Magma fractionation and emplacement mechanism in a subvolcanic plumbing system in a continental region: constraints from the late Neoproterozoic Wadi Dib ring complex in the Eastern Desert, Egypt.

We examined an alkaline ring complex in the Eastern Desert of Egypt, Wadi Dib (WDRC), to understand formation mechanisms intimately related structure and chemical diversity. The WDRC consists multiple circular rings oldest volcanic units, middle-stage plutonic unit, youngest dike these units show overlapping whole-rock major element compositions. compositional variation can be accounted for by a stepwise fractional crystallization starting with trachyte, without significant magma replenishment or crustal contamination. From margin center youngest, unit outer (syenite), inner 1 (quartz-bearing syenite) 2 (quartz syenite), granitic core (syenogranite). composition is progressively more fractionated inwards from through rings. Syenites innermost high degree deformation, which gradually decreases outwards abruptly outermost 1. deformed syenites microstructures suggesting reactive melt transportation. country rocks neighboring equivalent blocks present periphery ring, overlying all indicative pyrometamorphism. Spatial variations indicate increase cooling rate thus time. These geological, chemical, microstructural features suggest that represents evolving roof zone subvolcanic body located at depth few km. Intimate coupling growing sidewall mushy boundary layers later collapse layer occasional involvement piles induced segregation interstitial wall space driven pressure gradient collapse. ascended started crystallize form next generation increasing efficiency, thickened until on smaller horizontal scale inducing towards zone. Repetition sequence shallowing decreasing produced diversity WDRC.