Abstract
The granitoid rocks found in the Amazonian Craton, between the Xingu and Araguaia rivers (SE Para State, Brazil) can be divided into two groups: (1) granitoid and gneissic rocks of archean of late proterozoic ages (related to the 2,000 Ma Transamazonian event or older), and (2) post-tectonic or anorogenic granites of medium proterozoic ages (younger than the Transamazonian event). The first group is very poorly studied, making it difficult to establish the limits and evolution of the main geotectonic provinces within the craton. In the Rio Maria Region older (Archean?), gneisses and migmatites, greenstone belt sequences, and granodiorite batholiths were distinguished. The latter are the youngest unit, exhibiting ages of aproximately 2,600 Ma. Transamazonian ages are frequent in the basement Xingu Complex, but petrological studies of granitoids and gneisses related to this event are lacking. The second group includes many massifs, consisting of typical high-level granites, grouped in five different magmatic suites. These suites are not clearly defined and must be rediscussed the situation of each massif needing to be evaluated a case by case. Supposing the 1,700-l,800 Ma Rb-Sr age of the Central Serra dos Carajas Massif to be correct and accepting the Rb-Sr isochron ages of the Jamon (1,601 ± 21 Ma) and the Redencao (1350 ± 80 Ma) massifs, the existence of at least three post-Transamazonian periods of granitic magma generation is deduced. The needs for additional geochronological data and the introduction of different radiometric methods U/Pb, Pb/Pb) are emphasized. A comparison is attempted between the studied granites and the various granitic types recently defined in the literatura. However, taking into account that their tectonic settings are very different, a perfect correlation can not be expected. The Jamon Massif is a magnetite granite and exhibits strong analogies with the Caledonian I type granites. The Serra dos Carajas, Velho Guilherme, Antonio Vicente, and Mocambo Massifs have affinities with the A type granites and are generally mineralised (Sn, and less Nb, Cu, Mo). S type granitoids are not known in the studied region.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
