Chapter 26 Distribution Pattern and Provenance Implications of the Heavy Minerals in Neoproterozoic to Mesozoic Siliciclastic Successions in the Arabo-Nubian Shield and its Northern Periphery: A Review

Following the consolidation and erosion of the Arabo-Nubian Shield (ANS) in the Neoproterozoic, extensive siliciclastics were deposited above it and along its northern margins. These sediments consist of two thick successions, which are separated by an erosional surface representing a regional peneplain. They comprise Neoproterozoic-Early Cambrian orogenic, molasse-type, immature conglomerates and arkoses, and a Palaeozoic to Early Mesozoic succession of platformal, mature sandstones. The heavy mineral contents generally parallel those of the major framework components, e.g., a prevalence of unstable species in the lower, and dominantly ultrastable minerals in the upper succession. This maturation is controlled by provenance and chemical weathering at the source, during transportation or both. Environmental and climate changes are indicated by the presence or absence of detrital apatite, which disappears in the Late Palaeozoic and onward, reacting to acidic weathering in a warm climate, and in the abundance of garnet in the Middle Ordovician to Early Silurian successions due to colder climatic conditions with limited weathering. Authigenic apatite is present locally and is formed at a later phase, as a result of fluid migration during the early stages of the Tertiary Dead Sea Rift. The following three provenance-controlled heavy mineral suites may be distinguished. (1) An unstable heavy mineral assemblage of the Neoproterozoic immature, siliciclastic deposits, derived mostly from a Pan-African igneous/metamorphic terrain within the ANS. This records only mechanical abrasion and a short-distance of transport. (2) An ultrastable/stable heavy mineral assemblage of the Early Palaeozoic, mature, siliciclastic successions, derived mostly from Pan-African and older crust outside the ANS (interior of Gondwana), but with intermittent input from locally exposed basement rocks of the ANS. This assemblage underwent mainly chemical weathering over a long transport distance. (3) An ultrastable heavy mineral assemblage of the Late Palaeozoic-Early Mesozoic mature, siliciclastic sediments, sourced mostly from reworked older internal siliciclastics, and from beyond the ANS, but which also incorporate detritus from extensive exposures of the ANS basement. They were affected by chemical weathering and experienced long to moderate transport.