Anne-Magali Seydoux-Guillaume

• phD, HDR
• DR CNRS at French National Centre for Scientific Research

Dissociated zircon is largely used as a robust indicator of glasses generated by impact cratering and airbursts. The reaction of zircon dissociation, i.e. 'ZrSiO 4 ? ZrO 2 + SiO 2 ', requires high temperatures (>1670°C) only reached by extreme geological processes. Using high-temperature experiments, this study shows that zircon can dissociate and...

We present the first textural and chemical characterization at nanometer scale of chrysocolla [(Cu2-xAlx)H2-xSi2O5(OH)4.nH2O], black chrysocolla (a Mn-rich variety of chrysocolla) and pseudomalachite [Cu5(PO4)2(OH)4] from two distinct supergene copper deposits from Atacama Desert of northern Chile. These minerals are the most common copper minerals...

The causes of U-Pb isotopic discordance documented by Paquette et al. (2004) in monazite grains from the ultra-high temperature (UHT) granulite of the Andriamena unit of Madagascar are re-evaluated in the light of nanoscale crystal-chemical characterization utilising Atom Probe Tomography (APT) and state-of-the-art Scanning Transmission Electron Mi...

Tektites are terrestrial impact-generated glasses distributed over regions of Earth’s surface with ejection distances up to 10,000 km. The Australasian tektite strewn field is the largest and the youngest discovered so far (788 ka). However, the location of the source crater remains unsolved. The present work is the first to investigate the only mo...

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-bearin...

Engineering the polarization and spatial phase of ultrafast laser pulses represents a compelling strategy for enhancing control over laser–matter interaction and enabling rapid and innovative nano‐fabrication processes. Here, the single‐shot, ultrafast laser fabrication of high‐aspect‐ratio, vertically standing nano‐pillars with a diameter of ≈800$...

Understanding radionuclides mass transfer mechanisms in monazite (LREEPO4) and the resulting features, from the micro- to the nanoscale, is critical to its use as a robust U–Th–Pb geochronometer. A detailed multiscale characterisation of discordant monazite grains from a granulite which records a polymetamorphic history explores the mechanisms of T...

Impact-related damage in minerals and rocks provides key evidence to identify impact structures, and deformation of U-Th-minerals in target rocks, such as monazite, makes possible precise dating and determination of pressure-temperature conditions for impact events. Here a laser-driven shock experiment using a high-energy laser pulse of ns-order du...

The discordance of U–Th–Pb isotopic systems in geochronometers, and how such data are interpreted, are still major issues in the geosciences. To better understand the disturbance of isotopic systems, and how this impacts the derivation of geologically-meaningful ages, previously studied discordant monazite from the ultrahigh temperature paragneiss...

Brannerite, UTi2O6 is reported to occur in various uraniferous deposits worldwide. Natural brannerite specimens are found in the amorphous state and are usually considered to be refractory to dissolution due to the formation of TiO2 passivation layer. In the present work, brannerite was synthesized by wet chemistry route, then characterized prior t...

Mechanical twins form by the simple shear of the crystal lattice during deformation. In order to test the potential of narrow twins in monazite to record the timing of their formation, we investigated a ca. 1700 Ma monazite grain (from the Sandmata Complex, Rajasthan, India) deformed at ca. 980 Ma, by electron backscattered diffraction (EBSD), tran...

Rare-earth phosphates adopting the xenotime (REPO4; RE = Tb − Lu & Y, Sc) structure are proposed as a potential matrix for the confinement of minor actinides. Minor actinides (e.g., Np, Am, Cm) undergo a radioactive decay process in which high-energy recoil atom (70–100 keV) and energetic alpha particles (4.5–5.8 MeV) are produced. In this study, t...

Monazite U‐Th‐Pb geochronology is widely used for dating geological processes, but current analytical techniques are limited to grains greater than 5 μm in diameter. This limitation precludes the analysis of both micrometre‐scale discrete monazite grains and fine textures within monazite crystals that are commonly found. Here, we analyse reference...

Brannerite (UTi 2 O 6 ) is among the major uranium-bearing minerals found in ore deposits, however as it has been long considered as a refractory mineral for leaching it is currently disregarded in ore deposits. Brannerite is found in a variety of geological environments with the most common occurrences being hydrothermal and pegmatitic. On the bas...

The quantification of He and Ne diffusion behavior in crystals rich in U and Th such as zircon is key for the interpretation of (U-Th)/⁴He and (U-Th)/²¹Ne thermochronometric ages. Multiple parameters such as chemical substitution, channel obstruction and damage can modify the diffusivity compared to a pristine structure. To investigate the impact o...

