Abstract

In northern Chile (18-20°S), the western border of the high Andean Plateau (Altiplano) was uplifted by high-angle thrust faults and associated folds. These developed along the Precordillera, which is the morphostructural unit that connects the Andean Plateau, to the east, with the Central Depression, to the west. In the area of Moquella (19.3°S), this structural system is represented by a flexure (Moquella Flexure) and associated syntectonic deposits. The flexure was caused by a blind west-vergent thrust-fault which remained active, at least, between 21 Ma and 16 Ma. It accommodated approximately 700 m of the uplift of the western edge of the Andean Plateau, thereby contributing to 20% of the total uplift. The syntectonic deposits are represented by a 300-400 m thick, Neogene sedimentary and volcanic succession, referred to as Latagualla Formation, exposed in the Central Depression and extending up to the western border of the Precordillera. Part of the Neogene deformation and erosion of the western border of the Andean Plateau was recorded by deposits of this formation. The syntectonic trait of Latagualla Formation is evidenced by growth strata geometries associated with the flexure. In addition, large-scale landslides occurred along the flexural axis, being widely recognized also northward at the latitude of Arica, suggesting a regional extent for these phenomena.