Supplementary Materials for "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, along with rifted terrains and back-arc basins, are prominent along the northern margin of the Tarim-North China collage in the Central Asian Orogenic Belt (CAOB). However, their petrogenesis and tectonic implications remain elusive. Mafic arc magmas may provide insights into the thermal state of subducted slabs and subduction zone dynamics. This study examines the petrogenesis and tectonic implications of these magmas, focusing on arc mafic rocks from the Kalatashtagh area, NW China. Zircon U-Pb dating indicate they formed at 450 - 420 Ma, while zircon ε_Hf values imply a depleted mantle source. Whole-rock compositions resemble high-Al arc basalts. Investigations reveal a predominant (~5%) slab-derived sediment melt in the mantle source. Thermodynamic modelling indicates 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 1,500 km along the northern margin of the collage during 450 - 420 Ma. Geochemical evidence suggests that slab-derived sediment melts dominated over hydrous fluids in the sub-arc mantle wedge, indicating high slab surface temperature (SST). This elevated SST likely results from asthenosphere upwelling due to slab rollback, which also responsible for rifting of marginal terrains, and the formation of back-arc basins along the northern of the collage. This retreating-type accretionary orogenic belt may globally connect to form a subduction girdle, facilitating prolonged dispersal of Gondwana, drift and reunion of its derived continents in Asia, and opening of the Paleo-Tethys.