Basement structural control in the Magallanes-Malvinas fold and thrust belt, offshore Argentina

In this study, we examine the external part of the Magallanes-Malvinas Fold and Thrust Belt in offshore areas, including a portion in Tierra del Fuego onshore, in southern South America. Our investigations focus on the interaction between a thin-skinned fold and thrust belt and the basement in that deformation, considering preexisting structures acting as stress risers and localizing a possible tectonic inversion. The data is composed of around 14,000 km of 2-D multichannel seismic lines and three exploratory wells, used to analyse the anticlines of the fold and thrust belt in the area. The strike of these folds progressively evolves from NW-SE trending in western onshore regions, to WSW-ENE trending in eastern offshore areas. The fold and thrust belt shows a buttressing effect against the Rio Chico Arch. The most shortening is seen in the apex of the Rio Chico Arch around 67 degrees W, in the coast of Tierra del Fuego, and gradually decreases eastwards in offshore regions. A connection between basement-involved faults and folds offshore is inferred from the analysis of the Geminis and Ciclon anticlines, developed during the N-S last compressional stage of deformation in the late Oligocene/early Miocene. The Geminis anticline is a fault propagation fold with a total shortening of 205 m with a piggyback basin developed over its backlimb. The location and ENE-WSW strike-direction of the fold have been controlled by a basement-involved fault. The Ciclon anticline is a subtle fold trending WNW-ESE developed as a result of the slight tectonic inversion of a negative flower structure.