Abstract
The northeastern Caribbean exhibits high deformation and is fragmented by several faults into smaller tectonic blocks. One of these faults was the site of the catastrophic 12th of January 2010 earthquake. In this thesis I aim to constrain the main forces driving lithospheric deformation in the Caribbean region in general,
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and specifically in the northeastern Caribbean plate boundary zone. First I determine the lithospheric forces acting on the Caribbean plate. I find that frictional forces, including an extra push at the island of Hispaniola are the main forces driving the Caribbean plate. I investigate the mantle structure underneath the Caribbean plate using a seismic P-wave velocity model. Using the correlation between material temperature and seismic velocity I link the observed mantle structure to tectonic reconstructions, in particular to suggested sites of subduction of cold lithosphere. The tomography confirms Cenozoic subduction under the Lesser Antilles, under the Maracaibo block and under Central America, as well as Mesozoic subduction under the Greater Antilles and Central America. Moreover, the shape of the subducting slab under the Lesser Antilles leads us to infer that that the northeastern Caribbean plate boundary is not a simple STEP. Instead of vertical tearing of the subducting slab, the latter remains attached to the lithosphere at the surface. The particular structure of this slab, resembling an amphitheatre, has important implications for the evolution and deformation of the plate boundary. Finally I investigate these implications of the inferred slab structure in particular its laterally moving edge, using the calculated force magnitudes. The slab edge exerts a push on the overriding Caribbean plate, which henceforth is referred to as “slab edge push”. I compare the slab edge push with the implications of collision with the carbonate Bahamas platform, the generally accepted cause for the observed lithospheric deformation in the northeastern Caribbean plate boundary zone. For the Present, both the slab edge push and the Bahamas collision reproduce the observations of lithospheric deformation. Both scenarios fail to correctly predict the observed Miocene rotation of the Puerto Rico – Virgin Island microplate. Only a combination of the two scenarios correctly explains the observations of rotation, with the relative contribution of the slab edge larger than the contribution of the Bahamas collision. I conclude that the dominant mechanism causing deformation in the northeastern Caribbean plate boundary region is the slab edge push.
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