Transitions between advancing and retreating subduction regimes at convergent plate boundaries are crucial for understanding the evolution of accretionary orogenic belts. To thoroughly investigate the subduction processes of the North Tianshan Ocean, this study performed integrated whole-rock geochemistry, zircon U-Pb geochronology, and zircon Hf isotope analyses using volcanic rocks from the Bilikexi River section on the northern Yili Block. Detrital zircon U-Pb geochronology was also performed using sedimentary rocks within the study area. The volcanic rocks in the Bilikexi River section formed between 380 and 347 Ma. The detrital zircon U-Pb ages of the sedimentary rocks further constrain the maximum depositional age of the strata in the Bilikexi River area to post-late Devonian. Combined with regional stratigraphic correlations, this study reclassifies the Bilikexi River area strata as the Late Devonian-Early Carboniferous Dahalajunshan Formation rather than the previously assigned Middle Ordovician Nailenggeledaban Formation or Lower Silurian Nilekehe Formation. Geochemical data reveal that the Bilikexi River volcanic rocks exhibit the characteristics of active continental margin arc magmatic rocks. The basaltic andesites originated from the partial melting of a fluid-metasomatized mantle wedge. Dacites were derived from the partial melting of Meso-Neoproterozoic lower crusts with contributions from fluid-modified mantle materials. The rhyolites formed by the partial melting of Meso-Neoproterozoic crustal materials. In addition, based on geochronological mapping and geochemical analysis of Western Tianshan magmatic rocks, it was revealed that the North Tianshan Ocean exhibited different subduction states between ～400-370 and ～370-335 Ma. Based on regional data and analytical results, this study proposes that the North Tianshan Ocean underwent a tectonic transition from advancing to retreating subduction at the end of the Late Devonian (～370 Ma).
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