A Pan African origin and uplift for the gneisses and peridotites of Zabargad Island, Red Sea: a Nd, Sr, Pb, and Os isotope study

H. K. Brueckner, Mevert A. Elhaddad, Bruno Hamelin, Sidney Hemming, Alfred Kroner, Laurie Reisberg, Monique Seyler

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A Sr, Nd, Pb, and Os isotopic study of peridotites andgranulite-facies gneisses from Zabargad Island in the Red Sea suggests that thetectonothermal, petrogenetic, and geochemical evolution of these rocks occurredlargely during the Pan African Orogeny rather than the recent opening of theRed Sea. Sm-Nd model ages and whole rock errorchrons indicate that spinelIherzolites and gneisses differentiated from a common depleted mantle sourceabout 700 Ma. The Iherzolites were mylonitized, metasomatized, andamphibolitized during a structural event that juxtaposed the peridotites withthe gneiss complex and uplifted the gneiss/peridotite complex to relativelyshallow crustal levels. Most radiometric dating schemes suggest a Pan Africanage for this event. The gneisses generally have lower 143Nd/144Nd, 87Sr/86Sr, 208Pb/204Pb, 207Pb/204Pb,and 206Pb/204Pb ratios than the peridotites. Theyextend linear trends defined by the spinel and amphibole peridotites on Sr-Nd,Sm-Nd, and Pb-Pb diagrams, suggesting the gneisses were either the source orbuffering medium for the Pan African metasomatism. Only one post-Pan Africanevent had a significant effect on the geochemistry of the gneiss/peridotitecomplex: shallow level metasomatism by ultrahot (750–900°C) hypersalinesolutions with high 87Sr/86Sr (≈0.710) ratio led tothe development of gem-quality olivine crystals as well as low-pressure mineralassemblages in the peridotites, gneisses and younger rocks. Plagioclase-richassemblages with apparent igneous textures (“troctolites”) that are most commonin the southern peridotite body may have formed by interaction of these fluidswith peridotite (i.e., are “pseudo-troctolites”). Metasomatism changedthe 87Sr/86Sr, Sm/Nd, and Re/Os ratios of theplagioclase peridotites making them unsuitable representatives of the PanAfrican mantle.

Original languageEnglish
Pages (from-to)22283-22297
Number of pages15
JournalJournal of Geophysical Research
Issue numberB11
Publication statusPublished - 1995
Externally publishedYes


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