Aptian to recent compressional deformation, foothills of the Neuquén Basin, Argentina

Abstract

The Neuquén Basin lies in north-western Patagonia, on the eastern foreland of the Andes. It formed as a rift basin in the early Mesozoic and contains some 5000 m of Triassic to Aptian sediment, mainly marine. As a result of Andean orogeny, the western edge of the basin now forms part of the foothills. We describe some of the main compressional structures, drawing on surface and sub-surface data. We argue that regional eastward dips are due to west-verging thrust displacements on the Andacollo–Loncopué fault system. During a Late Cretaceous Peruvian phase (Aptian to Campanian), continental sediment accumulated in a retro-arc foreland basin, which was mainly of flexural origin. Nevertheless, more than 1500 m of Late Cretaceous sediment accumulated in the footwall of the east-verging Agua Amarga thrust. The Peruvian phase was responsible also for transpressional reactivation of a rift transfer zone, the Huincul Arch. The Incaic phase (Eocene) was responsible for north-westerly trending folds and thrusts, reactivation of Cretaceous thrusts, abundant andesitic lavas and high-level intrusions, and a swarm of north-easterly trending bitumen dykes. The Quechua phase (Miocene to Recent) produced northerly trending folds and thrusts and a Miocene foreland basin, containing some 1000 m of basalt lava flows. Structures that formed during the Incaic and Quechua phases are broadly compatible with the history of convergence at the Pacific margin of South America, as deduced from plate reconstructions.