Navegando por Assunto "Gondwana Ocidental"

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Acesso aberto (Open Access)
Bioestratigrafia e paleoecologia dos depósitos marinhos Pensilvanianos da Formação Piauí a partir de novas ocorrências de conodontes
(Universidade Federal do Pará, 2021-08-08) DIAS, Sanmya Karolyne Rodrigues; SCOMAZZON, Ana Karina; http://lattes.cnpq.br/5002093091311202; https://orcid.org/0000-0002-2189-2664; SOARES, Joelson Lima; http://lattes.cnpq.br/1345968080357131
Conodonts are primitive vertebrates useful along the Paleozoic and Triassic all over the world to establish age and marine environment facies and to correlate these sedimentary sequences. Among intracratonic Brazilian basins, the Parnaíba Basin presents evidence of the record of this marine invasion in the Pennsylvanian carbonate sequences in the Upper Member of the Piauí Formation, particularly the fossiliferous Mocambo Carbonate sequence. The study of the paleontological content of these carbonate rocks is significant for the understanding of the paleoecological and paleoenvironmental perspective of the succession, and for its biostratigraphic refinement, in the case of fossil guides such as conodont. The description of the conodont species allowed the taxonomic classification, biochronostratigraphical refinement and inferences of paleoecologic conditions of the study area from comparisons of this occurrence with biozones established for Pennsylvanian of Amazonas Basin and from classic areas such as North America, Russia and China. The conodonts fauna includes three distinct species - Diplognathodus orphanus, Idiognathodus incurvus and Adetognathus lautus -registered in Mocambo Carbonate outcrops, marine portion of the Piauí Formation, in José de Freitas (PI) region and suggesting a late Bashkirian age for the sequence. Of these three species, the inedited occurrence of Diplognathodus orphanus, an excellent biostratigraphic marker of Atokan, are registered here. The occurrence of these taxa together with megaspore, ostracods, benthic foraminifers and teeth fish, suggest a paleoenvironment of very shallow marine platform. These data make possible to correlate Mocambo Carbonate with the marine section of the Amazonas Basin, allowing the correlation of the Piauí marine portion of Parnaíba Basin with the transgressive-regressive epicontinental Itaituba-Piauí Sea in Northwest South America, Western Gondwana, during the late Paleozoic.
Acesso aberto (Open Access)
Evolução crustal do setor Sul da Província Borborema: Domínio Macururé, sistema Orogênico Sergipano, nordeste do Brasil
(Universidade Federal do Pará, 2023-09-29) PEREIRA, Fábio dos Santos; ROSA, Maria de Lourdes da Silva; http://lattes.cnpq.br/9814085660417748; https://orcid.org/0000-0002-5099-829X; LAFON, Jean Michel; http://lattes.cnpq.br/4507815620234645; https://orcid.org/0000-0003-0854-3053
The Sergipano Orogenic System (SOS), located in the southern Borborema Province, is part of a large Brasiliano/Pan-African orogen structured during the Gondwana supercontinent assembly, which spread out to central Africa up to Cameroon. Six domains compose the SOS, namely Estancia, Vaza Barris, Macurure, Maranco, Poco Redondo, and Caninde. The Macurure Domain stretches 350 km from the Sergipe coast to Macurure City, Bahia state. It consists of a succession of quartzites overlaying by a thick package of phyllites, schists, metarhytmites, and metagraywacke, with intercalations of amphibolite and calc-silicate rocks. The rocks were metamorphosed under greenschist-amphibolite facies and intruded by numerous late Cryogenian-Ediacaran granites and mafic plutons. In this work, new geochemical, U-Pb geochronological (zircon and titanite), and isotopic (whole-rock Rb-Sr, Sm-Nd, and Pb-Pb and in situ zircon Lu-Hf) results from the main units composing the Macurure Domain allowed to refine the local stratigraphy and improve the comprehension about sources and processes involved in the generation of the magmatic rocks. U-Pb isotope analyses on detrital zircon from quartzites yielded two main peaks in the ranges of 1980-1950 Ma and 1000-910 Ma, consistent with the Rhyacian Orogeny (2.2-1.9 Ga) e Cariris Velhos event (1.0-0.9 Ga). Paleoproterozoic dates overlap those