UPPER CENOZOIC MAGMATIC EVOLUTION OF THE ARGENTINE PUNA—A MODEL FOR CHANGING SUBDUCTION GEOMETRY

The spatial and temporal distribution and chemistry of Late Oligocene to Recent Central Andean Puna volcanic rocks can be broadly explained by temporal changes in the dip of the subducting Nazca plate and the thickness of the lithospheric mantle and crust beneath the Puna plateau. Temporal changes in lithospheric and crustal thickness are tracked by using REE elements as guides to pressure-sensitive residual mineralogy and source melting percentages. Thin lithosphere is tracked by large dacitic ignimbrite eruptions and the distribution of mafic lavas. The data suggest that the southern Puna has been in an intermediate position between a steepening slab to the north and a shallowing slab to the south throughout the late Tertiary.