Fig. 8: 3D sketch of Proto-Caribbean slab fragments in the mantle below the eastern Caribbean as inferred from this study.

For reference, some of the larger islands are marked on top (His—Hispaniola, PR—Puerto Rico, Gu—Guadeloupe, Ma—Martinique, Gr—Grenada), an approximate South American coastline is drawn and an approximate north is indicated. Lithosphere produced in the Equatorial Atlantic (teal coloured, with fracture zones in solid white lines) only recently entered the trench below the Lesser Antilles Arc (LAA). Most of the subducted lithosphere in the mantle below the islands was produced during Proto-Caribbean spreading (pale green, with dashed white lines for hypothetical fracture zones). There are gaps in the slab structure where the Proto-Caribbean mid-ocean ridge (marked with bold-red dashed lines) subducted while it was still spreading, leading to a slab window during subduction at the Northern and Southern Great Arc—nGAC and sGAC—before 70 Ma, or it subducted before the lithosphere had much time to cool, leading to further tearing until 40–50 Ma. There is a lateral tear at ~200 km depth in the slab below Grenada, which we propose may follow one of the hypothesised fracture zones, along which tearing occurred during subduction along the Outer Antilles Arc (OAA). In addition, the slab is probably contorted by the northward push of South America leading to further tearing along a fracture zone below Hispaniola/Puerto Rico, and one in the transition zone behind the central arc and folding in the transition zone as slow subduction entered increasing amounts of material at approximately the same location in the mantle. Other parts of the slab that subducted below the sGAC may have sheared off along the cratonic South American margin and could currently be residing in the upper mantle below the coast of Venezuela.