Dike distribution in the Oman-United Arab Emirates ophiolite

Mafic dikes and dunite veins are observed in the mantle section of the Oman - United Arab Emirates (O-UAE) ophiolites, as well as diabase dikes and hydrothermal veins in the crust section. They have been systematically measured during the mapping of this ophiolite and are represented by their trajectories in the folded map 3 in the back of this volume, and by local stereoplots included in this study. Mafic dikes in the mantle section correspond to basaltic melt being injected at decreasing temperatures from above or at peridotite solidus, down to below 450 degreesC. Hydrothermal veins associated with dioritic dikes issued from hydrous melting of host gabbros are observed down to the base of the crust, bearing evidence for sea water penetration into basal gabbros at or above 900 degreesC, that is very close to the ridge axis. Dike orientations record the stress field at the time of their injection. In most places, all types of dikes are dominantly parallel to the general trend of the nearest sheeted dike complex; thus the stress held has not visibly changed from melt injection in the asthenosphere below the ridge of origin to injection in a lithosphere up to a few Myr old, at distances beyond 100 km from the axis. Local preferred orientations, when they are considered in the frame of the paleo-ridge system of O-UAE, result in a coherent model throughout the belt: the sheeted dike complex dips moderately away from the presumed ridge axis and the mantle dikes, toward this axis. These opposite directions are explained by the presumed effect of subsidence toward the axis for the sheeted dikes and by the central feeding from an asthenospheric uprise for the mantle dikes.