Cryogenian-Ediacaran Crustal Growth And Evolution Of The Active Margin Of The Dahomeyide Belt, Ghana
Date
2023
Authors
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Publisher
Geological Magazine
Abstract
The study presents detailed petrographical, geophysical, structural and geochemical data of the
internal nappes zone to establish the deformational history, origin and tectonic setting and
constrain the crustal growth and evolution of the active margin of the Dahomeyide belt. Two
main lithological units, (i) deformed meta-granitoids (migmatites and gneisses) and
(ii) undeformed granitoids dominate the internal nappe zone. Granitoids are generally
I-type, metaluminous to weakly peraluminous, low-K tholeiite to high-K calc-alkaline and of
tonalite, granodiorite, and granite affinity. The overall trace element patterns of the studied
granitoids characterized by the enriched LILE and depleted HFS, with negative peaks of Nb-Ta,
Sr, P, and Ti are indications of arc-related magmatism. Structural analysis reveals four
deformation phases (D1-D4). D1 represents Northwest-Southeast (NW-SE) Pan African
shortening associated with a continent-continent collision, resulting in westward nappe
stacking. Progressive NW-SE shortening resulted in D2 and D3 top-to-the-NW dextral and
sinistral thrusting events during the Pan-African orogeny. D4 is an extensional event likely
associated with the orogenic collapse phase. The gneisses and migmatites, with dominant axial
planar foliations point to their formation in a collisional setting or influence by the Pan-African
collisional processes. Continental-arc signatures in these rocks imply continental subduction
during their protolith formation. The intrusive granitoid and pegmatite are undeformed.
meaning late- to post-orogenic emplacement. These findings suggest that the internal nappes
zone archived the subduction-collision and post-collisional phase of the Pan-African orogeny
and recorded large-scale migmatization and granitoid emplacement due to partial melting of
thickened lower crust between the mid-Cryogenian and late Ediacaran.
Description
Research Article
Keywords
crustal thickening, continent collision, crustal anatexis