Navegando por Assunto "Western Gondwana"

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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.