Navegando por Assunto "Isotopes"

Agora exibindo 1 - 3 de 3

Acesso aberto (Open Access)
Níveis de resiliência ecológica de quelônios continentais da Amazônia Legal
(Universidade Federal do Pará, 2024-12-23) GUIMARÃES, Lívia Isadora de Almeida; SILVA, José Francisco Berrêdo Reis da; http://lattes.cnpq.br/1338038101910673; HTTPS://ORCID.ORG/0000-0002-8590-2462; TOLEDO, Peter Mann de; http://lattes.cnpq.br/3990234183124986
Continental chelonians, especially the Amazonian ones, are among the groups which most demand new researches and integrated studies, whether in the systematic or ecological scope, whose knowledge helps in their preservation, as well as ecosystem and environmental services performed. Therefore, the present work aims to analyze the levels of climate resilience of continental species in the Legal Amazon, via correlation/interdisciplinarity between climate models and anthropogenic pressure with geochemical proxies, more specifically isotopes of carbon and nitrogen, with results that enable interpretations more precise information on climatic and isotopic refuges (isoscapes), as well as additional information related to trophic chains. Until then, climate models were developed, with simulations referring to Representative Concentration Pathways (or RCPs) and Shared Socioeconomic Pathways (or SSPs) for ten chelonian species, given their sufficient number of recorded observations and coordinates: Chelus fimbriata; Mesoclemmys gibba; Phrynops geoffroanus; Platemys platycephala; Podocnemis expands; Podocnemis unifilis; Rhinoclemmys punctularia; Kinosternon scorpioides, Chelonioidis carbonaria and Chelonoidis denticulata. Such coordinates were intercrossed with four environmental variables from the Worldclim digital platform, selected according level of influence on the species distribution, reported in the literature, as well as reduced inter-correlation. These procedures were performed by Rstudio software, through the Biomod2 package, which reunites a set of algorithms whose mathematics allowed the development of rasters, with informations of climatic suitability inherent to each species. So far, P. expansa, P. unifilis and, above all, Ch. denticulata, are considered the most threatened of population reduction, while Ph. geoffroannus and K. scorpioides projections have shown less climate vulnerability. This parameter tends to be maintained in future circumstances, even with anthropogenic interference. The other species also present certain levels of vulnerability, which are more limited when compared to Ch. denticulata e P. unifilis levels. Confrontation of projections with isotopic signatures from nitrogen and carbon, collected from bone tissues of specimens deposited at the Instituto Nacional de Pesquisas Amazônicas (INPA, Manaus/AM) and Museu Paraense Emílio Goeldi (MPEG, Belém /PA). with climate models and anthropogenic influence, tend to reinforce politics to preserve species and their niches, as a strategy to maintain regional biodiversity.
Acesso aberto (Open Access)
Origem e evolução do complexo granitoide neoarqueano de vila Jussara: implicações para a evolução crustal da província Carajás
(Universidade Federal do Pará, 2022-07-15) SILVA, Fernando Fernandes da; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506; https://orcid.org/0000-0001-7976-0472
New information on the geology, combined with the acquisition of geochemical and isotopic data (U-Pb, Hf and Nd) from the Vila Jussara Suite, are presented in order to discuss a petrogenetic model for the Neoarchean granitoids of the Carajás Province. This suite appears as a series of coalescing plutons with sigmoidal and elongated shapes, in the E-W direction, which follow the regional trend. The central areas of the plutons are slightly deformed, while the marginal portions have a mylonitic appearance and are delimited by sinistral shear zones belonging to the transcurrent system of the Itacaiúnas Shear Belt. These granitoids present a broad compositional spectrum, with four individualized lithotypes: (i) biotite-hornblende serial monzogranite, which is subdivided into oxidized and reduced types; (ii) biotitehornblende tonalite; (iii) biotite monzogranite; and (iv) porphyritic granite (hornblende biotite monzogranite/granodiorite). The geochronological data U-Pb and Pb-Pb in zircon provided an age of crystallization of 2.74 Ga for the granitic and porphyritic granite varieties, and for the biotite-hornblende tonalite variety, an age of 2.76 Ga. The isotopic data of Nd and Hf suggest that the magmas of the Vila Jussara suite are not juveniles [εNd (-3.5 to 1.5) and εHf (-1.2 to 3.5)] and were derived from rocks of Mesoarchean age (TDM > 3.0 Ga). The petrogenetic model adopted to generate the primary magmas of this suite admits as source rock the Mesoarchean granulites from the Ouro Verde area of the Canaã dos Carajás subdomain. Field relationships, geochemical and isotopic data suggest that the granitoids that make up the Vila Jussara Suite are not formed from a single parental magma, but by multiple magma injections generating extensive hybridization. Its magmas were placed along pre-existing structures under a transtensional tectonic regime dominated by pure shear in a post-collisional syntectonic context.