A new method based on the precipitation of uranium(IV) and titanium(IV) hydroxide precursors was developed to prepare pure brannerite UTi2O6 samples. In fact, U(IV) dissolved in HCl (6 mol L⁻¹) was mixed to Ti (IV) alkoxyde before a basification step with an excess of NH4OH to obtain a highly reactive nanometric (U,Ti)(OH)4 powder. The obtained pow...

A multi-method investigation into Lauzière granite, located in the external Belledonne massif of the French Alps, reveals unusually hot hydrothermal conditions in vertical open fractures (Alpine-type clefts). The host-rock granite shows sub-vertical mylonitic microstructures and partial retrogression at temperatures of < 400 ∘C during Alpine tecton...

Understanding the mechanisms of parent-daughter isotopic mobility at the nanoscale is key to rigorous interpretation of U–Th–Pb data and associated dating. Until now, all nanoscale geochronological studies on geological samples have relied on either Transmission Electron Microscope (TEM) or Atom Probe Microscopy (APM) characterizations alone, thus...

A multi-method approach investigation in the Lauzière granite, located in the external Belledonne massif of the French Alps, reveals unusually hot hydrothermal conditions in vertical open fractures (Alpine-type clefts), caused by advective heating. The host-rock granite shows sub-vertical mylonitic microstructures and partial retrogression at tempe...

Monazite, a common accessory rare-earth orthophosphate mineral in the continental crust widely used in U-Pb geochronology, holds promise for (U-Th)/He thermochronology and for the immobilization of Pu and minor actinides (MA) coming from spent nuclear fuel reprocessing. Previous results obtained on natural and plutonium-doped monazite have demonstr...

In Rogaland, South Norway, a polycyclic granulite facies metamorphic domain surrounds the late‐Sveconorwegian anorthosite–mangerite–charnockite (AMC) plutonic complex. Integrated petrology, phase equilibria modelling, monazite microchemistry, Y‐in‐monazite thermometry, and monazite U–Th–Pb geochronology in eight samples, distributed across the appa...

This contribution evaluates the relation between protracted zircon geochronological signal and protracted crustal melting in the course of polyphase high to ultrahigh temperature (UHT; T > 900 °C) granulite facies metamorphism. New U–Pb, oxygen isotope, trace element, ion imaging and cathodoluminescence (CL) imaging data in zircon are reported from...

The widespread use of monazite (LREEPO4) in U-Pb geochronology is underpinned by the assumption that it incorporates negligible amounts of Pb during initial growth, and that radiogenic Pb remains immobile after formation. We have investigated the nanoscale distribution of Pb in monazite from granulite facies rocks of the Sandmata Metamorphic Comple...

This paper highlights the benefits of nanoscale characterization of the most commonly used minerals (zircon and monazite) in U-Th-Pb geochronology to sharpen geochronological interpretations and convert isotopic ratios (a “date”) into a geologically meaningful age. Transmission electron microscopy (TEM) is a powerful analytical tool, and sometimes...

The Manangotry area in the South-East of Madagascar is famous for its giant monazite crystals. The studied occurrence is an outcrop near the Manangotry pass, were giant, cm-sized crystals have been found. The crystals are embedded in biotitite levels, also containing cm-sized xenomorphic ilmenite, and are associated with a 1m thick layer of apatite...

The present experimental study investigates the causes of anisotropic replacement and its impact on the element mass transfer during monazite alteration by combining in situ characterization of solid and fluid products. Starting material of standard Manangotry monazite was placed at 200 MPa with ¹⁸O doped fluids, at temperature (T) between 300 and...

In eleven Alpine clefts of the western Alps, in-situ dating of monazite-(Ce) and xenotime-(Y) has been attempted to gain insights on possible disturbances of the geochronological U-Th-Pb systems and age interpretations in hydrothermal conditions. In most clefts, monazite-(Ce) in-situ 208Pb/232Th dating using laser ablation-inductively coupled plasm...

The study of radiation damage resulting from alpha-decay from U and Th chains in radiocative U-Th minerals is of tremendous importance. Indeed, this damage critically affects the long term behavior of minerals. It is caused by both the ejection of recoil-nuclei and alpha-particles, leading to fundamental modifications in the physical and chemical p...

