Arabia. terminate to the west against a north-south suture which was later rejuvenated to form the Ahirkitib shear zone. West of this suturc was an immaturc volcanic arc which may have lain along the margin of the African continent. The rejuvenation which caused northeast and north-south strike-slip shear was probably a consequence o f soft collisions in East Arabia.

Controls on lode gold mineralization, Romite deposit, South Eastern Desert, Egypt

“…Elsamani et al (2001) suggested that gold mineralization in the Pan-African domains should be targeted near recognized sulfide concentrations, in collapse zones of extensional basins, within accretionary sutures, and along the shear zones that formed during the 650e550 Ma orogeny. The N-S Hamisana shear zone in the northern Red Sea Hills extends for more than 300 km, with an approximate width of 50 km (e.g., Bellevier et al, 1980;Stern et al, 1989). It contains internal evidence of polyphase ductile shearing followed by brittle deformation (e.g., Almond and Ahmed, 1987).…”

“…The N-S Hamisana shear zone in the northern Red Sea Hills extends for more than 300 km, with an approximate width of 50 km (e.g., Bellevier et al, 1980;Stern et al, 1989). It contains internal evidence of polyphase ductile shearing followed by brittle deformation (e.g., Almond and Ahmed, 1987).…”

Controls on quartzite bearing base-metal sulfide and invisible gold mineralization at Gabal Abu Houdied area, South Eastern Desert, Egypt

“…Goldfarb et al (2001) and Groves et al (2003) reported that, orogenic gold as well as base-metal sulfide deposits are typically formed during late stages of the deformational metamorphic-magmatic history of the evolving orogeny, synkinematic with at least one main penetrative Elsamani et al (2001) gold mineralization in the PanAfrican domains should be targeted near recognized sulfide concentrations, in collapse zones of extensional basins and along the shear zones that formed during the 650-550 Ma orogeny. The GAH area located at the extreme northern portion of the HSZ, this shear zone contains internal evidence of polyphase ductile shearing followed by brittle deformation (Almond and Ahmed 1987). In GAH area structural controls are observed at different scales from a map-scale to a microscopic scale.…”

Quantifying 3D post-accretionary tectonic strain in the Arabian–Nubian Shield: Superimposition of the Oko Shear Zone on the Nakasib Suture, Red Sea Hills, Sudan

“…2). These cross-cutting structures form N-to NNW-trending, 30 km wide complex deformational belt (Almond and Ahmed, 1987;Abdelsalam, 1994).…”

“…2; Abdelsalam, 1994). The intersection of the Oko Shear Zone and the Nakasib Suture forms a $30 km wide belt of complex deformation (Almond and Ahmed, 1987).…”