The Qianlishan complex, located in Hunan Province of South China, is closely associated with intense W-dominated polymetallic mineralization. The Qianlishan complex is composed of three phases: the main-phase porphyritic and equigranular granites, granite porphyry, and mafic dykes. Geochronologically, the zircon U-Pb dating results show that the porphyritic and equigranular granites have ages of approximately 159 and 158 Ma, respectively, similar to those of mafic dykes (approximately 158 Ma), while the granite porphyry was formed later at approximately 145 Ma. Geochemically, the mafic dykes are characterized by calc-alkaline high-Mg andesite (HMA) with high MgO, TiO₂, Mg#, and CA/TH index. They exhibit significantly depleted εNd(t) and εHf(t) with high Ba/La, La/Nb, and (La/Yb)_N, indicating that they formed from mixing melts of depleted asthenospheric mantle and metasomatized subcontinental lithospheric mantle (SCLM). The main-phase granites are peraluminous and are characterized by high SiO₂, low (La/Yb)_N ratios, and relative depletion in Ba, Sr, Ti, and Eu. They also display negative correlations between La, Ce, Y, and Rb contents, suggesting that they are highly fractionated S-type granites. Furthermore, they show high εNd(t) and εHf(t), CaO/Na₂O ratios, HREE, and Y contents, indicating that they were produced by parental melting of ancient basement mixed with mantle-derived components. In contrast, the granite porphyry shows A-type signature granites, with higher εNd(t) and εHf(t) and CaO/Na₂O ratios than the main-phase granites but similar Zr/Nb and Zr/Hf ratios to the mafic dykes, suggesting that they are the products of partial melting of a hybrid source with ancient basement and the mafic dykes. We thus infer that the slab roll-back led to generation of Qianlishan back-arc basalt and HMA and further triggered the formation of the Qianlishan granite.

The debate of hydrous and anhydrous mafic magmatism in the Emeishan large igneous province (ELIP) requires more robust petrological and mineralogical evidence. This paper reports zircon U–Pb ages, clinopyroxene and hornblende major element compositions, whole-rock geochemical and Sr–Nd–Pb isotopic data of hornblende-rich mafic plutonic rocks from the Xinhe igneous complex in the central ELIP to address this issue. Analytical results indicate that the Xinhe mafic rocks were emplaced at 260–259 Ma, consistent with the main eruptive phase of the ELIP. The Xinhe mafic rocks can be divided into hornblende gabbro and gabbroic diorite based on petrographic characteristics and MgO content. The Sr–Nd–Pb isotopic signatures of Xinhe mafic rocks are indicative of an EMI-type enriched mantle source, which is similar to the adjacent contemporaneous Miyi layered intrusions and basalts in the ELIP. The Xinhe mafic rocks exhibit a hydrous-type crystallization sequence (clinopyroxene–hornblende+plagioclase), which contrasts markedly with the anhydrous-like olivine+plagioclase–clinopyroxene sequence documented in the Miyi layered intrusions. This difference records contrasting magmatic water conditions during crustal magmatic evolution, although water enrichment during differentiation, differing pressure–redox histories, and fluid interaction may also contribute to the observed assemblages. Mantle-source water heterogeneity remains a plausible interpretation that requires independent confirmation.

Large Igneous Provinces (LIPs) refer to intraplate magmatic edifices dominated by mafic rocks, characterised by short-duration emplacement (0.1 × 106 km³) (Bryan & Ern...