Browsing by Author "Kamo, Sandra L."

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    An assessment of monazite from the Itambé pegmatite district for use as U–Pb isotope reference material for microanalysis and implications for the origin of the “Moacyr” monazite.
    (2016) Gonçalves, Guilherme de Oliveira; Lana, Cristiano de Carvalho; Cipriano, Ricardo Augusto Scholz; Buick, Ian S.; Gerdes, Axel; Kamo, Sandra L.; Corfu, Fernando; Marinho, Moacyr Moura; Chaves, Alexandre de Oliveira; Valeriano, Claudio de Morisson; Nalini Júnior, Hermínio Arias
    Large quantities of monazite from different pegmatite bodies of the Itambe pegmatite district were investigated to assess their suitability as U–Pb and Sm–Nd isotope reference materials for LA-ICP-MS and to track the origin of a piece of theMoacyrmonazite (termed here Itambé), awidely used reference material for LA-ICP-MS U–Pb geochronology. Monazite fromthe largest pegmatite bodies in the district (the Bananeira, Coqueiro and Paraíso pegmatites) are Ce-monazite, with negligible amounts of the huttonite and brabantite components. They are homogeneous in major and trace elements, which makes them potential candidates as compositional reference materials. U–Pb LA-ICP-MS and ID-TIMS analyses yielded identical ages within error. Although the ID-TIMS ages (507.7 ± 1.3 (207Pb⁎/235U) and 513.6 ± 1.2 Ma (206Pb⁎/238U)) were reversely discordant, spot ages determined by LA-ICP-MS geochronology were concordant at ca 508 Ma. The Bananeiro monazite was assessed as a LA-ICPMS U–Pb primary reference material against other known reference materials (treated as unknowns). This approach successfully reproduced the previously published ages of the reference materials.MREE/HREE fractionation (ie, (La/Gd)N and (Gd/Lu)N values), Eu/Eu⁎ and the chondrite-normalized REE patterns suggest that the “Itambé” monazite aliquot is very similar to that fromthe Coqueiro pegmatite. This similarity is likewise apparent in their Sm–Nd isotope compositions. Moreover, the εNdi values of the “Itambé” monazite fragment (εNdi=−4.2) and those fromall the major pegmatites in the district, are distinct fromother reference materials (eg, Managountry; εNdi = −22.3) as well as gem-quality monazite from c. 490–520 Ma pegmatites from the Araçuaí Orogen, further to the south. The εNdi can provide a further distinction for tracing Brazillian gemquality monazite reference materials.
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    Assessing the U-Pb, Sm-Nd and Sr-Sr isotopic compositions of the sume apatite as a reference material for LA-ICP-MS analysis.
    (2022) Lana, Cristiano de Carvalho; Gonçalves, Guilherme de Oliveira; Mazoz, Ariela Oliveira; Buick, Ian S.; Kamo, Sandra L.; Cipriano, Ricardo Augusto Scholz; Wang, Hao; Moreira, Hugo Souza; Babinski, Marly; Queiroga, Gláucia Nascimento
    This study has determined the trace element and the U-Pb, Sm-Nd and Sr-Sr isotope composition of the Sume apatite (from NE Brazil) to assess its suitability as a primary/secondary reference material for LA-ICP-MS. Reproducibility tests demonstrate that one batch (~ 100 g) of the Sume apatite (Sum e-570) is uniform in terms of Nd-Nd and U-Pb isotope compositions. Bulk isotope dilution TIMS/ICP-MS and LA-MC-ICP-MS analyses confirm that the apatite is well suited for use as quality control material for Nd isotopes and U-Pb geochronology. U-Pb ID-TIMS analyses yield weighted mean ratios of 0.09211 0.00053 (2s; 206Pb*/238U) and 0.06120 0.00063 (2s; 207Pb*/206Pb*) and a weighted mean 206Pb*/238U date of 568 3 Ma (95% c.l.). U-Pb LA-(SF/MC)-ICP-MS runs using Sume-570 as a primary RM and reproduces the dates of other established RMs within 1% deviation (except for Durango 2–4%). Major and trace element abundances show that Sume-570 is a fluorapatite derived from a syenitic source. It also strongly shows LREE-enriched chondrite-normalised REE patterns with significant negative Eu anomalies, due to crystallisation of plagioclase in the residue.
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    LA-ICP-MS U–Pb dating of rutiles associated with hydrothermal mineralization along the southern Araçuaí Belt, SE Brazil.
