LAUSR

Slow seismic velocity anomalies are commonly imaged beneath subducting slabs in tomographic studies, yet a unifying explanation for their distribution has not been agreed upon. In South America two such anomalies have been imaged associated with subduction of the Nazca Ridge in Peru and the Juan Fernandez Ridge in Chile. Here we present new seismic images of the sub-slab slow velocity anomaly beneath Chile, which give a unique view of the nature of such anomalies. Slow seismic velocities within a large hole in the subducted Nazca slab connect with a sub-slab slow anomaly that appears correlated with the extent of the subducted Juan Fernandez Ridge. The hole in the slab may allow the sub-slab material to rise into the mantle wedge, revealing the positive buoyancy of the slow material. We propose a new model for sub-slab slow velocity anomalies beneath the Nazca slab related to the entrainment of hotspot material.