Partial retention of radiogenic Pb in galena nanocrystals explains discordance in monazite from Napier Complex (Antarctica)

Turuani, Marion; Laurent, Antonin; Seydoux‐Guillaume, Anne‐Magali; Fougerouse, Denis; Saxey, David W.; Reddy, Steven M.; Harley, Simon L.; Reynaud, Stéphanie; Rickard, William D.A.

doi:10.1016/j.epsl.2022.117567

Cited by 11 publications

(31 citation statements)

References 47 publications

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“…The presence of inclusions with a radiogenic component different from the host mineral can result in a mixed chemical and isotopic system (Fougerouse et al, 2018;Turuani et al, 2022). In this study, Pb is found to have segregated in multiple ways that might have occurred at different moments in time.…”

Section: Implications For Geochronology: a Geological History From Su...mentioning

confidence: 53%

“…The texture and formation of trace element enriched clusters are explained via entrapment in defects generated via radiation damage (Seydoux-Guillaume et al, 2018;Seydoux-Guillaume, 2019). The damaged regions stand out due to structural difference with the host monazite while the bright spot (HAADF) stands out due to being enriched in trace elements, creating this mottled texture as previously observed by others (Seydoux-Guillaume et al, 2019;Turuani et al, 2022;.…”

Section: Monazite Inclusions In Rutilementioning

confidence: 59%

“…% Mg, 10 at% P and, 4 at% Ca while showing a depletion in REE concentrations compared to the monazite host. As is the case (Kusiak., 2015Lyon et al, 2019), called nanospheres and monazite (Turuani et al, 2022;Turuani et al, 2023) referred to as nanocrystals. Considering we observe a similar presence of Pb in the core that is related associated with U decay, it is unlikely these are primary Pb phases.…”

Section: Formation Of Trace-element Enriched Nanoscale Clustersmentioning

confidence: 99%

“…Regardless, the mobility results in several Pb reservoirs with, potentially unique, Pb isotopic signatures that record the timing of their formation and the decoupling of the U-Pb system. In ideal situations, this Pb signature can be independently studied (Fougerouse et al, 2018;Peterman et al, 2016;Seydoux-Guillaume et al, 2019;Turuani et al, 2022;Valley et al, 2014;Verberne et al, 2020).…”

Section: Implications For Geochronology: a Geological History From Su...mentioning

confidence: 99%

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Clustering and interfacial segregation of radiogenic Pb in a mineral host – inclusion system Tracing two-stage Pb and trace element mobility in monazite inclusions in rutile

2024

msam

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Accessory minerals like zircon, rutile and monazite are routinely studied to inform about the timing and nature of geological processes. These studies are underpinned by our understanding of the transfer processes of trace elements and the assumption that the isotopic systems remain undisturbed. However, the presence of microstructures or Pb-bearing phases in minerals can lead to the alteration of the Pb isotopic composition. To gain insight into the relationship between Pb isotopic alterations from inclusions and microstructures, this study focused on inclusions from an ultra-high temperature metamorphic rutile.The studied inclusions are submicron monazites, a common mineral rich in Pb but normally not present in rutile. The sample is sourced from Mt. Hardy, Napier Complex, East Antarctica, an ultra-high temperature (UHT) metamorphic terrane. By applying correlative analytical techniques including electron backscatter diffraction mapping, transmission electron microscopy (TEM), and atom probe tomography, it is shown monazite inclusions are often in contact with low-angle boundaries and yield no preferred orientation. TEM shows the monazite core has a mottled texture due to the presence of radiation damage and nanoclusters associated with the radiation damage defects that are rich in U, Pb, and Ca. Some monazites exhibit a core-rim structure. The rim yields clusters composed of Ca-and Li-phosphate that enclose Pb nanoclusters that are only present in small amounts compared to the core, with Pb likely diffused into the rutile-monazite interface. These textures are the result of two-stages of Pb mobility.Initial Pb segregation was driven by volume diffusion during UHT metamorphism (2500 Ma). The second stage is a stress-induced recrystallization during exhumation, leading to recrystallization of the monazite rim and trace element transport. The isotopic signature of Pb trapped within the rutile-monazite interface constrains the timing of Pb mobility to c. 550 Ma.

