## 5 Disscussion  
### Genetic Type of Granite  
There are various genetic classifications of granitoids [37; 38; 39; 40; 41], and the most popular is the I-S-M-A scheme. M-type granite refers to oceanic plagiogranite. The main types developed in the continental plate tectonic setting are I-type (source rocks are unweathered magmatic rocks), S-type (source rocks are sedimentary rocks), and A-type (unique mineral composition which can reflect the extensional tectonic environment) [42].  
The source rocks of S-type granites are sedimentary rocks, which suffered from weathering during formation, resulting in Na and Ca loss and Al supersaturation. Therefore, peraluminous is a typical feature of S-type granites. However, the most felsic part of I-type granites can also be peraluminous, which contributed to the boundary between I- and S-type to be delineated at ASI = 1.1 [43]. Additionally, the content and variation characteristics of P\({}_{2}\)O\({}_{5}\) are also key indicators for distinguishing S- and I-type granites. The study on Lachlan Fold Belt granites showed that the content of P\({}_{2}\)O\({}_{5}\) was increased with crystallization differentiation in S-type granites and decreased with crystallization differentiation in weakly peraluminous I-type granites [37]. The A-type granites have specific mineralogical and geochemical criteria that differentiate it from I and S-type granites [44]. In terms of petrochemistry, A-type granites are mainly characterized by high SiO\({}_{2}\), high FeO\({}_{T}\)/MgO, high total alkali content, high K\({}_{2}\)O/Na\({}_{2}\)O, high REE (except Eu), Zr, Nb, and Ta abundances, and low CaO, Ba, Sr, and Eu abundances [45; 46; 47].  
In terms of major elements, the LG has the characteristics of strong peraluminum and low CaO content, showing affinities to S-type. However, the extremely low P\({}_{2}\)O\({}_{5}\) content does not conform to the characteristics of S-type, while the P\({}_{2}\)O\({}_{5}\) contents of most of the S-type granites in the Lachlan fold belt were higher than 0.08% [37]. Then, LG may belong to the A-type because strong peraluminum and low CaO content are also characteristics of A-type granite, and the average Al\({}_{2}\)O\({}_{3}\) and P\({}_{2}\)O\({}_{5}\) content of A-type granite are indeed lower than that of S-type granite [37]. Meanwhile, LG has a high FeO\({}_{T}\)/MgO value, ranging from 7.42 to 15.62 with an average value of 11.03, which also fits the characteristics of A-type granite.  
The discrimination of the Na\({}_{2}\)O-K\({}_{2}\)O diagram verifies the above inference (Figure 8, [45]). Most of the data points of LG were plotted in the A-type granite area, and a few fell near the boundary between A-type and S-type, far from the I-type area. In terms of trace elements, enrichment of incompatible elements is a distinctive feature of A-type granites [46]. The discriminant diagrams based on Zr-Nb-Ce-Y-Ga show the prominent features of A-type granites for LG (Figure 9), which contribute to the conclusion that LG belongs to A-type granite.  
Figure 7: Chondrite-normalized REE pattern (**a**) and primitive mantle-normalized multi-element diagram (**b**) for the LG.  
Figure 8: Na\({}_{2}\)O-K\({}_{2}\)O discrimination diagram of the LG.  
Figure 9: Discrimination diagrams to distinguish A-type granitoids. FG—fractionated felsic granites; OGT—unfractionated M-, I- and S-type granites.  
Furthermore, the A-type granitoids can be chemically subdivided into two groups, namely group A\({}_{1}\), which has similar element ratios to oceanic island basalts, and group A\({}_{2}\) which has similar element ratios to average crust and island arc basalts [48]. While LG was subdivided into group A\({}_{2}\) according to the triangle diagram of incompatible elements (Figure 10).