Evolution of oceanic crust

Most of the East Pacific Rise crest is characterized by a 10 to 20 km wide axial block that stands several hundred meters above the regional water depth. A seismic refraction study of the flank of the East Pacific Rise shows that there are no significant changes in the structure of the crust and upper mantle along the 1.4 m.y. and 2.4 m.y. isochrons. Moreover, there is very little chronologic change in structure between the base of the axial block and the 2.4 m.y. isochron profile. It is concluded that first order variations in crustal structure are restricted to the axial block province and that the process of crustal generation in the study region has remained spatially and temporally stable for at least the last several million years.