## 2 Geological Background  
The Chinese Altay is located in the northern part of the Xinjiang Uygur Autonomous Region, between the Sayan Block to the north and the Junggar Block to the south (Figure 2a). According to [PERSON] et al. [32] and [PERSON] et al. [33], the Altay orogenic belt comprises six blocks (or units) (Figure 2b): the Northeast Altay Block, Northwest Altay Block, Central Altay Block, Qiongkuer-Abagong Block, Irtysh Block, and Buerjin-Ertai Block. The study area is situated in the Buerjin-Ertai Block. Strata in this area were relatively fully exposed, primarily consisting of Proterozoic and Paleozoic strata. The oldest stratum was Paleoproterozoicic Kumuqi Group, while the youngest was Quaternary stratum, Cretaceous strata were generally absent. In the Fuyun-Qinghe area, the major exposed Paleozoic strata included Late Ordovician Baihaba Formation, late Devonian Kangbutiebao Formation, Tuoranggekuduke Formation, Middle Devonian Altay Formation, Beitashan Formation, Ashele Formation, Yundukala Formation, and so on [34]. The Tuoranggekuduke Formation was a series of marine clastic rocks and volcanic sedimentary clastic rocks with lavas, containing brachiopods, corals, trilobites, and some other marine fossils, and this formation can be roughly divided into two lithological sections. The first section developed clastic and pyroclastic rocks, while the second section had more lavas; it was in unconformity contact with the overlying Beitashan Formation, and the lower part had no visible bottom. Previous studies obtained its formation age as the late Early Devonian. The Beitashan Formation was generally a set of pyroclastic rocks,  
Figure 1: Spreading ridge subduction model [31]. Reprinted with permission from ref. [31]. volcanic lavas, and terrigenous clastic rocks, which can be subdivided into two segments. The lower segment was composed of pyroclastic rocks and terrigenous clastic rocks, and the upper segment mainly contained volcanic lavas and pyroclastic rocks with a small amount of terrigenous clastic rocks. It was in conformity contact with the overlying Yundukala Formation, and in angular unconformity contact with the lower Tuoranggekuduke Formation. Previous scholars believe its formation age is the early Middle Devonian. The regional fault structures were well developed, exhibiting multi-stage characteristics. The primary faults included the Irtysh fault and the Kalaxiangeer fault (Figure 2c). The Irtysh fault strikes NW-SE, with a total length of 1500 km. The fault is narrow in the Fuyun-Qinghe area and is dextral strike-slip faulted by the Kalaxinger fault to the east. The eastern section is also called the Mayinebo fault, and the western section is called the Irtysh fault. The Kalaxinger fault, also known as the Ertai fault, is about 200 km in the NNW direction. In the Qinghe area, the fault transforms from the NNW strike-slip fault to the SE-SEE cleavage zone, presenting a large-scale broom structure [34]. Samples in this paper were mainly collected and compiled from the west of the Kalaxianger fault and south of the Irtysh fault. The main fold structures within the Fuyun-Qinghe area encompassed the Mengku composite syncline, the Suput anticline, and the Altay composite syncline, among others. The study area experienced volcanic activities from the Proterozoic to the Cenozoic. Volcanic activities were weak before the Late Ordovician, with the most intense and frequent activities occurring during the Late Paleozoic, particularly in the Devonian. Volcanic activities declined during the Carboniferous-Permian, transitioning from marine to terrestrial facies and becoming more spatially restricted. Sporadic volcanic activities occurred during the Mesozoic to Cenozoic. Extensive magmatic emplacement took place during the Early and Middle Paleozoic (500 Ma to 370 Ma) [32; 34; 35]. Intrusive rocks are widely distributed in the region, predominantly granitoids with minor basic and intermediate rocks.