The Mesozoic evolution of the Neuquén Basin and its relationship with the history of Western Gondwana.

SPALLETTI, L.A; FRANZESE, J.; VEIGA, G.; SCHWARZ, E.

Mendoza

Simposio; Gondwana 12 Conference; 2005

International Association for Goindwana Research

The Neuquén Basin of Argentina is composed of a near continuous Late Triassic to Early Cainozoic siliciclastic-carbonate succession deposited on the eastern side of the evolving Andean mountain chain. The evolution of western Gondwana is clearly recorded in the 4,000-m thick fill of the basin. From the Late Triassic to the Early Jurassic a series of rift depocentres were opened and a first synrift stage, characterised by extensional volcanism and coeval continental volcaniclastic sedimentation, occurred. This process was related to continental intraplate extension associated with the first stages of Gondwana break-up and the earliest development of the Andean magmatic arc along the proto-Pacific margin of the supercontinent. After the impact of the Karoo plume in the Early Jurassic, widespread intraplate extension was installed in western Gondwana, causing the opening and drift of the Weddell Sea. Along the proto-Pacific margin the Andean magmatic arc developed as a result of protracted subduction of the Pacific (Phoenix) plate beyond western Gondwana. Within this tectonic framework, the Neuquén Basin became a large ensialic backarc depression controlled by thermal subsidence, punctuated by localised extension and basin inversion (e.g.Huincul Arch). Relative sea level changes controlled the development of transgressive-regressive cycles of different magnitude. The maximum sag phase in the Neuquén Basin (Late Jurassic – Early Cretaceous) was accompanied by localised extensional reactivation in the backarc, widespread marine sedimentation, starvation and anoxia. Later on, the main Early Cretaceous tectonic event in western Gondwana was the impact of the Paraná plume and the opening of the South Atlantic Ocean. In the Neuquén Basin the sag regime was affected by pulses of tectonic inversion, uplift and relative sea-level falls. In the Late Cretaceous the drift of the South Atlantic produced the total isolation of South America from the rest of western Gondwana. It was also a period of strong reorganisation of the Pacific plates, with a marked shallowing in the position of the subducting slab. As a result, a compressional foreland regime started in the Neuquén Basin where a thick continental sedimentary record was developed. The depositional axis migrated progressively from west to east as the Neuquén Basin merged with other basins to the south to produce a unique giant depocentre. Finally, in the Late Cretaceous the compressional regime continued along the Andean margin and generalised subsidence dominated the taphrogenic basins facing the Atlantic Ocean. As a result, an Atlantic transgression invaded northern Patagonia and almost all the Neuquén Basin to the northwest. Although the tectonic and depositional history of the Neuquén Basin was extremely complex and could have been controlled by different regional and local factors, its main evolutionary stages were a clear response to the tectonic history of both the active Pacific Gondwana margin and the Gondwana break-up.