Amphibolites of the central zone: New shrimp U-Pb ages and implications for the evolution of the Damara Orogen, Namibia

Abstract

New SHRIMP U-Pb zircon and titaniie data are presented for two amphibolites from the Central Zone of the Damara Orogen, Namibia. These data (the first ages for amphibolites in the Central Zone) show that amphibolites are derived from both Palaeoproterozoic (2026.9 ± 2.3 Ma-sample ACAM-1) and Pan-African (557.2 ± 7.4 Ma-sample LKR021) precursors emplaced into the Palaeoproterozoic Abbabis Complex basement in the Central Zone. The younger amphibolites are interpreted as part of a mafic to dioritic phase of magmatism in the Central Zone (the Goas Suite), and major-And trace-element geochemistry from a suite of amphibolites from the southwestern Central Zone confirms this relationship. This phase of mafic to dioritic magmatism is contemporaneous with the onset of collision between the Congo and Kalahari Cratons. It is suggested that delamination of dense mafic lower cnist and underplating of mantle-derived magmas following crustal thickening may have led to partial melting of pre-Pan-African mafic lower crust, generating this mafic to dioritic suite of rocks. Metamorphic zircon overgrowths in sample LKR021 give an age of 520 ± 6.9 Ma, consistent with recent estimates for the age of peak metamorphism in the southwestern Central Zone. Titanites from LKR021 give an age of 493.4 ± 6.4 Ma, and this is interpreted as a cooling age for the Central Zone.