Interaction of a Subducted Paleo-Slab with Lowermost Mantle Material: Insights from Inferred Radially Anisotropic Structure in D″ Beneath Central America

We perform waveform inversion for the three-dimensional radially anisotropic S-wave velocity (VS) structure of the lowermost 400 km of the mantle (the D '' region) beneath Central America. We find high-velocity anomalies beneath Central America, interpreted as the Farallon paleo-slab, and low-velocity anomalies extending from Colombia to the Caribbean Sea, interpreted as a upwelling plume. We also infer a 3-D model of the anisotropy parameter (xi). In the regions corresponding to the Farallon paleo-slab, delta xi is positive 400-300 km above the coremantle boundary (CMB), becomes negative to the southeast 300-100 km above the CMB, and returns to positive 100-0 km above the CMB. In the regions corresponding to a passive plume, we find generally positive delta xi anomalies. These results suggest that 1) the subducted paleo-slab exhibits complex flow patterns due to interaction with the CMB and dense material just above the CMB, and 2) the root of the upwelling plume is pushed eastward by the subducted paleo-slab. The ease of moving the root of the plume might promote the Earth's thermochemical evolution.