The Wulanmoren Accretionary Complex Unravels Early Devonian to Late Triassic Multiple-Arc Amalgamation in the Tianshan Orogen (NW China)

Reconstructing the tectonic architecture of the southern Altaids is of great importance to piece together the continental growth history of the Central Asian continent. In this paper, we address the subduction-accretion process of the Paleo-Tianshan Ocean, one branch of the South Tianshan Ocean, in the southern Altaids, through a detailed geological and geochemical investigation of the Wulanmoren Accretionary Complex (WAC). The WAC is composed of ophiolitic melanges, ocean plate stratigraphy melanges, and turbiditic coherent units. In this study, we present key geological, petrological, and geochemical evidence indicating back-arc and ocean island affinity of the igneous rocks of the WAC. Zircon U-Pb dates of these rocks ages range between 380.2 +/- 1.3 and 302.0 +/- 5.3 Ma. The sedimentary matrix units of the melanges were deposited in the Early Devonian (similar to 405 Ma) to the Late Triassic (similar to 222 Ma), rather than Silurian strata as previously thought. However, the ages of some detrital zircons in the sedimentary matrix are Precambrian, pointing to a complex evolution involving multiple ocean island terrains and island arcs of different ages that accreted from the mid-Paleozoic to the Early Mesozoic.