    (2020) Santos, Maristella Moreira; Lana, Cristiano de Carvalho; Cipriano, Ricardo Augusto Scholz; Buick, Ian S.; Kamo, Sandra L.; Corfu, Fernando; Queiroga, Gláucia Nascimento
    The presence of hydrothermal rutile enables the dating of mineralization related to hydrothermal processes. Refinement of the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) technique is key to enabling the quick analysis of individual rutile crystals in high spatial resolution and dating of crystals with low U contents, as a prerequisite for the reliable characterization of hydrothermal deposits. For this study rutile crystals were selected from quartz and topaz veins that extend along the southeastern portion of the Araçuaí Belt, part of the long-lived (630 - 490 Ma) polyphase Brasiliano Orogen that formed during West Gondwana amalgamation. The purpose was to allow a systematic evaluation of in situ dating of hydrothermal rutile by LA-ICPMS. U–Pb ages from different rutiles range between 527 ± 6 Ma and 487 ± 5 Ma, indicating that different parts of the orogen were affected by episodic fluid flow under oxidizing conditions over a similar time interval. Our U–Pb dating results of rutiles associated with the Imperial Topaz mineralization in the Quadrilátero Ferrífero (southern portion of the São Francisco Craton, SE Brazil) constrains the age of those deposits to 500- 498 Ma, which is within the range of U–Pb ages of hydrothermal systems and mineralized zones previously reported for the region. The chemical composition of the studied hydrothermal rutiles, as determined by electron microprobe and LA-ICP-MS analysis, together with their U–Pb ages, suggests that the extensive fluid production required to form the hydrothermal deposits was generated from multiple sources. Fluid production was related to extensional collapse of the Araçuaí Orogen. The findings of this research clearly shows the utility of U–Pb rutile dating via LA-ICP-MS for geochronological study of a range of hydrothermal deposits.
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    LA-ICP-MS U–Pb dating of rutiles associated with hydrothermal mineralization along the southern Araçuaí Belt, SE Brazil.
    (2020) Santos, Maristella Moreira; Lana, Cristiano de Carvalho; Cipriano, Ricardo Augusto Scholz; Buick, Ian S.; Kamo, Sandra L.; Corfu, Fernando; Queiroga, Gláucia Nascimento
    The presence of hydrothermal rutile enables the dating of mineralization related to hydrothermal processes. Refinement of the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) technique is key to enabling the quick analysis of individual rutile crystals in high spatial resolution and dating of crystals with low U contents, as a prerequisite for the reliable characterization of hydrothermal deposits. For this study rutile crystals were selected from quartz and topaz veins that extend along the southeastern portion of the Araçuaí Belt, part of the long-lived (630 - 490 Ma) polyphase Brasiliano Orogen that formed during West Gondwana amalgamation. The purpose was to allow a systematic evaluation of in situ dating of hydrothermal rutile by LA-ICPMS. U–Pb ages from different rutiles range between 527 ± 6 Ma and 487 ± 5 Ma, indicating that different parts of the orogen were affected by episodic fluid flow under oxidizing conditions over a similar time interval. Our U–Pb dating results of rutiles associated with the Imperial Topaz mineralization in the Quadrilátero Ferrífero (southern portion of the São Francisco Craton, SE Brazil) constrains the age of those deposits to 500- 498 Ma, which is within the range of U–Pb ages of hydrothermal systems and mineralized zones previously reported for the region. The chemical composition of the studied hydrothermal rutiles, as determined by electron microprobe and LA-ICP-MS analysis, together with their U–Pb ages, suggests that the extensive fluid production required to form the hydrothermal deposits was generated from multiple sources. Fluid production was related to extensional collapse of the Araçuaí Orogen. The findings of this research clearly shows the utility of U–Pb rutile dating via LA-ICP-MS for geochronological study of a range of hydrothermal deposits.
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    A new appraisal of sri lankan bb zircon as a reference material for LA-ICP-MS U-Pb geochronology and Lu-Hf isotope tracing.
    (2017) Santos, Maristella Moreira; Lana, Cristiano de Carvalho; Buick, Ian S.; Schmitz, Mark D.; Kamo, Sandra L.; Gerdes, Axel; Corfu, Fernando; Tapster, Simon; Lancaster, Penelope; Storey, Craig Darryl; Basei, Miguel Ângelo Stipp; Tohver, Eric; Alkmim, Ana Ramalho; Nalini Júnior, Hermínio Arias; Krambrock, Klaus Wilhelm Heinrich; Leite, Cristiano Fantini; Wiedenbeck, Michael
    A potential zircon reference material (BB zircon) for laser abla tion-in ductively coupled plasma-mass spectrometry (LA-ICP-M S)U-Pb geochronology and Hf isotope geochemistry is described. A batch of twenty zircon megacrysts (0.5–1.5 cm3) from SriLanka was studied. Within-grain rare earth element (REE) compositions are largely homogeneous, albeit with somevariation seen between fractured and homogeneous domains. Excluding fractured cathodoluminescence bright domains,the variation in U content for all analysed crystals ranged from 227 to 368 lgg-1and the average Th/U ratios werebetween 0.20 and 0.47. The Hf isotope composition (0.56–0.84 g/100 g Hf) is homogeneous within and between thegrains – mean176Hf/177Hf of 0.281674 ± 0.000018 (2s). The calculated alpha dose of 0.59 3 1018g-1for a numberof BB grains falls within the trend of previously studied, untreated zircon samples from Sri Lanka. Aliquots of the samecrystal (analysed by ID-TIMS in four different laboratories) gave consistent U-Pb ages with excellent measurementreproducibility (0.1–0.4% RSD). Interlaboratory assessment (by LA-ICP-MS) from individual crystals returned results that arewithin uncertainty equivalent to the TIMS ages. Finally, we report on within- and between-grain homogeneity of theoxygen isotope systematic of four BB crystals (13.16‰ VSMOW).
