The 131-134Â Ma A-type granites from northern Zhejiang Province, South China: Implications for partial melting of the Neoproterozoic lower crust

Zircon U-Pb dating yields a weighted mean 206Pb/238U age of 130.9 ± 1.0 Ma for the Machebu granite, 134.4 ± 2.1 Ma for the Shenzhongwu granite and 131.9 ± 1.2 Ma for the Daixi granite. The εHf(t) values of the zircons in these plutons gradually increase from southwest to northeast, i.e., from − 14.5 ~ − 3.5 for the Machebu granite to − 1.5 ~ − 0.2 for the Shenzhongwu granite and from 5.1 ~ 8.6 for the Daixi granite, suggesting the origin of different parent rocks. These granites have two-stage Nd model (TDM2(Nd)) ages of 1099 Ma-838 Ma, and zircons from these granites and the Neoproterozoic basement in the Gan-Hang Belt plot on the same evolutionary trend in the εHf(t)-age diagram. It is interesting to note that the collection of literature data shows a positive correlation between SiO2 and εNd(t) for the late Mesozoic A-granites in the Gan-Hang Belt, and the Neoproterozoic A-granites in the Gan-Hang Belt cluster in two groups of the high-SiO2-εNd(t) group and low-εNd(t) group. The positive correlation of SiO2-εNd(t) demonstrated by the late Mesozoic A-granites can be well explained by a high-degree of melting of mixtures between the two groups of Neoproterozoic A-granites. We thus suggest that the late Mesozoic A-type granites in the Gan-Hang Belt could have been derived from the rejuvenated Neoproterozoic rocks rather than directly from the Mesoproterozoic metamorphic basement as a result of subduction.