Abstract: In this work, mafic microgranular enclaves have been found in the Caijiang granitic pluton, Jiangxi Province. This paper reports the geological and petrographic, as well as LA-ICP-MS zircon U-Pb geochronology and element geochemistry characteristics of these enclaves. Most of the enclaves are elliptical, showing quenched margin and back veins. They have typical magmatic texture and acicular apatite. Some enclaves contain feldspar xenocrysts. These enclaves have relatively lower SiO₂ (as low as 57.05 wt%) and higher MgO + Fe₂O₃ (up to 14.21 wt%). LA-ICP-MS zircon U-Pb dating shows that these enclaves were formed at 224 Ma, and there is a time gap of about 4-6 Ma with the host granite (230-228 Ma). Characteristics above indicate these enclaves are the masses of discrete mantle-derived basic magma or mixing products of mantle-derived magma and host magma. It is likely that the enclave magma was injected when the host granitic magma was in a state of crystal mush. The discovery of MMEs provide direct evidence for the underplating of mantle derived magma, and the formation of Caijiang granitic rocks at a high temperature. This work is of great significance to further study the heat source mechanism of Indosinian granites in South China.

Key words: mafic microgranular enclaves, Caijiang pluton, magma mixing, underplating, heat source mechanism