Petrogenetic relationship between plutonic and subvolcanic rocks in the Jurassic Shuikoushan complex, South China

Abstract

There has been a longstanding debate on whether plutonic and subvolcanic rocks have a petrogenetic connection, and the Jurassic Shuikoushan caldera complex in South China serves as an ideal case study for unraveling this geological puzzle. SIMS U–Pb dating of zircon indicates the formation age of plutonic (granodiorite) and subvolcanic rocks (dacite porphyry and rhyolite porphyry) from the Shuikoushan caldera complex at ca.159 Ma. In terms of geochemical composition, granodiorite and dacite porphyry exhibit higher levels of MgO (1.98–3.63%), MnO (0.07–0.11%), FeOt (5.12–6.15%), Sr (342–547 ppm), and Ba (754–1200 ppm) compared to the rhyolite porphyry. Conversely, they show lower concentrations of Rb (2.04–27.1 ppm), as well as lower ratios of Rb/Sr (0.004–0.055) and Rb/Ba (0.004–0.023). The distinct but complementary geochemical characteristics between these rock types are evident in the Shuikoushan caldera complex. Overall, zircon grains from all three rock types exhibit similar negative ε Hf(t) values (–8.1 to –12.4) with high δ 18O values (8.3–9.7‰), suggesting a common source region. Based on lithological and geochemical evidence, it is proposed that the rhyolite porphyry represents extracted melt from the mush reservoir. In contrast, the granodiorite and dacite porphyry are residual melts enriched in cumulates. This interpretation supports the idea that crystal–melt segregation processes were crucial in connecting the late Jurassic subvolcanic and plutonic rocks within the Shuikoushan complex.