Geomorphic imprint of an Early Pleistocene uplift phase of the Andean forearc and its underlying mechanisms

The Central Andes forearc preserves extensive low-relief marine and continental landforms that record long-term margin uplift, yet the timing and driving mechanisms of this deformation remain debated. Here we present eleven new in situ ¹⁰Be exposure ages from high fluvial terraces and four ages from a lower terrace, combined with geomorphic analyses across eight adjacent catchments (29.5–32.5°S), to reassess the chronology and tectonic significance of the degradational surfaces (pediplains). Exposure ages indicate that the high terrace was abandoned between ∼1 and 2 Ma (Early Pleistocene), while a lower terrace records a subsequent incision phase at ∼0.4–0.8 Ma. Morphometric analysis reveals a systematic upstream-decreasing pediplain relief pattern that terminates within the surface projection of the 50–55 km slab-depth contour, a region coincident with the downdip limit of megathrust Domain–C and deep coseismic deformation. In peninsular settings, notably the Altos de Talinay, this long-wavelength signal is overprinted by short-wavelength uplift likely related to localized underplating. Integrating our findings into a regional perspective, we identify a continuous Early Pleistocene uplift phase spanning a large segment of the Andean margin, from 16° to 42°S. This orogen-scale emergence implies a subtle but widespread change in subduction dynamics during the last ∼2 Myr.