## 2 Geological Setting and Petrographic Characteristics  
The CAOB is one of the largest and best-preserved Phanerozoic accretiony orogenic belts, and it is separated by the Siberian Craton to the north, Tarim-North China Craton to the south, and the Baltic Craton to the west (Figure 1a). It was formed by the accretion and amalgamation of microcontinents, magmatic arcs, accretionary complexes, seamount and oceanic plateaus, and ophiolitic melanges during the period from the Neoproterozoic to the Late Permian [1; 2; 24; 25; 10; 26]. The Chinese Tianshan is located in the southwest part of the CAOB and extends from east to west for about 1500 km and is bordered by the Tarim Craton in the south and the Junggar Terrane in the north. It can be subdivided into four parts, namely, the North Tianshan Accretiony Complex (NTAC), Kazakhstan-Yili Block (KYB), Central Tianshan Block (CTB), and South Tianshan Accretiony Complex (STAC), which are separated by the North Tianshan Suture, North Nalati Suture, and South Central Tianshan Suture, respectively (Figure 1b). The NTAC is mainly composed of the Devonian-Carboniferous turbidites and the ophiolite component, which was formed by the southward subduction of the North Tianshan Ocean in the Late Paleozoic [19; 27; 28; 29]. The STAC was formed by the northward subduction of the South Tianshan Ocean in the Paleozoic and it mainly composed of lower Cambrian to Carboniferous sedimentary rocks,ophiolites and metamorphic rocks [28; 30; 31]. KYB and CTB are two major microcontinents with Precambrian metamorphic basements in the westernmost of the Chinese Tianshan. The YB, an important Precambrian continental fragment in the southern limb of the Kazakhstan collage system, is a triangular area that extends westward into Kazakhstan, and it is bordered by the North Tianshan Suture to the north and North Nalati Suture to the south (Figure 1b). The Precambrian rocks are mainly exposed in the north and south margin of YB, and unconformably overlain by the Paleozoic sedimentary and volcanic rocks, which are intruded by the voluminous Ordovician-Permian granitidis [11; 28; 31; 34; 35; 37; 38]. The Precambrian rocks mainly outcrop in its northern and southern margins discontinuously, for example, the amphibolite, migmatite, quartztite, marble, and various schist in the Wenquan and Sayram areas [34]. The Cambrian-Silurian rocks consist mainly of cherts, siltstones, carbonates, felsic pyroclastic rocks, and normal clastic sedimentary rocks, and outcrop mainly in the Boluoken Mountain and the sedimentary sequences are complete, although the exposed area of Cambrian-Ordovician strata is limited. Late Paleozoic to Mesozoic strata have wide distribution in the YB and is characterized by sandstone, siltstone, and shale interbedded with volcanic rocks [35]. As mentioned above, volumes of Paleozoic magmatic rocks including both volcanic and intrusive rocks distribute along the north margin of YB, but the Late Silurian to Early Devonian magmatism is poorly reported. The study area is located in southern region of the Boertala River, Wenquan County. The Proterozoic strata are widely distributed along the Biezhentao Mountain, and the Neoproterozoic greissic granites were recognized in the Wenquan Complex (Figure 1c). The Precambrian strata are overlain unconformably by the Paleozoic rocks and they are intruded by the Paleozoic plutons. As shown in the geological map of Baskan Pass-Huocheng Sheet, the Late Paleozoic strata distribute in the Haerdaban area and mainly comprise sandstone, conglomerate, and limestone, which was originally divided into Upper Devonian and Low Carboniferous [34]. Recently, our investigation found that volcanic rocks can be recognized in the Agutu area (Figure 2a) and Buergasite area (Figure 2b), which includes rhyolite, rhyolite porphyry, and rhyolitic tuffs. The outcrops  
Figure 1: (**a**) Simplified map of the Central Asia Orogenic Belt and the location of the Tianshan orogen (modified after [32]). (**b**) Simplified geological map of the Chinese Tianshan belt (modified after [33]).