Early Paleozoic large-scale subduction retreat and slab rollback revealed by mafic arc magmas in the southern Central Asian Orogenic Belt

Early Paleozoic arc magmas are prominent along the northern margin of the Tarim–North China collage in the Central Asian Orogenic Belt, yet their petrogenesis and tectonic implications remain unclear. This study focuses on mafic arc rocks from the Kalatashtagh area, NW China, revealing that they formed between 450 and 420 Ma. Whole-rock compositions resemble high-Al arc basalts. Slab traces document that approximately 5% slab-derived sediment melt contributing to a depleted mantle source. Thermodynamic–geochemical modelling indicates that these magmas resulted from 20% melting of garnet lherzolite at about 120 km, followed by fractional crystallization of clinopyroxene, olivine, spinel and plagioclase. These findings, combined with regional data, suggest a continental arc extending over 1500 km along the northern margin of the collage during this period. Geochemical evidence indicates that slab-derived sediment melts predominated over hydrous fluids in the sub-arc mantle wedge. It probably resulted from high slab surface temperatures owing to asthenosphere upwelling induced by slab rollback. The process was also responsible for rifting of marginal terrains and the formation of back-arc basins along the northern margin of the Tarim–North China collage. This retreating-type subduction zone may globally connect to form a girdle, facilitating prolonged dispersal of Gondwana and opening of the Palaeotethys.