Miocene-Quaternary structural evolution of the Uyuni-Atacama region, Andes of Chile and Bolivia

We describe the Miocene-Quaternary geological-structural evolution of the region between the Salar de Uyuni and de Atacama, Andes of Chile and Bolivia. We recognized four main tectonic events based on fold geometry, fault kinematics and stratigraphic data. The oldest event, of Miocene age, is characterized by folding and reverse faulting of the sedimentary successions with an E-W direction of shortening in the northern part of the studied area and a WNW-ESE shortening in the southern part. The following two events, of Pliocene age, are characterized by lower shortening amounts; they occurred first by reverse faulting with a NW-SE-trending greatest principal stress (sigma(1), computed with striated fault planes) and a vertical least principal stress (sigma(3)), followed by pervasive strike-slip faulting with the same NW-SE-trending sigma(1) and a horizontal NE-SW sigma(3). The fourth event, dating to the late Pliocene-Quaternary is characterized by normal faulting: the sigma(3) still trends NE-SW, whereas the intermediate principal stress sigma(2) exchanged with sigma(1). Volcanism accompanied both the contractional, transcurrent and extensional tectonic phases. The Mio-Pliocene compression appears directly linked to a rapid convergence and an apparently important coupling between the continental and oceanic plates. The E-W to WNW-ESE direction of shortening of the Miocene structures and the NW-SE sigma(1) of the Pliocene structures seem to be more linked to an intra-Andean re-orientation of structures following the WNW-directed absolute motion of the South-American Plate. The extensional deformations can be interpreted as related to gravity forces affecting the highest parts of the volcanic belt in a sort of asymmetrical (SW-ward) collapse of the belt. (C) 2008 Elsevier B.V. All rights reserved.