LATE MIOCENE PLATEAU-WIDE SURFACE UPLIFT IN THE CENTRAL ANDES: AN INTEGRATION OF STABLE ISOTOPE PALEOALTIMETRY AND GEOMORPHOLOGY

The spatial and temporal elevation history of the Andean plateau has remained controversial, primarily because surface uplift is often interpreted in the context of observable and highly variable amounts of rock deformation that occured throughout and adjacent to the plateau. Attempts to match deformation histories (or the lack thereof) to today's topography result in myriad interpretations spanning asymmetric, piecemeal and early (Oligocene - middle Miocene) rise of the plateau. Shortening histories are often at odds with geomorphic and paleontologic observations that point toward substantial late Miocene surface uplift. Recent results from stable isotope paleoaltimetry in the center of the Altiplano demonstrate ~2.5-3.5 km of surface uplift occurring between ~10 and 6.8 Ma. Similarly, new geomorphic evidence on the western flank of the Andean plateau (Northern Chile) reveals a minimum of 1 km of surface uplift that occurred between 10 and 6.5 Ma. Prior work on the eastern side of the plateau (Eastern Cordillera/Interandean zone) identified remnants of a regionally extensive, low-relief, geomorphic surface preserved at varying elevations that formed between ~7 and 12 Ma. Incision of this surface, dated by tuffs that were deposited within incised valleys, suggest surface uplift occurred sometime between ~10 and 6.5 Ma, as observed in the Altiplano and western slope. Combined, these data clearly demonstrate that large magnitude surface uplift was plateau-wide between 18°S and 22°S and that this surface rise occurred in the late Miocene. The wide spatial extent and short time period of surface uplift over such a large region cannot be explained by activity occurring in the ranges that flank the eastern and western sides of the Altiplano and therefore must have resulted from a larger scale phenomenon such as removal of a dense lower crust and mantle lithosphere. Using the preserved low-relief geomorphic surfaces and paleoaltimetry data as indicators of the initial topographic condition of the plateau at ~10 Ma, we estimate the relative relief of the Eastern and Western cordilleras at ~10 Ma and explore the amount of ‘lost' lithosphere that can account for the magnitude and spatial extent of the observed surface uplift.