Age constraints on granitoids and metavolcanic rocks of the Sao Luis craton and Gurupi belt, northern Brazil: Implications for lithostratigraphy and geological evolution

Single-zircon Pb evaporation dating was undertaken on granitoids and metavo lcanic rocks of different lithostratigraphic units of the Sao Luis craton a nd the bordering Gurupi belt in northern Brazil, allowing the determination of the crystallization ages of these rocks and a partial reassessment of t he regional lithostratigraphy. In the Sao Luis craton, zircons from granito ids of the Tromai Suite (dominantly tonalitic) yielded Pb-207/Pb-206 ages b etween 2149 +/- 5 Ma and 2165 +/- 2 Ma, and a metapyroclastic rock of the m etavolcano-sedimentary Aurizona Group was dated at 2240 +/- 5 Ma. In the Gu rupi belt, the Itamoari Tonalite (the deformed correspondent of the Tromai Suite) gave an age of 2148 +/- 4 Ma, similar to the younger ages of the Tro mai Suite. Two felsic metavolcanics of the metavolcano-sedimentary Gurupi G roup showed crystallization ages between 2148 I Ma and 2160 +/- 3 Ma, which are similar to those of the granitoids of the cratonic domain. The Th/U ra tios of the whole set of analyzed samples, calculated from the Pb-208/Pb-20 6 ratio, ranged from 0.23 to 0.51, which is typical of magmatic zircons. Th e determined ages,are in good agreement with those of the correlative Eburn ean granitoids and Birimian sequences of the West African craton. A Rb-Sr internal isochron was calculated for a collisional-type granitoid ( Maria Suprema Granite) in the Gurupi belt, yielding an age of 1710 +/- 32 M a, interpreted as a partial resetting of the isotopic system. Considered as a minimum age, this dating places the granitoid in the Paleoproterozoic. The age of the rocks and of the establishment of the Gurupi belt have been controversial, owing to the widespread Neoproterozoic (Brasiliano/Pan-Afric an) Rb-Sr and K-Ar signature of its rocks. Our data, combined with other re cent geological and geochronological information, suggest that rocks of the present Gurupi belt have likely participated in collisional/accretionary p rocesses occurring in the final stages of the Transamazonian orogenic cycle in the Paleoproterozoic (2.0-2.1 Ga). This was part of the major process o f assembly of the Atlantica supercontinent. The belt was tectonically react ivated in the Neoproterozoic, with widespread reworking of older rocks and only localized rock generation, leading to its present configuration.