SHRIMP zircon U-Pb dating, geochemistry and zircon Lu-Hf isotopic composition of Hengtian granite porphyries in eastern Guangdong Province and their geological implications

The granite porphyry related to tungsten-tin polymetallic deposits was discovered in Hengtian area, eastern Guangdong Province. In this paper, the authors reported detailed studies of SHRIMP zircon U-Pb dating, major elements, trace elements and zircon Hf isotopic compositions of the granite porphyry. The granite porphyries are mostly grayish white dykes with porphyritic texture and massive structure. They mainly consist of phenocrysts (10%) and matrix (90%), the phenocrysts are composed of plagioclase, Kfeldspar, quartz and biotite with particle size of 0.6~6mm in mixed and disorderly distribution, whereas the matrix is composed of feldspar, quartz and biotite, with the feldspar particle size being generally 0.02~0.25mm. Zircon U-Pb age analysis for the granite porphyry yielded a weighted average ²⁰⁶Pb/²³⁸U age of 142±1Ma, indicating that the rock was formed in Early Cretaceous. Major and trace element characteristics show that the granite porphyry belongs to high potassium calc-alkaline peraluminous series en-riched in Rb, U, Nd, HF and depleted in Ba, Nb, Sr, P, Ti, similar to features of highly fractionated S-type granites. The ε_Hf(t) values of the granite porphyry are less than 0; in t-ε_Hf(t) and t-(¹⁷⁶Hf/¹⁷⁷Hf)_i diagrams, all points fall under the chondritic evolu-tion line and above the south of the Mesoproterozoic basement evolution line. Moreover, the ages are between 1.28Ga and 1.47Ga, indicating that rock-forming materials were mainly derived from the partial melting of metamorphic mudstone in Meso-proterozoic ancient crust.