Tectono-Climatic Controls on Uplift Transients of the Nahuelbuta Forearc Range, Northern Patagonian Andes

The landscape evolution of forearc ranges along accretionary convergent margins, such as the southern Chilean Coastal Cordillera, is strongly influenced by deep-seated accretion dynamics, enhancing reactivation of inherited upper-plate structures. The Nahuelbuta Range is the fastest uplifting and exhuming sector of the southern Chilean subduction margin. Stratigraphic markers and uplifted marine terraces indicate dome-shaped uplift across a ~100-km-wide zone since ~2 Ma. However, uplift mechanisms remain debated, and rates are resolved only for the last ~0.3 Myr. Furthermore, dense vegetation and weathering have hindered fault mapping, limiting the understanding of the Nahuelbuta Range deformational history.

We combined new surface geomorphic mapping, morphometric drainage analysis, and river inversion modeling to explore the tectonic and climatic influences on the Nahuelbuta Range landscape evolution. We identify a regional low-relief relic surface atop the Nahuelbuta Range, now warped and dissected by fluvial incision and faults. Drainage morphometric anomalies and microseismicity align with WSW- and ENE-trending faults, indicating ongoing trench-parallel shortening. River inversion analysis shows uplift and topographic rejuvenation between 3 and 2.5 Ma approximately, followed by two later discrete uplift episodes. Uplift transients correlate with Late Pliocene to Pleistocene Patagonian glacial expansion periods, suggesting that glacially intensified sediment flux to the trench enhanced basal accretion of sedimentary material. The location and wavelength of surface uplift events match depth and scale expected for slices of basal acreeted material. Seismic imaging of the sediment-rich subduction channel and microseismicity patterns supports this interpretation. We propose glacially driven tectonic underplating drives the oscillatory uplift history of the Nahuelbuta Range, while ongoing trench-parallel shortening enhance trench-parallel shortening and fault reactivation.