Geological setting of the Meatiq metamorphic core complex in the Eastern Desert of Egypt based on amphibolite geochemistry

Abst rac t -Large parts of the Central Eastern Desert of Egypt consist of Neoproterozoic nappes of ophiolite and island-arc volcanic rocks. Beneath these nappes metamorphic basement domes are exposed in tectonic w indows such as the Meatiq basement. The mineral and whole rock chemistry of amphibol i tes included in the teconical ly lowermost granitoid gneiss, within the metasedimentary cover of the gneiss and within shear zones bordering the Meatiq basement dome, are invest igated to determine their geodynamic setting. The amphiboli tes consist mainly of plagioclase, hornblende, quartz and, locally, c l inopyroxene. The metamorphic mineral assemblage is retrograded f rom upper amphibol i tefacies peak metamorphic condit ions to lower amphiboli te-facies. The Niggli c m g plot identif ies them as orthoamphiboli tes, and whole rock chemistry indicates a basalt to basaltic andesite composit ion for most of the amphibolites. Immobile trace elements such as Zr, Y and Ti suggest that one group of amphibol i tes is derived from within-plate basalts and another belongs to the MORB tectonic setting. This is consistent with the result of the AFM plot, which indicates a tholei i t ic composi t ion for all the amphibolites. REE patterns confirm the trace element results, wi th a typical LREE deplet ion for the N-type MORB amphibolites. The f irst group of amphiboli tes is enriched in LREE and displays a concave pattern. The amphibol i te inclusions in the Um Ba'anib gneiss record d i f ferent geologic sett ings f rom the format ion of oceanic crust to wi th in-plate basalt ic magmat ism prior to the intrusion of the Um Ba'anib granitoid. Copyright © 1997 Elsevier Science Ltd. All rights reserved