Résumé
The Orocaima silicic large igneous province (SLIP) of the Amazonian Craton constitutes one of the largest SLIPs recognized on Earth and possibly the most voluminous Paleoproterozoic magmatic event in Amazonia. Nevertheless, the triggering mechanisms behind this episode of large-volume felsic magmatism and its relationships with regional tectonic and/or mantle processes remain debated. Here, we present new high-precision geochronologic as well as geochemical results from multiple mafic dike swarms in the Guyana Shield of the Amazonian Craton, namely the Guaniamo, Aro, and Manteco-Supamo swarms, and show that these are geochemically unrelated but temporally and geographically associated with the Orocaima SLIP. The radial arrangement of these swarms, their clear tholeiitic geochemical affinity, and their emplacement in regions far from known arc-related magmatic centers in the Amazonian Craton at 1.98 Ga, suggest a plume-related origin for these mafic magmas. Discovery of this previously unrecognized LIP and its close association with the Orocaima suggests that heat transfer from an impacting plume triggered large-scale melting of the Amazonian lithosphere resulting in SLIP development, thus arguing against accretionary models for the origin of this voluminous silicic magmatic belt. Re-interpretation of paleomagnetic poles of the Aro swarm using our new geochronologic results, in addition to inter-cratonic correlations with other coeval LIPs globally, enables a better paleogeographic reconstruction of Amazonia in the Paleoproterozoic and a more accurate understanding of the role of this major craton in the global Precambrian supercontinent cycle.