THE IVORY-COAST GHANA TRANSFORM MARGIN - A MARGINAL RIDGE STRUCTURE DEDUCED FROM SEISMIC DATA

The Ivory Coast-Ghana (ICG) marginal ridge is a prominent feature of t he ICG transform margin and includes a fossil ridge partially buried b y a thick, undeformed sedimentary cover. The fossil ICG ridge is 130 k m long and 25 km wide, and towers over the adjacent rifted basin (deep Ivorian basin, DIB) and the oceanic crust by 1.3 km and more than 4 k m, respectively. It formed in three successive stages. (1) During the rifting of the DIB, both vertical and horizontal motions between the D IB and the South American plate varied along the plate boundary. This relative motion occurred in an accommodation zone that tilted the nort hern slope of the ICG ridge along en-echelon, mainly strike-slip, faul ts. (2) After the rifting of the DIB, the relative motion remained con stant along the transform plate boundary. At this time strike-slip def ormation was localized into a narrow and highly deformed belt that tru ncated the accommodation zone. (3) Finally, the transform motion occur red between the DIB and an oceanic plate. Thermal exchanges between th e two adjacent plates induced thermal uplift of the ICG ridge that amp lified previous tectonic tilting.