Eocene to recent variations in erosion across the central Andean fold-thrust belt, northern Bolivia: Implications for plateau evolution

Quantifying the erosional and kinematic evolution of orogenic plateaus has been limited by insufficient age constraints on their deformation and erosion histories. Palinspastic restorations suggest the central Andean fold-thrust belt and plateau evolved concurrently in Bolivia. We present an analysis that synthesizes 19 new and 32 previous apatite and zircon fission-track and (U-Th)/He mineral cooling ages along a 200 km traverse across the plateau margin and entire thrust belt in northern Bolivia. The new apatite fission-track data are interpreted using a grain-age deconvolution algorithm with inverse thermal modeling of track lengths, grain ages and mineral composition proxy data. Results suggest: (1) Eo-Oligocene (∼ 40-25 Ma) initial rapid erosion of the plateau margin, (2) accelerated, distributed erosion across the entire thrust belt since the early to mid-Miocene (∼ 15 Ma), and (3) the magnitude of erosion decreases eastward from ∼ 10 to 4 km. We compare these results with two end-member models of the central Andes that contrast in duration and magnitude of deformation. The rapid Eo-Oligocene (∼ 40-25 Ma) erosion is only consistent with the end-member that emphasizes the long duration and large magnitude deformation controlled by the sequential stacking of basement thrust sheets. However, the distributed Miocene (∼ 15 Ma) to recent erosion is consistent with both end-members because the recorded cooling could have resulted from active deformation, protracted erosion or both. If the long duration model is correct, the time between the two phases of accelerated cooling brackets the cessation of the first basement thrust sheet and implies the early development of the Andean plateau analogous to its modern width, but unknown elevation by the early Miocene (∼ 20 Ma).