Late Jurassic Granitoids in Mufushan Complex and Their Significance for the Mesozoic Tectonic Evolution of Eastern South China

The Mesozoic tectono-thermal evolution of eastern South China plays an important role in forming the abundant magmatic rocks and associated giant polymetallic deposits. The middle-late Mesozoic granitoids in Mufushan and adjacent regions (e.g., Lianyunshan, Wangxiang, Taohuahsan, etc) represent the western front of the southeast China magmatic province. New zircon U-Pb dating suggests that the Mufushan two-mica monzogranites were emplaced at 149–144 Ma, a short time after the ~152 Ma granodiorites. These late Jurassic granitic magmas share broad similarities in geochemical-isotopic characteristics, with significant enrichment in LREE and LILE (e.g., Ba, Rb, Th, and K), depletion in some HFSE (e.g., Nb, Ta, Ti, and P) and positive Pb anomalies, comparable to those of arc-type rocks. The presence of Neoproterozoic zircons within the Mesozoic magmatic rocks indicates a certain amount of ancient material involved in the genesis of the magmas, suggesting a significant contribution from partial melting of the Neoproterozoic volcanic-sedimentary sequences to the middle-late Mesozoic granitoids. The two-mica monzogranites have εHf(t) values ranging from −13.4 to +3.5, overlapping with those of the granodiorites (−11.3 to +6.6), but both are lower than contemporaneous diorites (−2.4 to +0.59), suggesting a greater incorporation of enriched materials into the source for the granitoids. The two-mica monzogranites and granodiorites have εNd(t) values ranging from -10 to -8.8 and -7.9, with corresponding two-stage Nd model ages of 1.7–1.6 Ga and 1.6 Ga, respectively, falling within their Hf model ages which have two-stage Hf model ages of 2.0–1.4 Ga and 1.8–1.4 Ga, respectively. Compared with the geochemical and isotopic compositions of the coeval magmatic rocks in eastern South China, we favor that the late Jurassic Mufushan granodiorites evolved from variable mixing and differentiation of the diorites and granitoids, accompanied by other processes such as continuous magma assimilation. The well-developed early Cretaceous A-type granitic rocks in eastern South China reflect a dominant extensional tectonic regime induced by slab roll-back of the Izanagi plate. The involvement of subduction-related melts facilitated the underplating of mantle-derived magma and crustal heating, triggering large-scale partial melting of the lithosphere and magma enrichment, as well as the polymetallic deposits in eastern South China.