Geochemical Constraints on the Evolution of Late- to Post-Orogenic Granites in the Arabian Shield, with a Specific Focus on Jabal Al Bayda Area in the Central Hijaz Region, Saudi Arabia

Abstract

The Jabal Al Bayda, located in the Hijaz terrain of northwest Saudi Arabia, comprises magmatic rocks that represent the ending phase in the Precambrian development of the Arabian Shield. Two granitic suites have been studied petrologically and geochemically, the monzogranite and alkali granite suites, to gain knowledge about their origin and geotectonic implications. The geochemical characteristics of the monzogranites align with their formation in a subduction-related environment. These rocks have a composition that is rich in strontium and barium, and low in rubidium, and displays a high-K calc-alkaline to shoshonitic nature. In contrast, alkali granites typically have lower concentrations of Sr and Ba, and higher rubidium contents. The differences in geochemical composition between monzogranites and alkali granites found in Jabal Al Bayda indicate differences in their origin and geotectonic environment. The evolution of granitoid magmatism in the Jabal Al Bayda area is linked to the Hijaz orogenic cycle, during which northwest-dipping subduction led to the formation of the Midyan, Hijaz, and Jeddah arc assemblage, followed by the collision and accretion of these arcs along the Yanbu and Bir Umq sutures. Due to crustal thickening during the subduction-related stage, the deeper parts of the overlying metagraywackes and metatonalites contribute melt to the early crustal magma, which eventually solidifies to form monzogranites. Later on, during the post-orogenic stage, anatexis of metapelites can occur, leading to the generation of magmas that give rise to alkali granites.