STRUCTURAL AND LANDSCAPE EVOLUTION IN THE CENTRAL BOLIVIAN ANDES: INSIGHTS FROM FLEXURAL, THERMO-KINEMATIC, AND LANDSCAPE MODELLING

The central Bolivian Andes, due to its strong climate gradient, is an excellent location to study the relationship between climate and tectonics and their effects on the landscape. Using sequentially-modelled 2D-balanced cross-sections as the input to a landscape evolution model (Cascade), we have varied magnitude and location of precipitation and rock strength to examine the ability of the cross-section geometry and kinematics to reproduce the modern landscape during the recent (~15My) Subandean fold-and-thrust belt evolution in central Bolivia. Permissible shortening rates are constrained by matching depositional ages of basin strata and modelling the thermal history of the sequentially-modelled balanced cross-section with the advection-diffusion thermal model Pecube, to verify the model’s ability to reproduce regional thermochronometer ages. This methodology allows us to evaluate the viability of the cross-section to reproduce the landscape as a whole, the cooling signal, and to evaluate the geomorphic response to two different kinematic models, variations in bulk rock erodibility, global versus orographic precipitation, and convergence rate. Our results using this methodology highlight the importance of the delicate balance between overall erodibility and convergence rate as a control on the translation of legacy topography, a preserved topographic feature of past uplift, to reproduce the modern topography. Extracting from the modeled topography geomorphic indices of uplift (eg river channel steepness, Ksn) and comparing the modelled to modern-day Ksn, we are able to link these surface uplift indicators with subsurface geometry that can reproduce those metrics. We can trace the regional Ksn pattern to gain potential insight into the regional subsurface geometry, and thus better locate active, or recently active, faults in the region along strike. The combination of traditional structural techniques, like kinematically and flexurally sequentially modelled balanced cross-sections, with newer techniques of thermal and landscape modelling, allow us to investigate the geomorphic response of viable thermo-kinematic models and derive potential regional variations in along strike subsurface geometry and kinematics.