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 ~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 ~43 Myr. These data show that retroarc shortening in the Eastern Cordillera propagated westward from ~43 to 27 Ma as the wedge grew to attain critical taper and steady state. The thrust front then advanced rapidly eastward from ~25 to 17 Ma across the western Interandean zone, where a weak decollement modified the critical taper angle. The thrust front stalled for ~6 Myr but resumed eastward advance into the eastern Interandean zone and Subandean zone by ~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 ~13 Ma. Development of an orographic barrier and wetter climatic conditions resulted in relatively steady state wedge conditions from ~8.5 to 1.5 Ma. Rapid wedge growth after ~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.