observed in the Provincia Borborema basement, represented in the study area by the Jirau do Ponciano Dome and Arapiraca Complex. Negative to slightly positive εHf(t) values between -15.6 and +0.5 and Hf-TDMC model ages from 2.5 to 3.5 Ga characterize this population, suggesting extensive reworking of the Archean crust during the Rhyacian-Orosirian periods. Early Neoproteozoic zircon grains display sub- to superchondritic Hf isotope composition (-12.3 to +7.7) and Hf-TDMC model ages from 2.5 to 1.3 Ga, implying the addition of juvenile material and reworking of preexistent crusts during the Cariris Velhos event. Less abundant Mesoproterozoic (1120-1040 Ma) and late Neoproterozoic (880-740 Ma) zircon populations suggest that the sediment deposition took place before the Brasiliano Orogeny. The groups of magmatic rocks were individualized based on field, petrographic, and geochemical features. (i) The oldest plutonic rocks in the area are diorites and gabbros, with minor cumulate hornblendites. They generally show evidence of solid-state deformation and well-developed tectonic foliation, defined by the plagioclase, hornblende, and biotite orientations. These features point to emplacement in a pre- to early-collisional stage between 643 and 628 Ma. Geochemical data reveal a magnesian nature and affinities with the high-K calc-alkaline and shoshonite magmatic series. REE and multielement spectra exhibit enrichment in light REE and large ion lithophile elements, with deep troughs at Ti-Nb-Ta, typically interpreted as a subduction setting signature. Whole-rock isotope data indicate an evolved signature with subchondritic Nd (εNd(t) = -2.0 a -5.2) e radiogenic Sr (87Sr/86Sr(t) = 0.708-0.710), and Pb (206Pb/204Pb = 18.50-19.18; 207Pb/204Pb = 15.69-15.77; 208Pb/204Pb = 38.54-40.04), indicating derivation from an enriched mantle source. High 87Sr/86Sr(t) and Rb/Sr ratios, together with low Sr/Th and Ba/Rb ratios, suggest that the enrichment episode occurred in response to the introduction of sedimentary components in the mantle via subduction processes, leading to the formation of phlogopite as the main metasomatic phase. Hf-TDMC model ages between 2.47 and 2.09 Ga suggest that the enrichment of the lithospheric mantle beneath the southern Borborema Province occurred during the accretionary events of the Rhyacian Orogeny. Incorporating sediments by the mantle peridotites may have led to increasing Rb/Sr, (U-Th)/Pb coupled with decreasing Sm/Nd and Lu/Hf ratios, which resulted in the time-integrated crustal signature observed in the mafic rocks. (ii) Biotite- and muscovite-bearing leucocratic granodiorites, monzogranites, and syenogranites outcrop as stocks and sheets. They show magmatic foliation marked by the orientation of micas and surmicaceous enclaves, parallel to the schistosity of country rocks, indicating synchronous emplacement to the collisional event between 630 and 624 Ma. Leucogranites are metaluminous to strongly peraluminous, high-K calc-alkaline, and magnesian to ferroan. εNd(t) values and Nd-TDM model ages overlap those of their host5 rocks, suggesting derivation from mostly sedimentary protholiths. (iii) The younger group consists of monzonites, quartz-monzonites, granodiorites, and granites, with crystallization ages from 625 to 603 Ma. They are predominantly isotropic and truncate the regional foliation of the country rocks, indicating a late emplacement relative to the collisional event. The metaluminous and magnesian signatures, with high-K calc-alkaline and shoshonite filiations, resemble the composition of experimental liquids obtained by partial melting of basalt protoliths moderately enriched in incompatible elements. Lu-Hf isotope data provided subchondritic εHf(t) values between -8.3 and 4.0 with Hf-TDMC model ages from 1.77 to 2.03, indicating the reworking of ancient continental crust, possibly related to the Cariris Velhos event. The geochemical and isotopic data of this study, together with those available in the literature allows us to infer that the Neoproterozoic geodynamic evolution of the SOS along the western Gondwana margin can be explained by a lithospheric extension of the Borborema Province basement, followed by basin inversion, and continental collision.
