U–Pb ages and Hf-isotope data of detrital zircons from the late Neoarchean-Paleoproterozoic Minas Basin, SE Brazil.
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2017
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Resumo
Because of its world-class iron ore deposits and promising Au and U mineralizations, the late Neoarchean
to Paleoproterozoic Minas Basin (Minas Supergroup, SE of Brazil) is one of the best-studied basins in
South America. However, the lack of datable interlayered volcanic rocks prevented discourse over ages
of the strata, the sources and the nature of its ore deposits. In this paper, we present detrital zircon U–
Pb age patterns coupled with Lu–Hf data for 18 samples, representing different stages of the Minas
Basin evolution ( 2000 analyzed zircons). Age spectra for the main basal unit (Moeda Formation) show
a classic rift-related detrital zircon pattern, characterized by multiple autochthonous sources, which in
turn are much older than the age of deposition. Maximum age for the rifting event is constrained at
ca. 2600 Ma. Detritus accumulated at the base of the Minas Supergroup were derived from Archean
source rocks and their sedimentation was marked by differential uplift of the Archean crust, shortly after
the 2730–2600 Ma high-K calc-alkaline magmatism (Mamona Event). The age of the BIF deposits is
younger than 2600 Ma, most likely coinciding with the great oxygenation event between 2400 and
2200 Ma and the precipitation of banded iron deposits worldwide. Detrital zircons from the topmost
units of the Minas strata suggest that tectonic inversion and closure of the basin took place at ca.
2120 Ma with the deposition of the synorogenic Sabará Group. Rhyacian zircon supply showing juvenile
Hf signatures gives evidence of a late Rhyacian amalgamation between the Mineiro Belt and the craton.
The eHf signatures support the hypothesis that the Archean crystalline crust of the craton was mostly
built by crust–mantle mixing processes, with a successive decrease of eHf values in zircons crystallized
after 3250 Ma and minor mantle-like additions after Paleoarchean times. Regionally, our dataset supports
previous interpretations of a long-lived evolution of the southern São Francisco Craton comprising a succession
of convergent island arcs, small microplate collisions, and development
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Archean-Paleoproterozoic, Quadrilátero Ferrífero, Detrital zircons, Minas Basin
Citação
DOPICO, C. I. M. et al. U–Pb ages and Hf-isotope data of detrital zircons from the late Neoarchean-Paleoproterozoic Minas Basin, SE Brazil. Precambrian Research, v. 291, p. 143-161, 2017. Disponível em: <http://www.sciencedirect.com/science/article/pii/S0301926816303448>. Acesso em: 25 ago. 2017.