Abstract The Andean Orogeny in South America has lasted over 100 Ma. It comprises the Peruvian, Incaic and Quechuan phases. The Nazca and South American plates have been converging at varying rates since the Palaeocene. The active tectonics of South America are relatively clear, from seismological and Global Positioning System (GPS) data. Horizontal shortening is responsible for a thick crust and high topography in the Andes, as well as in SE Brazil and Patagonia. We have integrated available data and have compiled four fault maps at the scale of South America, for the mid-Cretaceous, Late Cretaceous, Palaeogene and Neogene periods. Andean compression has been widespread since the Aptian. The continental margins have registered more deformation than the interior. For the Peruvian phase, not enough information is available to establish a tectonic context. During the Incaic phase, strike-slip faulting was common. During the Quechuan phase, crustal thickening has been the dominant mode of deformation. To investigate the mechanics of deformation, we have carried out 10 properly scaled experiments on physical models of the lithosphere, containing various plates. The dominant response to plate motion was subduction of oceanic lithosphere beneath continental South America. However, the model continent also deformed internally, especially at the margins and initial weaknesses.

Abstract Thin-skinned gravitational gliding of sediments above a detachment layer of salt or shale is common on passive margins. Changes in surface slope result in a domain of extension upslope and a domain of contraction downslope. Contractional domains tend to occur under present-day deep water and are thus not well understood. In the deep-water Santos Basin, Brazil, a contractional domain contains a suite of salt-cored structures. Angular folds (chevron and box folds), as well as concentric folds, are common in the upper part of the Aptian evaporite sequence, which appears to comprise alternating layers. In general, angular and concentric folds form by flexural slip during shortening of mechanically layered sequences. Their occurrence in the Santos Basin is evidence in favor of horizontal contraction. The lower part of the Aptian evaporite sequence appears to be mostly rock salt. It has been squeezed out from under synclines into spaces created by growing anticlines. In places, the layered evaporite sequence has been thickened or even repeated across thrust faults and ramp anticlines. An overlying sequence of open-marine sediments has been condensed or eroded over anticlines but forms local depocenters. These depocenters are asymmetric (of foreland style) next to isolated thrusts but symmetric in synclines or between thrusts of opposite vergence. The structural styles have been reproduced in physical models, properly scaled for gravitational forces, in which salt is represented by silicone putty and sediments are represented by sand. The models were shortened horizontally by a screw jack. The experiments illustrate the importance of horizontal contraction and syntectonic sedimentation in shaping salt-cored structures. They have been used to establish criteria that may be diagnostic of construction.