Structure of the Cordillera de la Sal: A key tectonic element for the Oligocene-Neogene evolution of the Salar de Atacama basin, Central Andes, northern Chile

Abstract

The Salar de Atacama basin is the main topographic low of the Preandean Depression of the Central Andes of northern Chile. Although numerous studies have been carried out in this area, the origin of the depression is still a matter of debate. The integration of seismic reflection and surface structural data along the basin allows the characterization of Oligocene and Neogene tectonic activity of the Salar de Atacama. A key element to unravel the Neogene to recent history of the basin is found along the Cordillera de la Sal, which comprises more than 3000 m of continental sedimentary succession assigned to the San Pedro Formation. Detailed analysis of the seismic data shows that large depocenters involving distal alluvial facies and evaporitic members of the San Pedro Formation accumulated in close relation with Oligocene extension. Extension was controlled by a first order normal fault located along the western flank of the Atacama basin, which appears as a key structural feature of the internal architecture of the Salar de Atacama. The rise of the Cordillera de la Sal ridge during the Neogene involved compression and sinistral strike slip in its southern domain, in combination with salt diapirism in its north domain. This transition is related to the thickness and distribution of the evaporitic lower members of the San Pedro Formation, which also controls the depth of the detachment level beneath the Cordillera de la Sal. Our results show that the current relief of the Salar de Atacama basin is mainly due to Oligocene extension and subsequent Neogene tectonic inversion.