Cretaceous structures in the Duolong region of central Tibet: Evidence for an accretionary wedge and closure of the Bangong–Nujiang Neo-Tethys Ocean

This article focuses on the Cretaceous structures in the Duolong region, northern Tibet. Our aim was to constrain the metallogenic setting of the Duolong giant porphyry Cu–Au deposit and to discuss the implications for the closure of the Bangong–Nujiang Neo-Tethys Ocean. There are two tectonic stages in the Duolong region, during the Early to Late Cretaceous. The first stage is characterised by numerous large-scale folds and faults with NE–SW compression. The 40Ar/39Ar plateau age of sericite from mylonite is 127.8±1.1Ma, which represents the timing of tectonic emplacement of the Jurassic Mugagangri Formation (JM) and ophiolite. This stage corresponds to the northward subduction of the Bangong–Nujiang Neo-Tethys Ocean. The second stage is characterised by the Duolong thrust nappe with a series of sinter deposits, slip surfaces, fault fracture zones, klippes, and tectonic windows. Basalt from the hanging wall yields a zircon U–Pb age of 110.4±1.7Ma, which is older than the Upper Cretaceous Abushan Formation (Ka) of the footwall. A red layer obtained from drillcores is younger than the overlying Jurassic strata, on the basis of the youngest detrital zircon U–Pb age of 116±2Ma. This stage is correlated with the closure of the Bangong–Nujiang Neo-Tethys Ocean. We suggest the Upper Triassic Riganpeicuo Formation, JM and ophiolite successively accreted to the southern margin of the South Qiangtang terrane during the Late Jurassic to Early Cretaceous; these constitute the main body of the epicontinental accretionary wedge. This accretionary wedge includes many Early Cretaceous epicontinental arc volcanic rocks and granites, and the Duolong Cu–Au deposits were formed in an Andean-type active continental margin setting. We also conclude that the Bangong–Nujiang Neo-Tethys Ocean closed during the late Early Cretaceous to early Late Cretaceous, and that continental collision continued until the end of the Late Cretaceous.