O complexo Atuba: um cinturão paleoproterozóico intensamente retrabalhado no Neoproterozóico

Studies of terranes between the northern Ribeira and southern Dom Feliciano Belts allow the characterization of three geotectonic domains with different evolutions: the Luís Alves, Curitiba and Paranaguá terranes. The Atuba Complex occurs in the Curitiba Domain, which has a northwestern limit with metassediments of the Açungui and Setuva Groups and a southwestern limit with the granulitic gneisses of the Luis Alves domains. The contacts are expressive shear zones. The predominant rocks of the Curitiba Domain are banded, migmatitic gneisses in amphibolite grade with biotite-amphibole gneissic mesosomes and tonalitic/granodioritic to granitic leucosomes, here called the Atuba Complex. The migmatites are Paleoproterozoic (2.000 ± 200 Ma) and remigmatized in Neoproterozoic (600 ± 20 Ma). During the latter period temperatures reached more than 500º C. The structural pattem indicated shear-controlled tectonics with an important lateral component, and low-angle, south-southeastwards transport direction. The terranes of the Atuba Complex appear to represent deep-level rocks which were migmatized, granitized and then added to the border of the Luis Alves Microplate during the Neoproterozoic. This late Neoproterozoic tectonic scheme which continued to the Cambro-Ordoviciano seems to be the result of larger-scale processes of continental agglutination which ended with the formation of western Gondwanaland.Os estudos realizados nos terrenos localizados entre os Cinturões Ribeira (N) e Dom Feliciano (S) permitiram caracterizar a existência de três domínios geotectônicos com evoluções próprias e distintas: Domínios Luis Alves, Curitiba e Paranaguá. O Complexo Atuba se insere no âmbito do Domínio Curitiba, que se limita a noroeste com as seqüências metassedimentares dos Grupos Açungui e Setuva, e a sudeste com os gnaisses granulíticos do Domínio Luis Alves, contatos esses que se fazem por importantes zonas de cisalhamento. Predominam no Domínio Curitiba rochas gnáissicas bandadas, migmatíticas, do fácies anfibolito, representadas principalmente por biotita-anfibólio-gnaisses contendo leucossomas de composições tonalitogranodioríticas além de graníticas, que compõem o aqui denominado Complexo Atuba. Caracteriza-se por migmatitos formados no Paleoproterozóico (2.000 ± 200 Ma), remigmatizados no Neoproterozóico (600± 20 Ma), período esse em que as isotermas atingiram temperaturas superiores a 500 ºC. O padrão estrutural observado é indicativo de uma tectônica controlada em grande parte por cisalhamento, com importante componente lateral, e transporte relativo em direção a sul-sudeste. As rochas pertencentes ao Complexo Atuba representam terrenos relativamente profundos, do fácies anfibolito, migmatizados, granitizados acrescidos à borda do Domínio Luis Alves (Microplaca Luis Alves) durante o Neoproterozóico. Este quadro tectônico definido no final do Neoproterozóico com continuidade até o Cambro-Ordoviciano, parece ser o resultado de processos maiores, envolvendo aglutinações de massas continentais, que culminaram com a formação do Gondwana Ocidental

U-Pb geochronology of Martin Garcia, Sola, and Dos Hermanas Islands (Argentina and Uruguay): Unveiling Rhyacian, Statherian, Ectasian, and Stenian of a forgotten area of the Rio de la Plata Craton

The Río de la Plata Craton is one of the three major cratons of South America. The craton is largely covered by sedimentary basins where its most exposed area is Buenos Aires-Piedra Alta Province (Chernicoff et al., 2014). This province includes the Martín García Island in the confluence of Uruguay River and the Río de la Plata estuary. Despite to be a reference area for the craton the Martín García Island lacks modern geological investigation. We present U-Pb SIMS (secondary ion mass spectrometer) geochronological data on zircon and titanite, as well as Hf isotope determinations on zircon, from rocks of Martín García Island (Argentina), Sola and Dos Hermanas Islands (Uruguay) and from Paso Severino Formation (Uruguay). We investigated: 1) Rhyacian intermediate-to acidic plutonic, arc-type rocks of the Florida Belt dated between 2090 Ma and 2115 Ma, derived from juvenile Neoarchean crust (TDMHf: 2.52 Ga; average εHf: +3.62); 2) Rhyacian metadacite (San José metamorphic belt) of 2127 Ma; 3) Statherian metagabbros of 1724–1734 Ma, with Transplatense inheritance; 4) Early Ectasian metagabbro of 1392 Ma, with Rhyacian inheritance; and 5) Stenian metagabbros of 1193 Ma (TDMHf: 2.00 Ga, εHf: 0.1). Most of the dated orthogneisses show Brasilian-age (from 778 to 550 Ma) Pb loss in the zircons, interpreted to be caused by shearing or uplifting during Neoproterozoic. The results show that the area is not exclusively Rhyacian in age but encompasses Statherian, Ectasian, and Stenian gabbros. The last two are interpreted as distal intrusions associated to the Sunsás Orogen. All post-Transplatense metagabbros have geochemical signature of island arc basalt derived from primitive mantle with enrichment of LILE and depletion of HFSE. These characteristics point to the recurrence of magma chambers intermittently active during the Rhyacian, Statherian, Ectasian, and Stenian, all with a similar source. The term “Transplatense” is used to replace “Trans-Amazonian” events that occurred within the craton.Fil: Santos, João O. S.. University of Western Australia; AustraliaFil: Chernicoff, Carlos Jorge. Curtin University; Australia. Secretaría de Industria y Minería. Servicio Geológico Minero Argentino; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Zappettini, Eduardo Osvaldo. Curtin University; AustraliaFil: McNaughton, Neal J.. Macquarie University; AustraliaFil: Gréau, Yoann. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin