The Cordilleran cyclicity model predicts that detachment of dense continental lithosphere should be accompanied by rapid uplift of an orogenic plateau and resulting rapid advance of deformation in the frontal fold-thrust belt. In the central Andean plateau, recent isotopic studies argue for rapid surface uplift of the southern Altiplano in Bolivia between 16 and 13 million years ago, which has been attributed to removal of dense material at depth. The Cordilleran cyclicity model predicts that the Andean fold-thrust belt should have responded to this rapid uplift event through rapid eastward propagation of the deformation front. However, accurate records of the timing and magnitude of deformation in the thrust belt in southern Bolivia are not available, which leaves this key prediction untested. In this project, we are performing a field-based study aimed at documenting the response (or lack thereof) of the Andean fold-thrust belt to the rapid rise of the hinterland plateau. The project involves geologic mapping along an east-west transect through the thrust belt in southern Bolivia, which will support construction of a balanced cross-section. By sequentially restoring deformation in the cross-section, we are generating a record of shortening over the last ~20-30 million years. This record will be integrated with deformation timing constraints from analysis of field relationships of sedimentary rocks deposited during crustal shortening, and timing estimates for erosion of multiple thrust sheets obtained from low-temperature cooling histories. The final goal of the project will be to generate a timing record of forward propagation rates of the thrust front and of contemporaneous depositional centers. Together, these records will allow us to evaluate the orogenic response to rapid hinterland surface uplift, and therefore to test a key prediction of the Cordilleran cyclicity model. This project is training graduate and undergraduate students (including a Bolivian graduate student studying in the U.S.) in a STEM field, and is contributing to the broadening of representation of underrepresented groups in the earth sciences; it is facilitating a new collaboration between U.S. investigators at two institutions (University of Nevada Reno and the University of Texas at Austin); and it is fostering a valuable international collaboration between U.S. and Bolivian scientists. This award is being co-funded by NSF's Office of International Science and Engineering.