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Section: Implications For Geochronology: a Geological History From Su...mentioning

confidence: 53%

Section: Monazite Inclusions In Rutilementioning

confidence: 59%

Section: Formation Of Trace-element Enriched Nanoscale Clustersmentioning

confidence: 99%

Section: Implications For Geochronology: a Geological History From Su...mentioning

confidence: 99%

See 2 more Smart Citations

Clustering and interfacial segregation of radiogenic Pb in a mineral host – inclusion system Tracing two-stage Pb and trace element mobility in monazite inclusions in rutile

2024

msam

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“…Evidence of mineralogical processes that affect geochronometers and that induce element mobility may be recorded within the crystal. The benefits of examining geochronometers at the nanoscale using transmission electron microscopy (TEM) and atom probe tomography (APT) to address broader issues of element mobility has been demonstrated for zircon (Utsunomiya et al 2004;Kusiak et al 2015Kusiak et al , 2019Valley et al 2015;Peterman et al 2016Peterman et al , 2019Piazolo et al 2016;Whitehouse et al 2017), monazite (Seydoux-Guillaume et al 2003Fougerouse et al 2018Fougerouse et al , 2021aBudzyń et al 2021Budzyń et al , 2022Turuani et al 2022), rutile (Verberne et al 2020), xenotime (Joseph et al 2021;Budzyń et al 2023) and baddeleyite (White et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Nanoscale features revealed by a multiscale characterisation of discordant monazite highlight mobility mechanisms of Th and Pb

Turuani

Seydoux‐Guillaume

Laurent

et al. 2023

Contrib Mineral Petrol

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HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

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Microstructural and isotopic analysis of shocked monazite from the Hiawatha impact structure: development of porosity and its utility in dating impact craters

Hyde,

Kenny,

Whitehouse

et al. 2024

Contrib Mineral Petrol

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U–Pb geochronology of shocked monazite can be used to date hypervelocity impact events. Impact-induced recrystallisation and formation of mechanical twins in monazite have been shown to result in radiogenic Pb loss and thus constrain impact ages. However, little is known about the effect of porosity on the U–Pb system in shocked monazite. Here we investigate monazite in two impact melt rocks from the Hiawatha impact structure, Greenland by means of nano- and micrometre-scale techniques. Microstructural characterisation by scanning electron and transmission electron microscopy imaging and electron backscatter diffraction reveals shock recrystallisation, microtwins and the development of widespread micrometre- to nanometre-scale porosity. For the first time in shocked monazite, nanophases identified as cubic Pb, Pb3O4, and cerussite (PbCO3) were observed. We also find evidence for interaction with impact melt and fluids, with the formation of micrometre-scale melt-bearing channels, and the precipitation of the Pb-rich nanophases by dissolution–precipitation reactions involving pre-existing Pb-rich high-density clusters. To shed light on the response of monazite to shock metamorphism, high-spatial-resolution U–Pb dating by secondary ion mass spectrometry was completed. Recrystallised grains show the most advanced Pb loss, and together with porous grains yield concordia intercept ages within uncertainty of the previously established zircon U–Pb impact age attributed to the Hiawatha impact structure. Although porous grains alone yielded a less precise age, they are demonstrably useful in constraining impact ages. Observed relatively old apparent ages can be explained by significant retention of radiogenic lead in the form of widespread Pb nanophases. Lastly, we demonstrate that porous monazite is a valuable microtexture to search for when attempting to date poorly constrained impact structures, especially when shocked zircon or recrystallised monazite grains are not present.

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Partial retention of radiogenic Pb in galena nanocrystals explains discordance in monazite from Napier Complex (Antarctica)

Cited by 11 publications

References 47 publications

Clustering and interfacial segregation of radiogenic Pb in a mineral host – inclusion system Tracing two-stage Pb and trace element mobility in monazite inclusions in rutile

Clustering and interfacial segregation of radiogenic Pb in a mineral host – inclusion system Tracing two-stage Pb and trace element mobility in monazite inclusions in rutile

Nanoscale features revealed by a multiscale characterisation of discordant monazite highlight mobility mechanisms of Th and Pb

Microstructural and isotopic analysis of shocked monazite from the Hiawatha impact structure: development of porosity and its utility in dating impact craters

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