## 6 Discussion
### Genetic Model  
Overall, the evolution of the ANS during the Pan-African period was marked by intense tectonic activity, magmatic intrusions, metamorphism, and the formation of various geological structures. These processes played a crucial role in shaping the distinctive geological features observed in the AS today and contributed to the formation of mineralized granitic rocks that exhibit significant enrichments of rare metals. The geodynamic transition observed in the Jabal Sayid and Dayheen areas, from subduction-related granodiorite-diorite association to collision-related monzogranite and finally to post-collision or anorogenic peralkaline granites and related pegmaties, can be successfully modeled by considering three distinct magmatic stages:  
1. Subduction-related magmatism: During this stage, the early mafic magma produced subduction-related granodiorite-diorite in the early stage of underplating. This mafic magma, likely derived from the subducting oceanic lithosphere, interacted with the overlying continental crust. The interaction resulted in the production of subduction-related granodiorite-diorite (Figure 16A). This stage represents the initial phase of magmatic activity related to subduction. Slab breakoff can lead to a change in subduction dynamics and the cessation of subduction-related magmatism. Subduction initiation and the formation of arc terranes occurred between 870 and 620 Ma [10]. 2. Collision-related magmatism: As the tectonic processes continued, crustal thickening occurred in the region, and consequently the subducted oceanic slab broke off (Figure 16B). The deeper portions of the overlying crust, composed of metatonalites and graywackes, were subjected to increased pressure and temperature conditions. These conditions brought these rocks above their solidus temperatures, leading to partial melting. The resulting melt contributed to the early mafic magma, giving rise to a new generation of intermediate magma that produced monzogranites. Ref. [6] reported zircon U-Pb ages of 625 \(\pm\) 11 Ma for the hornblende-biotic granite and 613 \(\pm\) 4 Ma for the monzogranite in the core of the Dayheen ring complex. These ages suggest that the monzogranite is younger than the rimmed hornblende-biotic granite. This age relationship contradicts the interpretation based on the present geochemical results, which suggest that the monzogranite is related to the collision stage, while the hornblende-biotic granite formed later in a post-collision stage. This implies that the monzogranite in the core of the ring complex is indeed older than the peralkaline rocks in the rim, consistent with the geological fact that the monzogranite was emplaced earlier than the rimmed granitic rocks, as stated by [56]. 3. Post-collision magmatism: The geochemistry and previous geochronology show that the Dayheen and Jabal Sayid rare-metal-bearing peralkaline granites and related pegmaties were probably generated in a post-collision extensional setting. During this stage, anatexis, or partial melting, took place in the crustal material, leading to the generation of a new magma, which produced peralkaline granites and related pegmaties (Figure 16C). The magma composition was likely influenced by progressive chemical fractionation processes, which caused the development of peralkaline A-type granites and related pegmaties. The development of the Najd fault system is believed to have facilitated the ascent of magmas and the formation of peralkaline granitoids within the AS [9; 57; 58; 59; 60; 61]. This fault system provided pathways for the upward migration of magmas from deeper levels to shallower crustal levels, where they eventually crystallized and formed peralkaline granitoids. The extensive crystal lization and differentiation processes that occur during the emplacement and cooling of post-collision granite magma can lead to the enrichment of rare metals and other related elements in the Jabal Sayid and Dayheen areas.