Combining zircon texture, REE patterns and U-Pb-Hf isotopes to decipher the formation process of orbicular rocks: A case study from Huangling orbicular granodiorite, Yangtze craton, China

The petrogenesis of orbicular rocks is still enigmatic because of the unique texture and variable compositions. In this study, we focus on the textural characteristics and mineral compositions from Huangling Orbicular Granodiorite (HOG), where orbicules with rhythmic growth texture and radial growth texture exist in the same outcrop. Textural and isotopic studies of zircons from different parts of the representative orbicules show three age groups of 1961 ± 19 Ma, 890 ± 6 Ma and 852 ± 6 Ma, corresponding to the ages of protolith crystallization, melt emplacement, and input of a new magma, respectively. Combined with field relationship, Ti-zircon crystallization temperature, trace element modelling and Hf isotopic data, the HOG may be derived from high-temperature contact process that involved the partial melting of granodiorites in contact and interaction with a quartz-bearing dioritic intrusion.