Tectonic Rotations Along the Western Central Andes

Abstract

Despite the evidence for protracted deformation, crustal shortening, and exhumation since at least 100 Ma along the Central Andes, the uplift of the Eastern Cordillera and Bolivian Orocline formation did not start until the Eocene–Oligocene. Moreover, the Central Andes also exhibit much younger recent surface uplift (e.g., 10 Ma) that would postdate significant shortening. Recent investigations were focused on the formation of the Bolivian Orocline by 2D Map-View Restoration of Non-plane Deformation experiments. Results from these 2D restorations support the hypothesis of the Paleogene formation of the Bolivian Orocline, due to differential shortening, concentrated in the Eastern Cordillera of Bolivia, Southern Peru, and northwestern Argentina. The “out of plane of cross-section” motion of material and the rotational components of deformation appear to be essential aspects for the formation of the Central Andes, although they are generally not included in models for orogenic systems evolution. One of the most remarkable results of the 2D restoration is the persistence of an “excess rotation” of 10–20° in northern Chile and 20–30° in Southern Peru which cannot be easily explained even if all the differential Paleogene shortening in the Eastern Cordillera and the Neogene shortening in the Sub-Andean zone were considered. Here, we discuss that a major proportion of rotation needs to be balanced in the forearc region by two major conjugate oblique shear zones (i.e., the Abancay Deflection and the Antofagasta–Calama Lineament). These shear zones are probably related to inherited lithospheric discontinuities and major changes in the magnitude of rotation likely occurring along these zones.