Late Jurassic high-silica granites in the interior and coastal South China and their tectonic implication

Abstract

The South China Block is predominantly influenced by the Paleo-Pacific dynamic domain during the Late Mesozoic, resulting in the formation of volcanic-intrusive complexes along the interior and coastal regions, which provide significant insights into magmatic evolution and geodynamic processes. This paper presents new zircon ages and geochemical data for the Late Jurassic granites in Zhuhai and its surrounding islands. The inland granites from Zhuhai (163–159 Ma) consist of biotite granites and two-mica granites with (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.70901–0.70993, ε_Nd (t) values from −10.1 to −8.9, and ε_Hf (t) values from −12.5 to −4.2. In contrast, the island biotite granites form Wanshan and Dong'ao islands (155–150 Ma) exhibit lower (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.70418–0.70722, higher ε_Nd (t) values from −7.0 to −6.1, and ε_Hf (t) values from −8.5 to −2.0 than inland granites. The two groups share similar (²⁰⁶Pb/²⁰⁴Pb)_i ratios of 17.95–18.96, (²⁰⁷Pb/²⁰⁴Pb)_i ratios of 15.72–15.76, and (²⁰⁸Pb/²⁰⁴Pb)_i ratios of 38.53–39.16. Geochemical characteristics indicate that the inland granites formed from the partial melting of Paleoproterozoic crustal metasedimentary rocks, while the island granites were derived from a mixed source region of ancient metaigneous rocks with a juvenile crustal component. Subsequent extreme crystallization and amalgamation formed granitic plutons. Our study, together with geological observations and previous data, suggests that the Late Jurassic magmatism in the interior and coastal regions of the southeastern South China Block likely corresponds to western and eastern sides of Cathaysia and formed in response to the far-field effects of the subduction of the Paleo-Pacific Plate beneath the Eurasia.