The Moho transition zone in the Oman ophiolite-relation with wehrlites in the crust and dunites in the mantle

Field data in the Oman ophiolite show that the Moho transition zone (MTZ), which is on average 300 m thick above mantle diapirs, reduces to 50 m away from diapirs, with a sharp transition at the outskirts of the diapirs. We s how here that this reduction is dominantly due to compaction of a dunitic m ush present above diapirs in the MTZ, with upward injection of a wehrlitic magma in the crust, and, to a lesser extent, due to tectonic stretching. In order to explain the fraction of wehrlites injected into the crust, which is in the range of 25%, it is necessary that mantle upwelling is active, wi th a mantle flow velocity away from diapirs several times faster than the s preading velocity. If this velocity exceeds 5 times the ridge spreading-rat e, a significant part of the MTZ may be entrained down into the mantle, flo wing away from the diapir as tabular dunites.