GEOLOGICAL SETTING OF THE MEATIQ METAMORPHIC CORE COMPLEX IN THE EASTERN DESERT OF EGYPT BASED ON AMPHIBOLITE GEOCHEMISTRY

Large parts of the Central Eastern Desert of Egypt consist of Neoprote rozoic nappes of ophiolite and island-are volcanic rocks. Beneath thes e nappes metamorphic basement domes are exposed in tectonic windows su ch as the Meatiq basement. The mineral and whole rock chemistry of amp hibolites included in the teconically lowermost granitoid gneiss, with in the metasedimentary cover of the gneiss and within shear zones bord ering the Meatiq basement dome, are investigated to determine their ge odynamic setting. The amphibolites consist mainly of plagioclase, horn blende, quartz and, locally, clinopyroxene. The metamorphic mineral as semblage is retrograded from upper amphibolite-facies peak metamorphic conditions to lower amphibolite-facies. The Niggli c-mg plot identifi es them as orthoamphibolites, and whole rock chemistry indicates a bas alt to basaltic andesite composition for most of the amphibolites. Imm obile trace elements such as Zr. Y and Ti suggest that one group of am phibolites is derived from within-plate basalts and another belongs to the MORE tectonic setting. This is consistent with the result of the AFM plot, which indicates a tholeiitic composition for all the amphibo lites. REE patterns confirm the trace element results, with a typical LREE depletion for the N-type MORE amphibolites. The first group of am phibolites is enriched in LREE and displays a concave pattern. The amp hibolite inclusions in the Um Ba'anib gneiss record different geologic settings - from the formation of oceanic crust to within-plate basalt ic magmatism - prior to the intrusion of the Um Ba'anib granitoid. Cop yright (C) 1997 Elsevier Science Ltd.