DEGEO - Departamento de Geologia
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/8
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Resultados da Pesquisa
Item Unravelling the protracted U-Pb zircon geochronological record of high to ultrahigh temperature metamorphic rocks : Implications for provenance investigations.(2023) Tedeschi, Mahyra; Vieira, Pedro Leonardo Rossi; Amaral, Matheus Henrique Kuchenbecker do; Ribeiro, Bruno Vieira; Barrote, Vitor Rodrigues; Reis, Humberto Luis Siqueira; Stutenbecker, Laura; Lana, Cristiano de Carvalho; Soares, Antônio Carlos Pedrosa; Dussin, Ivo AntonioThe assessment of detrital zircon age records is a key method in basin analysis, but it is prone to several biases that may compromise accurate sedimentary provenance investigations. High to ultrahigh temperature (HT-UHT) metamorphism (especially if T > 850 °C) is herein presented as a natural cause of bias in provenance studies based on U-Pb detrital zircon ages, since zircon from rocks submitted to these extreme and often prolonged conditions frequently yield protracted, apparently concordant, geochronological records. Such age spreading can result from disturbance of the primary U-Pb zircon system, likewise from (re)crystallization processes during multiple and/or prolonged metamorphic events. In this contribution, available geochronological data on Archean, Neoproterozoic and Palaeozoic HT-UHT metamorphic rocks, acquired by different techniques (SIMS and LA-ICP-MS) and showing distinct compositions, are reassessed to demonstrate HT-UHT metamorphism may result in modes and age distributions of unclear geological meaning. As a consequence, it may induce misinterpretations on U-Pb detrital zircon provenance analyses, particularly in sedimentary rocks metamorphosed under such extreme temperature conditions. To evaluate the presence of HT-UHT metamorphism-related bias in the detrital zircon record, we suggest a workflow for data acquisition and interpretation, combining a multi-proxy approach with: (i) in situ U-Pb dating coupled with Hf analyses to retrieve the isotopic composition of the sources, and (ii) the integration of a petrochronological investigation to typify fingerprints of the HT-UHT metamorphic event. The proposed workflow is validated in the investigation of one theoretical and one natural example allowing a better characterization of the sedimentary sources, maximum depositional ages, and the tectonic setting of the basin. Our workflow allows to the appraisal of biases imposed by HT-UHT metamorphism and resulting disturbances in the U-Pb detrital zircon record, particularly for sedimentary rocks that underwent HT-UHT metamorphism and, finally, suggests ways to overcome these issues.Item U-Pb and Lu-Hf zircon data of the grenvilian arc-related Zâmbué, Fíngoè and Cazula supracrustal complexes, Southern Irumide Belt, NW Mozambique.(2022) Petry, Thales Sebben; Philipp, Ruy Paulo; Jamal, D. L.; Lana, Cristiano de Carvalho; Alkmim, Ana RamalhoThe supracrustal rocks from the Zˆ ambu`e and Fíngo`e Supergroups and the Cazula Group in the Mesoproterozoic Southern Irumide Belt (SIB) of NW Mozambique provides a sedimentation record associated with the Rodinia supercontinent. The Zˆ ambu`e Supergroup comprises a succession of thick massive orthoquartzites and meta-arkoses, with minor calc-silicatic schists, marble, and a basal complex of ortho- and paragneisses. The Fíngo`e Supergroup and Cazula Group are composed of metasandstones, calc-silicatic schists, and metapelites interlayered with felsic, mafic, and ultramafic metavolcanic rocks. U-Pb and Lu-Hf isotopic determinations of detrital zircon from five key samples show similar ages for the main source rocks. Detrital zircon from the Zambu ˆ `e Supergroup range between 1208 and 1086 Ma in age, with a restricted contribution of Paleoproterozoic source rocks. The maximum depositional age was established at 1110 ± 2 Ma. The Fíngo`e Supergroup shows zircon ages between 1233 and 1106 Ma, with a subordinate contribution of Paleoproterozoic and NeoArchean zircon grains. The calculated maximum depositional age of 1142 ± 6 Ma is similar to the crystallization age of 1094 ± 9 Ma obtained from a meta-andesite, and indicates the syn-orogenic nature of these volcanism. In the Cazula Group samples, the zircon ages range between 1164 and 1076 Ma, with minor Paleoproterozoic contributions. The maximum depositional ages were established at 1076 ± 1 Ma and 1139 ± 1 Ma. The Lu-Hf data show predominantly positive εHf(t) values (+2 and +10) and TDM 2 ages ranging between 1.75 and 1.50 Ga, indicating isotopic signatures of juvenile sources, with limited older continental crust contributions. The age results, the well-defined young age modes of the detrital zircon associated with the arc magmatism of the Southern Irumide Belt and the Hf isotopic composition demonstrate that the Zambu ˆ ´e and Fíngo`e Supergroups and Cazula Group represent arc-related basins. Structural data indicate a complex and polyphasic evolution, with the development of the metamorphic foliations associated with Mesoproterozoic transpressional oblique tectonics, related to accretionary and collisional phases of the Irumide Orogeny (1200–1000 Ma).Item Detrital zircon U–Pb and Lu–Hf constraints on the age, provenance and tectonic setting of arc-related high-grade units of the transition zone of the Araçuaí and Ribeira orogens (SE Brazil).