Late Mesozoic Subduction-Accretion in the southern Qiangtang: Insights from the Sumxi Igneous Complex of west-central Tibet
Knowledge of the time of the closure of the Bangong-Nujiang Tethyan Ocean (BNTO) is critical for understanding the Mesozoic tectonics of the Tibetan Plateau. This study investigated the ca. 110–106 Ma Sumxi igneous complex (high-Nb basalts, magnesian andesites, and adakitic granites) in westernmost part of the Qiangtang terrane. Detailed studies imply strong slab-mantle interactions and arc affinities of Sumxi lavas, indicating that oceanic subduction may have lasted at least until ca. 105 Ma. Moreover, geochronological and geochemical data compilation of magmatic rocks in southern Qiangtang reveal episodic features, with two main high-flux events (~180–145 Ma and ~125–100 Ma) separated by magmatic lulls (~145–125 Ma). The episodic arc activity contributed greatly to the crustal thickening and surface uplift of the central Tibet before the onset of Lhasa-Qiangtang continental collision. The supporting information Text S1 describes the methods for zircon U–Pb dating, Hf isotopes, whole-rock major- and trace-element and Sr–Nd isotope analyses. The figures consist of trace elements versus Nb correlation diagrams for Sumxi basalts and basaltic andesites (Figure S1), and U/Yb vs. Nb/Yb (ratios in log10) and U/Yb vs Y diagrams of zircons from the Sumxi igneous rocks (Figure S2). The Tables S1-S4 show the data of zircon U–Pb isotope (Table S1), trace element data of zircons from the Sumxi Igneous Complex (Table S2), zircon Lu–Hf isotope (Table S3), and whole-rock major (wt. %), trace (ppm) elements and Sr–Nd isotopes (Table S4).