Lithostratigraphy, structure and SHRIMP U-Pb zircon geochronology of metamorphic rocks from the Namibe region (southwestern Angola): a fragment of the Southwestern Congo Shield deformed during the Eburnean orogeny
DOI:
https://doi.org/10.21701/bolgeomin/136.1/007Keywords:
Southwestern Congo Shield, Eburnean orogeny, Epupa Complex, Namibe Group, AngolaAbstract
The Namibe region of southwestern Angola is part of the Southwestern Congo Shield, which constitutes a crustal domain subjected to tectono-metamorphic processes related to the Eburnean orogeny. The geological mapping work carried out in the PLANAGEO Project has made possible to distinguish two Neoarchean to Paleoproterozoic metamorphic assemblages: (1) the ortho and paragneisses of the Epupa Complex; and (2) the supracrustal metasediments of the Namibe Group. The Epupa Complex is made up of granitic, tonalitic and dioritic orthogneisses, leucogneisses and pelitic paragneisses, variably migmatized. The Namibe Group includes basal amphibolites and calcitic/dolomitic marbles overlaid by a thick and monotonous sequence of alternating slates, schists and metagreywackes with intercalations of quartzites and metaconglomerates. The cartographic relationships, the lithological contrast and the absence of orthogneisses indicate that the Namibe Group was unconformably deposited on top of the Epupa Complex. During the Eburnean orogeny, both the Epupa Complex and the Namibe Group underwent polyphase ductile deformation and regional metamorphism that, in large sectors, reached partial melting conditions. Eburnean structures can be grouped into two main ductile deformation events, D1 and D2, together with two other less penetrative late events, D3 and D4. U-Pb SHRIMP zircon and 40Ar/39Ar muscovite geochronological data indicate that the Eburnean thermal peak of metamorphism, the crystallization of leucosomes, the emplacement of anatectic leucogranites, and the cooling of the assemblage took place in a relatively short time interval (~10 Ma).
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