Hostname: page-component-78c5997874-fbnjt Total loading time: 0 Render date: 2024-11-10T07:21:40.345Z Has data issue: false hasContentIssue false
  • English
  • Français

Multipoint Background Analysis: Gaining Precision and Accuracy in Microprobe Trace Element Analysis

Published online by Cambridge University Press:  12 February 2019

Julien M. Allaz Open the ORCID record for Julien M. Allaz [Opens in a new window] ,
Michael L. Williams ,
Michael J. Jercinovic ,
Karsten Goemann  and
John Donovan
Julien M. Allaz*
Affiliation:
Department of Geological Sciences, University of Colorado Boulder, 2200 Colorado Avenue, Boulder, CO 80309-0399, USA Department of Geosciences, University of Massachusetts Amherst, 611 North Pleasant Street, 233 Morrill Science Center, Amherst, MA01003-9297, USA
Michael L. Williams
Affiliation:
Department of Geosciences, University of Massachusetts Amherst, 611 North Pleasant Street, 233 Morrill Science Center, Amherst, MA01003-9297, USA
Michael J. Jercinovic
Affiliation:
Department of Geosciences, University of Massachusetts Amherst, 611 North Pleasant Street, 233 Morrill Science Center, Amherst, MA01003-9297, USA
Karsten Goemann
Affiliation:
University of Tasmania, Central Science Laboratory, Dobson Road, Sandy Bay, TAS 7005, Australia
John Donovan
Affiliation:
University of Oregon, CAMCOR, 1443 E. 13th Av., Eugene, OR 97403, USA
*
*Author for correspondence: Julien M. Allaz, E-mail: julien.allaz@erdw.ethz.edu
Get access

Abstract

Electron microprobe trace element analysis is a significant challenge. Due to the low net intensity of peak measurements, the accuracy and precision of such analyses relies critically on background measurements, and on the accuracy of any pertinent peak interference corrections. A linear regression between two points selected at appropriate background positions is a classical approach for electron probe microanalysis (EPMA). However, this approach neglects the accurate assessment of background curvature (exponential or polynomial), and the presence of background interferences, a hole in the background, or an absorption edge can dramatically affect the results if underestimated or ignored. The acquisition of a quantitative wavelength-dispersive spectrometry (WDS) scan over the spectral region of interest remains a reasonable option to determine the background intensity and curvature from a fitted regression of background portions of the scan, but this technique can be time consuming and retains an element of subjectivity, as the analyst has to select areas in the scan which appear to represent background. This paper presents a new multi-point background (MPB) method whereby the background intensity is determined from up to 24 background measurements from wavelength positions on either side of analytical lines. This method improves the accuracy and precision of trace element analysis in a complex matrix through careful regression of the background shape, and can be used to characterize the background over a large spectral region covering several elements to be analyzed. The overall efficiency improves as systematic WDS scanning is not required to assess background interferences. The method is less subjective compared to methods that rely on WDS scanning, including selection of two interpolation points based on WDS scans, because “true” backgrounds are selected through an exclusion method of possible erroneous backgrounds. The first validation of the MPB method involves blank testing to ensure the method can accurately measure the absence of an element. The second validation involves the analysis of U-Th-Pb in several monazite reference materials of known isotopic age. The impetus for the MPB method came from efforts to refine EPMA monazite U-Th-Pb dating, where it was recognized that background errors resulting from interference or strong background curvature could result in errors of several tens of millions of years on the calculated date. Results obtained on monazite reference materials using two different microprobes, a Cameca SX-100 Ultrachron and a JEOL JXA-8230, yield excellent agreement with ages obtained by isotopic methods (Thermal Ionization Mass Spectrometry [TIMS], Sensitive High-Resolution Ion MicroProbe [SHRIMP], or Secondary Ion Mass Spectrometry [SIMS]). Finally, the MPB method can be used to model the background over a large spectrometer range to improve the accuracy of background measurement of minor and trace elements acquired on a same spectrometer, a method called the shared background measurement. This latter significantly improves the accuracy of minor and trace element analysis in complex matrices, as demonstrated by the analysis of Rare Earth Elements (REE) in REE-silicates and phosphates and of trace elements in scheelite.

Keywords

Bremsstrahlungelectron probe microanalysismonazite datingtrace element analysiswavelength-dispersive spectrometry
Type
Materials Science Applications
Information
Microscopy and Microanalysis , Volume 25 , Issue 1 , February 2019 , pp. 30 - 46
Copyright
Copyright © Microscopy Society of America 2019 

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

Footnotes

†

Current address: ETH Zürich, Department of Earth Sciences, Inst. für Geochemie und Petrologie, Clausiusstrasse 25, 8092 Zürich, Switzerland

This paper is dedicated to the memory of Professor Robert J. Tracy (October 2, 1944 – January 6, 2019), a colleague, a friend, a monazite lover, and a great microprobe specialist

