This project is to study a section of upper mantle peridotites and a lower crustal granulite-facies complex exposed on the island of Zabargad, Red Sea, as part of a continuing study on the evolution of the upper mantle and lower crust as continental rifts evolve to oceanic rifts.The crustal complex contain garnet- granulite-facies silicic gneisses, and amphibolitized metagabbros and metapyroxenites. The silicic gneisses are probably remnants of the pre-rift ;lower continental crust formed ;during the Pan African cycle. The high-P meta-igneous rocks are interpreted as metamorphosed basic magmas that underplated the crust prior to and during rifting. the peridotites include isotopically depleted spinel lherzolites that were partially hydrated to amphibole peridotites by fluids with the isotopic signature (low 87Sr/86Sr and 143Nd/144Nd) of subcontinental mantle metasomatism. They are believed to have been part of the sub-Red Sea mantle. Both the crustal complex and the peridotites show successive re- equilibration assemblages from granulite to amphibolite to greenschist facies conditions suggesting they were uplifted together from deep tectonic levels. The PIs will test the hypothesis that the entire section was once very close to the base of the Pan African crust and was raised and exposed recently and rapidly, possibly along a major detachment fault that may be exposed on Zabargad, as a result of the opening of the Red Sea. Schedule for study are petrology, major, trace and Ree elements, mineral chemistry, and Sr, Nd, Pb and possibly Os isotopes of the Zabargad peridotites and crustal rocks. A major goal will be to determine initial ages, recrystallization ages and uplift rates of the crustal rocks. Rb-Sr, Sm-Nd and U-Pb whole-rock and mineral results from Lamont-Doherety Geological Observatory will be coordinated with U-Pb zircon, 40Ar/39Ar amphibole, and zircon, sphene and apatite fission track ages from other laboratories. The objectives are (a) to determine the time, rate and mechanism of uplift of the Zabargad complex, (b) define the nature of the lower continental crust in a transitional rift, (c) investigate the processes of underplating in a pre-oceanic rift, (d) clarify the petrological and geochemical evolution of the crust and mantle in a major rift prior to sea floor spreading, and (e) infer whether "active" or "passive" rifting prevailed in the Red Sea Rift. The results expected from this project will help us understand the crustal evolution of Atlantic-type passive margins.