(2022) Mendes, Raíssa Santiago; Caxito, Fabrício de Andrade; Soares, Antônio Carlos Pedrosa; Neves, Aparecida; Calegari, Salomão Silva; Lana, Cristiano de CarvalhoSedimentary basins with epiclastic and volcanoclastic components are important geotectonic components for understanding the complex evolution of orogenic systems. The age, provenance and tectonic setting of ancient basins are, however, often hard to constrain, especially in the high-grade core of ancient mountain belts where original sedimentary and stratigraphic relations have been largely obliterated by deformation and metamorphism. In this case, analytical tools such as whole-rock geochemistry and U–Pb and Lu–Hf analyses on detrital zircon grains can be deployed to unravel the provenance and tectonic setting of high-grade metasedimentary and metavolcaniclastic units. Here, we apply these analytical tools on samples from gneissic paleosomes of migmatites found in the eastern transition zone between the Neoproterozoic–Eopaleozoic Araçuaí and Ribeira orogens (southeastern Brazil). The studied paleosomes comprise peraluminous paragneiss rich in biotite, garnet and sillimanite, metaluminous hornblende-bearing gneiss free of peraluminous silicates, and intermediate terms between these compositions, all of them with geochemical characteristics pointing to sources located in magmatic arc systems. Overall, U–Pb data from detrital zircon grains bracket a maximum sedimentation age for all samples between 600 and 627 Ma, while εHf(t): +5.7 to − 18.7 and Hf TDM model ages of 1.0–2.2 Ga suggest moderately juvenile to evolved sources for the gneiss protoliths. However, despite the similarity in age range, the analyzed samples show contrasting isotope data indicating significant variability in the source areas. Sample 7 only has grains with negative εHf (− 5.9 to − 18.7), most of them ranging in age from 708 Ma to 758 Ma, with very few older (1021–1143 Ma) and younger (642–651 Ma) zircons grains, indicating evolved crustal sources of distinct ages (e.g., the Late Tonian – Early Cryogenian South Bahia Alkaline Province, the Early Cryogenian magmatism found in the West Congo Belt, the Stenian to Early Tonian Espinhaço and Matadi-Noqui igneous rocks, and magmatic rocks of the early Rio Doce arc). Conversely, sample 13 has twenty grains with positive εHf values and ages between 602 and 758 Ma, suggesting sourcing from (meta)igneous rocks of the Rio Negro arc and their remelting products, and forty grains with negative εHf values with ages between 591 and 646 Ma suggesting magmatic sources in the Rio Doce arc. Additionally, the two youngest spot ages (553 Ma and 571 Ma) have highly negative εHf values (− 11.1 and − 16.4) suggesting their origin from collisional anatexis. Similarly, sample 12 shows detrital grains within the consistent time interval (ca. 596 Ma – 798 Ma) of the Rio Negro arc and Rio Doce arcs, reinforcing that the fragments of these arcs, or zircons that were inherited from these terranes, are potential sources to the sedimentary protoliths of the paragneisses. The regional scenario together with our field and analytical data, compared with data available in the literature, suggest the sedimentary protoliths of the studied samples filled orogenic basins related to the Rio Doce magmatic arc. Most detrital zircon ages are close to the maximum depositional age, a classical signature of orogenic basins related to magmatic arcs. The studied paragneiss unit correlates with the Nova Ven´ecia Complex, located on the intra-arc to back-arc zones of the Araçuaí orogen, and with the orogenic succession of the distal Andrelândia Group, shared by both the Araçuaí and Ribeira orogens. Furthermore, our data also suggest the juvenile Rio Negro - Serra da Prata arc system was either amalgamated with the Rio Doce arc or that fragments of these arcs were incorporated as unmelted xenoliths and xenocrystals within the Rio Doce arc rocks before ca. 614 Ma, providing key hints to unravel the evolution of the Araçuaí - Ribeira orogenic system (AROS) and its role in the Gondwana assembly.Item Geodynamic evolution of the Minas Basin, southern São Francisco craton (Brazil), during the early paleoproterozoic : climate or tectonic?