Intra-oceanic arc origin of the northern Beishan Orogenic Belt (NW China): implications for the palaeogeographic interpretation of Precambrian zircons and insights into crustal growth

Abstract

The Queershan arc complex, located in the northern Beishan Orogenic Belt of the Altaids, has been widely classified as an intra-oceanic arc (IOA) system; however, the occurrence of Precambrian zircons challenges the IOA origin, implying contributions from reworked continental crust. In this paper, we reconstruct the palaeogeographic evolution of the Queershan arc complex based on sedimentary facies analysis and zircon U-Pb-Hf data. The Queershan complex comprises a Carboniferous–Permian IOA unit (357–289 Ma) with a Mariana-like petrological sequence, originating from the subduction of an oceanic plate beneath a remnant Devonian arc terrane (398–364 Ma). Precambrian zircon xenocrysts in the IOA unit spanning a broad age range from 2557 Ma to 542 Ma, match those in forearc deposits, suggesting assimilation from subducted sediment. The distribution of Hf model ages of zircons in the Queershan arc complex demonstrates juvenile crustal growth from Late Neoproterozoic to Late Palaeozoic times with a peak at 442 Ma. Our findings show that the occurrence of Precambrian zircon grains does not necessarily negate a relatively juvenile origin for IOAs.