Widespread ca. 1.4 Ga intraplate magmatism and tectonics in a growing Amazonia

Abstract

High-quality U–Pb (Isotope Dilution-Thermal Ionisation Mass Spectrometry; ID-TIMS) baddeleyite ages were obtained for the Salto do Céu (SC) gabbroic sill (1439 ± 4 Ma) and Nova Lacerda mafic dyke swarm (1387 ± 17 Ma) located ca. 150 km apart in the Jauru terrane (Paleo- to Mesoproterozoic) – SW Amazonia. From a geodynamic perspective, the new ages mark widespread Mesoproterozoic extensional tectonics and associated magmatism (e.g. dolerite dykes and rapakivi suites) in a growing continental margin. The SC sill is coeval with the nearby Rio Branco anorogenic rapakivi granite. Intermittent extensional tectonics (1.44 and 1.39 Ga) is widespread in the central and northern portions of the Amazonian Craton, given by co-magmatic charnockites and rapakivi granites, and mafic–ultramafic complexes. On a global scale, this activity may be coeval with a major intra-continental-related igneous event in Laurentia and Fennoscandia, as well as with mafic dykes in NW West African Craton. This suggests large igneous province (LIP)-scale magmatism. A further aspect is that the 1.4 Ga magmatism is age-equivalent with convergent-margin processes (Alto Guaporé orogen and the related Rio Alegre oceanic remnant) that evolved outboard the active margin of the proto-Amazonian Craton. This may represent a coincidence in time between intraplate rifting, LIP magmatism (plume related) and subduction. Other causal mechanisms are also considered such as pulses of back-arc extension behind the accreting arcs. Our data provide new clues as to the longevity of the Columbia (or Nuna) supercontinent, and are consistent with previously published paleomagnetic poles from Mesoproterozoic intraplate magmatism in Amazonia, Laurentia and Baltica (South America-Baltica model).