Zircon U-Pb Age and Hf Isotope Characterization of Sheshan Granodiorite in Southern Edge of Dayaoshan, Guidong: Constraints on Caledonian Diagenesis and Mineralization

In this paper, we present laser ablation (MC)-ICP-MS U-Pb dating and Hf isotopic compositions of zircons from two representative granitoid samples collected from Shedong W-Mo deposit in the southern edge of the Dayaoshan. Highly precise U-Pb results indicate that zircons from Sheshan biotite granodiorite (SD256) and granodiorite-(porphyry) (SD190) which emplaced in the Pingtoubei quartz sandstone yields weighted mean ²⁰⁶Pb/²³⁸U age of 438.7±3.0 Ma (MSWD=0.22) and 438.1±2.6 Ma (MSWD=0.28), respectively. And the zircons crystallized in the Kwangsian granites yield ¹⁷⁶Hf/¹⁷⁷Hf ratios of 0.282 406 to 0.282 518, ε_Hf(438 Ma) values ranging from -3.7 to 0 and Hf model ages (T_DM2) of 1 226 to 1 417 Ma. Our U-Pb and Hf isotopic data can be interpreted as the crystallization time of granites, and indicate that it was formed in the ~438 Ma (Caledonian) and may have been formed by reworking of Mesoproterozoic juvenile crust (1.2-1.4 Ga) closely related to partial melting. Together with other published geochronological data, it is proposed that the late Early Paleozoic granites predominantly have a similar formation age and exhibit a planar-shaped distribution, rather than a north-east-striking-distribution pattern in the hinterland of the South China. Moreover, the Caledonian tectonic-magmatic-metallogenic movement may be the one of key reasons for the large-scale magmatism and metal mineralization in the following tectonic episodes, such as Indosinian and Yanshanian in the South China.