Geologia Isotópica U-Pb e Lu-Hf no tonalito Cândido Mendes e arenito da formação igarapé de areia: aplicação em proveniência sedimentar e implicações para evolução do cráton São Luís

Abstract

Using the Lu-Hf isotopic signature in zircon of known U-Pb age allows the characterization of the magma that crystallizes this mineral. Thus, it is a potential tool for sedimentary provenance investigation. The application of this method in provenance studies was tested using detrital zircons from sandstones of the Igarapé de Areia Formation, occurring in the São Luís Cratonic Fragment (SLCF) and the Gurupi Belt (GB) in the Gurupi region, NE of Pará an NW Maranhão. Most zircon grains of the sandstone have Rhyacian age, which allows for evaluating the applicability of the Lu-Hf isotopic system for provenance studies. The morphological analyses of these zircon grains indicate a magmatic origin. The U-Pb data yield Ryancian (2051 to 2256 Ma) and Orosirian (1912 to 2049 Ma) ages. These ages are compatible with the timing of the orogenic event that formed the SLCF. The Bom Jesus Granodiorite, a large granitoid from the Intrusive Tromaí Suite of the SLCF, is representative of the Paleoproterozoic calc-alkaline magmatic event and has a U-Pb zircon concordant age of 2149±5.4 Ma. The Lu-Hf isotopic signatures of the zircons of both tonalite and sandstone are similar, with ƐHf(t) ranging from 0.65 to 6.82 and from 1.84 to 6.07, respectively. Furthermore, the zircon model ages show similar results, with Hf-TDMC from 2.36 to 2.53 Ga for the Igarapé de Areia Formation and from 2.28 to 2.67 Ga for Intrusive Tromaí Suite, indicating a source area for the sandstone made up by juvenile Paleoproterozoic crust. These results support the hypothesis that the sedimentary sources of the sandstone were the rocks located in the SLCF and GB and their Birimian equivalents in the West African Craton (WAC). The lithological and geochronological similarity of the Paleoproterozoic rocks of the Gurupi region with rock units from the Baoulé-Mossi Domain from WAC is well established. In turn, Neoarchean Hf TDMC model ages may indicate a small contribution from the Archean crust, which is recorded more clearly in the rocks of the Baoulé-Mossi Domain. This contamination process may have occurred during the subduction and melting of sediments from the Archean crust or by incorporating a Paleoproterozoic Island arc into Archean terranes. The Lu-Hf isotope system has proved to be a handy tool for investigating sedimentary provenance.