## 6 Discussion
### Petrogenesis of the Jabal Al Bayda Granitic Magma  
Several models have been postulated to explain the petrogenesis of the granitic rocks in the ANS. These alternative models include (1) the fractional crystallization model, as proposed by [54; 55; 56; 57], and other researchers, which suggests that the granitic rocks in the ANS formed through the process of fractional crystallization of mantle-derived magmas; (2) the magma mixing model, as suggested by [58], which proposes that the granitic rocks in the ANS formed through mixing of felsic and mafic magmas; and (3) the partial melting model, as proposed by [59; 60; 61; 62; 63; 64], and others, which suggests that the granitic rocks in the ANS formed through partial melting of either an ancient, enriched lithospheric mantle or a relatively young and less evolved crust. By examining the geochemical characteristics of the Jabal Al Bayda granitic rocks, it would be possible to assess which of these alternative mechanisms best explains their petrogenesis. The high silica contents (average of SiO\({}_{2}\) is 68 wt% and 76 wt% for monzogranites and alkali granites, respectively) and enriched and fractionated LREE patterns observed in the Jabal Al Bayda monzogranites and alkali granites are inconsistent with a model of fractional crystallization of mantle materials. The Rb/Sr ratio is a geochemical indicator that can be used to distinguish between mantle-derived magmas and those derived from continental crust. Mantle-derived magmas typically have very low Rb/Sr ratios (Rb/Sr \(<\) 0.1; [65]), while continental crustal rocks tend to have higher Rb/Sr ratios [66]. In the case of the Jabal Al Bayda granitic rocks, the average Rb/Sr ratios of 0.53 for the monzogranites and 10.51 for the alkali granites, as reported in Tables 1 and 2, are higher than the Rb/Sr ratios expected for mantle-derived magmas. These elevated Rb/Sr ratios are more consistent with a continental crustal source rather than a mantle source (Figure 9a). The Nb/Ta ratios and Y/Nb ratios further support the model of the Jabal Al Bayda granitic rocks originating from the partial melting of a relatively juvenile crust. Mantlederived rocks typically exhibit higher Nb/Ta ratios (>17.5), whereas continental crustal materials have lower Nb/Ta ratios (<17.5) (66,67). In the case of the Jabal Al Bayda granitic rocks, the average Nb/Ta ratios of 13.40 for monzogranites and 13.66 for alkali granites, as reported in Tables 1 and 2, are consistent with crystallization from crustal-sourced magmas rather than mantle-derived sources. Additionally, the Y/Nb ratio can also help in distinguishing between magmas derived from the mantle and those derived from the continental crust. Mantle-derived sources typically have low Y/Nb ratios (<1.2), while crustal sources exhibit higher Y/Nb ratios (>1.2) (2). In the case of the Jabal Al Bayda granitic rocks, the average Y/Nb ratios of 2.46 for monzogranites and 1.48 for alkali granites, as reported in Tables 1 and 2, are consistent with a crustal source rather than a mantle source. The absence of significant evidence of magma mixing in the petrography of the Jabal Al Bayda granitic rocks indeed suggests that magma mixing may not have played a prominent role in their formation. Additionally, the consistent chondrite-normalized REE and trace element patterns observed in all the studied samples, as depicted in Figure 7, further support the idea that the granitic rocks at the Jabal Al Bayda were not formed through a magma mixing process. Figure 9: \(Cont.\)  
As already mentioned, the geochemical compositions of the Jabal Al Bayda granitic plutons show an evolutionary trend from high-K calc-alkaline to alkaline (shoshonite series) types. In the discrimination diagram by [68], the shoshonite series of the alkali granites and monzogranites are plotted as A-type (Figure 9b-d). The high-K calc-alkaline to shoshonite monzogranites are plotted in A-type field and extend into the fractionated felsic I/S/M-granites field.