This study presents zircon U–Pb geochronology and Hf and O isotope data for granitic rocks in the Zijinshan ore field, southwestern Fujian Province, China. The intrusive rocks comprise monzogranite, granite and granodiorite. The magmatic zircon U–Pb ages from these granitic rocks can be divided into four episodes: episodes 1 (157.9–159.9 Ma) and 2 (141 Ma) in the Late Jurassic and episodes 3 (108.1–103.2 Ma) and 4 (97.5–99.7 Ma) in the Middle and Late Cretaceous, respectively. Patterns of rare-earth elements (REE) show enrichment in light REE and obvious negative Eu anomalies. These rocks are also enriched in Rb, Th, U, La, Ce, Nd and Hf, and depleted in Ba, Nb, Sr, P and Ti. The increasing La/Yb ratio and decreasing heavy REE content with decreasing age may imply an increasing contribution of mantle-derived materials from the Late Jurassic to Cretaceous. The zircon ϵHf(t) and δ18O values, ranging from −37.7 to −2.8 and 12.0 ‰ to 6.3 ‰, respectively, indicate that the lower crust is an important source of granitic rocks. There was a significant increase in ϵHf(t) values and a decrease in δ18O values in the younger magmatic episodes (3 and 4), which ranged from −11.4 to −0.6 and 10.7 to 6.3 ‰, respectively. This suggests an increasing contribution of mantle-derived magma to the crustal melts from the Late Jurassic to late Early Cretaceous in response to the changing regional tectonic setting from compression to extension and an increasing interaction between the crust and mantle.

Mesozoic porphyritic rocks from the Zijinshan area, southwestern Fujian Province, China, are andesitic to rhyolitic in composition. The whole-rock SiO2 contents of these rocks are between 62.5% and 78.1%. Magmatic zircon from the Mesozoic porphyritic rocks was determined via secondary-ionization mass spectrometry (SIMS) for the U-Pb age and Hf and O isotopes. The zircon U-Pb ages could be mainly divided into three age groups: Group 1: ~138.8 Ma; Group 2: 109.2~107.4 Ma; and Group 3: 99.7~98.2 Ma. The εHf(t) and δ18O values of the porphyritic zircons showed that the porphyritic rocks in Group 2 were more affected by mantle-derived magma. Combined with previous research results, the medium-acidic magmatism in the southwestern Fujian Province can be divided into eight periods: Paleoproterozoic, Mesoproterozoic, Middle Neoproterozoic, Silurian to Lower Devonian, Permian to Triassic, Middle Jurassic to early Lower Cretaceous, late Lower Cretaceous, and late Lower Cretaceous to early Upper Cretaceous. The Paleoproterozoic crust was the predominant magmatic source for the subsequent Mesoproterozoic to Jurassic magmatism, but the only melts that were closely related to mineralization were derived from partial melting of the Mesoproterozoic crust and a more depleted upper mantle.