The Gurupi Belt, northern Brazil: lithostratigraphy, geochronology, and geodynamic evolution

Abstract

The Gurupi Belt is located in northern Brazil on the southern margin of the São Luís Craton, which is dominated by juvenile calc-alkaline rocks formed in intra-oceanic island arcs between 2240 and 2150 Ma. The Gurupi Belt consists of:(i) small lenses of an Archean metatonalite of 2594 Ma; (ii) calc-alkaline/TTG tonalites and gneisses of 2147–2168 Ma and juvenile Nd isotope signature, formed in intra-oceanic arc setting; (iii) an I-type monzogranite that intruded by ca. 2159 Ma, formed by the reworking of the oceanic arcs; (iv) a metavolcano–sedimentary succession with calc-alkaline volcanic rocks of 2148–2160 Ma and juvenile Nd isotope signature formed in arc systems;(v) several peraluminous, muscovite-bearing, collision-type granites of 2070–2100 Ma with Nd isotopes indicating variable reworking (partial melting and/or erosion) of Paleoproterozoic and Archean crust; (vi) a ubgreenschist-to greenschist-facies supracrustal sequence of unknown age (tentatively considered to be older than 2159 Ma); (vii)an amphibolite-facies metasedimentary sequence in which the youngest detrital zircon has age of 1100 Ma, and Nd isotopes and sedimentological evidence indicating Archean, Paleoproterozoic, Mesoproterozoic, and Neoproterozoic sources; (viii) a deformed (gneissic) nepheline syenite of 732 Ma formed by mixing of mantle and crustal sources; (ix) a peraluminous, muscovite-bearing post-tectonic granite of 549 Ma. Combined geological and geochronological information indicate that the Paleoproterozoic rocks are part of a Trans-Amazonian/Eburnean orogen initiated by an accretionary phase (2240–2150 Ma), better represented in the adjacent São Luís Craton, and terminated by collisional event (2100–2080 Ma) that amalgamated juvenile and reworked Paleoproterozoic terrains and an Archean terrain existing to the south. This landmass amalgamated in the Paleoproterozoic broke up before 732 Ma, forming a rift, as suggested by the emplacement of the nepheline syenite pluton. The rift received detritus coming from Archean, Paleoproterozoic, Mesoproterozoic, and Neoproterozoic sources. We infer that the rift evolved to an oceanic basin and that the closure of this basin occurred at the end of the Neoproterozoic (580–550 Ma), as part of the Brasiliano/Pan-African cycle of orogenies