Late Paleozoic Reconstruction of Trench Migration in the Western Central Asian Orogenic Belt: Implications for Geodynamics of the Kazakhstan Orocline

Abstract The Central Asian Orogenic Belt is characterized by several large‐scale oroclines, whose formation has been linked to along‐strike variations in trench migration. However, establishing a genetic relationship between oroclinal bending and trench migration remains challenging due to strong overprinting of subduction‐related records by subsequent collisional orogeny. In this study, we reconstruct trench migration patterns around the Kazakhstan Orocline using crustal thickness proxies to investigate how spatial and temporal variations in trench migration interacted with oroclinal bending. Our analysis of Devonian to Carboniferous detrital zircons from sedimentary rocks in the southern and northern limbs of the Kazakhstan Orocline (West Junggar and Chinese West Tianshan) reveals that these zircons were predominantly derived from proximal magmatic arcs associated with the subduction of the Junggar Ocean. Zircon‐based crustal thickness proxies (LREE/HREE, Ce/Yb and Dy/Yb ratios) indicate a tectonic transition in the West Junggar from slab rollback (∼390–360 Ma) to trench advance (∼360–323 Ma). In contrast, the Chinese West Tianshan records an early phase of trench advance (∼390–355 Ma), followed by the trench retreat (∼355–323 Ma). Integrating these findings with the kinematic history of the Kazakhstan Orocline, we propose that the southern limb of the orocline was stabilized by an advancing double subduction system beneath the Yili Block, while simultaneous trench retreat in the West Junggar facilitated bending of the subduction system and clockwise rotation of the northern limb. Our study underscores how trench retreat governs the curvature of subduction systems, shedding new light on oroclinal bending processes in accretionary orogens.