EROSION, GEOLOGIC HISTORY, AND THE OROGENIC STRUCTURE OF THE CENTRAL ANDES

Orogenic structure in the central Andes (15°S—33°S) systematically varies with mean annual precipitation, suggesting that erosional processes may be strongly coupled to orogenesis. However, geodynamic models of the central Andes can explain the salient characteristics of the kinematic and petrologic observations of the mountain belt without considering erosion. Here, we explore the range of possible interactions between deformation, erosional processes, changing geodynamic conditions, and the state of the South American craton prior to orogenesis to assess the relative role of geologic history, geodynamic conditions and erosional processes in shaping this portion of the orogen. We note that variations in factors such as mountain belt width correspond to changes in deformation style, which may ultimately be linked to factors such as the presence or absence of mechanically anisotropic sediments in the foreland and/or pre-existing crustal-scale structures that may be reactivated during subsequent deformation episodes. While the overall structure of different segments of the Andean orogen may be largely controlled by these geologic factors, depending on the deformation style, erosional processes may importantly influence the details of the tectonic and topographic development of different segments. In particular, we identify three different morphotectonic provinces, including the internally-drained Altiplano-Puna plateau, the thin-skinned fold-and-thrust belts of Bolivia and central Argentina, and basement-cored uplift provinces of the Pampean range, in which the the nature of interactions between erosional and tectonic processes may be expected to be drastically different. In our view, the pre-orogenic geologic history and changing geodynamic conditions set the stage for the nature and strength of coupling between erosional processes, tectonic deformation, and mountain belt structure in different parts of the orogen. These results indicate that concepts of coupling between tectonic and erosional processes that are derived from simple models may be appropriate for simple mountain belts and portions of orogens for which the model assumptions appear reasonable; however, their application to large, complex orogens such as the central Andes may be more problematic.