Geochemistry, zircon U–Pb geochronology, and Hf isotopes of the metavolcanic rocks in the Tongbai orogen of central China: Implication for Neoproterozoic oceanic subduction to slab break-off

[Display omitted] Abundant metavolcanic rocks (leptynite, leptite, and amphibolite) occur in the Tongbai orogen, central China, but their age, origin, and tectonic significance are poorly constrained. Here we report geochemistry, zircon U–Pb ages, and Hf isotopes of these metavolcanic rocks to determine their petrogenesis and geodynamic implications. Our data indicate that all the leptynites, leptites, and amphibolites were initially formed at 760–720 Ma and then underwent later metamorphism. These rocks exhibit arc-related geochemical compositions characterized by enriched large ion lithophile elements and light rare earth elements and depleted heavy rare earth elements. Leptynites and leptites present similar characteristics, including high SiO2 (72.14–77.24 wt%), MgO (0.19–0.44 wt%), and Sr (239–827 ppm) compositions and low Y (6.9–16 ppm) and Yb (0.70–1.17 ppm), along with high Sr/Y and (La/Yb)N values. The leptynites exhibit no or slightly negative Eu anomalies in both the whole-rock and zircon. Based on the high K2O (3.75–4.31 wt%) and slightly lower Al2O3 (