The Mesozoic granitic magmatism in Haliheiba: implications from geochronology, geochemistry and Hf isotopes

The Mesozoic granitic magmatism in Haliheiba is poorly understood because of lacking systematic data. Hence, this paper presents petrological observations, zircon U–Pb ages, geochemistry and Hf isotopes for these rocks. These rocks comprise granidiorite and quartz monzonite. Zircon LA-ICP-MS U–Pb dating yields emplacement ages of 247.6 ± 1.1 Ma and 247.0 ± 1.5 Ma for granidiorite and quartz monzonite, respectively. Geochemically, the granidiorite has SiO₂ contents of 65.86–67.37 wt% and alkali concentrations of 7.97–8.44 wt%; the quartz monzonite has SiO₂ contents of 66.95–67.28 wt% and alkali concentrations of 8.52–8.63 wt%, which belong to calc-alkaline series and are metaluminous rocks. These granitoids are enriched in light rare earth elements (LREEs) with (La/Yb)_N values from 5.27 to 12.09 and have slightly to moderately negative Eu anomalies with δEu values from 0.53 to 0.78 in the chondrite-normalized REE diagram. Furthermore, these granitoids are relatively enriched Rb, U, Th, K, and Pb and slightly depleted in Nb, Ta, Ba, Ti, and P in the primitive mantle-normalized spider diagram. The above geochemical signatures reveal that these granites have I-type affinity. Zircon Hf isotope data show that these granitoids possess high positive εHf(t) values from +8.9 to +14.9 and fairly young Hf model ages from 305 to 620 Ma, indicating that they are mainly derived from partial melting of juvenile crustal components. Combined with regional geology, our results indicate that the Triassic magmatism in Haliheiba most likely resulted from the subduction of the Paleo-Asian Ocean beneath the North China Craton. Our results together with regional isotopic data suggest that a significant crustal accretion event occurred during the Neoproterozoic to Paleozoic in the Great Xing’an Range.