Constructing the Cretaceous Highly Silicic Plutons in SE China through the Magmatic Plumbing System

Abstract High-silica plutons (SiO2 > 75 wt %) play a key role in deciphering the evolution and origin of the upper continental crust. Therefore, studying vertical cross sections of high-silica plutons is essential for gaining new insights into magmatic evolution and the thermal and material processes that shape the Earth's crust during pluton formation. In this study, we present extensive data on the bulk-rock geochemistry, zircon U–Pb ages, Hf isotopes, and trace elements for a range of high-silicic rocks from top-to-bottom cross-section in the Jiuzhen batholith and Yunhe pluton in southeastern China. Geochemical and zircon trace element features of the granitic rocks from the Jiuzhen batholith and Yunhe pluton indicate that these high-silica rocks originated from middle- to upper-crustal magma reservoirs via crystal-melt segregation. In the Jiuzhen batholith, the coarse-grained porphyritic granite in the upper unit originated from the reactivation of a pre-existing, highly evolved, water-rich magma reservoir with lower crystallinity, while the coarse-grained porphyritic granite in the lower unit was segregated from the same magma reservoir with higher crystallinity and involved a higher proportion of mantle material in its formation. The fine-grained granite was later extracted from the nearby magma reservoir of coarse-grained porphyritic granite in the upper unit, indicating they were formed through in situ differentiation of the silica magma reservoir in the shallow crust. Similarly, the geochemical characteristics of granites from different units of the Yunhe pluton suggest they were produced by the solidification of high-silica melts extracted from a common water-poor magma reservoir. As the high-silica magmas accumulated to form a magma reservoir in the shallow crust and subsequently underwent further cooling and crystallization, the proportion of melt decreased, leading to an enrichment of volatiles and silica in the residual melt. The upward migration of these residual melts within the high silicic magma reservoir resulted in vertical compositional variations within the Yunhe pluton. Our research on the Jiuzhen batholith and Yunhe pluton has revealed that the composition of high-silica magmas is influenced not only by crystal-melt segregation within deep magma reservoir but also by in situ crystal-melt segregation occurring within magma reservoirs formed through the aggregation of felsic melts in the shallow crust.