Caldera-style migratory volcanism at Gabel Tarbtie, Southern Egyptian Nubian Shield: Petrological, geochemical, and structural insights

Abstract

The Gabel Tarbtie ring complex represents important caldera style magmatism in the Egyptian Nubian Shield. The massive association formed from a migratory magmatic midst ex-position as circular entities in three adjacent sectors with analogous lithological and structural features: two sectors forming the Tarbtie South (TS) and the other forms the Tarbtie North (TN). The rocks forming the two rings occur as a wide spectrum of petrographic sets including nepheline syenite, biotite-amphibole – aegirine bearing syenite, carbonitized syenite, nordmarkite, syenogranite, carbonatite and pyroclastics. The whole association is injected by andesitic to basaltic dykes, and affected by fenitization processes. Geochemically, the Gabel Tarbtie rocks belong to anorogenic intraplate A₁-type alkaline complexes. They have high amounts of alkalis and show enrichment in some HFS elements (i.e. Ba, Nb, Zr, Y), mainly having meta-aluminous ferrouan nature. It is believed that during the post-orogenic times tension and uplift could cause migration of the decompression portion, and advance partial melting which promotes magma generation. The Gabel Tarbtie association was developed as result of migratory magmatic pulses evolved over a 15 km along NW lineaments or deep-seated fractures. Subsequently, the mature caldera outline was influenced by NE structural trend.