NATURE OF THE TRANSITION FROM CONTINENTAL TO OCEANIC-CRUST AND THE MEANING OF REFLECTION MOHO

The evolution from continental to oceanic crust in the Gulf of Guinea involves the "foundering" of highly stretched and tilted slivers of continental crust, the emplacement of mafic volcanic material above and between these slivers, and the progressive lateral replacement of continental fault blocks with oceanic igneous rocks. This "oceanization" of continental fault blocks appears to be a gradual process and may occur over flow-line distances of 150 km or more. It is hypothesized that the reflection Moho is a dynamic surface that may mark the abrupt transition to a more ductile regime (partial melt?). If so, the reflection Moho may have little paleostructural memory, except possibly in the vicinity of fracture zones. This casts uncertainty on the meaning of traditional measurements of crustal thickness and the applicability of extension computations that utilize the Moho as a datum.