First evidence for Archean continental crust in northern Vietnam and its implications for crustal and tectonic evolution in Southeast Asia

Southeast Asia, or, in a more strict sense, the Indochinese continent, was previously considered to be composed entirely of Proterozoic to Phanerozoic rocks, and reliable evidence for Archean crust was lacking. Gneisses from the Cavinh Complex, south of the Red River shear zone, northern Vietnam, however, show Archean Nd model ages of 3.4-3.1 Ga. Zircon separates from the rocks yielded U-Pb dates of 2.8-2.5 Ga, the first convincing evidence for the presence of a Late Archean complex in Southeast Asia. Given that the Red River shear zone was propagating in the South China block with a left-lateral offset of ∼600 km, the Cavinh Complex can be correlated with the Late Archean Kangding Complex in the western margin of the Yangtze craton, southwestern China. The Cavinh Complex therefore represents one of the oldest crustal nuclei of the South China block.