U-Pb baddeleyite ages of key dyke swarms in the Amazonian Craton (Carajás/Rio Maria and Rio Apa areas): Tectonic implications for events at 1880, 1110 Ma, 535 Ma and 200 Ma

Abstract

U-Pb baddeleyite ages for key mafic dykes of the Amazonian Craton reveal four significant intraplate episodes that allow connections with global igneous activity through time and supercontinent cycles. The oldest dykes (Carajás-Rio Maria region) are diabases with ages of 1880.2 ± 1.5 Ma and 1884.6 ± 1.6 Ma, respectively, corresponding with the Tucumã swarm which crops out to the west and is age-equivalent. The magmatic activity has a genetic link with the ca. 1.88 Ga Uatumã Silicic Large Igneous Province (SLIP), characterized by felsic plutonic-volcanic rocks. There is an age correlation with LIP events (ca. 1880 Ma) in the Superior, Slave, Indian and other cratons. This magmatism could be derived from significant perturbations of the upper mantle during the partial assembly of Columbia. Gabbronorite of the Rio Perdido Suite (Rio Apa Terrane) crystallized at 1110.7 ± 1.4 Ma, and is identical to that of the Rincón del Tigre-Huanchaca LIP event of the Amazonian Craton. This event was synchronous with the initiation of Keweenawan magmatism of central Laurentia (Midcontinent Rift) and also with coeval units in the Kalahari, Congo and India cratons. The two youngest U-Pb dates (535 and 200 Ma) occur in the Carajás region. Diabase of the Paraupebas swarm yields an age of 535.1 ± 1.1 Ma, which may be correlative with the giant Piranhas swarm located ca. 900 km apart to the west. The Paraupebas swarm is correlative with post-collisional plutonism within the Araguaia marginal belt. Therefore, the Cambrian dykes may reflect reactivation of cooled lithosphere, due to crustal extension/transtension active along the craton’s margin during assembly of West Gondwana. This magmatism is also contemporaneous with the 539–530 Ma Wichita LIP of southern Laurentia. The youngest studied Carajás region dyke was emplaced at ca. 200 Ma, corresponding with 40Ar/39Ar ages for the Periquito dykes west of Carajás and with most K-Ar ages of the giant Cassiporé swarm, located north of the study area. The newly dated ca. 200 Ma dyke fits well into the known, brief span of ages for the CAMP Large Igneous Province event, around the present central and northern Atlantic Ocean.