Analysis of geomorphic indices in the southern Central Andes (23°-28°S): Evidence for pervasive Quaternary to Recent deformation in the Puna Plateau

- Mountain-front sinuosity index can be used to infer fault ages.
- Geomorphic indices point to pronounced Quaternary to Recent deformation.
- T-factor suggests stochastic variations of erosion.
- Climate has limited influence on the evolution of first-order landforms.
- Quaternary deformation in the Puna is more pervasive than previously thought.

Satellite data-based morphotectonic analyses are popular methods to identify active crustal deformation of large and partly remote regions, such as the Central Andes. For the southern Central Andes between 23° to 28°S, the mountain-front sinuosity (Smf-) index was estimated for 189 first-order mountain fronts, as well as valley shape (Vf-) ratios and basin symmetry (T-) factors for 3366 second-order, tributary drainage basins. The correlation between known fault ages and Smf-indices shows that the indices can be used as a proxy to infer the ages of faults for which radiometric ages do not exist. Vf-ratios and Smf-indices point to pronounced Quaternary to Recent surface deformation on first-order reverse faults delimiting mountain fronts. By contrast, analysis of the transverse topographic symmetry (T-) factor, which has been used to assess rotational components of drainage basins, points to stochastic variations of erosion, possibly due to local lithological heterogeneity, rather than to a tectonic influence on basin geometry. We also examined 32 mainly NNE-SSW trending first-order basin margins for tilt of alluvial fan deposits and lateral stream migration. The symmetry of first-order basins in the southern Central Andes seems to be strongly controlled by Quaternary deformation on bivergent first-order reverse or thrust faults. Quaternary deformation of the upper crust in the Puna Plateau is apparently more pervasive than previously appreciated and has important ramifications for the Neogene to Recent morphotectonic evolution of the southern Central Andes.