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 V-p and V-s tomographic models, and hence the Poisson's ratio (nu) structure beneath the NR. Results show a similar to 2 km thick seismic layer 2A with nu 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 nu values of 0.27-0.29 consistent with pillow basalts/sheeted dykes units. A similar to 3 km layer 2B overlies a similar to 10 km layer 3 with nu values of 0.24-0.3 at the 2/3 boundary layer. The lowermost layer 3 presents nu values of 0.28 +/- 0.02 suggesting an increase in Mg content (>= 10% wt). The NR crust (similar to 15 km thick) requires an increment of the asthenospheric mantle potential temperature in similar to 100 degrees C formed by passive adiabatic decompression melting.