Delineating convergent continental margin basin systems in the North Altyn belt: implications for diachronous closure of the Proto-Tethys Ocean

The subduction and closure of the Proto-Tethys Ocean dominated a significant global tectonic event in the Phanerozoic, which established the foundational tectonic framework for East Asia. Particularly, the North Altyn ophiolitic mélange belt recorded the subduction-collision history of the North Altyn segment of the Proto-Tethys Ocean, but the spatial-temporal distribution of related convergent margin successions is poorly constrained. The late Cambrian to late Ordovician Elantage Formation and Lapeiquan Group in the northern Altyn belt are coeval with the North Altyn ophiolite and therefore preserve key records of the evolution of the North Altyn Ocean. Detailed petrography, detrital zircon age patterns, isotopes, and geochemical characteristics indicate that these stratigraphic sequences were deposited in retro-arc and fore-arc basins at ca. 520-440 Ma, respectively. εHf(t) values suggest that arc magmatic rocks from the northern margin of the Central Altyn Block are the main provenances for the Elantage Formation, whereas the provenance of Lapeiquan Group is dominated by arc magmatic rocks within the North Altyn ophiolitic mélange belt. A ca. 520-440 Ma trench-continental arc and retro-arc basin system in the northern Altyn further suggest a Silurian closure time for the North Altyn segment of the Proto-Tethys Ocean. In addition, together with a review of age and spatial patterns of the ophiolites, trench-arc systems, metamorphism, and magmatic rocks across the other East Asian continental blocks, we argue for a diachronous closure of the Proto-Tethys Ocean from the Ordovician to the Late Silurian. This research was funded by the National Key R&D Program of China (grant 2023YFF0803604), National Natural Science Foundation of China (grants 42322208).