Mesozoic palaeogeography and palaeoenvironmental evolution of Patagonia (southern South America).

LUIS SPALLETTI; JUAN FRANZESE

Patagonian Mesozoic Reptiles

Indiana University Press

Lugar: Indiana, USA; Año: 2007; p. 29 - 49

The Mesozoic palaeogeography of southernmost South America (Patagonia) is depicted through a series of palinspastic maps showing interpreted sedimentary and tectonic environments, as well as magmatic events associated with basin development. These maps are in 15 Ma steps from the Early Triassic to the Late Cretaceous. Grain of the basement controlled many of the palaeogeographic features of this region of Gondwana, in particular the development of sedimentary basins and the lines of opening of the South Atlantic. Besides, along the west side of South America a largely convergent active (proto-Pacific) margin persisted since at least Permian time. The break-up of Gondwana resulted from the interaction of a series of hotspots or mantle plumes that impinged on or between the cratonic regions of Gondwana. Patagonia has been affected by two significant mantle plumes during Mesozoic time: the Karoo plume impacted at about 183 Ma, and the Paraná-Etendeka plume impacted at c.132 Ma. The Paraná-Etendeka plume seems to have been at least partially responsible for the splitting of South America from Africa. The evolution of the Mesozoic basins of Patagonia was controlled by two major tectonic regimes: subduction along the western margin of Gondwana and intracontinental extension and opening of the southern Atlantic Ocean. Narrow and isolated Triassic depocenters, the large Jurassic-Cretaceous San Jorge and Cañadón Asfalto Basins of central Patagonia, and the Cretaceous failed rift arms created during the opening of the South Atlantic were formed as a response to intracontinental extension. Jurassic and Cretaceous intra-arc and back-arc extensional basins were formed as the result of subduction along the Pacific margin of Patagonia. The majority of these basins were floored by continental crust. Conversely, in southernmost Patagonia, the marginal Rocas Verdes Basin was floored by oceanic crust. Two giant basins, the Neuquén basin to the north and the Austral basin to the south of Patagonia, show a more complex evolution. They started as a series of continental extensional troughs. During the Jurassic and Early Cretaceous they behaved as large back-arc basins characterised by starvation and widespread marine sedimentation. Finally, as a result of acceleration of Late Cretaceous plate convergence they passed through a retro-arc flexural stage with a progressive change from marine to continental-dominated sedimentation.