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    The Diamantina monazite : a new Low‐Th reference material for microanalysis.
    (2018) Gonçalves, Guilherme de Oliveira; Lana, Cristiano de Carvalho; Cipriano, Ricardo Augusto Scholz; Buick, Ian S.; Gerdes, Axel; Kamo, Sandra L.; Corfu, Fernando; Rubatto, Daniela; Wiedenbeck, Michael; Nalini Júnior, Hermínio Arias; Oliveira, Luiz Carlos Alves de
    Most monazite reference materials (RMs) for in situ U-Pb geochronology are rich in Th; however, many hydrothermal ore deposits contain monazite that is low in trace element contents, including Th, U and Pb. Because of potential problems with matrix effects and the lack of appropriate matrix-matched RMs, such variations can bias dating of hydrothermal deposits. In this paper, we describe a polycrystalline low-U and low-Th Diamantina monazite from the Espinhac o Range, SE Brazil. It has a U-Pb ID-TIMS weighted mean 207Pb*/235U ratio of 0.62913 ± 0.00079, 206Pb*/238U of 0.079861 ± 0.000088 and 207Pb*/206Pb* of 0.057130 ± 0.000031, yielding a weighted mean 206Pb*/238U date of 495.26 ± 0.54 Ma (95% c.l.). In situ dates acquired with different methods (LA-(Q, SF, MC)-ICP-MS and SIMS) are within uncertainty of the ID-TIMS data. U-Pb LA-(Q, MC)-ICP-MS runs, using Diamantina as a primary RM, reproduced the ages of other established RMs within < 1% deviation. The LA-MC-ICP-MS analyses yielded homogeneous Sm-Nd isotopic compositions (143Nd/144Nd = 0.511427 ± 23, 2s; 147Sm/144Nd = 0.1177 ± 13, 2s) and eNd(495 Ma) of -18.7 ± 0.5 (2s). SIMS oxygen isotope determinations showed measurement reproducibility better than ± 0.3‰ (2s), confirming Diamantina’s relative homogeneity at test portion masses below 1 ng.
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    U-Pb ages of shocked zircon grains link distal K Pg boundary sites in Spain and Italy with the Chicxulub impact.
    (2011) Kamo, Sandra L.; Lana, Cristiano de Carvalho; Morgan, Joanna V.
    The U–Pbages of shockedzircon crystals from the Chicxulubimpact crater and Cretaceous-Paleogene (K-Pg) boundarysites in Haiti, the USA, and Canada, and the pattern of decreasing particle size with paleodistance from the crater, have been used as evidence of a genetic link between Chicxulub and the K–Pgboundary. Despite this, the inference that the K–Pgboundary layer formed as a direct consequence of the Chicxulubimpact has been repeatedly questioned. Here we present U–Pb (ID-TIMS) ages and textural evidence of shock metamorphosed zircongrains from the K–Pgboundary at Caravaca, Spain, and Petriccio, Italy, that establish a causal connection between the impact and formation of the K–Pgboundary layer. The shockedzircongrains give data that produce a characteristic age pattern, which indicates a primary source age of 549.5 ± 5.7 Ma and a secondary event at the approximate time of impact at 66 Ma. The intensity of the shock features is proportional to the degree of isotopic resetting, and all textural features and ages are analytically identical to those of previously analyzed zircon from Chicxulub and K–Pgboundarysites in North America. Caravaca and Petriccio were > 8000 km from Chicxulub at the time of impact, and are therefore the farthest K–Pgsites identified that can be linked to Chicxulub through the dating of individual shockedzircongrains. We conclude that the combined age data and textural observations provide unambiguous evidence that ejecta from the Chicxulubimpact formed the global K–Pgboundary layer. These data cannot be explained by the alternative scenario that the Chicxulubimpact occurred ~ 300 ka prior to the K–Pgboundary.