K-Ar and 40Ar/39Ar dating of volcanic rocks from the Maricunga belt of north-central Chile indicate that igneous activity took place throughout most of Miocene time at various places in the 150 by 30 km belt. No migration patterns of volcanism appear in the Miocene rocks of the belt. Volcanic activity ceased by the end of the Miocene. All the Miocene volcanic rocks studied are calcic andesites to dacites with about 62% SiO2, 18% A12O3, 4% Fe2O3 (total), and 2% K2O. Initial 87Sr/86Sr (Sri) values fall into two groups, one of lower values around 0.7050 to the west and the other of higher values around 0.7060 to the east. It is postulated that the two Sri groups reflect two adjoining coherent lower-crustal magma sources of possibly different age and subtly different composition that form part of the western edge of the South American craton. ?? 1994.