A new magma chamber model based on structural studies in the Oman ophiolite

Abstract

Structural mapping in the mafic-ultramafic transition zone and in the overlying crustal section of the Oman ophiolite has revealed the importance of magmatic flow in the formation of layering in the gabbros, and the mechanical coupling between this flow and the asthenospheric flow of the underlying peridotites. The crustal section near the spreading axis, and in particular the magma chamber are fed by two independent melts: a dominant gabbroic melt episodically injected from depth and a subordinate wehrlitic crystal mixture produced by compaction of the transition zone. Layering in the gabbros can be partly produced by tectonic transposition of the gabbroic and wehrlitic mixtures during magmatic flow. Whatever its origin, the layering orientation in the newly created crust does not necessarily reflect its original attitude. The final orientation of the layering is determined by the attitude of the magmatic flow plane at the time it was frozen. A new magma chamber model is proposed which solves some of the physical difficulties of previous models and accounts for the seismic imaging of magma chambers beneath oceanic ridges.