UPb geochronology of the central Ribeira belt (Brazil) and implications for the evolution of the Brazilian Orogeny

doi:10.1016/0301-9268(95)00103-4

Precambrian Research

Volume 79, Issues 3–4, September 1996, Pages 347-361

https://doi.org/10.1016/0301-9268(95)00103-4 Get rights and content

Abstract

The Ribeira belt in southeastern Brazil was generated during the Brazilian Orogeny, the South American equivalent of the Pan-African Orogeny (∼ 700-450 Ma). The central sector of the belt is characterised by a series of northwest-vergent crustal-scale thrust stacks emplaced under amphibolite-grade conditions. Major shear zones separate four lithotectonic domains: Andrelândia to the northwest, Juiz de Fora, Paraíba and Coastal domains. Analyses of zircon, monazite and titanite from a variety of rock types from the four domains lead to the following conclusions. All domains record an important tectono-thermal event at 590-565 Ma, represented by partial melting, granitoid intrusion and remobilisation of older basement gneisses, and corresponding to thrusting and development of dextral shear zones. Also recorded are older metamorphic ages (611-604 Ma) of unknown significance. Only the Paraíba and Coastal domains, in the south, record a younger metamorphic event (M2) at 535-520 Ma most likely associated with another episode of thrusting and shear zone development. The absence of M2 metamorphism in the Andrelândia and Juiz de Fora domains can be explained by post-535-520 Ma emplacement of the Paraíba domain. Late- to post-tectonic activity is represented by 503-492 Ma metamorphism. Precursors of the basement gneisses are 2185-2134 Ma old rocks generated during the Transamazonian Orogeny some of which contain a significant Archean component with minimum ages of 2981-2846 Ma. The ages presented above define specific metamorphic events for the Brazilian Orogeny for the first time in southeastern Brazil. In addition, together with previously published data they indicate that the basement rocks found in the allochthonous domains of the central Ribeira belt represent an extension of the units present in the southern São Francisco craton and indicate that the foreland was more extensive than the presently defined ‘craton’.

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The Ribeira Belt represents a deeply eroded orogen which exposes rocks from the different stages of magmatic arcs and associated metasedimentary basins. This contribution focus on the last collisional episode between the Outer Magmatic Arc System (OMAS) and the Cabo Frio Terrane (Angola craton). The OMAS represents a long-lived magmatic arc that collided against the Inner Magmatic System (IMAS) at ca. 590 Ma (M1 metamorphism), and against the Cabo Frio Terrane at ca. 530 Ma (M2 metamorphism). The nature of the magmatism recorded in the first collisional episode, and the subduction polarity of the second is a current topic of debate. New U-Pb age and Lu-Hf analyses in zircon grains from units close to the contact are presented to propose a tectonic model for the closure of the oceanic space between the OMAS and the Cabo Frio Terrane. The results in combination with published data suggest that the metasedimentary rocks of the São Fidélis Group are in a back-arc position of the OMAS and were affected by both the M1 and M2 metamorphic episodes, reflected by the presence of metamorphic zircons with ages between ca. 592–553 Ma and 543–533 Ma. The orthogneiss of the Tinguí Complex intrusive in the back-arc metasedimentary units yielded a crystallization age of 578 ± 9 Ma, coeval with the syn-collisional stage M1. A younger metamorphic overprint at 529 ± 7 Ma was also detected (syn-M2). The orthogneiss of the Região dos Lagos Complex (Cabo Frio Terrane) rendered a crystallization age of 1968 ± 26 and a M2 metamorphic overprint at 522 Ma. Zircon analyses from folded leucosomes in the orthogneiss also indicated a crystallization age of 523 ± 10 Ma, which constrain the time of folding after thrusting. Undeformed post-collisional granitoids and pegmatites yielded crystallization ages between 496 and 499 Ma, closing the tectonic evolution of the belt with the orogen collapse. Our results corroborate with terrane accretion model for the Central Segment of the Ribeira Belt.
Age and petrogenetic constraints of the post-collisional Parati Granite, southeast Brazil
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The Ribeira orogen is one of the orogens formed in the Pan-African-Brasiliano collisional event. Post-collisional Cambrian-Ordovician magmatism occurred after the main agglutination event of this orogen, being recorded in its central segment by a series of granitic bodies exhibiting few or no deformation, which have been divided into three suites, Suruí, Nova Friburgo and Sana. This work brings a contribution to the understanding of the generation of these bodies through the geochemical - petrological study of the Parati Granite. In addition, unpublished data about crystallization temperature and pressure conditions during the emplacement, as well as a proposition on source and generation model for this granite is also presented. The Parati Granite has a batholithic size showing a predominant inequigranular porphyritic facies with feldspar phenocrysts, besides another inequigranular to equigranular facies also composed of feldspar, quartz, biotite, hornblende and titanite. Geochemically, it is a high potassium, Hi-BaSr metaluminous, magnesian to slightly ferroan calc alkaline granitoid. REE and multielemental diagrams along with biotite composition suggest that Parati Granite was generated from crustal melting with involvement of an enriched mantle, which is corroborated by isotopes of Sr, Nd and Hf. Geothermobarometry results point to crystallization temperature ranging from 760° to 810 °C and pressures varying from 3 to 5 kbars. Geochronological data indicate crystallization age interval between ca. 520 to 505 Ma. Due to the similarities of geochemical patterns and isotopic data, it is believed that the source of this granite could be rocks of the Rio Negro Arc. As a geodynamic model, slab breakoff followed by uplift can be considered as a mechanism responsible for the formation of Parati Granite, as it explains its mantle and crustal signatures.
Sedimentary provenance in continental rifts: U–Pb detrital zircon, Nd and Sr isotopes and lithogeochemistry of the Eocene alluvial sandstones of the Resende Basin, SE–Brazil
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Multiproxy analysis of detrital minerals is a powerful tool for unravelling the source-to-sink evolution of syn-rift sedimentary basins that represent important depositional settings during major rift events. The Cenozoic Resende half-graben in SE Brazil is a classic example of a syn-rift basin developed under oblique extension, which preserves evidence of tectonic episodes and palaeoclimatic conditions during the opening of the Atlantic. Sediment in the basin was sourced from the surrounding basement rocks, which to the faulted margin consists of older Proterozoic orthogranulites and orthogneisses, whilst to the flexural margin is characterised by Neoproterozoic passive margin paragneisses. Cretaceous intra-plate alkaline stocks crop out at the western edge and in the central-south basement of the basin and represent a distinct provenance fingerprint. This study uses new detrital zircons U–Pb ages combined with previously published elemental and Nd and Sr isotopic data to characterise the sedimentary provenance of Eocene alluvial deposits and to understand how sediment sourcing has changed throughout the evolution of the basin. U–Pb detrital zircon analyses from samples collected across the Resende Basin are presented herein. Samples yield a spread of detrital age spectra from the Archaean to the Cretaceous. Precambrian zircons range from ca. 3228 Ma to ca. 542 Ma. Cretaceous zircons yield ages between ca. 138 Ma and ca. 67 Ma. The sediment source location is interpreted by comparing the yielded detrital zircon spectra with the age spectra of zircons from the basement rocks. The dominance of detrital zircons yielding ages of ca. 1500 Ma and ca. 1000 Ma is interpreted to be sourced from the Neoproterozoic basement rocks to the flexural border of the half-graben. Cretaceous zircons from samples with whole rock εNd_40Ma > −10 are found in both the western and eastern portions of the half-graben but not in the central portions. It is interpreted that an along-axis fluvial system was responsible for a small increase in the compositional maturity of the Resende sandstones from west to east, resulting in the progressive dilution of Cretaceous alkaline igneous detritus along the basin axis. Preserved metamorphic rims in zircon grains indicate low transport abrasion, suggesting that Cretaceous zircons in the eastern depocentre could be associated with other small proximal sources. U–Pb zircon analyses and Nd and Sr isotopes provide reliable insights regarding sediment provenance and transport processes, whilst element geochemistry supplies evidence for hydraulic sorting effects. Consequently, the data represents a more robust estimation of the provenance patterns of the Resende Basin, showing chemical and geochronological differences that support the division of the basin into three depocentres (western, central, and eastern) connected by a longitudinal fluvial system sourced mostly by sediments coming from the south-western flexural border. This study highlights the usefulness of using multiple provenance proxies to unravel the complex development of rift basins, assessing multiple source terrains and the variable degrees of mixing in sedimentary basins.
Upper plate exhumation during continental collision: An example from the paranapanema paleocontinental active margin, SE Brazil
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The Southern Brasília Orogen is the result of Ediacaran continental collision between the active margin of the Paranapanema paleocontinent and the passive margin of the São Francisco paleocontinent. The active margin was deformed into the Socorro-Guaxupé Nappe and the associated Embu Domain. This paper presents new U–Pb zircon data and geothermobarometric estimates that allow to reconstruct the metamorphic evolution in these upper plate units. A pre-collisional metamorphism M1 with an age peak in metamorphic rims of zircon grains in the range 680–630 Ma is related to the development of the Socorro-Guaxupé magmatic arc with batholiths dated in a similar time span, 690 - 630 Ma. This metamorphism reached medium pressure granulite facies, now exposed by the tilted uplift and erosion due to the collision. Another peak is detected in metamorphic rims of zircon grains, in the range 630–590 Ma, labeled M2, related to the collision and corresponds to the main metamorphism in the lower plate and accretionary wedge-like nappe stack, underlying the Socorro-Guaxupé Nappe. This nappe stack was affected by greenschist facies metamorphism in the autochthonous underlying craton, grading to high pressure granulite facies in the upper nappe, with local occurrences of retroeclogite lenses. In the Socorro-Guaxupé Nappe and Embu Domain this main metamorphism (M2) is characterized by three metamorphic zones decreasing in grade with distance from the suture: a granulite facies orthopyroxene bearing zone; a high temperature amphibolite facies zone and a lower amphibolite facies zone. Geothermobarometric results in mineral associations related to M2 show temperatures decreasing from about 770 °C to ∼620 °C and pressures decreasing from about 9 kbar close to the suture to about 5 kbar in the southern and western parts of the studied region. On the upper Paranapanema plate, relative to the Socorro-Guaxupé Nappe and Embu Domain units, at the base of the plate, an older metamorphism (M1) is verified with temperatures between 960 and 890 °C and pressures between 11 and 9 kbar, reequilibrated at approximately 700 °C with a pressure of about 9 kbar (M2, continental collision). For this reason, it can be assumed that the rim of the Paranapanema plate was exhumed during the continental collision, since the temperature and pressure of the metamorphic peak determined during the continental collision are lower than those determined for the pre-collisional magmatic arc metamorphism.
Long-term magmatism in the Ribeira Orogen, Western Gondwana: SHRIMP U-Pb and O isotope data for two Ediacaran-Cambrian magmatic events in the Rio de Janeiro area
