Geochronology, Geochemistry, and Geological Implications of the Early Paleozoic Penggongmiao Granite Batholith in the Western Part of Cathaysia Block, Hunan Province, South China

Zircon U–Pb dating of the Penggongmiao granite batholith in the western part of Cathaysia block, Hunan Province, South China, together with Hf isotopes and whole-rock elemental analyses, reveal critical insights into its depositional history. Zircon U–Pb geochronology traces the primary crystallization phase to between 445.3 ± 2.0 and 440.5 ± 1.9 Ma. An earlier onset indicated by 464.1 ± 0.9 Ma for fine- and medium-grained porphyritic granodiorite, suggests emplacement began before the Middle Ordovician. Geochemically, the rocks exhibit a calc-alkaline, ferruginous, and peraluminous composition, characterized by K2O + Na2O content of 6.46–8.32 wt %, Mg# values of 21–42, and A/CNK ratios of 1.11–1.31. High εHf(t) values ranging from –7.50 to –4.20, with TDM2 ages of 1.54–1.73 Ga, point to magma derived predominantly from sedimentary sources, with strongly mantle contributions. Major and trace element data indicate that the batholith formed in a post-orogenic extensional setting during a transition from compressional orogeny to non-orogenic conditions. The evidence suggests that formation was the likely result of asthenospheric mantle upwelling due to the rollback of the Yangtze and Cathaysia blocks during subduction. This tectonic process caused partial melting of the lithospheric mantle and overlying ancient crustal material, producing a granite of mixed crust-mantle origin dominated by crustal sources.