Abstract: The oldest rocks exposed on the western Cathaysia Block in southeastern (SE) China are younger than Mesoproterozoic.However, the U-Pb and Hf-isotope systematics of xenocrystic zircons, brought to the surface by the Mesozoic-Cenozoic basaltic rocks in Guangxi Province, suggest the presence of unexposed Archean basement, with zircon populations of 3.85 Ga, 3.55 Ga,3.3~3.2 Ga and mainly 2.9~2.5 Ga and Hf model ages (t DM) of 2.5 Ga to ≥3.9 Ga, beneath the western Cathaysia Block. This basement experienced complex modification through time, including the addition of juvenile mantle material at ca 3.6~3.2 Ga, 2.5 Ga, 1.0 Ga and 0.5 Ga. The zircons also record thermal events that reworked (remelted) the older crust of the block at ca 2.0~1.8 Ga and 1.6~1.5 Ga.