INSIGHTS INTO COUPLING BETWEEN GEOMORPHIC AND TECTONIC PROCESSES IN THE CENTRAL ANDES FROM THEORY, SANDBOX EXPERIMENTS, AND NUMERICAL MODELS

The central Andes (15°S–34°S) hosts several morphotectonic environments and climatic gradients. We used mechanical formulations of frictional failure, sandbox (analog) experiments, and numerical models (the Gale numerical model using a strain-weakening, Drucker-Prager constitutive rule) to study how erosion may be coupled to tectonic processes within the different morphotectonic sectors of this orogen. We first used analytical, analog, and numerical models to explore links between erosion of, and the geometry and kinematics within the Aconcagua fold-and-thrust belt. These models predict a continuous geometric adjustment of the fold-and-thrust belt to erosion, thickening and widening is likely accommodated by discrete propagation of fore-shears into the foreland, the geometry and frequency of motion along shear bands varies systematically with erosional efficiency, and the geometric aspects of these models are consistent with the available restored structural sections of the fold-and-thrust belt. Second, we examined the role of pre-existing weaknesses in localizing deformation during orogenesis, which were meant to coarsely simulate the accommodation of deformation along high-angle structures in basement-cored uplifts such as those of the Sierras Pampeanas. Analytical and numerical models of these features suggest that the tempo and sequence of deformation is distinct from that expected in fold-and-thrust belts. Slip along weak structures built overlying topography until body forces were sufficient to favor deformation along stronger structures below flat topography. More vigorous erosion tended to prevent migration of deformation to stronger structures, while inefficient erosion permitted this. Finally, we used observations and analytical models of the dismemberment of fluvial systems draining highland areas to determine the erosional and tectonic conditions that are required to produce the low-internal-relief morphology of these plateau realms. Each of these distinct morphotectonic sectors appears to correlate, to some degree, with tectonic and geologic elements that pre-date the modern Andean orogenesis. Thus, the tectonic and geologic history of this area likely created a template that set the nature and strength of interactions between erosional and tectonic processes.