Seismic Evidence for Thermal and Chemical Heterogeneities in D″ Region Beneath Central America From Grid Search Modeling

Large lateral variations in the depth, sharpness, and magnitude of the D″ discontinuity are observed beneath Central America and the Caribbean using a new innovative grid search modeling method. The strong correlation between the D″ topography and the underlying seismic velocities suggests a large lateral gradient in the thermal condition in the lowermost mantle. Low-velocity patches were identified among the high-velocity areas, coinciding with regions showing a disruption in the D″ discontinuity. The low-velocity zones may be attributed to the heat trapped in the middle of the Farallon slab remnant while those farther to the west are likely to be associated with the upwelling generated at the edge of the ancient slab. A broad range in the sharpness of the D″ discontinuity was also observed, suggesting the existence of different chemical components in the region, as a result of a disparate mixture of basalt, harzburgite, and pyrolite.