2.17-2.10 Ga plutonic episodes in the Mineiro belt, Sao Francisco Craton, Brazil: U-Pb ages, geochemical constraints and tectonics

Geologic information supported by in situ U-Pb zircon ages, and geochemistry coupled with zircon Hf and Nd-Sr isotopic analyses on orthogneisses, metagranitoids and metadiorites unravel the nature and tectonic significance of a calc-alkaline continental arc in the Mineiro belt - southern portion of the sao Francisco Craton. The zircon U-Pb ages defined two plutonic episodes: 2174-2149 Ma (metaquartz-diorite, metagranitoids and orthogneisses) and 2145-2100 Ma (metadiorites, metagranitoids and orthogneisses) whereas several samples contain inherited zircons with concordant (207)pb/(206)pb ages as old as 2785 Ma. Our rocks show variable SiO2 contents (54.8-77.1 wt.%), are metaluminous to peraluminous and mostly magnesian and variably enriched in LREE. The older rocks have La/Yb-N = 2.24 to 11.87 whereas the metadiorites have La/Yb-N = 9.60-13.82 and the youngest rocks in the range 7.79-91.27. Most samples show Nb and Ti negative anomalies that can be attributed to a subducted source whereas some yield marked Pb positive anomalies that highlight the important role of crustal contamination/assimilation. Dy/Dy* and coupled Dy/Yb values (from 0.7 to 0.5 and 1.4 to 2.0, respectively) indicate the metaigneous rocks derived from a LREE enriched MORB source in a subduction zone with mixed Paleoproterozoic and Archean material. This scenario is consistent with the U/Pb data from inherited nuclei and xenocrysts, the range of the zircon epsilon(Hf(t)) (from +8 to -10) and epsilon(Nd(t)) (from -7 to +0.3) values, as well as with the Lu-Hf T-DM ages that vary between 2.3 and 3.2 Ga. Our data and regional geologic-tectonic correlations are consistent with the onset of an ultimate collisional event in the Mineiro belt that followed a long-lived accretionary regime active in Proterozoic times, outboard the Archean core of the sao Francisco Craton. (c) 2015 Elsevier B.V. All rights reserved.