Information on the nature of the upper mantle in a young rift zone with lithosphere transitional from continental to oceanic was obtained from the island of Zabargad, probably an uplifted fragment of Red Sea lithosphere. The island exposes exceptionally fresh, mantle-derived peridotite (spinel Iherzolite) bodies. The mineralogy and major-element, rare-earth element, and mineral chemistry of the spinel Iherzolites suggest that they equilibrated last at depth ≥ 30 km in the mantle and that they have oceanic rather than continental affinity. It is unlikely that the Zabargad ultramafics are part of a late Precambrian–early Paleozoic ophiolite, as found elsewhere in circum–Red Sea regions; rather, they were uplifted probably in connection with the development of the Red Sea Rift. The Zabargad peridotites are in tectonic contact with continental metamorphic basement rocks; it appears, therefore, that regions of an embryonic rift such as the Red Sea can be covered with continental-type crust but be underlain by an upper mantle having already oceanic affinities.

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