## 5 Discussion
### Petrogenesis of Baiyinhushuo Granitoid  
The Baiyinhushuo granodiorite, with high Sr content and Sr/Y and La/Yb ratios, is a typical adakite (Figure 7), which has special geodynamic significance [37]. In recent years, a large number of adakites of the Late Permian-Early Triassic have been discovered in the southeastern section of the Central Asian Orogenic Belt; they are distributed along the Xar Moron River suture zone [7; 14; 19]. Currently, there are three views on the geological \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Scheme 87.**} & **Rb** & **Sr** & **Sr** & **Sr** & **Sr** & **Sr** & **Sm** & **Nd** & **Sr** & **Sm** & **Nd** & **Nd** & **Nd** & **Nd** & **Nd** \\  & **(**ug/g**)** & **(**ug/g**)** & **(**2o**)** & **(**2o**)** & **(**2o**)** & **(**2o**)** & **(**2o**)** & **(**2o**)** & **(**2o**)** & **(**2o**)** & **(**2o**)** & **(**2o**)** & **(**2o**)** & **(**2o**)** & **(**2o**)** \\ \hline HSI7-09 & 60.98 & 509.54 & 0.3466 & 0.70508 & 0.703882 & 2.83 & 15.23 & 0.1122 & 0.512900 & 0.512721 & 5.10 & 7.72 & 387 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Sr-Nd isotopic compositions of the representative samples for the Baiyinhushuo pluton. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Spot**} & **t (Ma)** & **Sr** & **Sr** & **Sr** & **Sr** & **Sr** & **Sr** & **Sr** & **Sr** & **Sr** & **Sr** & **Sr** & **Sr** & **Sr** & **Sr** \\ \hline HSI7-05-10 & 242.8 & 0.012445 & 0.000207 & 0.000465 & 0.000006 & 0.283006 & 0.000017 & 8.28 & 13.5 & 343 & 405 & \(-0.99\)background of the adakite on both sides of the Xar Moron suture zone: one suggests that they derived from the remelting of the juvenile lower crust [7, 8, 14, 15]; one suggests that subducted slabs broke off, and the remaining slabs in the mantle melted and interacted with the mantle [16]; and another viewpoint suggests that the Triassic adakites were caused by plate subduction of the oceanic crust [17]. The Mg\({}^{\#}\) of adakite is an important parameter for determining the origin of magma, and experimental petrological studies have confirmed that the Mg\({}^{\#}\) formed by the partial melting of dehydrated basaltic rocks is usually lower than 45 [38]. High-Mg adakitic rocks are generally believed to be formed by partial melting of the thickened lower crust after detachment and interaction with mantle peridotite [39], or by melting of the subducted oceanic crust and interaction with the mantle wedge [40]; some scholars also believe that they are formed by the mixing of mantle-derived basic magma and crustal acidic magma [41]. The Mg\({}^{\#}\) of the Baiyinhushuho adakite ranges from 46.73 to 61.78, with an average value of 56.14, which is higher than that of the adakite formed by the partial melting of the MORB, and is also higher than that of the adakite derived from lower crustal melting, such as the Mg\({}^{\#}\) of the adakites, which ranges from about 35.72 to 46.16 and is formed by underplating in the North China Craton [42, 43, 44]. In the MgO-SiO\({}_{2}\) diagram (Figure 8), the samples fall in the field of subducted slab-derived adakitic rocks, indicating that the source of Baiyinhushuho adakite is subducted slab of CAOB. In addition, the adakites derived from the thickened lower crust are often Na-rich and K-poor and belong to the peraluminous magma [45], while the adakites of Baiyinhushuho have K-rich and Na-poor characteristics, making them different from the adakites derived from the lower crust. The high-Mg adakitic adesite of the Middle Triassic (244 Ma) was also discovered in the adjacent Linxi region, which derived from the partial melting of the remnant oceanic slab preserved in the mantle of the subduction zone [46] and is similar to the geochemical characteristics of the Baiyinhushuho adakite. Therefore, we believe that the Baiyinhushuho adakite was most likely generated by the partial melting of subducted oceanic crust.