Evolução geotectônica dos arcos magmáticos Neoproterozóicos Serra da Prata e Rio Negro no Terreno Oriental da Faixa Ribeira, com base em dados litogeoquímicos, geocronologia U-Pb e isótopos de Sm-Nd e Sr

Abstract

The evolution of the Ribeira belt resulted from the progressive amalgamation of several terranes against the eastern margin of the São Francisco Craton between ca. 620 and 580 Ma. The Oriental Terrane includes a diachronic evolution of two magmatic arc domains against the craton at ca. 580 Ma: Italva and Costeiro domains. This work brings new field, U-Pb geochronology, lithogeochemistry and isotopic (Sm-Nd and Sr) data from Serra da Prata and Rio Negro magmatic arcs and their tectonics relationships. Rocks from the Serra da Prata arc (860 - 830 Ma) are composed of medium-K calc-alkaline diorites and tonalites, with geochemical LILE and ETR signatures compatible with intra-oceanic magmatic arc scenarios. Isotope data, 87Sr/86Sr(i) = 0.7050 to 0.7079, εNd(i) = +3.4 to +5.1 and TDM =1.09 - 0.92 Ga near the age of arc crystallization, reveal their juvenile contribution. The Italva Group is composed of siliciclastic metasediments (Euclidândia Unit), whose the provenance pattern suggests that the Serra da Prata arc was the main source (800 - 850 Ma). Besides that, marbles (São Joaquim unit) with amphibolite (MORB e IAT) intercalations with crystallization age of 835 Ma define the minimal age of platform carbonates deposition into Italva basin. Unpublished and published data show that Rio Negro arc is composed of medium to high-K calc-alkaline rocks from gabbro to granodiorites and geochemical signatures of LILE and ETR compatible with continental magmatic arcs. U-Pb geochronology and isotopic data, 87Sr/86Sr(i) < 0.705 to 0.721, Nd(i)= -14 a +5 and TDM = 2.47 - 0.99 Ga, reflect their progressive evolution from a primitive intra-oceanic arc (from ca. de 790 Ma) to continental arc (to ca. de 605 Ma). The developement of Costeiro basin includes metasediments from Macuco unit (biotite gneisses with associated marbles) and São Fidélis Group (high-grade metasedimentary successions), both intruded by Rio Negro arc rocks. U-Pb provenance studies show Neoproterozoic sources from Serra da Prata and Rio Negro arcs for the Macuco unit. During the most intense interval of activity of the Rio Negro arc, between 630 and 620 Ma, intrusive, metamorphic and migmatitic events were recorded all over the Italva domain, interpreted as possible pre-arc basement for the construction of the Costeiro domain. The data from both magmatic arc episodes contrast with the evolution of the younger Serra da Bolívia (620 - 590 Ma) and Rio Doce continental arcs (630 - 590 Ma). Nevertheless, these data are similar to other juvenile magmatic arcs such as Santa Quitéria (ca. 880 to 830 Ma) in the Borborema Province, Goiás magmatic arcs in the Brasilia belt (ca. 900 to 786 Ma) and São Gabriel-Passinho arc in the Dom Feliciano belt (ca. 900 to 700 Ma), located respectively along the northern and western margin of the São Francisco craton and eastern margin of the Rio de La Plata craton. In a Western Gondwana scenario, the combination of the evolution of Tonian juvenile intra-oceanic arcs and Cryogenian-Ediacaran continental arcs, suggests more than 200 m.y. of subduction, continuous or not, around the older cratonic blocks that made up Western Gondwana which requires a protracted consumption of oceanic lithosphere