Metamorphic conditions and igneous activity in the Um Zariq area, East Sinai, Egypt: Mineralogical and petrological evidences for the transformation from collisional to an extensional regime in the Arabian-Nubian shield

Abstract

The authors present new petrographic and mineralogical data for the Um Zariq Formation which belongs to Arabian–Nubian Shield metamorphic exposures in the Sinai Peninsula. The formation is believed to be a metasedimentary sequence whose protolith was deposited during the Sturtian Snowball Earth Event (SEE). Our new field data indicate the occurrence of metasomatised limestones/dolostones (calc-silicates) which is distinct from those reported from The Feiran-Solaf Metamorphic Complex. We highlight the presence of a lamprophyre body close to the Kid A-type granite; the Malhaq vogesite - a variety of hornblende-phyric lamprophyre with orthoclase feldspar-. Based on mineral assemblages, field observations and petrographic study, metapelites record an early greenschist/lower amphibolite facies regional metamorphism. Intrusion of the syn-collisional deformed granites (CA1) synchronised with the regional metamorphism at ca. 660±25 Ma. Both of the metamorphic events overprinted on the metapelites and calc-silicates. The contact metamorphism formed cordierite and andalusite in the metapelites and pyroxenes in the calc-silicates. Calc-silicates, on the other hand, record anisotropic fabrics, higher T metamorphic mineral assemblages with hornfelsic texture. The Um Zariq metapelites protoliths were deposited at a deeper stratigraphic level and thus, recorded the regional and contact metamorphism contrary to the shallower carbonates. The peak metamorphic conditions were followed by retrograde metamorphism marked by chlorite and prehnite from metapelites and prehnite, epidote and chlorite in calc-silicates. The Um Zariq igneous activity (Kid A-type Granite and the Malhaq Lamprophyre) marks the transformation from collisional to extensional regime in the Arabian–Nubian Shield at ca. 600 Ma.