Acesso aberto (Open Access)
Petrogênese da Suíte Igarapé Gelado: implicações para o magmatismo neoarqueano da Província Carajás, Cráton Amazônico
(Universidade Federal do Pará, 2025-04-30) MESQUITA, Caio José Soares; DALL’ AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
The Igarapé Gelado suite (IGS) is located near the northern border of the Carajás Province, almost at its boundary with the Bacajá Domain, along the Cinzento lineament, and is intrusive in metavolcanic mafic rocks and banded iron formations. The central-eastern portion of the IGS comprises four rock varieties: tonalite to granodiorite with varying contents of biotite and amphibole, (1) with associated clinopyroxene and/or orthopyroxene (PBHTnGd) or (2) devoid of pyroxenes (BHTnGd); and monzogranites that exhibit variable biotite and amphibole content and can be (3) moderately (BHMzG) or (4) strongly (RBHMzG) reduced. The PBHTnGd shows ferrosilite and/or augite with subordinate hedenbergite. The amphiboles are K-hastingsite and, subordinately, Fe-Tschermakite in monzogranites. Biotites are ferroan, and in reduced granites show #Fe > 0.90. These micas are similar to those of alkaline to subalkaline rocks and compositionally akin of primary magmatic biotites. Plagioclase is oligoclase. The integration of thermineral chemistry;mobarometry results and thermodynamic modeling and their comparison with the paragenesis present in natural rocks improved the estimation of crystallization parameters (T, P, ƒO2, H2O), and allowed a better interpretation of magmatic evolution. The IGS granites crystallized at pressures of 550 ± 100 MPa, higher than those attributed to other Neoarchean granites in Carajás provinve. The estimated liquidus temperature for the IGS pyroxene variety is ~1000±50°C. BHTnGd and BHMzG formed within a similar temperature range to PBHTnGd, while RBHMzG had lower liquidus temperatures (≤900°C). Solidus temperatures of around ~660 °C were estimated for the four IGS varieties. The BHMzG magma evolved under conditions of low ƒO2, slightly above or below the FMQ buffer (FMQ±0.5), like those of the Planalto suite and the reduced granites of the Vila Jussara and Vila União suites of Carajás province. In the magmas of the PBHTnGd and BHTnGd varieties the oxygen fugacity attained FMQ+0.5. The RBHMzG crystallized under strongly reduced conditions equivalent to FMQ-0.5 to FMQ-1. The magmas of the monzogranitic varieties evolved with a H2O content of ≥4 wt%, attaining 7 wt% in the case of the reduced monzogranites. This is comparable to, or slightly exceeding, the levels typically attributed to the Neoarchean granites of Carajás province (≥ 4% wt%). In contrast, the variety with pyroxene has a water content (~4 wt%) like that of Café enderbite and Rio Seco charnockite from Carajás province, and Matok Pluton from Limpopo belt. Based on the chemical composition, the rocks from IGS are ferroan, reduced to oxidized A-type-like granites, akin to other Neoarchean granite suites from the Carajás province. The IGS are younger than the 2.76-2.73 Ga Neoarchean granites from the Carajás province. A crystallization concordia age of ~2.68 Ga was obtained by U-Pb SHRIMP in zircon for the RBHMzG variety, and similar upper intercept ages were furnished by the other IGS varieties, except for ages of ~2.5 Ga that resemble the ages of the IOCG Salobo deposits associated with reactivation of the Cinzento Lineament. Tmineral chemistry;he deformation of the IGS rocks was influenced by shear zones linked to that lineament, forming elongated bodies with varied foliation. These zones facilitated the migration and deformation of magmas from the final crystallization stages until their complete cooling, characterizing a syntectonic process. This syntectonicity is associated with the inversion of the Carajás Basin, and the younger crystallization age of these rocks indicates that the inversion occurred up to 2.68 Ga, extending the previously estimated interval (2.76– 2.73 Ga). The IGS displays negative to slightly positive values of εNd(t)(-2.86 to 0.18) and εHf(t)(-3.3 to 0.1), and Paleoarchean to Mesoarchean TDM ages [Nd-TDM(2.98-2.84) and Hf-TDM C (3.27-3.12)]. The positive values of εNd(t) and εHf(t) for the RBHMzG variety, suggest possible juvenile contribution or contamination in the source of its magma. The IGS rocks come from the melting of 19% (PBHTnGd) or 14% (BHTnGd) of contaminated mafic granulite, - and from melting of 9% (BHMzG) and 7% (RBHMzG) of a tholeiitic mafic granulite. The area of occurrence of the IGS is marked by hydrothermalism and mineralizations that locally modified the composition of rocks and minerals, allowing the leaching of REE and Y that changed the composition of some samples of BHMzG approaching them of (false) A1- subtype granites. In addition, these processes were responsible for zircon alteration, which resulted in grains showing enrichment of U, Th, and LREE, and massive textures, that furnished upper intercept U-Pb ages, contrarily to the zircon crystals of the RBHMzG variety that preserved primary characteristics and presented Concordia ages.