Abstract

Re-examination of the Vourinos ophiolite shows it to be composed of metamorphic tectonites, cumulates, plagiogranites, dikes, and lava. The contact between the tectonites and the cumulates is exposed and sharp. Beneath the cumulate contact, the rocks have been highly deformed and complexly folded; above that contact, they simply have been tilted vertically to expose a stratiform complex 1,500 m (4,800 ft) thick. The stratiform intrusion is characterized by cyclic units, rich in olivine at the base, and rich in feldspar at the top. Some cumulus diorites are present at the top of the section which grade into quartz diorites (plagiogranites) with hypautomorphic textures. Lineate lamination characterizes the cumulates and may indicate the direction or orientation of the Mesozoic mid-oceanic ridge crest with respect to the present position of the complex. A siliceous dike swarm cuts the upper part of the stratiform complex. The section suggests that in the case of Vourinos, a large magmatic chamber formed at a mid-oceanic ridge crest and that intrusion was a much more important process than extrusion in the formation of oceanic crust in that area. The reported presence of cumulates in many other ophiolite complexes suggests that these relations may obtain generally at most or all spreading ridges. The contact between the tectonites and the cumulates of the complex would not have corresponded with seismic M.

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