Structural Styles and Tectonic Framework of the Fold and Thrust Belt in Tierra del Fuego and Offshore Austral-Malvinas Basins, Argentina

Abstract

Abstract Description The Andes Patagónicos bend to the east at the latitude of Tierra del Fuego island, were they constitutes the Cordillera Fueguina. This cordillera plunges eastward into the offshore and represents the southern border of Austral and Malvinas basins. The studied area includes the outer foothills of the fold and thrust belt located in Austral and Malvinas basins and their associated tertiary foreland deposits. The regional tectonic framework is mainly a resultant of the interaction between South America, Pacific, Antarctica and Scotia plates during Late Cretaceous and Tertiary times. The fold and thrust belt of Malvinas basin is a frontier area where no hydrocarbon exploratory wells have been drilled so far. Most of the data available are 2D regional seismic lines. Repsol YPF, as the operator of a consortium, recently acquired a 2500 km2 3D survey on this fold and thrust belt. Five restored cross sections in the area are shown and its timing reconstructed. Once the cross sections timing is established, it's associated and related to the tectonic evolution of the area. Application Once the traps formation timing is defined, a reliable basin modelling can be performed to reduce the uncertainty associated to the trap charge and type of hydrocarbons. Result, Observations and conclusions The structural style is quite variable along the outer foothills region. It changes eastward from a thin skin deformation style in Tierra del Fuego (Argentina) to a thin skin combined with basement inverted faults in Malvinas basin. The main decollements are Lower Cretaceous and Paleogene shales. The evolution of the fold thrust belt has been mainly controlled by the Scotia Plate activity, resulting in an intercalation of compressional/transpressional periods with others of extensional/transtensional character. It is postulated that the structures studied in the outer foothills were developed during Oligocene and Lower Miocene times. These ages correlate quite well with a period of high oceanic crust generation at Scotia Plate. Significance of subject matter In a fault thrust belt, different compressive pulses configure the traps final geometry. The timing of these different pulses is critical for a correct basin modelling and a prospects risk evaluation. Introduction The area is located in Tierra del Fuego Island and Austral-Malvinas basins. The study area involves the Andes Cordillera, where this bends to the east and plunges eastwards. (Figure 1) Austral and Malvinas basins started as Jurassic to Early Cretaceous extensional basins originated during the Gondwana break-up. During the Late Cretaceous-Tertiary ages, these basins were affected by Andean compression and flexural subsidence leading to a foreland-basin stage.