Acesso aberto (Open Access)
Proveniência das rochas metassedimentares do setor norte do Cinturão Araguaia com base em geocronologia U-Pb em zircão
(Universidade Federal do Pará, 2022-02-24) MARINHO, Luísa Cardoso; MOURA, Candido Augusto Veloso; http://lattes.cnpq.br/1035254156384979
The Araguaia Belt is an orogen in central Brazil formed during the West Gondwana assemblage by the end of the Neoproterozoic. Phanerozoic rocks of the Parnaíba Basin cover the north and east portion of the belt. The Amazonian Craton limits the Araguaia belt to the west and the Goiano Massif in the south and southeast. The metasedimentary rocks of the belt are assemblage in the Estrondo (quartzites and schists) and Tocantins (schists, phyllites, and metarenites) groups. Detrital zircon from quartzite of the Morro do Campo Formation (lower Estrondo Group), dated by the Pb-evaporation method, revealed populations of different ages for the northern (Xambioá) and southern (Paraíso do Tocantins) regions of this orogen (Pinheiro et al., 2011). Quartzite from Xambioá presented detrital zircon ages between 1.4 and 3.1 Ga, with the main population between 2.6 and 3.0 Ga. In Paraíso do Tocantins the quartzite showed ages varying between 0.7 Ga and 2.8 Ga, but those within 1.0 and 1.2 Ga are predominant. Later, LA-MC-ICP-MS U-Pb zircon dating (Gorayeb et al., 2020) confirmed the expressive contribution of Mesoproterozoic detrital zircon in quartzites from the southern segment of the Araguaia Belt. However, the low sampling density and the analytical limitations of the Pb-evaporation technique do not allow a clear definition of the source area of these sediments. Thus, this work extended the LA-MC-ICP-MS U-Pb dating in detrital zircon for the quartzites of the northern segment of the Araguaia Belt to obtain more accurate ages and define the source area of these sediments. The metasedimentary rocks of the Morro do Campo Formation form several dome-like structures along the northern segment of the belt, in the core of which Archean and Paleoproterozoic basement orthogneisses crop out. The studied quartzites were sampled, from north to south, at the Xambioá, Grota Rica, Cantão, and Colmeia structures. In the Xambioá structure, the quartzite presented the main population with ages between 1600 – 2000 Ma (62%) and three secondary populations of ages 2420 – 2760 Ma (21%), 1430 – 1580 Ma (12%), and 2140 – 2360 (5%). For the quartzite of the Grota Rica structure, the data revealed the main population between 1600 – 1880 Ma (42%) and three secondary populations of ages 2640 – 2990 Ma (25%), 1240 – 1580 Ma (24%), and 1920 – 2080 Ma (9%). The quartzite of the Cantão structure showed the main population with ages between 1300 – 1600 Ma (54%) and three secondary populations with ages of 1600 – 1900 Ma (29%), 1030 – 1300 Ma (11%), and 800 – 950 Ma (5%). Finally, in the Colméia structure, the a main population was defined aged between 980 – 1280 Ma (81%) and two secondary populations aged 2840 – 3000 Ma (10%) and 1850 – 2080 Ma (9%). The ages obtained showed a wide variation of detrital zircon populations. However, quartzites from the structures of Xambioá and Grota Rica register significant contributions of zircon grains from the Paleoproterozoic (Siderian-Riatian-Orosirian-Statherian) and, secondarily, from the Meso-Neoarchean. In the quartzites of the structures of Cantão and Colméia, located further south, Mesoproterozoic detrital zircons predominate (Ectasian/Callimian/Sthenian), and in the latter the presence of zircons stenianos is relatively more expressive. On the other hand, the similarity between the detrital zircon populations from Colmeia and Paraíso do Tocantins indica quartzites that the contribution of rocks formed in the Stenian is not restricted to the southern portion of the Belt Araguaia. Comparison of U-Pb zircon ages of rocks from Massif terrains Goiano/Goiás Magmatic Arc and the Amazon and São Francisco cratons with the detrital zircon ages of quartzites from the Araguaia Belt suggest the terrains of the Goiano Massif/Goiás Magmatic Arc as the most likely source of the sediments. These terrains encompass rocks with ages corresponding to zircon populations. found, and constitute the crustal segment closest to the basin precursor of the Araguaia orogen. Furthermore, they occupy a geographical position compatible with a source area situated to the southeast of this belt, as suggested by previous works of sedimentary origin. It is also recommended to complement the provenance study of quartzites using the Lu-Hf method in zircon for better characterize source areas based on ƐHf values and Hf-TDM model ages C.