Niangniangding granite pluton is located in the middle of Tongbai-Dabie Orogen,and its emplacement age and tectonic environment are still unclear.Niangniangding granite samples were collected to carry out zircon U-Pb geochronol-ogy,rock geochemistry and Sr-Nd isotope studies,and to explore the characteristics of magma source area,petrogenesis,tectonic environment and its relationship with Yangxinyan beryllium occurrence.The results show that the zircon U-Pb age of Niangniangding granite is(752.6±9.0)Ma,which belongs to the product of Nanhua magmatism and only consti-tutes the host rock of Yangxinyan beryllium occurrence.Niangniangding granite has the characteristics of high silicon(SiO2 content is 72.56％to 77.26％),rich alkali(Na2O+K2O content is 7.37％to 8.86％)and peraluminous(A/CNK is 0.97 to 1.22).Its Rb,K,Th are relatively enriched,Ba,Sr,Ti and P are obviously losses,and REE distribution curve is right-leaning LREE enrichment type,with obvious negative Eu anomaly(δEu is 0.2 to 0.7),indicating that Niangniangding granite is aluminum A-type granite.Its(87Sr/86Sr)i is 0.710 605 to 0.710 608,εNd(t)is-4.94 to-5.05,and the corresponding Nd model age tDM is 1.83 to 1.84 Ga,which has the characteristics of upper continental crust and may be the product of partial melting of ancient basement in Early-Middle Proterozoic.Its main elements CaO,MgO,TFeO,TiO2 and SiO2 show a negative correlation,and the magmatic evolution mechanism should be dominated by crystal-lization differentiation.On the whole,Niangniangding granite was formed in the Neoproterozoic extensional background.
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