Reevaluating the Abbabis Complex: Intrusive relationships and melt connectivity in a syn-orogenic migmatite–granite system, Damara Orogen, Namibia

Thomas Lloyd Jones, Alex Otto, Ed Becker, Andy Wilde

The Abbabis Complex in the Damara Orogen has long been interpreted as a pre-Damaran (c. 1–2 Ga) basement terrane unconformably overlain by Neoproterozoic metasedimentary rocks of the Damara Supergroup. New field mapping and geochemical data from the Ida Dome and Husabberg Anticlinorium encourages re-evaluation of this interpretation. The Abbabis Complex comprises migmatites, larger leucogranite dykes and pluton-like accumulations, as well as metasedimentary rafts and schlieren. Leucogranite and migmatite bodies cross-cut overlying metasedimentary units along a gradational intrusive contact. Units mapped as “Abbabis Complex” correspond to domains where granite and migmatite become volumetrically dominant. Leucosomes of migmatites in the Abbabis Complex show similar major and trace element compositions, as well as near-identical fractionation trends, to leucogranite dykes intruding into the overlying Damara Supergroup. Leucogranite dykes are systematically more evolved, consistent with their distal location on overlying dome limbs. These relationships support field evidence that migmatites and overlying dykes formed part of an interconnected mid-crustal melt-transfer network. We interpret the Abbabis Complex in the study area predominantly as a syn-orogenic, melt-dominated migmatite–granite complex formed during high-temperature Damaran metamorphism (peaking at c. 520 Ma), involving partial melting of mainly metasedimentary protoliths and upward migration of correspondingly weakly peraluminous melt.