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Trace metal analysis in carbonates using the Cameca NanoSIMS

Trace metal analysis in carbonates using the Cameca NanoSIMS. John Eiler Sharp Professor of Geology and Geochemistry Director, Caltech Microanalysis Center California Institute of Technology With contributions from Jess Adkins, Anne Dekas , Rinat Gabitov , Alex Gagnon,

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Trace metal analysis in carbonates using the Cameca NanoSIMS

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  1. Trace metal analysis in carbonates using the CamecaNanoSIMS John Eiler Sharp Professor of Geology and Geochemistry Director, Caltech Microanalysis Center California Institute of Technology With contributions from Jess Adkins, Anne Dekas, RinatGabitov, Alex Gagnon, Amy Hofmann and Katie Snell Wisc SIMS Paleoclimate Workshop June 25th, 2013

  2. Cation-exchange paleothermometry CaCO3 + Mgaq = MgCO3 + Caaq [ ]min [ ]fluid Mg Ca Ca Mg Keq ∞ x Mitsuguchi et al., 1996

  3. Global budgets Weathering Hydrothermal Alteration Sediments Stanley and Hardie, 1998; model of Hardie, 1996

  4. Hitch #1: Vital effects Foraminifera Deep-sea coral Eggins et al., 2004; Gagnon et al., 2007

  5. Hitch #2: Diagenesis PA: Primary Aragonite; SA: Secondary Aragonite; SC: Secondary Calcite Cements vs. ‘Primary’ Allison et al., 2007

  6. The CamecaNanoSIMS

  7. What puts the ‘nano’ in nanoSIMS Geometry of focusing and extraction lenses • Short working distance promotes small, dense probe • Extraction optics easily contaminated or damaged

  8. Minimum spot size Si metal in Al matrix <<1 pA Cs+; ca. 30 nm resolution Illustration of the ‘84/16 %’ definition 1 µm • Nominally 50 nm for Cs+, 150 nm for O- (‘84/16 %’ definition) • Actual minimum ca. 20 nm for Cs+, ca. 100 nm for O- • Brighter beams needed for trace element mapping typically in 100-300 nm range • Actually tricky to measure in many samples; assume it is ~500 nm unless proven otherwise

  9. Connection between beam current and resolution TiCN; Cs+ primary beam 2 pA; 93 nm resolution TiCN; Cs+ primary beam <<1 pA; 22 nm resolution 1 µm 1 µm • Images sharpen by minimizing beam current and carefully tuning primary beam • Count rates decrease and errors increase in proportion to beam current

  10. Even carefully tuned images ‘broaden’ features you can see clearly by SEM Sub-micron rutile inclusion in zircon Work of Amy Hoffman

  11. The analyzer and detector array of the nanoSIMS are also distinctive High-dispersion multi-collection Six mobile collectors Fixed collector Minimum mass spacing—1:58 Maximum mass spacing —22:1 • Conceived of as a tool for elemental mapping with exact spatial correlation of measured species • Also enables true multi-collection of almost any element/element ratio

  12. Transmission and mass-resolving power Relative sensitivity (%) Mass resolving power Absolute sensitivity comparison Data from CIT nanoSIMS 50L; image from Frank Stadermann

  13. Design purpose: Composition mapping at µm scale Organic matter in 0.85 Ga Bitter Springs fm. Chert; Oehler et al., 2006 • Field of view: 200x200 µm in principle; 20x20 in practice. 10x10 or 5x5 is ideal • Discretization: 64x64 to 1024x1024; typically set so 1 pixel ~ beam radius

  14. Design purpose: Composition mapping at µm scale Science, 2006 • Fundamental data of interest is presence/absence of signal and spatial associations. Quantification is a secondary issue • Most imaging artifacts are of secondary importance and cannot be seen in scaled images

  15. Three dimensional ion imaging % 15N 3 5 Interior Edge Work of Anne Dekas

  16. Common tuning conditions for ‘spot’ analyses result in horrendous imaging artifacts Zr/Si ratio of zircon 0.2 94Zr/28Si 0.1 10 20 Distance (µm) • Clearly unacceptable for even semi-quantitative ion imaging • Must be corrected by tuning the primary beam octapole (‘stigmator’) and various immersion lens electrodes Work of Amy Hofmann

