Evolution of the northward subduction of the Neo-Tethys: Implications of geochemistry of Cretaceous arc volcanics in Qinghai-Tibetan Plateau

The subduction history of the Neo-Tethys is critical for understanding the early-stage tectonic evolution of the Qinghai–Tibetan Plateau. Arc volcanics, which usually record the subduction process, thus can help trace the evolution of the Neo-Tethys. In this paper, we report for the first time zircon LA-ICP-MS U-Pb ages, whole-rock major and trace element geochemistry, as well as Sr–Nd–Hf isotopic data for the volcanic rocks from the Danshiting Formation at the southern edge of the Lhasa Terrane. Two samples collected from the Danshiting Formation volcanic rocks yield zircon U-Pb ages of 97.1 ± 0.8 Ma and 90.1 ± 0.7 Ma, respectively. The volcanic rocks of the Danshiting Formation are composed dominantly of basalts and andesites characterized by depletion of high-field-strength elements, low (87Sr/86Sr)i ratios (0.7042–0.7045), high εNd(t) (+2.1 to +2.7) and high εHf(t) values (mean + 11.6). These rocks show geochemical affinity of arc volcanic rocks. The volcanic rocks of the Danshiting Formation may have formed during the northward subduction of the Neo-Tethys. This paper, combined with the previous data, briefly divide the northward subduction of the Neo-Tethys into four periods: the Jurassic (195–150 Ma), when the magmatic activity was controlled by the northward high-angle subduction of the Neo-Tethys that produced volcanics of the Yeba and Bima formations; the Late Jurassic to Early Cretaceous (150–110 Ma), when the Neo-Tethys subducted at low-angles; the Late Cretaceous (110–80 Ma), when subduction was of the Andean-type and produced volcanic rocks of the Danshiting Formation; the Paleogene (70–40 Ma), when there was transition from ocean-to-continent subduction to continent–continent collision that produced volcanic rocks of the Linzizong Group.