Orogenic Wedge Evolution of the Central Andes, Bolivia (21°S): Implications for Cordilleran Cyclicity

Abstract

The Andes are an ideal setting to explore orogenic wedge evolution and the cyclical tectonic processes in Cordilleran convergent-margin systems. Paleoaltimetry data suggest that the hinterland plateau in southern Bolivia underwent rapid surface uplift at similar to 16-9 Ma, which is predicted to have induced rapid thrust belt propagation. We integrate fission track and (U-Th)/He ages from zircon and apatite with a sequentially restored cross section to quantify the timing and rates of thrust belt propagation in southern Bolivia for the last similar to 43 Myr. These data show that retroarc shortening in the Eastern Cordillera propagated westward from similar to 43 to 27 Ma as the wedge grew to attain critical taper and steady state. The thrust front then advanced rapidly eastward from similar to 25 to 17 Ma across the western Interandean zone, where a weak decollement modified the critical taper angle. The thrust front stalled for similar to 6 Myr but resumed eastward advance into the eastern Interandean zone and Subandean zone by similar to 11-8 Ma, which we interpret as a response to increased accretionary influx and rapid orogenic wedge expansion induced by eclogitic delamination and corresponding hinterland surface uplift at similar to 13 Ma. Development of an orographic barrier and wetter climatic conditions resulted in relatively steady state wedge conditions from similar to 8.5 to 1.5 Ma. Rapid wedge growth after similar to 1.5 Ma may be attributed to mass accumulation in the orogen interior or a weakened decollement. Our data reveal space-time variations in orogenic wedge evolution consistent with models of Cordilleran cyclicity and lithospheric removal, with important additional influences of erosion, climate, and rock rheology.