Please use this identifier to cite or link to this item: http://www.repositorio.ufop.br/jspui/handle/123456789/12056
Title: Two generations of mafic dyke swarms in the Southeastern Brazilian coast : reactivation of structural lineaments during the gravitational collapse of the Araçuaí-Ribeira Orogen (500 Ma) and West Gondwana breakup (140 Ma).
Authors: Mendes, Raíssa Santiago
Caxito, Fabrício de Andrade
Neves, Mirna Aparecida
Dantas, Elton Luiz
Medeiros Júnior, Edgar Batista de
Queiroga, Gláucia Nascimento
Keywords: Isotope geochemistry
Alkaline and tholeiitic magmatism
Paleocontinent rifting and breakup
Gravitational collapse of orogenic crust
Reactivation of structures
Issue Date: 2020
Citation: MENDES, R. S. et al. Two generations of mafic dyke swarms in the Southeastern Brazilian coast: reactivation of structural lineaments during the gravitational collapse of the Araçuaí-Ribeira Orogen (500 Ma) and West Gondwana breakup (140 Ma). Precambrian Research, v. 340, p. 105344, maio 2020. Disponível em: <https://www.sciencedirect.com/science/article/pii/S0301926819300051>. Acesso em: 10 mar. 2020.
Abstract: Mafic dyke swarms emplaced in regional NW-SE trending structures crosscutting the Precambrian basement in the Southeastern Brazilian coast are commonly interpreted as associated to West Gondwana breakup. Recently, however, U-Pb dating suggested that at least some of those dykes were emplaced earlier, at ca. 500–490 Ma, during the gravitational collapse of the Araçuaí Orogen. In order to clarify this issue, we studied dykes from the southern Espírito Santo State. Our results indicate that dykes emplaced in the same regional lineaments can be separated into two distinct groups, according to petrographic, geochemical, isotopic and geochronological characteristics. Group 1 is tholeiitic, with 87Sr/86Sr(i) of 0.7041–0.7065, εNd(t) of −3.4 to −5.5 and TDM ages between 0.8 and 1.5 Ga. Zircon crystals from a dyke of this group yielded the first robust lower Cretaceous U-Pb age for mafic dykes of SE Brazil with a Concordia age of 141.9 ± 1.9 Ma and εHf(t) in a range of −5.5 to −7.9. Group 2 is alkaline, shows higher 87Sr/86Sr(i) of 0.7064–0.7088, evolved εNd(t) < −12 and older TDM ages of 1.7–1.9 Ga. The youngest zircon crystals from a dyke of this group yielded a Concordia age of 504.7 ± 6.9 Ma and εHf(t) of −18.9. Our results suggest that the regional NW-SE trending lineaments of the Brazilian coast were active in at least three episodes, serving as conduits for mafic magmatism of distinct sources and tectonic settings: First, in the Cambrian, during the Araçuaí-Ribeira Orogen collapse, when they served as conduits for both the post-tectonic G5 Supersuite (530–490 Ma; composed of granitic and mafic plutons) and the alkaline dykes of Group 2; second, during the lower Cretaceous breakup of West Gondwana, when they served as conduits for the tholeiitic dykes of Group 1, synchronous to syn-rift evolution of the Phanerozoic Brazilian coast basins; and third, during the Cenozoic, when they were reactivated as normal brittle faults.
URI: http://www.repositorio.ufop.br/handle/123456789/12056
metadata.dc.identifier.uri2: https://www.sciencedirect.com/science/article/pii/S0301926819300051
metadata.dc.identifier.doi: https://doi.org/10.1016/j.precamres.2019.105344
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