Petrogenesis of early Cretaceous granitoids in the southern Great Xing’an Range, NE China: Constraints from the Haliheiba pluton

Abstract

Early Cretaceous granitoids are widespread in the southern Great Xing’an Range. However, the petrogenesis of these rocks is poorly understood. We therefore present field investigations, petrological observations, zircon U–Pb ages, whole-rock geochemistry and Hf isotope compositions for the Haliheiba pluton. The pluton comprises fine-grained biotite granite, medium- to coarse-grained biotite granite and porphyritic biotite granite, and mafic microgranular enclaves (MMEs) are unevenly distributed within the host granites. Zircon LA-ICP-MS U–Pb dating yields emplacement ages of ∼139 Ma for the three units. The host granites are characterized by high SiO2 contents (73.16–76.55 wt%) and alkali concentrations (7.92–8.62 wt%), enrichment in light rare earth elements (LREEs), Rb, U, Th, K, and Pb, depletion in heavy rare earth elements (HREEs), Sr, Ba, Ti, and P, and intensely negative Eu anomalies with δEu values from 0.14 to 0.47. The zircons in the host granites yield positive εHf(t) values of +5.0 to +11.2 and fairly young Hf model ages of 408 Ma to 731 Ma. These results indicate that the host granites have high-K calc-alkaline, metaluminous to weakly peraluminous A-type affinity and were mainly derived from partial melting of juvenile crustal materials originated from the depleted mantle, and fractional crystallization was involved in magma evolution. The MMEs have SiO2 contents of 63.45–64.14 wt% and have higher MgO, CaO, tFe2O3 and TiO2 contents than the host granites. The MMEs are enriched in LREEs relative to HREEs with slightly negative Eu anomalies (δEu values of 0.77–0.79) and are slightly enriched in Rb, U, Th, K, Sr, Pb and strongly to slightly depleted in Nb, Ta, Ti and P. These results, together with field investigations and petrological observations, indicate that crust-mantle magma mixing played an important role during the petrogenesis. Furthermore, the MMEs were intermediate members after magma mixing between mafic end-member magmas derived from lithospheric mantle and felsic end-member magmas derived from juvenile crustal materials. Combined with regional geology, our results suggest that a substantial crustal accretion in the southern Great Xing’an Range that occurred during the Neoproterozoic–Carboniferous, and the formation of the Early Cretaceous granitoids in this region was closely related to the lithospheric delamination triggered by the subduction of the Paleo-Pacific Ocean beneath Eurasia.