Variation in young oceanic crust and upper mantle structure

Abstract

Seismic refraction and single‐channel reflection data taken along 0.5‐, 2.5‐, and 4.5‐m.y.‐age isochrons near the East Pacific Rise during Project ROSE are used to determine if a systematic change in the P velocity‐depth function with age can be resolved. Inversion of these data suggests that any change in crustal P velocity structure related to age is smaller than variability in the seismic velocity‐depth function along an isochron. The emergence of a ‘normal’ crust‐mantle transition by 4.5‐m.y.‐age is seen in these data. Crust and crust‐mantle transition zone heterogeneity along these isochrons may be related to the along strike variability in processes at the ridge crest. The velocity‐depth functions for the three split profile refraction lines are compared with velocity‐depth functions for the Samail ophiolite, which is thought to represent oceanic crust of similar age. The velocity‐depth functions for the ROSE data are bounded by different velocity‐depth models for the Samail ophiolite; this suggests that those models are not in disagreement but represent the lateral heterogeneity that can be expected in young oceanic crust.