Multi-stage crustal accretion by magmatic flare-up and quiescence intervals in the western margin of the Sao Francisco Craton: U-Pb-Hf and geochemical constraints from the Almas Terrane

The global plate tectonic regime in early Paleoproterozoic times is highly debated. The interval 2.45-2.2 Ga is known for a minima in juvenile magmatism, but this is not a global phenomenon. New results of whole-rock geochemistry and U-Pb-Hf analysis in igneous and detrital zircons, allied with existing isotopic and geophysical data, allow to identify and constrain the duration of magmatic flare-up and quiescence events in the western Sao Francisco Paleoplate. Igneous samples yield ages indicating three accretionary magmatic events, an older with ages ca. 2476.4 +/- 9 Ma to 2462 +/- 13 Ma, an intermediate at 2390 +/- 14 Ma, and a younger from 2235 +/- 26 Ma to 2201 +/- 5 Ma, all presenting magmatic arc geochemical signatures. Xenoliths of quartzite and volcanic tuff from the upper greenstone sequence (Morro do Carneiro Fm.) are hosted in the 2211 +/- 9 Ma tonalite and the maximum depositional age of the Morro do Carneiro basin is dated 2234 +/- 12 Ma, indicating a synorogenic setting for this basin. Detrital zircon U-Pb age distribution for quartzites of the greenstone sequence shows peaks at 2.65, 2.47, 2.39, 2.27 and 2.23 Ga. Altogether, the studied rocks record an accretionary orogeny with four distinct episodes: Episode S1: 2.52-2.46 Ga, epsilon Hf(t) values from +0.57 to +6.36; Episode S2: 2.43-2.37 Ga, epsilon Hf(t) values from +0.10 to +4.30; Episode R1: 2.32-2.26 Ga, epsilon Hf(t) values from +1.61 to -7.23 (from detrital zircons); Episode R2: 2.24-2.20 Ga, epsilon Hf(t) values from +0.39 to -2.73. These early Paleoproterozoic accretionary orogenies mark the onset of amalgamation of the Sao Francisco continental paleoplate that surrounds the craton, with accretions of an exoticmicro-block and continental magmatic arcs, indicating evolution from dominant Siderian juvenile magmatism to Rhyacian crustal magmatism. These patterns show striking similarities to the orogenies in the Mineiro Belt and North China Craton. (C) 2020 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. (AU)