Ridge Subduction: Unraveling the Consequences Linked to a Slab Window Development Beneath South America at the Chile Triple Junction

The subduction of an active spreading center generates a clear signature in the temporal evolution of subduction zones. It disrupts the typical arc-type magmatism and intraplate seismicity, enhances the emplacement of backarc plateau lava and profoundly change the tectonics and topographic relief. These distinct observations are commonly linked to a slab window opening and mantle upwelling. The Chile Triple Junction provides the ideal setup to study the mid-ocean ridge subduction process where both sides of the spreading center continue to subduct. Here, we use 2-D numerical petrological-thermomechanical modeling to focus on transient geodynamic processes caused by mid-ocean ridge subduction. Model results show slab separation along the ridge axis with the opening of a slab window. During the opening, partial melts from the spreading center migrate toward the subcontinental mantle and high temperatures in the forearc are predicted. The temporal evolution of the modeled temperature is consistent with observed heat flow data, and with magmatism and high-temperature metamorphism recorded in Chilean forearc rocks. Such migrated partial melts might explain the low viscosity inferred and low seismic velocity anomalies imaged in the slab window beneath South America, and the common geochemical signature of the Chile Ridge, the Taitao Ophiolite and the backarc magmatism. Following slab separation, our models suggest forearc uplift and changes in the stress regime, processes which are consistent with deformation records. Summarizing, our model of the geodynamic evolution of the Chile Ridge subduction provides a consistent framework that explains diverse records of magmatism, metamorphism, deformation and mantle physical properties.

Automated summary

The subduction of an active spreading center in subduction zones disrupts typical arc-type magmatism and intraplate seismicity, enhances backarc plateau lava emplacement, and changes tectonics and topographic relief. The Chile Triple Junction is an ideal setup to study mid-ocean ridge subduction. 2-D numerical petrological-thermomechanical modeling shows slab separation and the opening of a slab window, with migrated partial melts explaining low viscosity and seismic velocity anomalies in the slab window and the geochemical signature of various magmatic features.