Geochemistry, U-Pb Geochronology and Sr-Nd-Hf Isotopes of the Early Cretaceous Volcanic Rocks in the Northern Da Hinggan Mountains

Whole‐rock geochemical, zircon U‐Pb geochronological and Sr‐Nd‐Hf isotopic data are presented for the Early Cretaceous volcanic rocks from the northern Da Hinggan Mountains. The volcanic rocks generally display high SiO₂ (73.19–77.68 wt%) and Na₂O+K₂O (6.53–8.98 wt%) contents, with enrichment in Rb, Th, U, Pb and LREE, and depletion in Nb, Ta, P and Ti. Three rhyolite samples, one rhyolite porphyry sample, and one volcanic breccia sample yield weighted mean ²⁰⁶pb/²³⁸U ages of 135.1±1.2 Ma, 116.5±1.1 Ma, 121.9±1.0 Ma, 118.1±0.9 Ma and 116.9±1.4 Ma, respectively. All these rocks have moderate (⁸⁷Sr/⁸⁶Sr)_i values of 0.704912 to 0.705896, slightly negative ε_Nd(t) values of –1.4 to –0.1, and positive ε_Hf(t) values of 3.7 to 8. Their zircon Hf and whole‐rock Nd isotopic model ages range from 594 to 1024 Ma. These results suggest that the Early Cretaceous volcanic rocks were originated from melting of subducted oceanic crust and associated sediments during the closure of the Mongol‐Okhotsk Ocean.