  17. Even after careful tuning for ‘flatness’, edge effects are generally still present After tuning for ‘flatness’ 0.2 94Zr/28Si Before tuning for ‘flatness’ 0.1 10 20 Distance (µm) • Improves by pre-sputtering large area and keeping image ≤ 10 µm • No recognized solution, other than ‘gating’ or culling data • May be obscured by saturation of images • Community should insist on demonstrations that stoichiometric ratios yield roughly ‘flat’ images in domains of interest Work of Amy Hofmann

  18. The accuracy of ‘good’ images 40Ca ion intensity image of Oka carbonatite Image ‘Spots’ 6.44E-3 6.52E-3 42Ca/40Ca Cps 88Sr/40Ca 2.42E-4 2.78E-4 ~ several% artifacts in average element and isotope abundance ratios are common Work of Alex Gagnon

  19. The accuracy of ‘good’ images Integrals of 20x20 µm ion images of carbonate standards and samples Oka carbonatite 1.2 88Sr+ 42Ca+ 0.8 BCC carbonatite standard 0.4 Coral 5 10 15 Sr/Ca (mmol/mol) • Images can provide quantitative data at ~% level accuracy with effort, but the community should insist that this accuracy is tested and demonstrated on a case- by-case basis Work of Alex Gagnon

  20. Where do spot measurements by nanoSIMS fit into our stable of tools for element/element ratio analysis? 100 ppm 1 % 1 ppm 10 % 1 % Precision (1 s.e.) 0.1 % 0.01 % 1µm 1mm 1nm 10-7 10-5 10-3 10-1 Spatial resolution (m) Concentration E-probe ATEM LA-ICPMS, conv. SIMS Bulk (e.g., solution ICP) M. Baker, pers. com; Cavosie et al., 2006; Klemme et al., 2008; Sobolev and Hofmann 2007; Hart and Cohen, 1997

  21. X = 1 m ‘Spot’ analyses of element/element ratios in carbonates Internal errors Various nominally homogeneous calcite standards; O- beam; 1-2 µm spots 24Mg/42Ca (100’s of ppm) 10 % 88Sr/42Ca (1000’s of ppm) 138Ba/42Ca (~1-10 ppm) Log (1 error) 1 % 2 3 4 5 Ni.Nj Ni + Nj ~ Ni for trace species Log (X0.5/X = external error for ratio [I]/[j]) Follows counting statistics down to ~3 ‰ 1.s.e. error, across a wide range in concentration Work of RinatGabitov

  22. There are limits imposed by drift in ratios during long sputtering Oka Carbonatite; analyzed on the NanoSIMS with a 2 µm rastered spot of O- 10 % Internal error (1 88Sr/42Ca 1 % 2 3 4 5 6 7 Ni.Nj Ni + Nj ~ Log (Ni)for trace species Log (X0.5/X = external error for ratio [I]/[j]) • Reflects gradual ‘drift’ in intensity and ratios after reaching nominal steady-state sputtering • Not sufficiently reproducible to correct completely by matching drift with standards • Appears to limit precision to no better than ~0.15 % 1 s.e., relative Work of Rinat Gabitov

  23. Point-to-point reproducibility 10 % Point-to-point reproducibility (1) 24Mg/42Ca 88Sr/42Ca 138Ba/42Ca 1 % 1 % 10 % Average internal error (1s.e.) • Tracks counting statistics errors down to ~0.3-1.0 %, 1 s.e. • Likely only applies to central half of 1” rounds and central 3/4 of 1 cm rounds • Illustrated data didn’t require heroic efforts at polishing, but normal caution regarding topography effects is appropriate

  24. Slopes of calibration curves vary session-to-session much more than for other SIMS instruments • This could reflect fractionations associated with changing the acceptance angle when the immersion lens stack is tuned • Session-to-session reproducibility for secondary standards (i.e., assuming given value for a primary standard) follows internal errors down to ~0.8 % 1 s.e..

