Medium-to high-pressure garnet-amphibolites from Gebel Zabara and Wadi Sikait, south Eastern Desert, Egypt

Abstract

Garnet-amphibolites from Gebel Zabara and Wadi Sikait in the southern Eastern Desert of Egypt occur as highly flattened metamorphosed basic volcanic bands enclosed within garnetiferous metasediments. Samples from both localities have almost the same metamorphic assemblage of garnet-amphibole-plagioclase-ilmeniterutile. An electron microprobe study indicates that garnet, amphibole and plagioclase are cryptically zoned only in samples from Wadi Sikait. The composition of amphiboles (tschermakitic hornblende to tschermakite) reflects a temperature range equivalent to that of the staurolite-kyanite zone of the metapelitic sequences. Geothermometric calculations of the pairs garnet-amphibole and amphibole-plagioclase indicate average temperatures of 550°C for samples from Wadi Sikait and Gebel Zabara, respectively. Pressures of about 6.8 kbar and 7.7 kbar are obtained using some mineral equilibria of both silicates and opaque phases. The garnet-amphibolites are considered as a part of the infrastructural suite in the Eastern Desert. A comparison with the Pan-African amphibolites from the Eastern Desert and Sinai is presented.