(2020) Rossignol, Camille Yann; Lana, Cristiano de Carvalho; Alkmim, Fernando Flecha deLike many other cratons around the world, the São Francisco Craton is characterized by an early Paleoproterozoic (2.5–2.1 Ga) unconformity that is reported worldwide as the result of global glacial events leading to a major sea-level drop. To document the duration and the cause(s) of the stratigraphic hiatus in the São Francisco Craton, this study provides U–Pb dates obtained on detrital zircon grains from the Piracicaba Group, which directly overlies the unconformity. Our results show that this sedimentary unit is younger than 2333 ± 11 Ma and consequently deposited during the late Siderian or the early Rhaycian. This maximum depositional age demonstrates that the early Paleoproterozoic stratigraphic gap lasted for at least 60 Ma. Based on quantitative analyses of the age distribution of the Piracicaba Group, we evidence a major shift in sedimentary provenance between the sedimentary units located below and above the unconformity. This change is interpreted to be directly related to the development of a subduction system along the southern and eastern margins of the São Francisco proto-craton. Our results indicate that regional geodynamic events, and not only global glacial events and their consequences, must be accounted for in Earth system models for the early Paleoproterozoic.Item Stratigraphy and geochronological constraints of the Serra Sul formation (Carajás Basin, Amazonian Craton, Brazil).(2020) Rossignol, Camille Yann; Rego, Eric Siciliano; Narduzzi, Francesco; Teixeira, Lívia; Ávila, Janaína Nunes; Silva, Marco Antônio Leandro; Lana, Cristiano de Carvalho; Philippot, PascalThe Carajás Basin, Amazonian Craton, hosts extensive Neoarchean to Paleoproterozoic sedimentary archives, which are still poorly constrained regarding their depositional settings, ages, and type of basin in which they have been deposited. In this study, we performed detailed sedimentological investigations and U-Pb dating of detrital zircon in four drill cores intercepting the recently defined Serra Sul Formation. Our data show that this formation corresponds to various shallow to deep subaqueous environments. Shallow water environments are characterized by local occurrences of microbially-mediated structures, while deep water environments are characterized by polymictic conglomerates resulting from the mixing of materials of different origins during downslope debris flow. Both sedimentary facies and common occurrence of syn-sedimentary deformations attest for recurrent slope instabilities. Geochronological investigations allow to define a maximum depositional age of 2684 ± 10 Ma, that is several tens million years younger than other Neoarchean sedimentary units of the Carajás Basin. Major peaks in age distribution indicate that the Serra Sul Formation derives from local sources that constitute the basement of the Carajás Basin. The infilling of the Carajás Basin by local sources, together with sedimentary facies and depositional environments attesting for slope instabilities, suggest that the Serra Sul Formation was deposited during an active extensional tectonic phase. Such Neoarchean to early Paleoproterozoic tectonic setting compares with those documented in many other cratons worldwide and suggests that it could correspond to the break-up of one of the first documented supercontinent.Item São Francisco–Congo Craton break-up delimited by U–Pb–Hf isotopes and trace-elements of zircon from metasediments of the Araçuaí Belt.(2018) Schannor, Mathias; Lana, Cristiano de Carvalho; Fonseca, Marco AntônioDetrital zircon U–Pb geochronology combined with Hf isotopic and trace element data from metasedimentary rocks of the Araçuaí Belt in southeastern Brazil provide evidence for break-up of the Congo–São Francisco Craton. The U–Pb age spectra of detrital zircons from metasediments of the Rio Doce Group (RDG) range from 900–650 Ma and define a maximum depositional age of ca. 650 Ma. Zircon trace element and whole rock data constrain an oceanic island arc as source for the deposition setting of the protoliths to the metasediments. Zircon εHf(t) values from these rocks are positive between +1 and +15, supporting previous evidence of a Neoproterozoic extensional phase and oceanic crust formation in a precursor basin to the Araçuaí Belt. Recrystallization of detrital zircon at ca. 630 Ma is compatible with a regional metamorphic event associated with terrane accretion to the Paleoproterozoic basement after transition from an extensional to a convergent regime. The juvenile nature, age spectra and trace element composition recorded in detrital zircons of metasediments from the Araçuaí Belt correspond with zircons from metasedimentary rocks and oceanic crust remnants of other orogenic belts to its south. This suggests that rifting and oceanic crust formation of the entire orogenic system, the so-called Mantiqueira Province, was contemporaneous, most likely related to the opening of a large ocean. It further indicates that the cratonic blocks involved in the orogenic evolution of the Mantiqueira Province were spatially connected as early as 900 Ma.