Late Cretaceous to Oligocene Magmatic Evolution of the Neuquén Basin

Geochemical variations in arc- and within-plate magmatic associations since Late Cretaceous times are analyzed and correlated with the main tectonic changes that influenced the Neuquen Basin evolution. The collision and southward migration of the Farallon-Aluk mid-ocean ridge along the Chilean trench since 80 Ma have played an important role in controlling the Late Cretaceous to Oligocene magmatic evolution of the arc and retroarc zones. The passage of this spreading center through the Chilean trench induced the development of geochemically distinct magmatic associations since Late Cretaceous to Eocene times associated with the extensional reactivation of the Cretaceous fold and thrust belt. Then, by Late Oligocene times, a major plate tectonic reorganization occurred when the Farallon plate broke apart and the resulting Nazca plate started an orthogonal subduction regime beneath the South American plate with higher convergence rates. Then extensional basins and associated magmatism developed at this time destabilizing the Paleogene fold and thrust belt and establishing a more homogeneous tholeiitic signature along the Andean axis.