Petrogenesis of a high TiO 2 mafic dyke swarm from southwest Sinai

Abstract

A distinctive high Ti, Fe, P and Ba and low Mg, Cr and Ni mafic dyke swarm cross-cuts the Pan-African basement rocks in the area of Wadi Ager, southwest Sinai. These dykes trend northwest and dip vertical and subvertical, suggesting extensional tectonics in the northeast-southwest direction at the end of the Pan-African event. The dykes are mostly dolerites showing alkaline to calc-alkaline affinities. Essential mineral phases include plagioclase (An 54–67), augite (Wo 41.8–48.1), FeTi oxides and rare olivine. These rocks are akin to Proterozoic and Mesozoic rift-related high TiO 2 basaltic dykes and flows (e.g. Blue Ridge-Hudson Highlands of North America, Amundsen of Antarctica and the Paraná Basin of South America). It is plausible that the dyke swarm is derived from a homogeneous lithospheric source which suffered a very low degree of partial melting. The dyke swarm experienced fractional crystallisation dominated by the removal of plagioclase. This was, most probably, followed by a process of crustal contamination during magma ascent.