Navegando por Assunto "Geochronology"

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Acesso aberto (Open Access)
Estudo isotópico do depósito aurífero Volta Grande, domínio Bacajá, sudeste do cráton amazônico
(Universidade Federal do Pará, 2024-03-22) PIMENTEL, Helmut Sousa; VASQUEZ, Marcelo Lacerda; http://lattes.cnpq.br/4703483544858128; https://orcid.org/0000-0003-2729-9404; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
The area of the Volta Grande of the Xingu River is crucial for the geological understanding of the Siderian and Riacian periods in the Bacajá Domain, Maroni-Itacaiúnas Province, Amazonian Craton, which hosts significant gold mineralizations. The Bacajá Domain is composed of tectonic associations with NW-SE orientation that contain reworked Archean and Siderian fragments, mainly during the Riacian, with significant crustal growth during the Transamazonian Cycle (2.26 to 2.06 Ga). The objective of this thesis is to investigate the tectonic environment and discuss the crustal evolution in accretionary and continental collision settings. The study relied on field surveys, geological-geophysical mapping, petrography, geochemistry, geochronology, and isotopic geochemistry, employing U-Pb and Lu-Hf methods in zircon via SHRIMP and LA-ICP-MS, U-Pb in titanite via LA-ICP-MS and Sm-Nd on whole rock via TIMS. The geological-geophysical integration reveals the NW-SE trending Bacajá Shear Zone with well-defined edges and foliated terrains of high magnetic susceptibilities, plastically deforming the lithotypes within. Petrographic analyses identified metavolcanosedimentary rocks of the Três Palmeiras sequence, the Intrusive Oca Suite (composed of granodiorite, quartz monzodiorite, quartz monzonite, monzodiorite, and diorite), as well as granodiorite, monzogranite, and sienogranite of the Bacajaí Complex and the Arapari Intrusive Suite. The zoned hydrothermal orogenic gold mineralization occurs at the contact between the Três Palmeiras Group and the Intrusive Oca Suite. The geochemistry of mafic volcanic rocks from the lower Itatá Formation of the Três Palmeiras Group indicates evolved tholeiitic character in a mid-oceanic ridge and juvenile island arc setting, while the volcanic rocks of the upper Bacajá Formation are related to calc-alkaline volcanic arcs in active compressional continental margins. Three groups of granitoids representing different phases of magmatic and tectonic evolution in the Bacajá Domain during the Riacian were distinguished, with ages spanning around 110 M.y.: granitoids from the Intrusive Oca Suite at 2.20-2.17 Ga, syenogranite with biotite from the Bacajaí Complex at 2.17 Ga, and biotite-bearing monzogranite from the Arapari Intrusive Suite at 2.09 Ga. The Intrusive Oca Suite comprises intermediate to acid, calcic to alkali-calcic, ultramafic to medium-mafic, metaluminous to peraluminous rocks formed in a cordilleran granitic setting related to volcanic arcs. The REE of Intrusive Oca Suite granitoids exhibit strong magmatic fractionation, reflected in high (La/Lu)N ratios, enrichment in Rb, Th, and K, and depletion in Ba, Nb, P, and Ti, sourced from mafic rocks with varying K contents. The Bacajaí Complex consists of calcic to alkali-calcic, medium-mafic, and peraluminous quartz monzonite, granite, and granodiorite, sourced from x mafic rocks with low-K and high-K components and some input from metasediments. The rocks of the Arapari Intrusive Suite are medium-mafic, calcium-alkali to alkali-calcic, and metaluminous, sourced from mafic rocks with high-K content. The syn- to late-collisional granitoids (Bacajaí Complex and Arapari Intrusive Suite) are enriched in LILE and LREE, exhibiting negative anomalies in Ni, P, and Ti, and depletion in HFSE, typical of orogenic granites in volcanic arcs. In terms of isotopes, the Três Palmeiras sequence has Nd-TDM values ranging from 2.35 to 2.58 Ga, with εNd(t) varying from -0.41 to +3.20. The Intrusive Oca