Two distinct suites of Archaean (about 3100 Ma) granulite-facies orthogneisses, predominantly of intrusive origin, have been recognised in the Napier Complex of Enderby Land, Antarctica. One, mainly of tonalitic to granodioritic composition, is strongly depleted in Y and HREE, and is characterised by positive Eu anomalies. It probably represents new continental crust derived by hydrous partial melting of a hornblende and/or garnet-bearing mafic source. A generally younger undepleted suite, predominantly of trondhjemitic to granitic composition, has higher TiO2, P2O5, Y, Zr, Nb, REE, and Ga/AI, lower CaO, Sr, Ti / Y, Ce/Y. and Mg/ (Mg + total Fe), and commonly negative Eu anomalies. It apparently originated by relatively dry, lower-pressure melting of mainly felsic crustal rocks. Compositional differences between depleted tonalites and granodiorites are almost entirely confined to LIL elements (K, Rb, Ba, Pb, Th, and U), and can be explained by interaction of either the source material or the magma (during generation or, less likely, emplacement) with an LIL-element-enriched fluid phase. Such an enrichment process is difficult to model in detail because of LIL-element depletion during granulite-facies metamorphism. Depleted granitoids may be representative of a deeper crustal level than undepleted granitoids, which, together with a variety of metasediments, predominate in adjacent lower-grade (amphibolite to low granulite facies) late Archaean and Proterozoic terrains. The Archaean granitoids are dominated by two I-t ype (igneous-derived) suites, whereas those of post-Archaean age are largely u depleted I-type or S-type (sediment-derived).