Timing of mafic magmatism in the Tapajós Province (Brazil) and implications for the evolution of the Amazon Craton: evidence from baddeleyite and zircon U–Pb SHRIMP geochronology

The precise timing and possible sources of the mafic rocks in the Amazon craton are critical for reconstruction of the Atlantica supercontinent and correlation of mafic magmatism worldwide. New SHRIMP U–Pb baddeleyite and zircon ages and the reinterpretation of 207 existing dates indicate one orogenic (Ingarana) and four postorogenic (Crepori, Cachoeira Seca, Piranhas, and Periquito) basaltic events in the Tapajós Province, south central Amazon craton. Orogenic gabbro dikes that host gold mineralization are 1893 Ma and interpreted as associated with the Ingarana gabbro intrusions of the bimodal calk-alkalic Parauari intrusive suite. The age of 1893 Ma can be used as a guide to discriminate older and mineralized orogenic dikes from younger and nonmineralized Crepori- and Cachoeira Seca-related mafic dikes. ddeleyite U–Pb age of the postorogenic Crepori dolerite (gabbro–dolerite sills and dikes) is 1780±9 Ma, ∼150 my older than the ages provided by K–Ar. This value correlates well with the Avanavero tholeiitic intrusions in the Roraima group, in the northern part of the craton in Guyana, Venezuela, and Roraima in Brazil. Early Statherian tholeiitic magmatism was widespread not only in the Amazon craton, but also in the La Plata craton of southern South America, where it is known as the giant Piedra Alta swarm of Uruguay and the post-Trans-Amazonian dikes of Tandil in Argentina. choeira Seca troctolite represents laccoliths, Feixes, and São Domingos, whose baddeleyite U–Pb age is 1186±12 Ma, 120–150 my older than the known K–Ar ages. This age is comparable to other Stenian gabbroic rocks with alkalic affinity in the craton, such as the Seringa Formation in NE Amazonas and the basaltic flows of the Nova Floresta formation in Rondônia. te from the giant Piranhas dike swarm in the western Tapajós Province has a Middle Cambrian age (507±4 Ma, baddeleyite) and inherited zircons in the 2238–1229 Ma range. The Piranhas dikes fill extensional NNE and NE faults that are possibly related to an early rifting period before the Ordovician onset of the Amazon Basin sedimentation. Representative rocks of the Paleozoic Taiano magmatism of the northern Amazon craton were not detected in the Tapajós Province. Mesozoic dikes are widespread in the Amazon craton, related to Gondwana continental break-up with K–Ar ages in the 260–124 Ma range.