Abstract Isotope signatures and T DM model ages in Hong Kong and neighbouring Guangdong Province have indicated that the basement of the Cathaysia Block is probably an amalgamation of narrow crustal slices, ranging in age from latest Archaean to Mesoproterozoic. Inheritance ages from zircons contained within Mesozoic volcanic and plutonic rocks also show Proterozoic and Archaean components. Regional gravity survey studies display NNE- to NE-trending Bouguer anomalies that are indicative of sharp changes in rock densities at middle and lower crustal levels. The anomalies displayed on the gravity profile from Guangdong to Hong Kong have been modelled as narrow slices of Archaean and Proterozoic crust. A substantial E-W-trending Bouguer anomaly, which largely parallels the trend of the foliation in the Proterozoic schists of the region, is present to the east of Guangzhou. It is proposed that the basement of the Cathaysia Block consists of an amalgamation of NE- to NNE-trending Palaeo- to Mesoproterozoic and Archaean crustal terranes, which in places have retained the pre-amalgamation E-W-trending tectonic fabric. The discontinuities between the basement terranes, and the E-W structures have strongly influenced the geological evolution of the Phanerozoic sequences and igneous complexes in southeast China. These are most obviously manifest in the regional NE-trending fault and shear zones that displace the cover sequences.