Geochemistry and petrogenesis of El-Fringa metagabbro-diorite rocks, Wadi Sa’al area, south Sinai, Egypt

Neoproterozoic metagabbro-diorite-tonalite intrusive complexes (~881±58 Ma) of the basement complex of the Egyptian Eastern Desert and Sinai represent subduction-related magmatic edifice in the early stages of the Pan-African orogeny. These rocks exhibit petrological and geochemical characteristics of island arc-related magmas derived possibly from partial melting of a mantle wedge above a subduction zone or originated from partial melting of an amphibolitic lower crust by anatexis process at a volcanic arc regime. The El-Fringa metagabbro-diorite complex crops out at the northwest district of Wadi Sa’al and cuts the structural grain of the Sa’al metavolcanic group. It is composed of heterogeneous mafic and intermediate rock varieties, namely: hornblende metagabbro diorite to and quartz-diorite. Geochemically, this complex has transitional tholeiitic- and calc-alkaline magma. It is suggested that this complex was probably formed by fractional crystallization of a basaltic magma derived by partial melting of a metasomatised upper mantle in an island-arc setting.

The REE patterns of the studied rocks are more or less identical, i.e., generally enriched light REE with variably distinct positive Eu anomalies, and depleted heavy REE. The systematic increase in total REE abundances from least to most evolved gabbro and diorite varieties, which can be explained in terms of fractional crystallization. Field relationships, tectonic setting, mineralogical and geochemical characteristics of the El-Fringa complex are comparable with similar suits in the Eastern Desert and may represent a concomitant island arc magmatic increment.

Keyword: Metagabbro-diorite complex, Geochemistry, Island arc rocks, El-Fringa, Sinai, Egypt.