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A comprehensive study of zircon U–Pb dating and in situ Hf isotopes, whole-rock major and trace element geochemistry and Sr–Nd isotopes was carried out for three late Mesozoic granitic plutons (Waitun, Shipi and Taiyuan) in northwestern Fujian province, SE China. We assess the origin of the granites and their relationship to the evolution of the late Mesozoic volcanic–intrusive complex belt in SE China. LA-ICP-MS zircon U–Pb dating shows that three plutons were emplaced in the Middle Jurassic to Early Cretaceous (168–109 Ma), in which the Waitun and Shipi plutons are intrusive complexes. All the plutons are composed of high-K calc-alkaline I-type granites with a great diversity in elemental and isotopic compositions. The granites have SiO 2 contents of 68.3–78.5 wt.%, showing a gradual decrease in initial 87 Sr/ 86 Sr (0.7181 to 0.7091) and increase in ε Nd (T) (− 16.7 to − 8.1) and ε Hf (T) (in-situ zircon) (− 20.6 to − 6.9) with decreasing emplacement ages. Geochemical data suggest that the Middle Jurassic (~ 168 Ma) Waitun granites are of purely crustal origin, derived by partial melting of a mixed source of Paleoproterozoic metaigneous (~ 78%) and metasedimentary (~ 22%) rocks at a depth of 30–40 km triggered by underplating of basaltic magma. Mixing of such crustal melts with about 10% basaltic magma could account for the origin of the Late Jurassic (~ 161 Ma) Waitun granites. The Late Jurassic (~ 156 Ma) Shipi and Early Cretaceous (~ 134 Ma) Taiyuan granites were produced by extensive fractional crystallization of primary crustal melts, the source of which show relatively high proportion (~ 82%) of metaigneous rocks. The Early Cretaceous (~ 109 Ma) Shipi granites were generated by partial melting of a mixed source of Paleoproterozoic metaigneous (~ 92%) and metasedimentary (~ 8%) rocks at a depth of ~ 30 km plus additional (~ 15%) input from coeval basaltic magma. The granites were formed in a continental arc setting induced by northwestward subduction of the Paleo-Pacific plate. Progressive slab rollback since the Middle Jurassic from inland to the coastal area is the most likely mechanism for the generation of the granites. [ABSTRACT FROM AUTHOR]

The early Paleozoic orogen of South China is possibly one of the few examples of intraplate orogeny in the world. It is characterized by an angular unconformity between post-Silurian cover and pre-Devonian strata and by the intensive and extensive early Paleozoic granitic plutonism. However, synchronous mafic–ultramafic rocks have not been well-studied, but they are crucial for understanding the nature and evolution of the orogen. In this paper, we present the first detailed LA-ICP-MS zircon U–Pb dating, major and trace element geochemical and Sr–Nd–Hf isotopic data for a Silurian gabbroic pluton (Dakang) and a coeval granitic pluton (Guiyang), that have recently been identified in central Fujian, in the southeastern part of the orogen. We assess the origin of these mafic and granitic rocks and their relationship to the evolution of the early Paleozoic orogen in South China. LA-ICP-MS zircon U–Pb dating shows that the Dakang and Guiyang plutons were emplaced at 441–438 Ma and 431 Ma, respectively. The Dakang pluton consists of gabbros and minor intermediate rocks (diorite, monzodiorite and monzonite). These rocks are all metaluminous and potassic, and are enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE). They have initial 87 Sr/ 86 Sr of 0.7066–0.7098, ε Nd (T) of − 7.0 to − 3.3 and ε Hf (T) (in-situ zircon) of − 5.2 to − 4.4. Geochemical data suggest that the Dakang gabbroic magmas were derived by partial melting of previously subduction-modified lithospheric mantle in the spinel–garnet transition zone at a high temperature (~ 1300 °C). These primary magmas underwent fractionation crystallization of clinopyroxene and amphibole, forming the evolved gabbros and intermediate rocks. The Guiyang pluton consists of weakly peraluminous granites, which show low Ga/Al ratios (10,000*Ga/Al < 2.6) and so can be classed as I-type granites. They have initial 87 Sr/ 86 Sr of 0.7095–0.7113, ε Nd (T) of − 6.7 to − 5.9 and ε Hf (T) (in-situ zircon) of − 7.7 to − 0.8. Geochemical data suggest that the Guiyang granites were generated by partial melting of a mixed source of Paleoproterozoic metaigneous and metasedimentary rocks in the lower crust. Our new data, together with published data, confirm that lithospheric delamination occurred along the metamorphic core of the early Paleozoic orogen of South China during the Silurian (442–420 Ma), and that this represents a post-orogenic tectonic regime in the orogen core. [ABSTRACT FROM AUTHOR]