Development of a Modern-Style Trench-Arc-Backarc System in the Proto-Tethys Ocean (Qilian Orogenic Belt, NW China).

This article focuses on the development of a modern-style trench-arc-backarc (TABA) system in the Qilian orogenic belt of northwest China during the Early Paleozoic, documenting the evolution of the Proto-Tethys Ocean subduction. Through petrographic, geochronological (U–Pb zircon dating), and geochemical analyses of ophiolites, arc volcanic rocks, and back-arc basin sequences, the study identifies a three-stage tectonic evolution: (1) initiation of northward subduction and formation of an Andean-type continental arc (~530–500 Ma), (2) tectonic transition with crustal thinning and shift toward a Western Pacific-type margin (~500–490 Ma), and (3) development of a mature Japan-Sea-type back-arc basin with suprasubduction-zone (SSZ) ophiolites (~490–450 Ma). The findings provide evidence for cold, deep subduction characteristic of modern plate tectonics operating by the Early Cambrian and establish the Qilian orogenic belt as a key record of early TABA system formation and Proto-Tethys Ocean closure.