Post-Paleozoic magmatism in Angola and Namibia (SW Africa) is widespread along the continental margin (fl ood tholeiites of the Paraná-Etendeka system), and along transverse lineaments (alkaline and alkaline-carbonatitic complexes; sodic and potassic suites). These different magmatic suites are strictly associated in space and/ or time. Variable melting degrees of a veined lithospheric mantle are proposed for the most “primitive” magmas from geochemical modeling and Sr-Nd isotope systematics. A complex evolution emerges for some ultramafi c rocks (cumulus processes) and for differentiated rock compositions (assimilation and fractional crystallization, AFC, magma mixing), which may also involve anatexis of the crystalline basement and emplacement of S-type granites and rhyolites. Melting of a lithospheric mantle, without an appreciable contribution of the asthenosphere (thermal input excepted), is consistent with regional thermal anomalies in the deep mantle, mapped by gravity of the geoid, seismic tomography, and paleomagnetic analysis. The Walvis Ridge and Rio Grande “hotspot tracks” are interpreted as stress response in the lithosphere during rifting. A plume-related heat source is not favored by our results.
Post-paleozoic magmatism in Angola e Namibia: a review.
DE MIN, ANGELO;
2011-01-01
Abstract
Post-Paleozoic magmatism in Angola and Namibia (SW Africa) is widespread along the continental margin (fl ood tholeiites of the Paraná-Etendeka system), and along transverse lineaments (alkaline and alkaline-carbonatitic complexes; sodic and potassic suites). These different magmatic suites are strictly associated in space and/ or time. Variable melting degrees of a veined lithospheric mantle are proposed for the most “primitive” magmas from geochemical modeling and Sr-Nd isotope systematics. A complex evolution emerges for some ultramafi c rocks (cumulus processes) and for differentiated rock compositions (assimilation and fractional crystallization, AFC, magma mixing), which may also involve anatexis of the crystalline basement and emplacement of S-type granites and rhyolites. Melting of a lithospheric mantle, without an appreciable contribution of the asthenosphere (thermal input excepted), is consistent with regional thermal anomalies in the deep mantle, mapped by gravity of the geoid, seismic tomography, and paleomagnetic analysis. The Walvis Ridge and Rio Grande “hotspot tracks” are interpreted as stress response in the lithosphere during rifting. A plume-related heat source is not favored by our results.Pubblicazioni consigliate
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