## 6 Discussion
### Tectonic Setting
Thus, the volcanic rock assemblages and characteristics in the Fuyun-Qinghe area during the Early-Middle Devonian were quite similar to those of the Taitao Ridge and Taitao Peninsula. Combined with the arc rock assemblages and characteristics and the three magma sources mentioned above, it is speculated that the Fuyun-Qinghe area, the southern margin of the Chinese Altay, could be in a tectonic setting of PAO ridge subduction, while predecessors called the ocean the Junggar Ocean. The Chinese Altay also featured the presence of Alaska-type mafic-ultramafic complexes and dikes from the Devonian period (Early and Late Devonian) [2; 23], and the Middle Devonian Beitashan Formation picrite was found in Qinghe County [82; 102]. Furthermore, the Fuyun Suppute area developed Middle Devonian Altay Formation bimodal volcanic rocks [103]. The Ashele Formation bimodal volcanic rocks, as well as the Early Devonian bimodal intrusive rocks in the Habahe area, are also significant [88]. The widespread occurrence of ~400 Ma granites with positive \(\epsilon\)Hf(t) values, coupled with high-temperature, low-pressure metamorphism around 390 Ma [104], further supports the likelihood that the Chinese Altay was influenced by the PAO ridge subduction during the Devonian (see Figure 15). Therefore, this paper proposes the following model, based on the current distribution of rock types and potential tectonic positions, and the research by [PERSON] et al. [31]. The nature of the PAO slab is illustrated in Figure 15 The rock types and potential tectonic positions encompassed adakite, which was formed on both sides of the slab window, mafic-ultramafic complexes and dikes resulting from near-trench magmatism, as well as nascent serpentinite, HMA, boninite, picrite, MA, adakite, NEAB, and A-type granite, all derived from complex magmatism during normal arc subduction. Additionally, there were bimodal magmatic rocks formed by back-arc magmatism and alkaline basalt, among others. These represent the magmatic activities occurring in various positions within the subduction zones during this period, including young oceanic crust subduction, mid-ocean ridge subduction, near-trench magmatism, and back-arc magmatism. However, more in-depth and detailed studies are needed on the scope of the ridge and the matching of its components, such as the spatial distribution of ophiolite, bimodal volcanic rocks, and even alkaline series and calc-alkaline series rocks. This study combines the collected samples with previous geological data to preliminarily map the spatial distribution of the Devonian igneous rocks related to ridge subduction in the Fuyun-Qinghe area (Figure 15). In the northwest, the region features Suppute bimodal volcanic rocks, Kuerti back-arc basin ophiolites, and Maizi alkaline basalts generated by back-arc magmatism [105; 103; 22]. Moving southward, the region exhibits near-trench magmatic activities and slab window processes, manifested by picrites, boninites, HMA, nascent ophiolites, and A-type granites in areas such as Qiaoxiahala-Laoshankou-Buergen [106; 107; 108; 100; 101; 106; 107; 108]. The spatial distribution pattern of the aforementioned igneous rocks suggests that the northwest portion of the study area experienced back-arc magmatism during this geological interval, whereas the southeastern region was situated in proximity to the trench and concurrent development of a slab window. The distributional characteristics of adakite and NEAB may indicate the edges of the developing slab window. Notably, the inferred locations of  
Figure 15: The spreading ridge subduction model and its magmatism in the Fuyun–Qinghe area (modified after [31]). the mid-ocean ridge magmatic activity, which are primarily based on the current spatial distribution of volcanic rocks, may not fully represent the configuration of magmatic processes during this period. This discrepancy arises from potential post-magmatic tectonic reworking and/or the incomplete preservation of volcanic records in the study area.