Mantle flow pattern at oceanic spreading centres: relation with ophiolitic and oceanic structures

Abstract

Summary The rolling-mill effect concerning asthenosphere circulation beneath a fast-spreading centre (Rabinowicz et al. in press) is recalled and discussed in terms of its geological assessment. The model predicts a fast and narrow jet of asthenosphere which carries 70% of the total melt produced beneath the ridge. This explains both the structural data in most ophiolites and the formation of the crust within a few kilometres at fast-spreading ridges. It is proposed that the more diffuse activity at slow-spreading ridges from mid-oceans or marginal basins, along with the more diffuse magmatism recorded in a few ophiolites is related to the disappearance of this narrow stream as a consequence of an increase of viscosity due to lower temperatures beneath the ridge.