Abstract

The Nazca Ridge (NR) was formed near the interaction of a hotspot mantle plume and an active spreading center. We use active-source wide-angle seismic data to obtain 2-D Vp and Vs tomographic models, and hence the Poisson's ratio (ν) structure beneath the NR. Results show a ∼2 km thick seismic layer 2A with ν values of 0.25–0.32 in the uppermost crust interpreted as pillow basalts with a low degree of fracturing and/or hydrothermal alteration. The 2A/B boundary layer presents ν values of 0.27–0.29 consistent with pillow basalts/sheeted dykes units. A ∼3 km layer 2B overlies a ∼10 km layer 3 with ν values of 0.24–0.3 at the 2/3 boundary layer. The lowermost layer 3 presents ν values of 0.28 ± 0.02 suggesting an increase in Mg content (≥10% wt). The NR crust (∼15 km thick) requires an increment of the asthenospheric mantle potential temperature in ∼100°C formed by passive adiabatic decompression melting.