Grenvillian massif-type anorthosites in the Sierras Pampeanas

We report the discovery of massif-type anorthosites in the Andean basement of the Western Sierras Pampeanas of Argentina. U-Pb zircon dating (by sensitive high-resolution ion microprobe) of a cogenetic gabbronorite dyke yields ages of 1070 ± 41 Ma for igneous emplacement and 431 ± 40 Ma for metamorphism. These anorthosites are petrologically and geochemically comparable with those of the Grenville province of Laurentia. Palaeogeographical reconstructions of Rodinia at 1.0-1.1 Ga suggest that the Sierras Pampeanas anorthosites were part of a large anorthosite province in the late…