Geometric, Kinematic, and Erosional history of the Central Andean Plateau, northern Bolivia

Latitudinal changes in topography, climate, and thrust-belt geometry in the Central Andes have lead to conflicting hypotheses that climate or tectonics exert a first-order control on the orogens' evolution. Models of climate/tectonic interactions are limited by a lack of detailed observations for both the long-term deformation and erosion history of the Andean fold-thrust belt. We contribute to this problem by combining a sequentially restored, balanced cross section across the northern Bolivia portion of the thrust belt (15-16°S) with 10 new and 51 previously published mineral cooling ages, documenting the timing and magnitude of exhumation across the cross section. The cross section was balanced and restored using the sinuous bed method. The restored section was also sequentially forward modeled using stratigraphic and cooling age constraints. Results indicate the Eastern Cordillera (EC) records the highest magnitudes of shortening (123 km or 55%). The Interandean zone (IAZ) has shortened 48 km or 30%. In both the EC and IAZ individual thrust sheets are tightly folded and have minor offsets of 1-5 km. The fold-thrust belt of the SAZ has multiple levels of detachments allowing for thrust sheets with large 6-17 km of offset. Total shortening in the SAZ is 66 km or 40%. Total shortening for the entire fold-thrust belt in this region is 276 km (39%). New cooling ages support previously published ages that indicate rapid exhumation of the EC from ~40-25 Ma and distributed exhumation of the entire fold-thrust belt from ~15-0 Ma. Cooling ages in the EC and IAZ do not appear affected by individual thrusts. Integrating the sequential reconstructions with a compilation of mineral cooling ages and onlapping sedimentary basins provides a means of comparing independently derived exhumation estimates and determining long term shortening rates. Combined exhumation estimates suggest ~9 km of exhumation in the EC ~5-9 km in the IAZ and 3-4 km in the SAZ. Long term shortening rates are 8.13 mm/yr for the EC and IAZ, and 4.4- 8.25 mm/yr for the SAZ. The SAZ rates are based on a 15-0 Ma or 8-0 Ma deformation window (respectively), something that is not yet resolvable with the thermochronologic data. These rates imply either a pause or a dramatic deceleration in the rate of deformation and propagation of the Andean fold-thrust belt for 10-17 Ma between 25 and 15 or 8 Ma. The renewed acceleration of deformation in the late Miocene could be the result of geodynamic processes such as the loss of a mantle root..