Petrogenesis of the Late Ordovician Penggongmiao biotite monzogranite in southern Hunan, south China: constraints from geochronology, geochemistry, and Sr–Nd–Hf isotopes

The Penggongmiao complex pluton, located in the Nanling metallogenic belt of South China, provides a critical record of Early Paleozoic (Caledonian) magmatism, but the genesis and mineralization potential of the biotite monzogranite of the pluton have not been constrained. This study presents new whole-rock geochemistry, zircon U–Pb ages, and Sr–Nd–Hf isotopic data for the Penggongmiao biotite monzogranite to constrain its timing, origin, and metallogenic potential. Zircon U–Pb dating yields a weighted mean age of 451.6 ± 1.5 Ma, confirming its emplacement during the Late Ordovician. The biotite monzogranite is characterized by high SiO 2 (73.25–76.58 wt.%), being peraluminous and belonging to the shoshonite series. It exhibits enriched LREEs, large ion lithophile elements (LILEs; e.g., Rb, Th, U, Pb), and depleted high field strength elements (HFSEs; e.g., Nb, Ta, P, Ti), with marked negative Eu anomalies (δEu = 0.23–0.99). The zircon ε Hf (t) values range from −10.9 to −5.9 (T DM2 = 2,119–1,802 Ma), and whole-rock ( 87 Sr/ 86 Sr) i ratios are high (0.7063–0.7077) with negative εNd(t) values (−7.5 to −6.1). These signatures, combined with ACF and K 2 O–Na 2 O diagrams, indicate the S-type granite magma was derived from the partial melting of ancient Proterozoic metasedimentary crust. This magmatic event was likely triggered by the Caledonian intracontinental orogeny. Furthermore, low zircon Ce 4+ /Ce 3+ ratios (avg. 26) and Ti-in-zircon temperatures (avg. 745 °C), coupled with low W-Sn contents, suggest that the Penggongmiao biotite monzogranite has limited potential for magmatic-hydrothermal Cu or W–Sn mineralization. In addition, our findings demonstrate that the Penggongmiao biotite monzogranite possesses low oxygen fugacity and limited fractionation, thereby refining the magmatic-metallogenic framework of the Nanling region by distinguishing these sterile Caledonian batholiths from the fertile Mesozoic granitic systems.