The crystalline basement of the Central Andes between 21°S and 26°S consists of a variety of Neoproterozoic-Paleozoic arc-type and basinal assemblages. We characterize these assemblages through analysis of U-Th-Pb ages of zircons sampled from 16 different plutonic suites and from 21 different sandstones in northern Argentina and Chile. The ages of igneous zircons show that magmatism occurred in three main phases: ca. 550 Ma (late Neoproterozoic); 490-464 Ma (Late Cambrian to Middle Ordovician); and 318-264 Ma (late Carboniferous-Late Permian). Detrital zircon ages are mainly 600-450 Ma from Paleozoic strata all across the orogen, reflecting derivation primarily from local Neoproterozoic, Cambrian, and Ordovician magmatic constructs. These relations suggest that crystalline basement in this portion of the Andes was assembled within a broad extensional convergent margin system during early Paleozoic time. Because similar arc and basinal assemblages characterize much of the Terra Australis orogen, it is not possible to constrain the degree of tectonic mobility within this convergent system.