## 1 Introduction  
The CAOB is the largest Phanerozoic accretionary orogenic belt in the world, documenting the subduction and extinction history of the PAO Plate [1, 2, 3]. Over its extensive geological history, the expansion, subduction, closure, and extinction of the PAO have profoundly influenced the CAOB. The Chinese Altay, located in northern Xinjiang Province, is a crucial component of the western section of the CAOB. Its complex multi-stage tectonic evolution and extensive magmatism-tectonism-mineralization have been a hot topic for global researchers. It is generally accepted that the PAO began subducting during the Neoproterozoic to Early Paleozoicic [4; 5; 6; 7], with the most intense subduction occurring in the early Late Paleozoic. The closure time of the western segment of the PAO remains contentious, with proposed dates ranging from the Late Devonian [8], Early Carboniferous [9], Late Carboniferous or Permian [10; 11; 12; 13], Late Permian to Triassic [14], to the Middle to Late Triassic [15; 16]. Thus, at the latest, the western part of the ocean closed during the Middle to Late Triassic. The Chinese Altay was undoubtedly influenced by the evolution of the PAO during the Late Paleozoic. Most scholars agree that the PAO was in a subduction stage during this period [17; 18; 19]. However, debates persist regarding the specific subduction setting and the nature of the PAO slab. For instance, [PERSON] et al. [20] proposed that the Devonian volcanic rocks formed in an island arc setting with varying degrees of maturity, transitioning to an intraplate setting in the Permian. [PERSON] et al. [21] suggested that the eastern Junggar and southern margin of the Chinese Altay were in an island arc setting during the Early and Middle Devonian, followed by a collision setting in the Late Devonian, post-collision in the Early Carboniferous, and intraplate extension from the late Early Carboniferous to the Late Carboniferous. [PERSON] et al. [22] studied the ophiolites in the Kurt area and concluded that they were the products of a Late Paleozoic back-arc basin system. [PERSON] et al. [19] proposed that the Early Devonian Xiaodonggou granites in the Kelan basin formed in an active continental margin arc setting. [PERSON] et al. [17] found volcanic rocks with diverse source characteristics in the limited Devonian strata on the southern margin of the Chinese Altay, attributed to the complex accretion and tectonic processes during the Devonian to Carboniferous. Recently, scholars have proposed that ridge subduction could be a new model to explain the Late Paleozoic subduction processes in the Chinese Altay, based on studies of mafic complexes and veins [2; 23], basalts and dacites [24], gabbros [3], and granites [25]. They posited that ridge subduction played a significant tectonic role in the evolution of the Altay Orogenic Belt. The ridge subduction model has gained attention in recent years, exemplified by the Chile Trench (the Nazca-Atlantic-South American ridge-trench-trench triple junction [26; 27]), southern Alaska, western California [28] and so on (Figure 1). Mantle convection causes upwelling at the ridge axis, driving mid-ocean ridge expansion and crust formation. The basaltic oceanic crust formed at the ridge cools and subducts, with magma from the ridge intruding near the trench, marking the onset of ridge subduction [29]. In these regions, ridge subduction generates new magmatic arcs and distinctive rock assemblages with unique geochemical characteristics [26; 27]. [PERSON] et al. [30] proposed ridge subduction in the Chinese Altay and summarized the petrological evidence, though they did not address the spatial distribution of plates, the migration of triple junctions, or the pattern of ridge subduction. The ridge subduction model challenges traditional views on magmatic arcs. Despite its significance, it remains understudied, particularly regarding ancient mid-ocean ridge subduction. Nonetheless, it offers a crucial avenue for exploring extinct ancient oceanic slabs.