Evidence for Late Paleozoic subduction erosion, slab rollback and closure of the Irtysh-Zaysan Ocean from the evolving sediment provenance in the southwestern Central Asian Orogenic Belt

Accretionary orogens are characterized by complex subduction processes of oceanic lithosphere, the formation and closure of oceanic basin, and arc-arc collision. The Zharma-Saur arc in the southwestern Central Asian Orogenic Belt, had experienced the completed process of subduction and closure of the Irtysh-Zaysan Ocean during the Late Paleozoic, but controversy about its complex tectonic evolution still exists. Geochronological, isotopic and geochemistry data from Late Paleozoic volcanic-sedimentary strata in the eastern Zharma-Saur arc were conducted, aiming to decipher the tectono-sedimentary evolution of this important tectonic domain. The lithological and geochemistry analysis revealed the dominant input of magmatism-related detritus for all these sediments. The investigated Carboniferous sediments are dominated by Late Devonian–Carboniferous zircons (376–313 Ma) with positive εHf(t) values (+6.7 to + 16.6), sourced exclusively from the Zharma-Saur arc. However, the Early Permian sediment is characterized by a wide range of detrital zircon ages (2537–273 Ma) and εHf(t) values (−13.1 to + 13.9), which not only received detritus from the same arc domain but also contained detrital zircon grains sourced from the northerly Chinese Altai and Irtysh Complex, as well as southerly Boshchekul-Chingiz arc.

Based on our new data, combined with regional data, convincingly indicate that Middle Devonian subduction erosion of Irtysh-Zaysan Ocean gave rise to the destruction of the Ordovician Tarbagtay-Saur arc. Carboniferous slab rollback of Irtysh-Zaysan Ocean led to retreating migration of magmatism and transformation to an extensional setting as well as expansion of the back-arc ocean basin. The closure of the back-arc ocean basin and the Irtysh-Zaysan Ocean both occurred in the latest Carboniferous. This study distinguished these tectonic processes and characterized their evolution, which may be great importance for inferring tectonic framework of ancient accretionary orogens by sedimentary provenance analysis.