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 hy drothermal veins in the crust section. They have been systematically measur ed during the mapping of this ophiolite and are represented by their trajec tories in the folded map 3 in the back of this volume, and by local stereop lots included in this study. Mafic dikes in the mantle section correspond t o basaltic melt being injected at decreasing temperatures from above or at peridotite solidus, down to below 450 degreesC. Hydrothermal veins associat ed with dioritic dikes issued from hydrous melting of host gabbros are obse rved down to the base of the crust, bearing evidence for sea water penetrat ion 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 th e general trend of the nearest sheeted dike complex; thus the stress held h as not visibly changed from melt injection in the asthenosphere below the r idge of origin to injection in a lithosphere up to a few Myr old, at distan ces beyond 100 km from the axis. Local preferred orientations, when they ar e considered in the frame of the paleo-ridge system of O-UAE, result in a c oherent 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 subsidenc e toward the axis for the sheeted dikes and by the central feeding from an asthenospheric uprise for the mantle dikes.