Seismic stratigraphy and structure of the Caribbean igneous province

Abstract

Multichannel seismic reflection profiles reveal the tectonic and stratigraphic complexity of the Caribbean province. A smooth reflector B″ forms the top of widespread Cretaceous volcanic flows drilled during DSDP Leg 15 and ODP Leg 165. In addition we also show other seismic evidence of volcanism (sills and dipping horizons). The southern parts of the Venezuela and Colombia basins are underlain by rough basement that shows many characteristics of oceanic crust. Several thick volcanic plateaus separated by deep basins with thin crust comprise the Caribbean volcanic province. In the Venezuela basin only normal oceanic crust is present, but in other basins this crust is underlain by underplated volcanic material. The crust of the Venezuela basin is less than 5 km thick and was probably formed in the Pacific during the Jurassic. Refraction data indicate that a thin layer, 2V, is formed by original oceanic crust overlain by a thin volcanic layer. An intra basement reflection (sub-B″) marks the top of original oceanic crust that is sandwiched between an upper volcanic layer and lower underplated material. This underplated layer forms a very thick layer, 3V, beneath the Beata and Nicaragua volcanic plateaus. The upper part of layer 3V is gabbroic and outcrops on the Beata ridge. The thickening occurs mainly in the high-velocity lower part of layer 3V and is attributed to the presence of magnesian rocks (picrites or ultramafic cumulates). A highly reflective horizon (R) is located at the top of this layer. We present a model where the Galapagos plume is 2500 km wide but has narrow heads that formed the Caribbean volcanic plateaus separated by deep basins. The Caribbean igneous province is compared to similar volcanic features in the Indian Ocean (Kerguelen plateau) and in the Western Pacific Ocean (Ontong Java plateau, Nauru and Pigafetta basins. The thick plateaus of the Caribbean province resemble the Kerguelen and Ontong Java plateaus, whereas the deep basins present some similarities with the Nauru and Pigafetta basins. The Caribbean igneous province is younger (90-75 Ma) than the Indian and Pacific plateaus (110–130 Ma); however, several geological evidences from land and geophysical offshore observations indicate that the onset of volcanic activity in the Caribbean province could be as old as 115 Ma.