  25. Many of the carbonate standards available for trace element measurements by SIMS are crap ID-ICPMS data for sub-samples AG-1, NBS-19, 135-CC, HUJ-AR & UCI-CC also examined • Oka is poor overall, but its calcite matrix has the best long-term reproducibility (±0.8 %) • BlueCC is a close second, and lacks ‘nuggets’ of exotic carbonates • All of the 7 other commonly used standards we explored are much worse • 1 %-level accuracy requires independent analysis of the same crystal

  26. Where do spot measurements by nanoSIMS fit into our stable of tools for element/element ratio analysis? 1µm 100 ppm 1 % 1mm 1 ppm 1nm 10 % 1 % NanoSIMS NanoSIMS Precision (1 s.e.) 0.1 % 0.01 % 10-7 10-5 10-3 10-1 10-9 10-8 10-7 10-6 10-5 10-4 10-3 Concentration Spatial resolution (m) E-probe ATEM LA-ICPMS, conv. SIMS nanoSIMS Bulk (e.g., solution ICP)

  27. Semi-quantitative imaging of growth banding in biogenic carbonates Foraminifera Surface coral Mg/Ca Kunioka, 2006 Meibom et al., 2004

  28. Intergrown CaCO3 and Ca0.55Mg0.45CO3 in a sea urchin’s tooth! 5x5 µm ion image Ma et al., 2009

  29. Extended example of applied use as a quantitative tool Experimental studies of vital effects 43Ca 1. 2. • Calcein marks start of growth during experiment; later layers should carry ‘spikes’ • The sub-micron resolution of the NanoSIMSreduces culture time from several months to a few days Gagnon et al.2013

  30. Ion images of overgrowths Calcein stain 43Ca/42Ca Demonstrations of image ‘flatness’ Gagnon et al., 2012

  31. A conceptual model of coral biomineralization (after McConnaughey) (extracellular calcifying fluid)

  32. Instantaneous 2 hrs Growth Axis Well-resolved gradients should measure residence time in ECF ‘mother liquor’ Budget for a metal in ECF 43Ca Flow out [Ca]SW [Ca] Flow in P 25Mg Precipitation External solution Precipitated carbonate Spike Natural Time Gagnon et al., 2012

  33. Measured growth rates are generally faster than can be resolved by beam width Model of a sharp boundary, given beam ‘broadening’ Calcium turnover time (1/2) is less than 2 hrs, possibly much faster Fastest growing measured foram 1/2 = 1.2 hrs

  34. Growth Axis Comparison of profiles should provide evidence for mechanisms of uptake Mg2+ Ca2+ Growth Axis

  35. Growth Axis Growth Axis Delivery of metals to site of growth appears to be dominated by transport of seawater to growing crystal surface specific pumping Uptake of 25Mg and 43Ca spikes seawater transport

  36. This conclusion is corroborated by uptake of spikes that are unlikely to be biologically ‘pumped’ across membranes 43Ca spike 159Tb spike Gagnon et al., 2012

  37. Extracting quantitative partition coefficients from ion images of ~µm overgrowths Corals grown over a range of carbonate-ion concentrations Gagnon et al., 2013

  38. Related work has demonstrated that growth zonation is controlled by variable extents of Rayleigh distillation on carbonate growth from ECF Flow in Flow out ECF Keqarag-fluid Precipitation Septa of deep-sea corals; Gagnon et al., 2007 Surface corals; Gaetani et al., 2011

  39. This advance creates the possibility that models of vital effects will be quantitative tools of paleoclimate reconstructions Flow in Flow out ECF Keqarag-fluid Precipitation Thermometry using implied Kd controlling the distillation fractionation Fit to Rayleigh distillation model Gaetani et al., 2011

  40. Using the NanoSIMS to unravel the thorny problem of diagenetic modifications Fossil 34-91; a Paleocene mollusk from the Bighorn Basin Modified aragonite growth plates Mix of secondary calcite and entombed growth plates Work of Katie Snell

  41. Using the NanoSIMS to unravel the thorny problem of diagenetic modifications Fossil 34-91; a Paleocene mollusk from the Bighorn Basin 55Mn16O/40Ca16O Work of Katie Snell

  42. Summary and parting thoughts • NanoSIMS may be uniquely suited to quantitative trace element analysis of carbonates with µm to sub-µm zonation (synchrotron µ-XRF may be comparable) • Imaging can yield several-per cent errors at scales down to 300 nm; much better is likely unrealistic • 0.8-1 % (1 s.e.) long-term external precision for ~1 µm domains are demonstrated and half that seems possible • Real limitation at present is poor quality of interlaboratory standards • Relatively casual standardization could easily result in ~10 % errors • There is no established community-wide practice for achieving and documenting precision and accuracy; for the time being, this needs to be approached as an experimental tool, and data in the literature should be approached with a ‘show me!’ attitude.

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