Construction of Late Devonian Dundunshan arc in the Beishan orogen and its implication for tectonics of southern Central Asian Orogenic Belt

Abstract The Beishan orogen, located in the southern Central Asian Orogenic Belt, was formed by subduction-accretionary processes in the Paleozoic, and so provides key constraints on the current international controversy regarding the duration of the orogenesis and the time of its termination and formation of the final suture. This paper concerns the tectonic setting, in the Beishan, of Devonian volcanic and sedimentary rocks that belong to the Dundunshan subduction-generated volcanic arc. The Dundunshan arc comprises metaluminous to weakly peraluminous, calc-alkaline andesites, dacites, rhyolites, porphyries and tuffs, which have Late Devonian U–Pb zircon ages of 368.8 ± 3.1 Ma and 370.9 ± 1.3 Ma. The rhyolites have an arc geochemical signature. The Dundunshan sediments are predominantly clastic sandstones, the trace element geochemical data of which indicate derivation from a rhyolitic source with variable degrees of weathering, suggesting an active tectonic provenance. The Dundunshan arc is situated on the southern side of the Huaniushan arc, which, according to current published data, was generated by northward subduction in the Early Paleozoic, and this was followed by the Dundunshan arc in the Late Devonian. It is likely that the northward-dipping subduction zone retreated southwards, giving rise to southward younging of the arcs. Our data provide important constraints on a better understanding of the growth of arcs that dominate the Altaid accretionary orogen.