U-Pb ages and Hf-isotope data of detrital zircons from the late Neoarchean-Paleoproterozoic Minas Basin, SE Brazil

MOREIRA, HUGO; MARTÍNEZ DOPICO, C.I.; CASSINO, L.; LANA, CRISTIANO; ALKMIM, FERNANDO

PRECAMBRIAN RESEARCH

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2017 p. 143 - 161

0301-9268

Because of its world-class iron ore deposits and promising Au and U mineralizations, the late Neoarchean to PaleoproterozoicMinas Basin (Minas Supergroup, SE of Brazil) is one of the best-studied basins in South America. However, thelack of datable interlayered volcanic rocks prevented discourse over ages of the strata, the sources and the nature of its oredeposits. In this paper, we present detrital zircon U?Pb age patterns coupled with Lu?Hf data for 18 samples, representingdifferent stages of the Minas Basin evolution (∼2000 analyzed zircons). Age spectra for the main basal unit (MoedaFormation) show a classic rift-related detrital zircon pattern, characterized by multiple autochthonous sources, which inturn are much older than the age of deposition. Maximum age for the rifting event is constrained at ca. 2600 Ma. Detritusaccumulated at the base of the Minas Supergroup were derived from Archean source rocks and their sedimentation wasmarked by differential uplift of the Archean crust, shortly after the 2730?2600 Ma high-K calc-alkaline magmatism (MamonaEvent). The age of the BIF deposits is younger than 2600 Ma, most likely coinciding with the great oxygenationevent between 2400 and 2200 Ma and the precipitation of banded iron deposits worldwide. Detrital zircons from the topmostunits of the Minas strata suggest that tectonic inversion and closure of the basin took place at ca. 2120 Ma with thedeposition of the synorogenic Sabará Group. Rhyacian zircon supply showing juvenile Hf signatures gives evidence of alate Rhyacian amalgamation between the Mineiro Belt and the craton. The εHf signatures support the hypothesis that theArchean crystalline crust of the craton was mostly built by crust?mantle mixing processes, with a successive decrease ofεHf 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 asuccession of convergent island arcs, small microplate collisions, and development of Archean convergent and divergentbasins that evolved between Archean and Paleoproterozoic times.