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In the southeastern Brazilian margin, a Neoproterozoic to the Early Paleozoic long-term magmatic interval is recorded within the Oriental Terrane, part of the Ribeira Orogen, characterizing it as a hot orogenic belt. Metaigneous and igneous rock units of ca. 570–540 Ma and 510–480 Ma are coeval with two main collisional orogenies related to the Western Gondwana assembly: the Ribeira Orogeny (590–565 Ma) and the Búzios Orogeny (540–490 Ma). The Oriental Terrane, interpreted as a continental microplate amalgamated during the convergence between the São Francisco and Congo cratons, comprises Cryogenian to Ediacaran metaigneous rocks and Cambro-Ordovician plutons intrusive in metasedimentary sequences. Zircons from an orthogneiss and a porphyritic leucogneiss sample gave SHRIMP U-Pb crystallization ages of 558 ± 2 Ma and 560 ± 2 Ma, respectively, with high δ¹⁸O values from 7 ‰ to 10 ‰. Zircons from a tonalite pluton and tonalitic dikes, gave SHRIMP U-Pb crystallization ages of 483 ± 2 Ma and 492 ± 2 Ma, with lower δ¹⁸O values, between 6 ‰ to 8 ‰. These two magmatic pulses, integrated with a compiled database from other plutons in this terrane, corroborate with the hypothesis that they represent crustal scale magmatic provinces here interpreted as pre- and post-collisional in relation with the Búzios Orogeny. Their distribution within the tectonic map of the Oriental terrane reflect a paleogeography linked to their tectonic origin. The 570–540 Ma plutons are aligned ENE -WSW, parallel and close to the suture zone with the Cabo Frio Tectonic Domain, representing a crustal melt related to a NW-subduction. A subsequent magmatic hiatus of 30 ma is interpreted as the collision of the Cabo Frio Tectonic Domain. The post collisional period is marked the intrusion of non– linear 510–480 Ma pluton, widespread in the Oriental terrane.
Investigating assembly timing of Ediacaran Serra dos Órgãos batholith – Hints on prolonged magmatism at Ribeira belt, SE Brazil
2022, Journal of South American Earth Sciences
Citation Excerpt :
The Inner Magmatic Arc System comprises many ca. 650 to 595 Ma Araçuaí and Ribeira units, which present continental geochemical signatures, while the Outer Magmatic Arc System comprises units of juvenile character, the Tonian Serra da Prata (Peixoto et al., 2017) and the Late Tonian to Ediacaran Rio Negro Complex (Tupinambá et al., 2000, 2012). The collision resulted from the docking of the juvenile crust to the reworked continental margin culminated in a metamorphic regional peak related to a complex Ediacaran granite production event, where syn-to late-collisional I, S-type and hybrid granitoids intruded the Ribeira crust in both Inner and Outer Systems (Machado et al., 1996; Junho et al., 1999; Mendes et al., 2006; Silva et al., 2003; Retamal et al., 2017). Far from the northwest suture, a southeast suture was formed as a result of the docking of the Cabo Frio microcontinent along the Ribeira belt margin.
The Pan-African/Brasiliano orogeny, result of the West-Gondwana assembly from the Neoproterozoic to Ordovician, had produced the Ribeira and Araçuaí belts at the edges of the São Francisco and Congo cratonic margins. In the central Ribeira belt, the docking of accretionary systems to the reworked continental margin of the São Francisco paleoplate culminated in a complex Ediacaran granite production event. Syn-to late-collisional I- and S-type granites and hybrid granitoids intruded the reworked margins and accreted continental masses, as well as the Tonian to Ediacaran juvenile magmatic arcs represented by the Serra da Prata and Rio Negro Complexes. The Serra dos Órgãos batholith is the main intrusion emplaced at the juvenile crust, forming an elongated NE-SW trending tabular body that crops out in the highland region of Rio de Janeiro State, Southeast Brazil. Geochemical and geochronological data in addition to field and petrological evidence was gathered to explore the assembly timing of the SOB granitic end-member. Zircon U–Pb SHRIMP and LA-ICP-MS geochronological data yield a prolonged emplacement timelapse for the studied granites and, along with published U–Pb ages of the SOB granodioritic end-member, enable the characterization of the Serra dos Órgãos as a composite batholith. The wide time interval of heat input inside intermediate crust is consistent with a prolonged, slow-cooling hot orogenic belt model for the Araçuaí-Ribeira Orogenic System.

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UPb geochronology of the central Ribeira belt (Brazil) and implications for the evolution of the Brazilian Orogeny

Abstract

Precambrian Res.

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Tectonophysics

O Cratão do São Francisco

Rev. Bras. Geociênc.

O Pré-Cambriano do Brasil

The Precambrian evolution of the South American cratonic margin south of the Amazon River

Optimum linear regression and error estimation applied to UPb data

Can. J. Earth Sci.

UPb Archaean Geochronology of the São Francisco Craton (Eastern Brazil)

Rev. Bras. Geociênc.

Âges PbU, SrRb et ArK de formations métamorphiques et granitiques du sud-est du Brésil (États de Rio de Janeiro et de Minas Gerais)

Ann. Soc. Géol. Belgique

A geological comparison of South America with South Africa

Carnegie Inst. Washington Publ.

Mapa e texto explicativo das folhas Rio de Janeiro, Vitória e Iguapé, na escala 1:1000000 (SF23, SF24 e SG230)

Âges $Pb U$ , $Sr Rb$ et $Ar K$ de formations métamorphiques et granitiques du sud-est du Brésil (États de Rio de Janeiro et de Minas Gerais)