Kinematics of Neogene to Recent upper-crustal deformation in the southern Central Andes (23°–28°S) inferred from fault–slip analysis: Evidence for gravitational spreading of the Puna Plateau

Abstract

Elucidating the tectono-morphologic evolution of the Central Andes is important for understanding the mechanical behaviour of non-collisional orogens at convergent plate boundaries. Fault-kinematic data from the southern Central Andes are generally interpreted in terms of changes in plate (boundary) kinematics or vertical-axis rotation associated with the formation of the Andean orocline. However, none of these hypotheses accounts adequately for Neogene to Recent horizontal extension and vertical shortening of upper crust documented from the Puna Plateau and the adjacent Eastern Cordillera. Based on new and compiled fault-kinematic data, in total 4746 brittle faults at 317 stations, we propose that strain axis configurations in the southern Central Andes are controlled by (1) local deformation kinematics, (2) the far-field deformation caused either by the orogen-normal shortening component of plate convergence or by removal of lithospheric mantle and (3) differences in lithospheric thickness and respective surface elevation, i.e., gravitational potential energy. Specifically, the Puna Plateau and Eastern Cordillera have been undergoing horizontal shortening and gravitational spreading of the upper crust, whereas the topographically lower Pampean Ranges continue to undergo horizontal shortening only. Although less apparent in the fault-kinematic data than the E–W and NW–SE extension, orogen-parallel extension is inherent to the Puna Plateau and Eastern Cordillera and compensates likely for overall WNW–ESE shortening and enhanced surface elevation. The importance of orogen-parallel extension in the deformation kinematics of topographically elevated parts of the southern Central Andes is underscored by the strike–slip components on prominent reverse and thrust faults. The data supports geodynamic interpretations in which the evolution of topography and lithospheric thickness influence significantly changes in upper-crustal kinematics of the southern Central Andes.