Introduction

The IEA Nanomobility (Resolving element mobility at the nanoscale in phosphate minerals), managed by Dr. Anne-Magali SEYDOUX-GUILLAUME (CNRS, Laboratoire de Géologie de Lyon: Terre, Planète, Environnement, ENS, Université Lyon 1, France) in collaboration with the Geoscience Atom Probe group (Prof. Steve Reddy, Dr. Denis Fougerouse and Dr David Saxey) from the University of Curtin in Perth (Australia), will be effective in 2020 and 2021.

Missions and research themes

Phosphate minerals (monazite and xenotime) are of fundamental importance (i) to date rocks of various contexts, (ii) as a source of rare metals (e.g. REE), and (iii) as potential repositories for nuclear waste. However, particularly in the case of ancient rocks ((> 540 Myr), the multiple events that may affect rocks over geological time can result in extremely complex features within phosphates. Recent studies show such features down to the nanometre scale, indicating that it is essential to investigate these minerals at very high-spatial resolutions to understand the mechanisms responsible for element mobility, and provide reliable geological and geochronological interpretations. This project proposes to bring new constraints on nanoscale processes by combining Transmission Electron Microscopy (TEM) and Atom Probe Tomography (APT), and to develop nanogeochronology in monazite and xenotime. This will be possible thanks to the international partnership and the transfer of expertise between France (TEM) and Australia (APT).

Main OBJECTIVES OF THE PROJECT

This project will provide new data on the mechanisms responsible for element mobility at the nanoscale in phosphates. The first objective is to constrain the mechanisms responsible for the disturbance of the chronometric systems: how do these minerals preserve a nanoscale record of processes associated with metamorphism, alteration or deformation? The second objective is to develop the science of nanogeochronology. To achieve these goals, we will implement a new approach in the geoscience field, which combines the nanoscale techniques of Transmission Electron Microscopy (TEM, French expertise) and Atom Probe Tomography (APT, Australian expertise).

institutions and laboratories involved

France
• Laboratoire de Géologie de Lyon: Terre, Planète, Environnement, CNRS-ENS-Université Lyon 1, UMR5276, Lyon ; (http://lgltpe.ens-lyon.fr/)
• Laboratoire de géologie de Saint-Etienne, Université Jean Monnet, Saint Etienne, CNRS UMR 6524, Université Clermont-Auvergne, IRD (https://www.univ-st-etienne.fr/fr/lmv-ltl.html,)
• TEM facility from the CLYM, Consortium Lyon Saint-Etienne de Microscopie, FED 4092 (http://www.clym.fr/fr/node/156)

Australia
• Geoscience Atom Probe Facility, Curtin University, Perth,(http://www.geoscienceatomprobe.org/ )

Read more

Fougerouse, D., Reddy, S.M., Saxey, D.W., Erickson, T., Kirkland, C.L., Rickard, W.D.A., Seydoux-Guillaume, A.-M., Clark, C., and Buick, I.S. (2018). Nanoscale distribution of Pb in monazite revealed by atom probe microscopy. Chem. Geol. https://doi.org/10.1016/j.chemgeo.2018.01.020

Seydoux-Guillaume A-M., Fougerouse, D., Laurent A.T., Gardes, E., Reddy, S.M., Saxey, D.W. (2019). Nanoscale resetting of the Th/Pb system in an isotopically-closed monazite grain: a combined Atom Probe and Transmission Electron Microscopy study. Geoscience Frontiers, https://doi.org/10.1016/j.gsf.2018.09.004.

Reddy, S. M., Saxey, D. W., Rickard, W. D. A., Fougerouse, D., Montalvo, S. D., Verberne, R., & Riessen, A. (2020). Atom Probe Tomography: Development and Application to the Geosciences. Geostandards and Geoanalytical Research, 44(1), 5–50. https://doi.org/10.1111/ggr.12313

Fougerouse, D., Kirkland, C. L., Saxey, D. W., Seydoux‐Guillaume, A., Rowles, M. R., Rickard, W. D. A., & Reddy, S. M. (2020a). Nanoscale Isotopic Dating of Monazite. Geostandards and Geoanalytical Research, ggr.12340. https://doi.org/10.1111/ggr.12340

Fougerouse D., Reddy S.M., Seydoux-Guillaume A.-M, Kirkland C.L., Erickson T.M., Saxey D.W., Rickard W.D.A., Jacob D., Leroux H., and Clark C. (2020b). Mechanical twinning of monazite expels radiogenic Pb. Geology. https://doi.org/10.1130/G48400.1

Figure. APT 3D-reconstruction (left) and TEM images (STEM-HAADF and S-Ca chemical maps ; right) from the same monazite crystal; note the presence of nanoclusters rich in Ca, S (TEM/APT) et Pb (APT). For APT each « point » corresponds to one atom, and the total volume analyzed to 20 millions of atoms. After Seydoux-Guillaume et al. (2019)