The Wilson cycle of the Hongliuhe-Xichangjing backarc ocean in the Altaids and its contribution to crustal reworking

Backarc basins, as primary sites for oceanic crust generation within accretionary orogen, play a critical role in crustal reworking. However, it remains enigmatic how backarc basins contribute to crustal reworking. The Hongliuhe–Xichangjing Ocean (HXO), as a significant Early Paleozoic branch of the Paleo-Asian Ocean, has sparked considerable debate regarding the timing and processes of its formation and closure. This study proposes a Wilson cycle for the HXO, based on sedimentary sequences and provenances from two accretionary complexes along its margins. On the southern margin, the detrital zircon age spectra of Cambrian to Early Ordovician strata are bimodal with age peaks at ca. 980 and 2440 Ma derived from the Dunhuang and Shuangyingshan blocks. The age spectra of Late Ordovician strata are unimodal with age peaks at 472–458 Ma, showing derivation from a juvenile arc on the Shuangyingshan block. On the northern margin, the age spectra of Cambrian strata are bimodal with the age peaks at 558 Ma and 671 Ma sourced from volcanic arcs near the Tuva-Mongolia block. In the Silurian, the age spectra shift to unimodal pattern with age peaks at ca. 441–451 Ma, showing their derivations from the Gongpoquan arc. The differences in source areas of both margins in the Cambrian indicate the existence of HXO, while the provenance shift from Cambrian to Middle-Late Ordovician reveals that they both transformed from passive margins to active continental margins. The Wilson cycle involves backarc spreading during the Early Cambrian, oceanic extension from the Middle Cambrian to Early Ordovician and bipolar subduction from the Middle Ordovician to Late Carboniferous. The formation of HXO and subsequent backarc expansion resulted from its bipolar subduction fragmented the uniform continent, which is a key mechanism for crustal reworking in the Altaids. Resurrected subduction of the HXO produced accretionary complexes, leading to lateral crustal growth.