Defining the Potential of Nanoscale Re‐Os Isotope Systematics Using Atom Probe Microscopy

Abstract

Atom probe microscopy (APM) is a relatively new in situ tool for measuring isotope fractions from nanoscale volumes (< 0.01 μm3). We calculate the theoretical detectable difference of an isotope ratio measurement result from APM using counting statistics of a hypothetical data set to be ± 4δ or 0.4% (2s). However, challenges associated with APM measurements (e.g., peak ranging, hydride formation and isobaric interferences), result in larger uncertainties if not properly accounted for. We evaluate these factors for Re‐Os isotope ratio measurements by comparing APM and negative thermal ionisation mass spectrometry (N‐TIMS) measurement results of pure Os, pure Re, and two synthetic Re‐Os‐bearing alloys from Schwander et al. (2015, Meteoritics and Planetary Science, 50, 893) [the original metal alloy (HSE) and alloys produced by heating HSE within silicate liquid (SYN)]. From this, we propose a current best practice for APM Re‐Os isotope ratio measurements. Using this refined approach, mean APM and N‐TIMS 187Os/189Os measurement results agree within 0.05% and 2s (pure Os), 0.6–2% and 2s (SYN) and 5–10% (HSE). The good agreement of N‐TIMS and APM 187Os/189Os measurements confirms that APM can extract robust isotope ratios. Therefore, this approach permits nanoscale isotope measurements of Os‐bearing alloys using the Re‐Os geochronometer that could not be measured by conventional measurement principles.

Atom Probe Tomography: Development and Application to the Geosciences

“…Several recent studies have compared APT compositional results from geological samples with those from other geoanalytical techniques (Pérez‐Huerta et al , Daly et al , Exertier et al , Reinhard et al , Saxey et al ). Most comparisons provide excellent agreement, within the uncertainty arising from counting statistics in the atom probe data.…”

“…The atom probe provides a unique tool for investigating the nanoscale isotopic composition of minerals. Benchmarking of atom probe analysis of U isotopes in certified U 3 O 8 reference materials has shown that major isotopic ratios agree with known compositional values (Fahey et al ) and there are comparative thermal ion mass spectrometry (TIMS) and atom probe studies that show that Re‐Os analysis by atom probe may yield similar, though less precise, ages to more traditional TIMS analyses (Daly et al ). A number of studies have also investigated the mechanisms that can affect the distribution of radiogenic 207 Pb/ 206 Pb ratios in zircon (Figure ; Valley et al , , Peterman et al , Blum et al ), baddeleyite (White et al , Moser et al ) and monazite (Fougerouse et al , Seydoux‐Guillaume et al ).…”

“…Since the development of laser‐assisted APT, there has been growing interest in applying nanoscale geochemical characterisation to a broad range of geological materials including glass (Gin et al , Hellmann et al , Gin et al ), diamond (Heck et al , Lewis et al , Schirhagl et al , Mukherjee et al ), Fe‐Ni metal alloys (Einsle et al ) and silicides (Gopon et al ), platinum‐group alloys (Parman et al , Daly et al , ), oxides (Bachhav et al , , Fahey et al , Taylor et al , Frierdich et al , Gamal El Dien et al , Genareau et al , Taylor et al ), carbonates (Felmy et al , Branson et al , Pérez‐Huerta et al , Pérez‐Huerta and Laiginhas ), sulfides (Fougerouse et al , Dubosq et al , Fougerouse et al , Gopon et al , Wu et al ), sulfates (Weber et al ), zeolites (Schmidt et al ) and rock‐forming silicates, such as feldspars (White et al , Cao et al ) and olivine (Bloch et al , Cukjati et al , Figure ). However, a high proportion of the published APT work to date has focussed on trace element mobility, particularly Pb, in accessory minerals.…”

Atomic worlds: Current state and future of atom probe tomography in geoscience

“…Application of APM to radiogenic isotope geochemistry has been demonstrated using the U-Pb system [8 10]. And other radiogenic systems, such as Sm-Nd and Re-Os, also appear amenable to the technique, where concentrations permit [72]. Within this field, the atom probe is an ideal tool for determining the origin and history of geological materials from sub-micron isotopic signatures, which are often not resolvable using other techniques.…”

Analytical Methods for Os Isotope Ratios and Re-PGE Mass Fractions in Geological Samples

“… Daly et al (2017b) performed APM analyses of sub-micrometer PGE-rich refractory metal nuggets contained within a Sc-Zr–rich ultrarefractory inclusion from the ALH 77307 CO3.0 meteorite. More recently, Daly et al (2018) employed the laser-assisted APM technique to measure Re and Os isotope ratios of pure Os, pure Re, and synthetic Re-Os-bearing alloys, demonstrating that the APM technique permits nanoscale Os isotope ratio measurements of Os-bearing alloys to yield similar, though less precise, ages to NTIMS analyses. At current, development and application of the analytically expensive and highly-specific APM technique in geosciences is still in its early stages ( Reddy et al, 2020 ).…”