Rooting of the Sheeted Dike Complex in the Oman Ophiolite
The root zone of the sheeted dike complex representing a thin zone (hundred meters thick) of extreme thermal gradient (∼5°C/m) is regarded as a thermal boundary between the convective magma chamber system below, and the main convective hydrothermal circuit which closes above, at the base of this root zone. The root zone of the sheeted dike complex is located at the top of the high level foliated gabbro unit, where the foliation steepens, and where the first diabase dikes appears. It is a complex zone characterized by mutual intrusions of microgabbros dikes (that we call protodikes) with brownish microgranular contacts against the gabbro matrix. Upward, viscous flow in the protodikes and in the reheated enclosing gabbros generate a diffuse transition to the sheeted complex. Protodike margins stretched in the enclosing flowing doleritic gabbros form a complicated network which can be depicted thanks to microstructural analysis. Later diabase dikes cross-cut the section. These relationships are obscured by the hydrothermal circulation which has generated, in particular, isotropic amphibole gabbro veins. These veins tend to propagate horizontally; they may be interpreted as the downward closure of the main hydrothermal convective circuit.
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