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From passive margin to continental collision: Geochemical and isotopic constraints for E-MORB and OIB-like magmatism during the neoproterozoic evolution of the southeast Brasília Belt

2019; Elsevier BV; Volume: 359; Linguagem: Inglês

10.1016/j.precamres.2019.105345

1872-7433

Pedro F. Piauilino, Natalia Hauser, Elton Luiz Dantas,

Paleontology and Stratigraphy of Fossils

Metamorphic rocks derived from mafic rocks can be found in metamorphic belts, and their geochemical and isotopic characteristics may be valuable sources of information for interpretation of ancient geologic magmatic scenarios. The southern Brasília Belt, between the Amazonian and São Francisco cratons in Central Brazil exhibits different amphibolite rocks that were emplaced into Veríssimo Sequence and Araxá Group metasedimentary sequences, during the Neoproterozoic. The obtained results indicate that the studied amphibolite rocks from Pires do Rio-Catalão area represent three magmatic events associated with three magmatic environments: 1) a passive margin development at 979 Ma, a forearc/back-arc basin at ∼819 Ma, and a continental collision at ∼651 Ma. The first magmatic event, related to continental extension and passive margin development is represented by the emplacement at 979 ± 17 Ma of E-MORB low-K tholeiitic basalts with positive εNd(t) values between +4.4 and −2 and TDM between 1.26 and 1.82 Ga, related with the Veríssimo metavolcanosedimentary Sequence. The zircon populations include a high amount of metamorphic, inherited grains. The second magmatic event, related with an forearc/back-arc extension is represented by E-MORB basalts with negative Nb-Ta anomalies and slightly positive εNd(t) values of +0.78 to +2.71, cogenetic with the Araxá Group. An OIB-like basalt sample is also related to this stage and has a U-Pb age of 819.7 ± 6.3 Ma. εNd(t) values of +1.82 to +2.57, εHf(t) in zircon around-zero and TDM ages from 1.03 to 1.18 Ga. The third event is represented by syn- to late-tectonic OIB-like basaltic/gabbroic magmatism at 651 ± 6 Ma, with positive εNd(t) value of +2.57 and younger TDM age at 1.18 Ga, that can be associated to regional continental collision and closure of the Neoproterozoic ocean. Also, provenance studies into metasedimentary rocks support that passive and active margins could be successively superposed during the main thrusting tectonic event in the Brasiliano orogeny, but slices of different stratigraphic units preserve their depositional isotopic signature. These findings suggest that the occurrence of main mafic magmatic events over a timespan as long as the entire evolution of the Brasília Belt (1.0–0.6 Ma) might be a key to individualize superposed tectonic basins in Central Brazil.