PETROLOGICAL AND GEOCHEMICAL STUDIES ON THE OPHIOLITE AND ISLAND ARC ASSOCIATION OF WADI HAMMARIYA, CENTRAL EASTERN DESERT, EGYPT

The Wadi Hammariya area is covered by two main rock units, viz. dismembered ophiolite assemblage (serpentinites and their derivatives, metagabbros, amphibolites and metabasalts) and metamorphosed island arc association (calc–alkaline metavolcanics and their pyroclastics and volcaniclastic metasediments). The ophiolite assemblage comprises peridotite serpentinites, metapyroxenites, serpentinites, carbonate serpentinites, serpentine schists, chloritite, talc-carbonate rock; pyroxene hornblende-, hornblende-and leuco-metagabbros; amphibolite; spilitic metabasalts, and metabasaltic andesites. This ophiolitic assemblage has been metamorphosed up to the greenschist facies. The island arc association comprises metavolcanics (meta-andesites, metatuffs, metadacites, metarhyodacites, and metagranophyres) and volcaniclastic metasedimentary rocks (meta-mudstones, metasiltstones, slates, metagreywackes, metaconglomerates, and quartz schists). This rock association, particularly the volcaniclastic metasediments, represents the mélange host rocks for the ophiolitic assemblage. Major and trace elements geochemistry indicate that the present ophiolitic metagabbros and metavolcanics can be compared with the suprasubduction zone ophiolitic mafic–ultramafic cumulates, similar to high Mg and low Ti basaltic magma which show tholeiitic affinity. The island arc metavolcanics show that they are derived from a calc–alkaline magma in an island arc or plate margin setting. The metagreywackes originated from acidic and intermediate oceanic island arc and/or active continental margin sources to be deposited in a back-arc basin setting.