Mixing of Felsic Magmas in Granite Petrogenesis: Geochemical Records of Zircon and Garnet in Peraluminous Granitoids From South China

Mixing of felsic magmas from different sources may be common in granite petrogenesis, but challenging to unravel. Nevertheless, this is identified by a combined study of in situ zircon and garnet geochemistry with whole‐rock geochemistry for the Jiuling batholith in South China. The Jiuling batholith is composed of low‐Si granitoids and high‐Si granites. Although they show similar whole‐rock Sr‐Nd‐Hf isotope compositions, the low‐Si granitoids exhibit higher MgO, FeO, TiO 2 , Al 2 O 3 , and Middle rare earth elements contents, and higher Zr saturation temperature than the high‐Si granites. Two groups of zircons and garnets are identified in the form of either individual grains or different domains of a grain. Although they exhibit highly variable O and Hf isotope compositions, Group I zircons show higher δ 18 O and lower ε Hf ( t ) values than Group II zircons. Group I garnets are higher in FeO and MgO but lower in CaO and MnO than Group II garnets. Group I garnets show more remarkable negative Eu anomalies than Group II garnets. Groups I and II garnets exhibit distinct δ 18 O values, in equilibrium with Groups I and II zircons, respectively. These differences indicate that the two groups of zircons and garnets were derived from two different batches of felsic magmas. Batch I magma may be derived from partial melting of ancient sedimentary rocks at higher temperature, whereas Batch II magma would probably form by partial melting of relatively juvenile crust at lower temperature. Therefore, the Jiuling batholith is produced by mixing between two batches of granitic magmas with different trace element and isotope compositions.