Suite includes rocks with Nd-TDM between 2.24 and 3.06 Ga and εNd(t) ranging from -5.99 to +2.44. U-Pb zircon crystallization ages for this suite are 2203 ± 23 Ma, with Hf-TDM C values between 2.4 and 2.8 Ga and εHf(2.20Ga) ranging from -0.45 to +5.24 for the Ouro Verde body; 2173 ± 7 Ma with Hf-TDM C ranging between 2.3 and 2.6 Ga, and ɛHf(2.17Ga) between +2.04 and +7.65, added to a U-Pb age of 2171 ± 17 Ma in titanite, for the Central body, and 2171 ± 13 Ma, with Hf-TDM C values between 2.4 and 3.4 Ga and εHf(2.17Ga) ranging from -10.32 to +4.34 for the Buma body, indicating distinct crustal generations between the Mesoarchean and Siderian/Riacian. The Bacajaí Complex has a crystallization age of 2165 ± 10 Ma, Hf-TDM C values between 2.5 and 2.8 Ga, and εHf(2.16Ga) ranging from -0.35 to +3.04, with mantelic sources from the Neoarchean. The Arapari Intrusive Suite has a crystallization age of 2094 ± 13 Ma, Nd-TDM at 2.38 Ga, εNd(2.09Ga) at -1.15, Hf-TDM C values between 2.6 and 2.8 Ga, and εHf(2.09Ga) varying from -2.77 to +1.59, indicating a mixture of mantle and crustal sources generated from the Neoarchean to the Siderian. The geological evolution of the study region is marked by various events. In the Siderian, volcanic-sedimentary sequences with tholeiitic basalts and island arc andesites were followed by the emplacement of diorites to granites around 2.20 to 2.09 Ga and collision, originating continental arcs. The most advanced and late stage of the Transamazonian orogeny in the Volta Grande region is represented by the emplacement of peraluminous granitoids from the Arapari Intrusive Suite, closing the complex geological bevolution of the region. The analyses in this study highlight the proposed similarity based on petrographic, geochronological, and isotopic similarities between the Volta Grande region and the Lourenço and Carecuru domains, located in the state of Amapá, in the northeastern portion of the Maroni-Itacaiúnas Province.
Acesso aberto (Open Access)
Evolução tectono-metamórfica e petrogênese de gnaisses migmatíticos e granitoides mesoarqueanos do Subdomínio Sapucaia (Província Carajás): uma abordagem geocronólogica, isotópica e estrutural
(Universidade Federal do Pará, 2025-05-09) NASCIMENTO, Aline Costa do; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506; https://orcid.org/0000-0001-7976-0472
The Sapucaia Subdomain, located between the Rio Maria Domain and the Canaã dos Carajás Subdomain, exhibits a Mesoarchean lithostratigraphy that includes greenstone belts, TTG suites, migmatized gneisses, sanukitoids, potassic granites, and "hybrids." This study presents a description of the main migmatitic structures of the basement within this subdomain and proposes the individualization of the Caracol, Colorado, Água Azul and São Carlos orthogneisses, grouping them into the Caracol Gneiss-Migmatitic Complex. Intruding this complex and the Sapucaia greenstone belt sequence, the Água Fria Trondhjemite represents a second generation of sodic magmatism, along with the Mg-rich granodiorites of the Água Limpa Sanukitoid Suite and the Xinguara Potassic Granite. The migmatites exhibit features indicative of in situ and in-source syn-anatectic melting, characterized by stromatic metatexites, net-structured metatexites, schollen, schlieren diatexites, and rare occurrences of patch metatexites. The paleosome is composed of orthogneiss and amphibolite, while the leucosome is quartz-feldspathic and the melanosome is biotite-rich. The unsegregated neosome is represented by a fine-grained granodiorite. Anatexis occurred under upper amphibolite-facies conditions (~650–700°C). The orthogneisses of the Caracol Complex are metagranitoids with high SiO2 and Na2O contents, low MgO, and strong REE fractionation. The sanukitoids of the Água Limpa Suite follow a calc-alkaline trend, enriched in Mg, Ni, Cr, and LILEs. Despite being younger, the Água Fria Trondhjemite exhibits geochemical affinity