Microgeochemical data and transmission electron microscope (TEM) imaging of S-rich monazite crystals demonstrate that S has been incorporated in the lattice of monazite as a clino-anhydrite component via the following exchange Ca2+ + S6+ = REE3+ + P5+, and that it is now partly exsolved in nanoclusters (5–10 nm) of CaSO4. The sample, an osumilite-b...

We document the textural relations and chemical composition of (Y,REE,U,Th)–(Nb,Ta,Ti) oxide minerals in a granitic pegmatite from the Evje-Iveland district, southern Norway, using a combination of scanning and transmission electron microscopy, electron probe micro-analysis and infrared absorption spectroscopy. The (Y,REE,U,Th)–(Nb,Ta,Ti) oxide min...

Helium diffusion in U-Th-rich minerals, especially apatite, is considered as strongly impacted by damage, even at low U-Th content. To get direct evidence and better understand the impact of damage on He diffusion, we conducted a study on vacancy damage in apatite, at nanometric to atomic scales, using different methodologies. Firstly, damage was c...

The (Y,REE,U,Th)–(Nb,Ta,Ti) oxides, like euxenite, fergusonite, pyrochlore, zirconolite, are known to contain nanometric spherical cavities or bubbles, interpreted to contain radiogenic helium. In-situ analyses by Scanning Transmission Electron Microscopy (STEM) coupled with Electron Energy Loss Spectroscopy (EELS) inside nano-bubbles from an euxen...

Alteration experiments on natural monazite crystals (Manangotry standard, Madagascar) under alkali conditions at 300, 400, 500 and 600 °C and 200 MPa were conducted to clarify mechanisms behind incomplete resetting of U-Th-Pb geochronological systems in monazite replaced by dissolution and precipitation processes. Above 400 °C, experimental product...

Scanning Transmission Electron Microscopy (STEM) images coupled with U-Pb isotopic analysis give new insight into mobility of U and Pb in zircon. Zircon crystals included in xenotime and in plagioclase of a pegmatitic assemblage comprising euxenite correspond to irradiation related alteration of zircon with amorphization, microporosity, swelling, r...

To promote crystallography through the "Midi-Pyrénées" Region, our association, « Les Cristallographes en Midi-Pyrénées » has scheduled different events from October 2013 until the end of 2014. These events will cover scientific demonstrations and/or lectures open to the general public. 1) Events - The Novela (7-12 October 2013), organized by the T...

Low-temperature alteration of monazite is documented in three centimeter-sized monazite crystals from Norway (Arendal), Madagascar (Ambato), and Sri Lanka. The three crystals have different chemical compositions, especially in their U, Th, Y and Pb contents and have 208Pb/232Th ages ranging from 491 to 900 Ma. Optical microscope (OM), Scanning Elec...

Infrared femtosecond laser induced damage has been studied in order to determine, with analytical protocols, the processes involved in laser ablation in this regime. Transmission Electron Microscopy (TEM) coupled with Focused Ion Beam (FIB) milled cross-sections of natural ablated monazite were used. Craters were formed using N = 1 and 3 shots, E0...

The analytical study of infra red femtosecond laser induced particles has been performed using Transmission Electron Microscopy (TEM) and Low Pressure Impaction (ELPI). Various natural and synthetic matrices have been tested: monazite (phosphate), zircon (silicate), NIST610 (glass), spinel (oxide), quartz (silicate structure), silicon (semiconducto...

The most serious problem associated with conventional Raman spectroscopy is fluorescence and this is known as the Raman Achilles' heel. For minerals that exhibit even weak luminescence in the recorded spectral range, the Raman scattering will overlap partially or completely. The aim of this chapter is, on one hand, to present the various ways to ge...

Femtosecond (fs) laser ablation systems have now been used for about a decade for elemental analysis in chemical and geosciences laboratories. Published studies investigated the influence of various analytical parameters, such as laser pulsewidth, wavelength, energy or ablation duration, on the quality of the analytical data produced by fs Laser Ab...

Effects of strongly radioactive primary minerals (mainly monazite) on the surroundings are compared in various rocks of similar chemical and mineral composition (mainly granites and paragneisses) of the Moldanubian area in the Bohemian massif. All these rocks cooled to <150 °C at similar time (300-250 Ma b.p.). aureoles of secondary phases formed w...

A commercial femtosecond laser system operating at its fundamental wavelength (lambda = 800 nm, near Infra-Red) was used to ablate both synthetic and natural quartz on polished and unpolished surfaces. Ablation rates and maximum depths were determined using two distinct optical setups: a 25 mm focal length Cassegrain reflecting objective, and a 50...

