Structure and Geodynamics of the Nazca Ridge

The Nazca Ridge (NR) is a major hotspot track >1000 km long and ~200 km wide, hosted in the oceanic Nazca plate in a N42°E direction [Hampel et al., 2002]. It was formed by the Easter Island/Sala y Gómez Island hotspot plume system near the Pacific-Farallon/Nazca spreading center in the early Cenozoic [Pilger 1994; Bello-González et al., 2018]. Subduction and collision of this hotspot track modify the geodynamics and tectonics of the Peruvian outer forearc region and disrupt and erode material from the overriding South American plate [e.g., Hampel et al., 2004]. Thus, it is crucial to understand the structure and composition of the NR.

We use wide-angle seismic refraction and reflection data to obtain a ~177 km long, 2D velocity-depth model. We also study the density structure spanning 200 km at each side of the seismic profile, and we model the free air gravimetric anomaly. Using an elastic flexural model, we estimate the elastic thickness Te beneath the NR. The seismic results show an anomalously thick crust of ~17 km beneath the Nazca Ridge, and an adjacent oceanic crust about 7 km thick. The NR has a Te < 5 km and most of the material was emplaced within the lower crust, presenting velocities <7.5 km/s. Therefore, the NR has an extensive buoyant root locally compensated. We also found that the Independencia Fracture zone (entering the trench at ~15 ° S) that crosses the profile has almost no influence neither in the bathymetry nor in the seismic structure. This suggests that hotspot magmatism masked the fracture zone signature.