Tectonic and climatic controls on uplift transients of the Nahuelbuta Forearc Range, Northern Patagonian Andes

The landscape evolution of forearc ranges along sediment-rich convergent margins, such as the Patagonian Coastal Range, is strongly influenced by deep-seated accretionary processes. The Nahuelbuta Range is the fastest uplifting and exhuming sector of the Northern Patagonian margin. Thermochronology and stratigraphic markers suggest an uplift onset across a 100-km-wide zone between ∼6 Ma and ∼2 Ma. However, uplift mechanisms remain debated, and rates are constrained only for the last ∼0.30 Myr, given by emerged marine terraces. Furthermore, dense vegetation and weathering have hindered fault mapping, limiting the understanding of the Nahuelbuta Range tectonic uplift history. We combined new surface geomorphic mapping, morphometric drainage analysis, and river-inversion modeling to explore the tectonic and climatic influences on the landscape evolution of the Nahuelbuta Range. We identify a low-relief relic landscape atop the Range, now warped and dissected by fluvial incision and faults. High morphometric anomalies and microseismicity align with trench-perpendicular faults, suggesting ongoing north-south shortening. River-inversion modeling shows uplift and topographic rejuvenation of the Range between 3 Ma and 2.5 Ma, followed by two later discrete uplift episodes. These uplift transients correlate with Late Pliocene to Pleistocene glacial expansion and the following travel time along the subduction channel of delivered sediments. The location and scale of uplift transients match predictions for those of tectonic underplating. We propose that glacially-driven tectonic underplating drives the oscillatory Quaternary uplift of the Nahuelbuta Range, while ongoing north-south shortening enhances trench-perpendicular fault reactivation. Seismic imaging of the sediment-rich subduction channel and microseismicity patterns supports this interpretation. ▪ Mapping and river modeling reveal a warped, low-relief relic surface atop the Nahuelbuta Range, abandoned between 3 Ma and 2.5 Ma, indicating the onset of rapid uplift. ▪ Drainage anomalies and microseismicity align with WSW- and ENE-trending inferred reverse faults, suggesting ongoing trench-parallel shortening. ▪ The timing of the three modeled long-wavelength uplift pulses correlates with Late Cenozoic glacial expansions. ▪ The scale and duration of uplift align with cycles of tectonic underplating, suggesting a combined role of glacially modulated basal accretion and trench-parallel shortening.