with the gneisses but with higher K2O content. The Xinguara Granite is calc-alkaline, rich in SiO2 and K2O, with pronounced negative Eu anomalies, indicating a crustal origin. Geochronological data indicate protolith crystallization of the gneisses between 2.95–2.93 Ga, with regional metamorphism between 2.89–2.84 Ga, coeval with the granulites of the Carajás Province. The sanukitoids of the Água Limpa Suite and the Água Fria Trondhjemite date to 2.87 Ga, followed by the Xinguara Granite at 2.86 Ga. Isotopic data from the orthogneisses reveal positive ƐHf(t) and ƐNd(t) values (+0.65 to +3.9), with Hf-TDM C and Nd-TDM model ages between 3.21 to 2.98 Ga, suggesting a juvenile source. The sanukitoids show ƐHf(t) and ƐNd(t) values ranging from –3.31 to +1.76, model ages from 3.28 to 2.91 Ga, δ18O values between 5.0 and 7.6‰, and feldspar Pb compositions with μ > 10, indicating a mantle source contaminated by crustal material. The Água Fria Trondhjemite exhibits ƐHf(t) and ƐNd(t) values ranging from +1.14 to +3.59, with Hf-TDM C model ages of 3.05 to 3.21 Ga. The Xinguara Granite has a Nd-TDM model age of 2.94 to 2.86 Ga, with ƐNd(t) values between +1.32 and +2.55. The temporal proximity between mantle extraction and the crystallization age of these granitoids suggests a rapid crustal growth process in the region. Geochemical data indicate that the melt responsible for the high (La/Yb)N ratio gneiss group derived from the melting of non-enriched metabasalts, previously transformed into garnet-amphibolite. Sources compositionally similar to the average Archean metabasalts from the Sapucaia and Identidade Greenstone Belts could generate such melts, though at different degrees of partial melting (25–30% or 10–15%). The low (La/Yb)N ratio gneiss-forming melt could also be derived from a similar source but without garnet. The sanukitoid melt resulted from 19–20% partial melting of a mantle source enriched by 32% of a TTG-like melt within the garnet stability field. The Água Fria Trondhjemite formed from 5–10% partial melting of metabasalts, whereas the Xinguara Granite resulted from different degrees of melting of sources similar to the older gneisses. Experimental petrology suggests that the sanukitoids crystallized at 1000–970°C in the liquidus stage and 700°C in the solidus stage, with crystallization pressures of 900–600 MPa and emplacement pressures of 200–100 MPa. These rocks exhibit mineralogy indicative of crystallization under oxidizing conditions (NNO +0.3 to +2.5) and high-water content (H₂Omelt > 6–7%). The Mesoarchean evolution of the Sapucaia Subdomain occurred in three main phases: (1) >3.0 Ga, formation of the primitive felsic crust; (2) between 2.95–2.92 Ga, formation of the Caracol Complex gneisses; (3) 2.89–2.84 Ga, crustal thickening during sinistral transpressive tectonic associated with exhumation and metamorphism of the TTG basement. Crustal stabilization allowed for the formation of younger sanukitoid and TTG magmas (Água Fria Trondhjemite). The ascent of these magmas supplied heat for the melting of regional basement metagranitoids, leading to the formation of anatectic granites. During this stage, gneissic foliation was obliterated by deformation and intrusion of younger granitoids. The integration of the data suggests that tectonic processes facilitated the generation of both crustal and mantle-derived magmas at the end of the Mesoarchean in the Sapucaia Subdomain. It can be inferred that crustal growth in the Sapucaia Subdomain was initially controlled by mantle plumes associated with vertical tectonics, similar to observations in the Pilbara and Dharwar cratons. However, unlike the Rio Maria Domain, the dome-like structuring of the gneissic basement in this subdomain was intensely obliterated by the action of sinistral transpressive tectonics (non-coaxial deformation), forming sigmoidal bodies with an E-W orientation.
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.