Le but de ce mémoire n'est pas de faire une présentation exhaustive de toutes mes activités de recherche mais d'essayer de cibler celles qui à la fois me correspondent le mieux, celles qui me tiennent le plus à cœur, parmi les activités de recherche que j'ai menées depuis que je suis partie de Potsdam (thèse). Je présenterai donc dans une première...

The characteristics of Infra Red femtosecond laser-induced aerosols are studied for monazite (Moacyr) ablation, in order to evaluate optimal conditions for Inductively Coupled Plasma - Mass Spectrometry (ICP-MS) analysis. Various parameters are tested within wide ranges in order to cover near all of the usual LA-ICP-MS settings: pulse energy (E0),...

The LREE orthophosphate monazite is a common accessory mineral, important as a U-Th-Pb geochronometer in both metamorphic and magmatic rocks. In order to correctly interpret measured ages, it is essential to properly understand mechanisms that control them. Few studies have shown that coupled dissolution-crystallisation in the presence of a fluid p...

Effects of infrared femtosecond laser ablation (800 nm, 60 fs, 5 Hz, 85 μJ/pulse, objective × 15) of a well-characterized monazite on its micro- and nano-structure were investigated. Craters were produced by single and multiple pulses (N = 10, 20, 50, 150 and 300) to follow the evolution of laser-induced damage in monazite using Scanning Electron M...

We studied the influence of pulse energy (E0) and pulse width (τ) of Near Infra Red femtosecond Laser Ablation coupled to Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). A particular emphasis was put on the 206Pb/238U and 208Pb/232Th repeatability from Moacyr monazite (Itambe, Brazil). Synthetic glass (Standard Reference Material) NIST610...

Coupe FIB (15 µm x 8 µm x 0.1 µm), réalisée à l'interface entre un zircon et une euxénite in situ en lame mince, encore en place dans l'échantillon, avant extraction et analyse en MET. Etude en collaboration avec C. Dominici (CP2M-Marseille)

Processes linked to the creation of laser induced aerosols are not yet fully understood, especially in the Infra Red femtosecond regime. It is of great interest to understand these mechanisms in order to better constrain chemical fractionation observed on LA-ICP-MS signals. A meticulous study of particles produced by IR-fs laser ablation (lambda=80...

Performances of laser ablation have been widely explored, especially for industrial purposes. Nevertheless, some study fields remain unknown, notably the use of Infra-Red femtosecond pulses for the ablation of hard transparent materials. Thus, we present analytical results on quartz, which is the most widespread mineral in earth sciences, especiall...

Combining observation and simulation, radiohalos formed around uranothorianite (UTh) from the Tranomaro granulitic skarns (SE-Madagascar) were studied. These structures consist of UTh grains surrounded by both aluminous diopside (Cpx) and calcite (Cc1) crystals. Optical microscope and Scanning Electron Microscope (SEM) images revealed (1) the prese...

Image en électrons rétrodiffusés au MEB de zonations chimiques dans un zircon de Norvège. Etude en collaboration avec B.Bingen (NGU, Trondheim, Norvège)

Monazite is a potential matrix for conditioning minor actinides arising from spent fuel reprocessing. The matrix behavior under irradiation must be investigated to ensure long-term containment performance. Monazite compounds were irradiated by gold and helium ions to simulate the consequences of alpha decay. This article describes the effects of su...

Radiation damage in radioactive minerals has been studied in geosciences for two main reasons. First, U-Th-rich minerals are used for U-Th-Pb datation, and it is essential to understand the effects of radiation damage on lead retentivity. Second, the effect of long term accumulation of radiation damage is a key parameter for assessing the durabilit...

Images MET (BF) et spectres EDX associés des deux types de particules formées après ablation femtoseconde de la monazite de Moacyr. A) billes et b) agglomérats. Etude en collaboration avec F-X d'Abzac. Ref. d'Abzac, Thèse, 2010, Université P. Sabatier, Toulouse

Fracturation radiale autour d'un cristal géant d'allanite (20 cm de diamètre) d'une pegmatite de Norvège. Le gonflement de ce minéral qui résulte de son amorphisation liée à son auto-irradiation (désintégration de U et Th), provoque une fracturation à l'échelle macroscopique. Etude en collaboration avec B.Bingen (NGU-Trondheim, Norvège)

Observations en microscope électronique en transmission (MET) effectuées dans 2 coupes FIB préparées transversalement dans 1 cratère d'ablation femtoseconde (1 tir). A- Scanning TEM (STEM) d'une partie de la coupe FIB montrant 4 zones différentes: un niveau de matériel resolidifié (i), une zone très endommagée avec le cliché de diffraction correspo...

