Intra-oceanic arc basement and its insights to crustal growth in the southern Altaids, NW China

Increasing reports of Precambrian zircon xenocrysts within intra-oceanic arcs (IOAs) challenge the previous definition of intra-oceanic arcs IOAs and the established view of excessive crustal growth caused by IOAs in accretional orogenic belts such as the Altaids. The Dananhu–Queershan arc complex, situated in the southern segment of the Altaids, has been widely classified as an IOA system. This study reconstructs the paleogeographic evolution of the Queershan arc complex based on sedimentary facies and zircon U-Pb-Hf data. The Queershan complex comprises a Carboniferous–Permian IOA unit (357–289 Ma) with Mariana-like petrological sequence, uncomfortably resting on a remnant Devonian arc terrane (398–364 Ma). Precambrian zircon xenocrysts in the IOA unit spanning span a broad age range (2557 and 542 Ma) match forearc deposits, suggesting assimilation from subducted sediment. The distribution of Hf model ages for the Queershan arc complex demonstrates juvenile crustal growth at ca. 680–320 Ma (peak at 442 Ma).