Flexural unloading and uplift along the Cote d'Ivoire-Ghana transform margin, equatorial Atlantic

Recent Ocean Drilling Program sampling of the Cote d'Ivoire-Ghana margin of West Africa provides for the first time the opportunity to study the devel opment of a marginal ridge that formed along a sheared passive margin adjac ent to the continent-ocean transition after the end of intracontinental wre nching. We model its evolution using a two dimensional flexural backstrippi ng technique. The model is constrained by existing seismic refraction and r eflection data on the crustal structure and stratigraphy and paleobathymetr ic evidence from the cores. Following rifting at 120 Ma (Aptian), intracont inental wrenching continued until similar to 105 Ma (mid Albian), when Sout h America and Africa separated along this transform. While the possible pre sence of thicker crust under the Marginal Ridge compared to the Deep Ivoria n Basin may explain some of the ridge's topography, the entire uplift can b e readily modeled as a flexural response to unloading along a shallow-dippi ng (similar to 25 degrees) fault at the time of continental separation. For ward subsidence modeling of the Marginal Ridge suggests that an effective e lastic thickness of 2.5 lan at 105 Ma is most appropriate to match the obse rved structure. Conduction of heat from the oceanic plate across the contin ent-ocean transition drove temporary uplift of at least 1200 m peaking just before 89 Ma, when sedimentary data show deposition within the photic zone (0-50 m). This study shows that significant, transient thermal uplift can be found in sheared continental passive margin settings even where magmatis m is insignificant.