Tomographic Mantle Structure of the Eastern Caribbean: Slab Ponding & the Interplay between Rollback, Lithospheric Tearing, and Collision

Slab rollback is an integral phenomenon to the evolution of arcuate subduction zones, and one that still escapes detailed understanding. As island arc slabs undergo rollback, slab morphology and the locations of the trench, forearc basins, and the arc itself respond. We use body wave tomography to analyze the mantle structure beneath the modern eastern Caribbean region. In particular, we consider the Lesser Antilles slab, which has experienced significant rollback over the past 120 Ma, since westward subduction initiated in the modern Pacific. Encoded in the morphology of the slab is a history of subduction rearrangement as a response to not only rollback, but collision and lithospheric tearing as well. We investigate the preservation of regional dynamics in the form of mantle velocity anomalies and, likewise, how various dynamic processes affect one another across multiple depth scales. The relative slowness model we interpret was inverted for using 3-dimensional sensitivity kernels and 17k optimized teleseismic (Δ > 30°) P wave travel time residuals from 467 events recorded across a regional, multi-network array of 128 broadband seismometers. Our initial results indicate that the Lesser Antilles slab has ponded on the lower mantle ( 700km) and that there are appreciable along-strike changes in slab character. Among our preliminary interpretations is the notion that the lithospheric boundary conditions of the arc, at the northern and southern termini of the trench, are affecting the course of rollback and, subsequently, the bathymetry proximal to the arc.