RELATIONSHIPS AMONG CLIMATE, TOPOGRAPHY, AND DELAMINATION IN THE ANDES: A NUMERICAL MODELING INVESTIGATION

Along-strike variations in the topography of the modern Andes have been variably attributed to differences in convergence/shortening rates, climatically-controlled erosion rates, and the presence/absence of Cenozoic eclogite production and delamination. All of these processes are coupled, however, making it difficult to uniquely determine the relative importance of each process and the feedbacks among them. In this paper we develop a mass-balanced numerical model that couples an actively-shortening, critically-tapered orogen and crustal root with eclogite production, delamination, and climatically-controlled erosion. Tectonic shortening rates and mean annual precipitation rates are the primary inputs to the model. The model reproduces the mean height and width of the modern Andes from 5ºN to 50ºS latitude quite well and helps to identify the relative influence of each controlling factor on the resulting topography. In the region of the Andes between 5ºS and 32ºS, where shortening rates are relatively high, the orogen has grown to a sufficient size since Eocene time to cause eclogite production and delamination. The model provides quantitative estimates for the relationship between the size of the eclogitic root and the magnitude of surface uplift and eastward thrust-tip propagation due to delamination in this region. To the north and south of this region, relatively low shortening rates and high precipitation/erosion rates have slowed eclogite production such that delamination may not have occurred during the Cenozoic. We conclude that along-strike variations in shortening and eclogite production/delamination play the dominant roles in controlling the topography of the Andes, with erosion playing a significant but secondary role.