Origin and evolution of post-collisional volcanism: an example from Neoproterozoic Dokhan volcanics at Gabal Nugara area, Northeastern Desert, Egypt

Nugara volcanics are one of the northernmost outcrops of the Arabian?CNubian Shield. Two distinct volcanic successions are found in the Nugara basin: (1) old volcanic sequence composed of voluminous medium- to high-K calc-alkaline lavas and minor alkali basalt and (2) young volcanic sequence composed of subordinate tholeiitic mafic lavas. Their eruptions were punctuated by occasional volcaniclastic deposits that generated fall, flow, or reworked suites compositionally identical to the lava flows. These volcanics are a part of a post-subduction and extensional-related magmatic event in Northeastern Desert of Egypt. The volcanic rocks of the Nugara basin are characterized by strong enrichment in LILE relative to HESF, high LILE/HFSE ratios, and depletions of Nb on MORB-normalized multi-element diagrams. The geochemical features of the volcanic rocks suggest that they experienced fractional crystallization, along with mixing processes. Crustal contributions to the magma sources may also have occurred during magmatic evolution. These processes have resulted in scattered major and trace element variations with respect to increasing silica contents. The model proposed for their origin involves contrasting ascent paths and differentiation histories through crustal columns with different thermal and density gradients. The geochemical features of the most mafic samples suggest that the volcanic rocks in the region were derived from a mainly lithospheric mantle source that had been heterogeneously metasomatized by previous subduction events during convergence between the East and West Gondwanaland. The volcanic activity in the region is best explained by the delamination of lithospheric mantle slices that were heterogeneously enriched by previous subduction-related processes.