PETROGRAPHICAL AND GEOCHEMICAL STUDIES ON THE METAMORPHIC ROCKS OF THE AREA AROUND WADI ABU MREIWA, NORTH- EASTERN DESERT, EGYPT

Abstract

Abu Mreiwa area in the central Eastern Desert is covered by the ophiolites and the associated m~lange. Field relation, petrographical and petrochemical studies were carried out to evaluate their petrogenesis and geotectonic setting. The ophiolite sequence is represented successively up wards from the west to the east by underlying harzburgite serpentinite passing upwards through pyroxenite lenses into gabbros overlain by massive diabase and pillowed basalts at the top, followed by a thin wedge • of immature molasse type. metasediments and a young conglomerate sequence of The ophiolite units reveal a tholeiitic affinity and were formed in mid oceanic ridge environment. The associated ophiolitic m~lange comprise the opiolitic dismembers of serpentinites and metagabbros within island arc metavolcanic and volcanoclastic and immature volcanoclastic metasediment matrix. They are represented by metaandesites, andesitic metadacites and immature volcanoclastic metasediments. They were generated from calc-alkaline magma and are related to immature island arc phases. These island arc volcanics were intensively subjected to weathering and erosion and they I were deposited again forming turbidite formation of greywackes and mudstone representing the present volcanoclastic metasediments. ; However, the presence of the terrestial components (mudstone, siltstone and quartzite pebbles) through the volcanoclastic metasediments indicates that the deposition was closer to the continent and the deposition of turbidites would be in a back arc basin. The termination of the island arc stage was followed by a major orogeny which caused thrusting and mixing of the ophiolitic m~lange and metamorphism of the present rocks up to the green schist facies.