Following a long period of island arc-like orogenic activity, post-orogenic granites of Pan-African age (670-550 m.y.) were emplaced throughout the Arabian Shield. Most of these rocks are typical subsolvus calc-alkaline biotite monzogranite. The early Pan-African granites are associated with widespread small tholeiitic gabbro intrusions, many of which are layered. The calc-alkaline granites are not evenly distributed and their area of exposure relative to other rock types increases from southwest to north and northeast. In the northeastern part of the shield, they are associated spatially with rhyolites of similar composition and with molasse derived from granitic terrane.
The occurrence of 45 late alkali granites, most of which are peralkaline, is described and their chemistry discussed. Most of these rocks are medium- to coarse-grained hypersolvus alkali granites, but phenocrystalline and micrographic varieties are also common. The mafic silicate minerals of the alkali granites are arfvedsonite, aegirine, aegirine-augite, riebeckite, and sparse biotite, aenigmatite, and barkevikite. The alkali granites do not occur in the southwestern third of the Arabian Shield nor in the southeastern portion of the adjacent Nubian Shield of Africa. A syenite-shonkinite province located in the southwestern part of the Arabian Shield is identified.
No economic mineral deposits are known to be associated with the Pan-African granites. Numerous mineral occurrences and geochemical anomalies have been found that contain tungsten, molybdenum, tin, beryllium, zirconium, niobium, thorium, uranium, rare earths, and fluorite. The most important of these occurrences are tabulated and their distribution shown.
