TOPOGRAPHY OF THE 410 AND 660 KM DISCONTINUITIES BENEATH EASTERN CARIBBEAN

The 410 and 660 km discontinuities bordering the mantle transition zone (MTZ) beneath eastern Caribbean are imaged by stacking receiver functions under the non-plane wave assumption. Over 12000 P-to-S receiver functions from 2038 events recorded by 166 stations are grouped into circular bins with a radius of 1^o and are moveout corrected based on the 1-D IASP91 Earth model prior to stacking. After wavespeed correction based on the global body-wave velocity models TX2019slab and UU-P07, the topography of the discontinuities exhibits systematic lateral variations which are mostly caused by subducted cold slabs and thermal upwelling through slab edges and gaps. In the northern part of the Lesser Antilles subduction zone, a thinner than normal MTZ is observed and is attributable to a high wave speed layer. For those regions around the central and southern parts of the Lesser Antilles Subduction Zone, the thinner MTZ is related to a possible mantle upwelling along the edges of the slab and slab gaps in these areas. In the southeastern part of the Caribbean Plate, where the Caribbean slab subducted beneath the South American Plate, the observed thicker MTZ corresponds to an uplifted 410 km discontinuity and a depressed 660 km discontinuity.