Kinematic models for the thickness of oceanic crust at and near mid‐oceanic spreading centers

Abstract

We consider analytical solutions for different cases of the one‐dimensional equation of mass transport as applied to an idealized mid‐oceanic spreading center in order to assess the conditions for the existence of thickness variations in oceanic crust and their possible magnitude. Models with an internally homogeneous crust suggest that in order to achieve the near‐constant crustal thickness of oceanic crust, the zones of volcanic accretion and of deformation must be more or less identical, especially if the far‐field plate velocity is not reached near the ridge in a jump‐like fashion, but increases more slowly over a certain distance; this indicates that accretion and strain are physically coupled. If crustal accretion occurs in a narrower strip around the spreading center than does deformation, there will be a maximum of thickness within the strain zone which is greater than the thickness far away from the ridge; if the accretion zone is broader than the zone of deformation, the near‐axis realms will have thinned crust throughout. A discontinuity of the plate velocity across the spreading axis causes a central strip of strongly thinned crust and generally damps variations in crustal thickness. An internally tripartite oceanic crust will almost unavoidably show some thickness variations near the spreading center. Transport by diffusive crustal flow is generally not of great importance at normal ridges, but may have some significance in thickened crust near hot spots. Although the solutions are restricted to the steady state, they show that the mere interaction of a few geometrical characteristics of the crust can produce a wide range of thickness variations in the regions near the spreading center.