Structural evolution and tectonic setting of the Porongos belt, southern Brazil

Saalmann, Kerstin; Remus, Marcus Vinicius Dorneles; Hartmann, Léo Afrâneo

doi:10.1017/s0016756805001433

Cited by 43 publications

(24 citation statements)

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“…The sedimentary rocks were derived mainly from felsic sources. Without exception, all samples show very evolved negative initial eNd(t) (calculated for t = 780 Ma) values and high TDM model ages (Chemale 2000;Saalmann et al 2006b) (Fig. 4).…”

Section: Tectonic Evolution Of the Porongos Beltmentioning

confidence: 96%

“…The Porongos belt is made up deformed greenschist to amphibolite facies volcano-sedimentary successions (Porongos group) of poorly defined age that is tectonically interleaved with Palaeoproterozoic basement gneisses (Encantadas gneiss). These gneisses are exposed in the cores of regional SW-NE-trending antiformal structures (Jost and Bitencourt 1980) or fault-bounded horsts (Saalmann et al 2006b). The Porongos belt is cut by narrow fault-bounded grabens filled with siliciclastic sedimentary rocks (Camaquã basin).…”

Section: Tectonic Evolution Of the Porongos Beltmentioning

confidence: 99%

“…Geochemical data indicate intense recycling of old crust (Saalmann et al 2006b). The sedimentary rocks were derived mainly from felsic sources.…”

Section: Tectonic Evolution Of the Porongos Beltmentioning

confidence: 99%

“…The following brief overview on the structure of the Porongos belt follows the scheme presented by Saalmann et al (2006b); in order to distinguish the structural phases from those in the São Gabriel block, they are labelled with Roman numbers. Comprehensive descriptions are given in a number of papers (Jost 1982;Jost and Bitencourt 1980;Remus et al 1987Remus et al , 1991Porcher and Fernandes 1990;Hartmann et al 2000b;Basei et al 2000;Saalmann et al 2005aSaalmann et al , 2006b.…”

Section: Tectonic Evolution Of the Porongos Beltmentioning

confidence: 99%

“…Comprehensive descriptions are given in a number of papers (Jost 1982;Jost and Bitencourt 1980;Remus et al 1987Remus et al , 1991Porcher and Fernandes 1990;Hartmann et al 2000b;Basei et al 2000;Saalmann et al 2005aSaalmann et al , 2006b.…”

Section: Tectonic Evolution Of the Porongos Beltmentioning

confidence: 99%

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Multiple accretion at the eastern margin of the Rio de la Plata craton: the prolonged Brasiliano orogeny in southernmost Brazil

Saalmann

Gerdes

Lahaye

et al. 2010

Int J Earth Sci (Geol Rundsch)

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119

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The Neoproterozoic-Eoplalaeozoic Brasiliano orogeny at the eastern margin of the Rio de la Plata craton in southernmost Brazil and Uruguay comprises a complex tectonic history over 300 million years. The southern Brazilian Shield consists of a number of tectono-stratigraphic units and terranes. The São Gabriel block in the west is characterized by c.760-690 Ma supracrustal rocks and calc-alkaline orthogneisses including relics of older, c. 880 Ma old igneous rocks. Both igneous and metasedimentary rocks have positive eNd(t) values and Neoproterozoic TDM model ages; they formed in magmatic arc settings with only minor input of older crustal sources. A trondhjemite from the São Gabriel block intruding dioritc and tonalitic gneisses during the late stages of deformation (D 3 ) yield an U-Pb zircon age (LA-ICP-MS) of 701 ± 10 Ma giving the approximate minimum age of the São Gabriel accretionary event. The Encantadas block further east, containing the supracrustal Porongos belt and the Pelotas batholith, is in contrast characterized by reworking of Neoarchean to Palaeoproterozoic crust. The 789 ± 7 Ma zircon age of a metarhyolite intercalated with the metasedimentary succession of the Porongos belt provides a time marker for the basin formation. Zircons of a sample from tonalitic gneisses, constituting the Palaeoproterozoic basement of the Porongos belt, form a cluster at 2,234 ± 28 Ma, interpreted as the tonalite crystallization age. Zircon rims show ages of 2,100-2,000 Ma interpreted as related to a Palaeoproterozoic metamorphic event. The Porongos basin formed on thinned continental crust in an extensional or transtensional regime between c. 800-700 Ma. The absence of input from Neoproterozoic juvenile sources into the Porongos basin strongly indicates that the Encantadas and São Gabriel blocks were separated terranes that became juxtaposed next to each other during the Brasiliano accretional events. The tectonic evolution comprises two episodes of magmatic arc accretion to the eastern margin of the Rio de la Plata craton, (i) accretion of an intra-oceanic arc at c. 880 Ma (Passinho event) and (ii) accretion of the 760-700 Ma Cambaí/Vila Nova magmatic arc (São Gabriel event). The latter event also includes the collision of the Encantadas block with the Rio de la Plata craton to the west. Collision and crustal thickening was followed by sinistral shear along SW-NE-trending orogenparallel crustal-scale shear zones that can be traced from southern Brazil to Uruguay and have been active between 660 and 590 Ma. Voluminous granitic magmatism in the Pelotas batholith spatially related to shear zones is interpreted as late-to post-orogenic magmatism, possibly assisted by lithospheric delamination. It marks the transition to the post-orogenic molasse stage. Localized deformation by reactivation of preexisting shear zones continued Electronic supplementary material The online version of this article (

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Section: Tectonic Evolution Of the Porongos Beltmentioning

confidence: 96%

Section: Tectonic Evolution Of the Porongos Beltmentioning

confidence: 99%

“…Geochemical data indicate intense recycling of old crust (Saalmann et al 2006b). The sedimentary rocks were derived mainly from felsic sources.…”

Section: Tectonic Evolution Of the Porongos Beltmentioning

confidence: 99%