Tomographic Imaging of Slab Segmentation and Deformation in the Greater Antilles

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 similar to 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 similar to 15 degrees N down to similar to 200 km. Between Puerto Rico and Hispaniola, another gap down to similar 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. Plain Language Summary We use a regional array of seismic stations and global earthquake data to construct a 3-D model of the top 1,000 km of the Earth's mantle in a subduction zone. We image a subducting slab and observe that the slab is tearing while it sinks. Based on regional tectonic knowledge, we infer that this deformation is related to the presence of microplates near the tear. We believe that microplates facilitate tearing by allowing tectonic blocks to move apart from one another and diverge. This divergence at the surface is accommodated at depth via tearing and slab segmentation.