The most widely accepted models for ocean-crust formation and composition fail to predict the thickening of the oceanic crust with age, yet such thickening has been described in the Pacific Ocean for years. To reconcile this apparent long-standing conflict, we have reexamined the evidence for the thickening of the Pacific crust by using a statistical treatment of a large number of seismic profiles and by doing a detailed reanalysis of several profiles fanning a transect across the southern Pacific Ocean. From the statistical studies, we find that crust younger than 30 Ma has a mean thickness of 5.67 km, whereas crust between 30 and 100 Ma has a mean thickness of 6.01 km. This 0.34-km difference, although statistically significant, is far less than that reported in several previous studies. Our results from the South Pacific transect suggest that changes in the crustal thickness are not systematic, and from both studies it appears that crustal thickening is not particularly important. The small thickening that we do observe is probably the result of isolated processes that are not active under the oceanic crust as a whole. As a result, arguments favoring a large component of serpentinite in the crust cannot be based upon evidence for crustal thickening beneath the Pacific Ocean.

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