U–PB LA-ICP-MS DETRITAL ZIRCON AGES OF THE QUARTZITES OF THE GUAJERU GREENSTONE BELT,NORTHERN SÃO FRANCISCO CRATON, BRAZIL

The Gavião block (GB) in the northern portion of the São Francisco Craton (SFC), located in northeast Brazil, is one of the oldest Archean fragments of the South American Platform. The GB underwent polycyclic evolution from juvenile components dated between 3.64 and 2.04 Ga. Several Archean and Paleoproterozoic greenstone belts occurr in this sector of the SFC, such as Itapicuru, Umburanas, Guajerú, Ibitira-Ubiraçaba, Riacho de Santana, and Mundo Novo belts. The Guajerú greenstone belt (GGB), object of this study, is in the southwest of GB and is a narrow and elongated unit in Archean gneiss-migmatite rocks. The GGB corresponds to a sequence constituted, from base to top, by metaultramafic rocks, transformed into serpentinites, and talc schists associated in smaller proportions with metamafics, followed by calcium-silicate rocks, banded iron formations, meta-limestones, shales and quartzites on the top of the sequence. This work presents U/Pb LA-ICP-MS analyses of detrital zircons from quartzite. The ages of detrital zircons are an important tool for studying the provenance and evolution of sedimentary rocks, and more such studies in greenstone belt basins are needed to elucidate the tectonothermal history. The U-Pb zircon ages obtained were separated into population groups, indicating contributions from different crustal sources within and adjacent to the GGB. The populations of zircon of Archean age (2660±20, 2920±20 Ma, 3114±22, and 3258±20 Ma), which were likely derived from Archean cores in the interior of the SFC. These zircons suggest the history of magmatic pulses that reworked the juvenile Archean crust. On the other hand, a population of Paleoproterozoic zircons with ages of 2442±20 Ma lacks an obvious exposed source in this sector of GB, which may indicate that plutons with this age were exposed during the deposition of these sediments or that zircons of this age were recycled from crust elsewhere in the SFC or no longer attached to the SFC. Ages between 2192±26 Ma and 2011±22 Ma, obtained exclusively from the edge of zircon crystals, mark the record of the Paleoproterozoic tectonic-metamorphic event, which gave rise to the granites of this sector of GB. These data indicate the provenance of crustal materials of different ages and an indication of a maximum age of deposition for the quartzite of 2.44 Ga.