Multi-proxy insights into the structure and geometry of the tectonic boundary at the Cordillera de Domeyko-Salar de Atacama border: An example of the interplay between basement and foreland basins

Abstract

The study of the Cordillera de Domeyko and the Salar de Atacama Basin in northern Chile has been critical to understand the generation of the Andean Cordillera and the migration of the deformation front eastwards. However, the relation between the uplift of the range, its temporal pattern, and the formation of the Preandean Depression have not been fully understood. In this article, we forward modeled two gravimetry surveys, consisting in 185 stations crossing the boundary between the Salar de Atacama Basin and Cordillera de Domeyko, with the goal of understanding the physical traits of each domain and the variations in basin geometry. We interpreted two seismic reflection profiles, along with log data from one well in the basin center, and additionally, we analyzed an inversion of the magnetic anomaly for both lines. The results of the analysis show the segmentation of physical properties into two domains. The first is interpreted as basement (Triassic-older) units, while the other shows the presence of gravity lows correlated with late Mesozoic-Cenozoic units cropping out along the western edge of the basin. The magnetic anomalies identified were correlated with variations within the basement and outcrops of crystalline intrusives. Within the sedimentary units, the Late Cretaceous-Paleogene Purilactis Group and Paleogene-Eocene formations were distinguished from the evaporite-rich Oligocene-Miocene Paciencia Group. The latter was deposited after a compressive event (Incaic Event) which thrusted basement units eastwards, inverted Mesozoic extensional faults, and generated the accommodation space required for its deposition. The basin then experienced renewed compression during the Miocene. This interplay between basement uplift and thrusting, along with fault inversion and basin generation, is a characteristic found in other parts of the Salar de Atacama Basin and the orogen, suggesting that this tectonic style might be prevalent in other basins comprising the Preandean Depression and along the Central Andes.