Geochemistry and isotopic signatures of metavolcanic and metaplutonic rocks of the Faina and Serra de Santa Rita greenstone belts, Central Brazil : evidences for a Mesoarchean intraoceanic arc.
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2017
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The Archean-Paleoproterozoic Terrane of Goiás, Central Brazil, is an allochthonous block within the
Neoproterozoic Tocatins Province and consists of an association of Archean TTG complexes and goldbearing
Archean-Paleoproterozoic greenstone belts. The Faina and Serra Santa Rita greenstone belts,
located in the southern portion of the terrane, are investigated using geochemistry and isotope geology
to establish the time of magmatism and tectonic environment. Our data show that the ultramafic rocks
have some chemical characteristics similar to modern boninites, whereas the amphibolites are subdivided
into two groups: the type 1 basalts group are tholeiites with flat REE patterns and are similar to
back-arc basin basalts; the type 2 basalts group have high Nb contents and are comparable to Nbenriched
basalts. Felsic to intermediate rocks present some of the main chemical diagnostic features of
adakites, in which the metandesites and metatonalites are comparable to high-SiO2 adakites, and the
metadiorites, characterized by very high MgO, Cr and Ni contents, are comparable to low-SiO2 adakites
or high-Mg andesites. Metavolcanic and metaplutonic rocks show two main periods of magmatic crystallization
ages with juvenile and slightly crustal contaminated rocks. The first occurred at 2.96–2.92 Ga
with positive ƐNd (t) values of +2.16 to +2.77, while the second formed at 2.8 Ga with slightly negative
ƐNd (t) value of 0.15. The volcanic and plutonic protoliths of the two greenstone belts were formed in
an intraoceanic forearc-arc-back-arc system. The initial stage corresponds to ultramafic lava eruption
in the forearc region of a proto-island arc, at 2.96 Ga. The evolution of the island arc and subduction progression
led to oceanic slab-melting and generation of adakites. At 2.92 Ga, the adakitic melt was totally
consumed by peridotite mantle and the subsequent melting of these hybridized mantle wedge generated
high-Mg andesites that lodged in the crust as dioritic intrusions with high MgO, Cr and Ni contents. The
late-stage corresponds to a continental arc formation at 2.8 Ga, marked by tonalitic magmatism and
amalgamation with other island arcs and continental arcs of the TTG complexes of the Archean-
Paleoproterozoic Terrane of Goiás.
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Serra de Santa Rita, Archean-Paleoproterozoic, Terrane of Goiás Faina, Tocantins province
Citação
BORGES, C. C. A. et al. Geochemistry and isotopic signatures of metavolcanic and metaplutonic rocks of the Faina and Serra de Santa Rita greenstone belts, Central Brazil: evidences for a Mesoarchean intraoceanic arc. Precambrian Research, v. 292, p. 350-377, 2017. Disponível em: <http://www.sciencedirect.com/science/article/pii/S0301926816301541>. Acesso em: 25 ago. 2017.