Structural Architecture of the Ocean-Continent Boundary at a Transform Margin, Gulf of Guinea, West Africa

Migration of the 16sec TWT PROBE seismic reflection dataset provides amongst the clearest images of crustal structure at the ocean-continent boundary of a transform continental margin. Despite this, there is considerable uncertainty as to the structural architecture and composition of the so called transitional crust occupying the zone between the continental shelf and the oceanic crust of the Gulf of Guinea. This uncertainty is due largely to the complex transform nature of the Gulf of Guinea whereby the ocean continent boundary is defined by several fracture zones across a c.60 km wide region. This project uses combined geological interpretation and gravity modelling of new migrations of selected PROBE lines to define the whole-crustal structural architecture and composition of this intermediate crust. In contrast to classic transform margins elsewhere, the Gulf of Guinea margin is characterised by a series of seaward dipping faults that define deep half graben basins and penetrate to Moho level. Gravity modelling provides a constraint on the complex structure within the fracture zones, resulting in a greater understanding of the transform margin formation. Three fracture zones define two distinctly different blocks of transitional crust formed as a result of small offsets in the Mid-Atlantic Ridge. The density variation between the two blocks indicates that the seaward block is highly deformed continental crust, heavily intruded with dykes. Whereas the landward block is less intruded, deformed continental crust.