We performed diffusion annealing of Pb-bearing monazite thin films deposited on Ca-bearing monazite polycrystals to investigate Pb2+⇔Ca2+ interdiffusion. Experiments were run at temperatures ranging from 1300 to 1500 °C with samples sealed in Pb-buffered capsules. The Focused Ion Beam (FIB) technique was used to cut TEM foils within grains, excludi...

In order to compare the irradiation-induced behaviour of monazite and ThSiO4, a large single crystal of monazite from Norway (Arendal monazite) containing several ThSiO4 inclusions was investigated. The estimated theoretical self-irradiation dose received by monazite near those inclusions was approximately 3 x 10(19) alpha-decay/g. Transmission ele...

Various geological arguments suggest that monazite can be an interesting waste-form for actinides such as Np, Pu, Cm and Am. We set up a simple procedure for making dense pellets of monazite–brabantite solid–solution ceramics with composition Ca0.092Th0.092Ce0.089La0.727PO4. It consists of co-milling CaCO3, ThO2, CeO2, La2O3, and NH4H2PO4, 1250 °C...

We have measured Pb diffusivity in synthetic NdPO4 crystals from an epitaxial Nd0.66Pb0.17Th0.17PO4 thin film deposited on (-1 0 1) faces. Annealings were performed at room pressure at temperatures ranging from 1200 to 1500 °C for 1 h to 1 month. Samples were analysed using transmission electron microscopy (TEM) and Rutherford backscattering spectr...

We have performed hydrothermal experiments with a crystalline microlite and a heavily self-irradiation-damaged (i.e., X-ray amorphous) betafite in a solution containing 1mol/l HCl and 1mol/l CaCl2 at 175°C for 14 days. The well-crystalline microlite grains were partly (∼5–10μm rim) replaced by a Ca and Na-poorer, defect pyrochlore phase with a larg...

Images en électrons secondaires au microscope électronique à balayage (MEB) d'un cristal d'uranothorianite (UTh) de Madagascar en inclusion dans de la calcite (Cc) et du diopside (Cpx). Les rectangles entre les croix correspondent aux traces laissées par la découpe FIB (C). Notez une intense fracturation autour de l'inclusion radioactive (A) et une...

Textures d'altération en électrons rétrodiffusés au MEB dans une monazite de Norvège. Ces textures sont interprétées comme des réactions d'altération par dissolution-précipitation couplée en présence de fluides conduisant au remplacement partiel de la monazite primaire magmatique (Mnz1 et Mnz1') par une monazite secondaire (Mnz2) associée à une pha...

Image en électrons secondaires au MEB d'une découpe FIB (Focused Ion Beam) réalisée en bordure d'un cratère d'ablation laser femtoseconde. Etude en collaboration avec R. Wirth (GFZ-Potsdam, Allemagne)

For more than 100 years mineralogists, physicists, chemists, geologists, and biologists have discussed the formation of periodic Liesegang patterns observed in natural and experimental systems. Spectacular examples of minerals showing complex periodic patterns are agate, malachite, and sphalerite. Here we report the first observation of Liesegang-l...

The microstructure of monazite was studied using scanning electron microscopy (SEM), electron microprobe analysis (EMP), X-ray diffraction patterns (XRD), and transmission electron microscopy (TEM). Four well-characterized monazites were investigated, having very different concordant U-Pb ages (24 to 1928 Ma), and up to ∼15 wt.% ThO2, and ∼0.94 wt....

Electron-microprobe (EMP) U-Th-Pb dating on polyphase and discordant monazites from polymetamorphic granulites of the Andriamena unit (north-central Madagascar) reveals inconsistent chemical ages. To explain these drastic variations, transmission electron microscopy (TEM) foils were prepared directly from thin sections by using the focused ion beam...

Natural monazite is known in contrast to zircon, to almost never be found in the metamict state (Ewing, 1975) despite the fact that it received intensive radiation doses during geologic history by U and Th incorporation. Radiation damages in natural monazite seems to be limited to isolated domains within the crystal (Meldrum et al., 1998). Such pro...

Electron Microprobe (EMP) U-Th-Pb dating on polyphasic and discordant monazites from poly-metamorphic (Ultra High Temperature UHT) granulites of the Andriamena unit (North-Central Madagascar) reveal inconsistent chemical ages. The reason for this observation was investigated at the nano-scale using transmission electron microscope (TEM) techniques....