Late‐ to post‐orogenic basins of the Pan‐African – Brasiliano collision orogen in southern Africa and southern Brazil

Abstract

†Universidade do Vale do Rio dos Sinos, Caixa Postal 275, 93022-000, Sao Leopoldo, Brasil ‡Companhia de Pesquisa de Recursos Minerais, Rua Banco da Província, 105 90840-030 Porto Alegre, Brasil §Geological Survey, X112, Pretoria 0001, South Africa ¶Universidade Federal do Rio Grande do Sul, Av. Bento Gonç alves, 9500, 90820-190, Porto Alegre, Brasil AB STRACTLate-to post-orogenic basins formed on both sides of the Pan-African -Brasiliano orogen when the Congo and Kalahari Cratons collided with the Rio de la Plata Craton during the formation of western Gondwana. Trace fossil evidence and radiometric age dating indicate that deposits on both sides are coeval and span the Cambrian-Precambrian boundary. A peripheral foreland basin, the Nama Basin, developed on the subducting southern African plate. Lower, craton-derived fluviomarine clastics are overlain by marine platform carbonates and deltaic flysch derived in part from the rising subduction complex along the northern (Damara Belt) and western (Gariep Belt) orogenic margins. Rare, thin volcanic ash layers (tuffs and cherts) are present. Upper sediments consist of unconformable red molasse related to collisional orogenesis. Orogenic loading from the north and west led to crustal flexure and the formation of a remnant ocean that drained to the south and closed progressively from north to south. During final collision SE-, E-and NE-verging nappes overrode the active basin margins. Although younger than most of the post-orogenic magmatism, its setting on the cratonic edge of the subducting plate precluded marked volcanism or granitic intrusion, the only exception being the youngest intrusions of the Kuboos-Bremen Suite dated at 521±6 Ma to 491±8 Ma.Two foreland-type basins, perhaps faulted remnants of a much larger NE-SW elongated retroarc foreland basin, are found west of the Dom Feliciano Belt on the edge of the Rio de la Plata Craton in southern Brazil. In the southern Camaqua Basin, basal fluvial deposits are followed by cyclical marine and coarsening-up deltaic deposits with a notable volcanic and volcaniclastic component. This lower deformed succession, comprising mainly red beds, contain stratabound Cu and Pb-Zn deposits and is overlain unconformably by a fluviodeltaic to aeolian succession of sandstones and conglomerates (with minor andesitic volcanics), derived primarily from an eastern orogenic source and showing southerly longitudinal transport. In the northern Itajaí Basin, sediments range from basal fluvial and platform sediments to fining-up submarine fan and turbidite deposits with intercalated acid tuffs. The Brazilian basins had faulted margins off which alluvial fans were shed. They also overlie parts of the Ribeira Belt. Thrust deformation along the orogenic margin bordering the Dom Feliciano Belt was directed westward in the Camaqua and Itajaí basins, but reactivated strike-slip and normal faults are also present. Late-to post-orogenic granitoids and volcanics of the Dom Feliciano Belt, ranging in age from 568±6 Ma to 529±4 Ma, occur in the forelan...

Proveniência de arenitos da Formação Cerro da Angélica (Grupo Bom Jardim, Ediacarano do RS) na porção sul da sub-bacia Camaquã central e suas implicações tectônicas

“…Beckel (1992) considerou uma evolução em diferentes tipos de bacias ao longo do tempo, sucedendo-se progressivamente bacias de antepaís, piggy-back, pull-apart e intra-montanas. Gresse et al (1996) associaram a evolução das coberturas do Rio Grande do Sul com as bacias tardi-à pós-orogênicas do sul da África, considerando uma bacia de retroarco de antepaís (sensu Ingersoll 1988) para as unidades pré e sin-vulcânicas, então denominadas grupos Maricá e Bom Jardim, e uma origem decorrente de colapso orogênico para as formações Santa Bárbara e Guaritas, agrupadas no Grupo Camaquã (sensu Robertson, 1966).…”

“…Fragoso-Cesar, 1991; Gresse et al, 1996;Paim et al, 2002;Teixeira et al, 2004). A partir de 1992, estes modelos passaram a incorporar a idéia de origem sin-transcorrente para uma ou mais unidades superiores do Supergrupo Camaquã, conforme proposto por Oliveira & Fernandes (1991 e Machado & Sayeg (1992).…”

Estratigrafia E Evolução Paleogeográfica Do Grupo Santa Bárbara (Ediacarano) Na Sub-Bacia Camaquã Ocidental, Rio Grande Do Sul, Brasil

“…01). Nessa região afloram espessas sucessões sedimentares siliciclásticas do Ediacarano e do Eopaleozóico, tradicionalmente consideradas como depósitos de bacias relacionadas à orogenia brasiliana (Almeida 1967, 1969, Fragoso-Cesar et al 1984, 1985, Fragoso-Cesar 1991, Gresse et al 1996, Paim et al 2000, depois interpretadas como bacias transcorrentes de fases tardias do evento colisional (Oliveira & Fernandes 1991, Fernandes et al 1992, Machado & Sayeg 1992 ou como bacias distensionais tipo rifte sem vínculo claro com a orogênese brasiliana (FragosoCesar et al 2000, 2001a, b , 2002, 2003, Fambrini 2003, Fambrini et al 2005.…”

Zircon U-Pb geochronology, Sm-Nd and Pb-Pb isotope systematics of Ediacaran post-collisional high-silica Acampamento Velho volcanism at the Tupanci area, NW of the Sul-Rio-Grandense Shield, Brazil

“…The CB is a retroarc basin that includes a set of preserved sedimentary and volcanogenic units, which were deposited between 620 and 535 Ma (Brito Neves & Cordani 1991, Gresse et al 1996, Brito Neves et al 1999, Chemale Jr. 2000, Fragoso-César et al 2000, Paim et al 2000, Sommer et al 2006, Janikian et al 2008. The basement of the CB is heterogeneous and ranges from paleoproterozoic granulitic complex to associations of metamorphic and deformed igneous rocks related to the BrasilianoPan-African orogeny (Paim et al 2000, Lima et al 2007.…”