## 6 Discussion
### Tectonic Setting
(CAB, calc-alkali basal; IAT, island arc tholeiite; MORB, mid-ocean ridge basalt; WPB, within-plate basalt; N-MORB, normal mid-ocean ridge basalt; E-MORB, enriched mid-ocean ridge basalt; WPT, within-plate tholeiite; WPAB, within-plate alkali basalt; legends are the same as in Figure 7). diverse rock assemblages cannot be solely attributed to a cold and old back-arc basin. In the context of slab break-off, basaltic rocks typically exhibit affinities to both arc basalts and intraplate basalts, accompanied by rock assemblages such as intraplate basalts, A\({}_{2}\)-type siliceous rocks, and contemporaneous bimodal volcanic rocks [99]. Consequently, the geochemical features and rock assemblages of the Early-Middle Devonian volcanic rocks in the Fuyun-Qinghe area do not align with a slab break-off tectonic setting. Ridge subduction can induce ridge-trench interaction and trigger asthenosphere upwelling through slab windows, resulting in particular rock assemblages and geochemical characteristics, such as adakites, NEABs, HMAs, boninites, A-type granites, bimodal volcanic rocks, picrites, and so on [25; 30]. The Taitao Peninsula and Taitao Ridge from the Chile Triple Junction produced the most complete magma products related to ridge subduction from the Neogene to the Quaternary, which provided a typical example and abundant references for studying oceanic ridge subduction in the Chinese Altay. [PERSON] et al. [26] summarized six major ridge and near-trench magmatic activities in the Taitao Peninsula and Taitao Ridge. The four segments of the active oceanic ridge in southern Chile (Seg.1 \(\rightarrow\) Seg.4) were mainly of the MORB type, while the Taitao Ridge was mainly of the MORB type with subduction imprints. In other words, calc-alkaline igneous rocks originated from the asthenosphere below the slab window and the subduction slab at the edge of the slab window. The igneous rocks from the Taitao Peninsula possessed both MORB and MORB with subduction imprint characteristics. The coexistence of the MORB type with subduction imprints and arc CA series rocks in the petrological-geochemical types is uncommon but arises from the ridge-trench interaction during active ridge subduction, plate divergence, and convergence. Similarly, [PERSON] et al. [65] investigated two Pliocene to Pleistocene volcanic-sedimentary units on the Taitao Peninsula, categorizing them into those with MORB affinities, CA (calc-alkaline) affinities, and intermediate characteristics. They proposed that the varying metamorphic overprints resulted from the collision of two distinct ridge segments with the South American margin near the Taitao Peninsula. Additionally, the Bahia Barrientos Ophiolite (BBO), associated with the subduction of the Chile Ridge, is also present in the Taitao Peninsula. The tectonic emplacement of the ophiolites occurred around the same time as the subduction of the Chile Ridge at approximately 6 Ma, with the Taitao Ridge being interpreted as a nascent ophiolite [26]. Our samples included adakite, NEAB, HMA, MA, and sub-bonninite. Some of these rocks exhibited dual characteristics resembling both MORB-like and arc-like features, with the majority being calc-alkaline series rocks, which aligned with the subduction-imprinted MORB and typical calc-alkaline igneous suite found in the Taitao Ridge [26]. Our samples also contained alkaline basalts related to a slab window, potentially indicating the presence of alkaline plateau basalts associated with a deep slab window generated after the cessation stage of arc volcanism (or closer to back-arc position) [66]. In the Mayinebo Ophiolitic Melange belt in the southern part of the study area, previous research had determined the zircon U-Pb ages of gabbros and a pillow basalt within the belt. The gabbros were formed at 404.6 \(\pm\) 2.9 Ma and 403 \(\pm\) 5 Ma, while the pillow basalt was formed at 397 \(\pm\) 6 Ma [100; 101], whose dating results closely align with the ages presented in this study. They might represent near-trench ophiolites analogous to BBO.