Magmatic occurrences of post-permian age of the South American Platform

F. F. M. de Almeida, C. D. R Carneiro


Several types of magmatic processes related to the breakup of Gondwana affected the greater part of the South American Platform: (1) Tholeiitic intrusions and effusions such as lava flows, sills and dykes, with maximum intensity from the middle Jurassic to the pre-Aptian Early Cretaceous, and Permian-Triassic tholeiitic dykes locally in the northern half of the continent. (2) Alkaline and peralkaline magmatism (mafic to felsic with minor associated carbonatites) developed when South America and África were moving apart; this was mostly post - Albian in age but lasted until the Miocene. A few alkaline intrusions are synchronous with the Jurassic-Early Cretaceous volcanism. (3) Several kimberlite intrusions recognized in Brazilian cratonic áreas of middle Proterozoic age, as well as in áreas affected by late Precambrian orogenic processes. The maximum thickness of basaltic lava flows and sills in the interior of intracratonic basins reflects the influence of older geological structures. Many Precambrian faults and fractures intruded by diabase show displacement within dyke swarms. Dykes apparently unrelated to older fractures belong to áreas subjected to tensional stresses during continental separation. The alkaline magmatism at the borders of the Paraná basin in Brazil, Paraguay and Bolivia is generally controlled by arches and faulted flexures. The relationship between oceanic fracture zones and Paleogene magmatism in the continental crust is clearly displayed in at least two sites, corresponding to projections of the Romanche and Fernando de Noronha oceanic fracture zones

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