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

Abstract

Abstract 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 Brasilia Belt, between the Amazonian and Sao Francisco cratons in Central Brazil exhibits different amphibolite rocks that were emplaced into Verissimo Sequence and Araxa Group metasedimentary sequences, during the Neoproterozoic. The obtained results indicate that the studied amphibolite rocks from Pires do Rio-Catalao area represent three magmatic events associated with three magmatic environments: 1) a passive margin development at 979\u202fMa, a forearc/back-arc basin at ∼819\u202fMa, and a continental collision at ∼651\u202fMa. The first magmatic event, related to continental extension and passive margin development is represented by the emplacement at 979\u202f±\u202f17\u202fMa of E-MORB low-K tholeiitic basalts with positive eNd(t) values between +4.4 and −2 and TDM between 1.26 and 1.82\u202fGa, related with the Verissimo 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 eNd(t) values of +0.78 to +2.71, cogenetic with the Araxa Group. An OIB-like basalt sample is also related to this stage and has a U-Pb age of 819.7\u202f±\u202f6.3\u202fMa. eNd(t) values of +1.82 to +2.57, eHf(t) in zircon around-zero and TDM ages from 1.03 to 1.18\u202fGa. The third event is represented by syn- to late-tectonic OIB-like basaltic/gabbroic magmatism at 651\u202f±\u202f6\u202fMa, with positive eNd(t) value of +2.57 and younger TDM age at 1.18\u202fGa, 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 Brasilia Belt (1.0–0.6\u202fMa) might be a key to individualize superposed tectonic basins in Central Brazil.