Flat slab subduction, a unique tectonic phenomenon, is characterized by subhorizontal plate motion extending over hundreds of kilometers. Despite its significance, the mechanisms driving flat slab formation remain debated. This study investigates the dynamic effects of mantle wedge hydration on flat slab subduction through advanced numerical modeling, focusing on the Chilean region. Our models incorporate magmatism, hydration, phase transitions, and dynamic pressure variations, revealing that reduced mantle wedge hydration and increased suction forces are critical for slab flattening. Hydration processes, especially serpentinization, create low-viscosity channels that enhance suction forces, while magmatic heat release influences mantle dynamics. The interplay of gravity and suction torques highlights the limited role of slab buoyancy and emphasizes the dominance of suctiondriven dynamics. The results reproduce key geological features, including flat slab geometry, volcanic gaps, and reduced magmatism, consistent with observations in South America. This study provides a comprehensive framework for understanding the geodynamic evolution of flat slab subduction systems worldwide.

Flat slab subduction, exemplified by the Pampean flat slab of the Nazca Plate, exhibits unique geological features such as enhanced seismicity, inboard deformation, and suppressed magmatism. Using thermo-mechanical models, we demonstrate how dehydration dynamics and mantle wedge evolution shape these phenomena. The model replicates landward-migrating dehydration fronts, high seismic coupling, reduced magma production leading to volcanic gaps, and foreland deformation linked to thermal weakening. These findings provide a comprehensive framework to understand the interplay of fluids, magmatism, and tectonics in flat slab subduction systems, consistent with observations in central Chile and western Argentina.