Crustal structure of the mid-ocean ridges: 1. Seismic refraction measurements

Abstract

Results of twenty-two seismic refraction stations over the northern mid-Atlantic ridge are combined with earlier data to obtain a better definition of the gross features of the ridge. The seismic crustal structure is found to be the same at equal water depths. The crust on the flanks is an uplifted ocean basin crust which does not thicken when water depth decreases. The relation between water depth, w km, and crustal thickness, C km, derived from the data is C = 0.80w + 1.20. It indicates that in the absence of a compensating mass within the mantle one would expect a positive gravity anomaly of 120 mgal per km of height of the ridge above the basin floor. In the axial zone, a 5.8-km/sec layer overlies a 7.3-km/sec ‘upper mantle.’ Three different areas in the North Atlantic Ocean are compared with the east Pacific rise section and a genetic relationship is inferred from these comparisons. The northern mid-Atlantic ridge is assumed to be in a later stage of evolution, the thickness and velocity of the basement layers being considered the best indicators of the degree of maturation of the mid-ocean ridges.