Tomographic Imaging of Slab Segmentation and Deformation in the Greater Antilles

Abstract

We present a new tomographic P wave model of the upper mantle in the east Caribbean region. The model was built using 3-D finite frequency sensitivity kernels and ~20,000 teleseismic P and PP traveltime residuals from 535 events recorded across 130 broadband seismometers. We observe high-velocity features corresponding to a Caribbean beneath northern South America and an arcuate slab beneath the Lesser and Greater Antilles island arcs. The latter exhibits an along strike gradient in dip with steep edges and a reclined middle, consistent with ongoing slab rollback and collision. We divide the arcuate slab into three sections from two lateral discontinuities. The southern and northern Lesser Antilles sections are separated by a gap ~15°N down to ~200 km. Between Puerto Rico and Hispaniola, another gap down to ~300 km separates the northern Lesser Antilles slab from a narrow slab fragment further east. We relate these discontinuities to the subducted North American-South American plate boundary and a slab segmentation tear, respectively. The northern and southern ends of the Lesser Antilles trench are actively deforming from collision and differential rollback. However, these areas exhibit different styles of lithospheric tearing, as manifest in the morphology of the slab. We infer the contrast in tearing relates to the presence of microplates at the northern boundary of the Caribbean plate. Microplates facilitate block divergence and differential trench retreat/rollback, which drive slab segmentation. These results offer new insight into the tectonics of the Caribbean region and the factors driving lithospheric tearing in slabs generally.