Early Mesozoic subduction of the Mongol‐Okhotsk Ocean and its effect on the central Great Xing'an Range: Insights from the monzodiorite in the Erdaohe deposit

Abstract

Stuck in the middle of the Mongol‐Okhotsk Ocean and the Palaeo‐Asian Ocean, the tectonic background of the Great Xing'an Range is ambiguous, especially with the tectonic transition in Early Mesozoic. Previous studies showed a major influence by the closure of the Palaeo‐Asian Ocean and the onset of the Mongol‐Okhotsk Ocean subduction on the southern and northern part of the Great Xing'an Range, respectively. However, the Early Mesozoic tectonic setting of the central Great Xing'an Range still needs further discussion. New zircon ages, whole‐rock geochemical data for monzodiorite in the Erdaohe deposit, central Great Xing'an Range, are presented. Zircon U–Pb dating yields a Triassic age of 226 Ma. Monzodiorite displays metaluminous and high‐K calc‐alkaline affinity evidenced by petrologic and geochemical studies. A mixed source of juvenile lower crust with mantle material of the monzodiorite is indicated by its high Mg# (44–61), low SiO2 (50–53 wt%) contents, depletion in Nb and Ta, positive εNd(t) (+2.5 ± 3.0) and zircon εHf(t) (+6.8 ± 8.9), and low ISr values (0.70322–0.70432). Our new geochronological and geochemical data with compiled data of previous research on magmatism from the Xing'an Block and adjacent areas indicate new insights into the Triassic tectonic evolution of the central Great Xing'an Range. The Triassic magmatism in this region is intimately associated with the flat‐slab subduction and slab break‐off of the Mongol‐Okhotsk Ocean.