References

Allaz, J, Selleck, B, Williams, ML & Jercinovic, MJ (2013). Microprobe analysis and dating of monazite from the Potsdam Formation, New York: A progressive record of chemical reaction and fluid interaction. Am Mineral 98, 1106–1119.Google Scholar
Carpenter, P, Counce, D, Kluk, E & Nabelek, C (2002). Characterization of Corning EPMA standard glasses 95IRV, 95IRW, and 95IRX. J Res Natl Inst Stand Technol 107(6), 703–718.Google Scholar
Cherniak, DJ, Pyle, J & Rakovan, J (2004). Synthesis of REE and Y phosphates by Pb-free flux methods and their utilization as standards for electron microprobe analysis and in design of monazite chemical U-Th-Pb dating protocol. Am Mineral 89(10), 1533–1539.Google Scholar
Donovan, JJ, Lowers, HA & Rusk, BG (2011). Improved electron probe microanalysis of trace elements in quartz. Am Mineral 96, 274–282.Google Scholar
Donovan, JJ, Singer, JW & Armstrong, JT (2016). A new EPMA method for fast trace element analysis in simple matrices. Am Mineral 101(8), 1839–1853.Google Scholar
Donovan, JJ & Tingle, TN (1996). An improved mean atomic number background correction for quantitative microanalysis. J Microsc Microanal 2, 1–7.Google Scholar
Duane, W & Hunt, FL (1915). On X-ray wave-lengths. Phys Rev 6(2), 166–172.Google Scholar
Dumond, G, McLean, N, Williams, ML, Jercinovic, MJ & Bowring, SA (2008). High-resolution dating of granite petrogenesis and deformation in a lower crustal shear zone: Athabasca granulite terrane, western Canadian Shield. Chem Geol 254, 175–196.Google Scholar
Dutch, RA (2009). Monazite chemical dating via electron probe microanalysis. MESA J 53, 34–40.Google Scholar
Fialin, M, Rémy, H, Richard, C & Wagner, C (1999). Trace element analysis with the electron microprobe: New data and perspectives. Am Mineral 84, 70–77.Google Scholar
Fiori, CE, Myklebust, RL, Heinrich, KFJ & Yakowitz, H (1976). Prediction of continuum intensity in energy-dispersive x-ray microanalysis. Anal Chem 48, 172–176.Google Scholar
Goldstein, JI, Newbury, DE, Echlin, P, Joy, DC, Lyman, CE, Lifshin, E, Sawyer, L & Michael, JR (2003). Scanning Electron Microscopy and X-ray Microanalysis. New York, NY: Springer Science+Business Media New York.Google Scholar
Geisler, T & Schleicher, H (2000). Improved U-Th-total Pb dating of zircons by electron microprobe using a simple new background modeling procedure and Ca as a chemical criterion of fluid-induced U-Th-Pb discordance in zircon. Chem Geol 163, 269–285.Google Scholar
Hietpas, J, Samson, S, Moecher, D & Schmitt, AK (2010). Recovering tectonic events from the sedimentary record: Detrital monazite plays in high fidelity. Geology 38, 167–170.Google Scholar
Janots, E, Engi, M, Rubatto, D, Berger, A, Gregory, C & Rahn, MK (2009). In-situ determination of heating rates in collisional orogeny. Geology 37, 11–14.Google Scholar
Jercinovic, MJ, Williams, ML, Allaz, J & Donovan, JJ (2012). Trace analysis in EPMA. IOP Conf Ser: Mater Sci Eng 32, 1–22.Google Scholar
Jercinovic, MJ, Williams, ML & Lane, ED (2008). In-situ trace element analysis of monazite and other fine-grained accessory minerals by EPMA. Chem Geol 254, 197–215.Google Scholar
Jercinovic, MJ & Williams, ML (2005). Analytical perils (and progress) in electron microprobe trace element analysis applied to geochronology: Background acquisition, interferences, and beam irradiation effects. Am Mineral 90, 526–546.Google Scholar
Kato, T & Suzuki, K (2014). “Background holes” in X–ray spectrometry using a pentaerythritol (PET) analyzing crystal. J Mineral Petrol Sci 109, 151–155.Google Scholar
Kramers, HA (1923). On the theory of X-ray absorption and of the continuous X- ray spectrum. Philos Mag 46, 836–871.Google Scholar
Llovet, X. & Salvat, F. (2016). PENEPMA: A Monte Carlo programme for the simulation of X-ray emission in EPMA. IOP Conf Ser: Mater Sci Eng 109(1).Google Scholar
Mahan, KH, Goncalves, P, Williams, ML & Jercinovic, MJ (2006). Dating metamorphic reactions and fluid flow: Application to exhumation of high-P granulites in a crustal-scale shear zone, western Canadian Shield. J Metamorph Geol 24, 193–217.Google Scholar
Mahan, KH, Wernicke, BP & Jercinovic, MJ (2010). Th–U–total Pb geochronology of authigenic monazite in the Adelaide rift complex, South Australia, and implications for the age of the type Sturtian and Marinoan glacial deposits. Earth Planet Sci Lett 289, 76–86.Google Scholar
Merlet, C & Bodinier, JL (1990). Electron microprobe determination of minor and trace transition elements in silicate minerals: A method and its application to mineral zoning in the peridotite nodule PHN 1611. Chem Geol 83(1–2), 55–69.Google Scholar
Montel, J-M, Foret, S, Veschambre, M, Nicollet, C & Provost, A (1996). Electron microprobe dating of monazite. Chem Geol 131, 37–53.Google Scholar
Pyle, JM, Spear, FS, Wark, DA, Daniel, CG & Storm, LC (2005). Contributions to precision and accuracy of monazite microprobe ages. Am Mineral 90, 547–577.Google Scholar
Reed, SJB (1975). The shape of the continuum X-ray spectrum and background corrections for energy-dispersive electron microprobe analysis. X-Ray Spectrom 4, 14–17.Google Scholar
Reed, SJB (1993). Electron Microprobe Analysis. Cambridge, UK: Cambridge University Press.Google Scholar
Reed, SJB (2000). Approaches to “standardless” wavelength dispersive analysis. Microsc Microanal 6, 145–149.Google Scholar
Reed, SJB & Buckley, A (1996). Virtual WDS. Mikrochimica Acta [Suppl.] 13, 479–483.Google Scholar
Rémond, G, Myklebust, R, Fialin, M, Nockolds, C, Phillips, M & Roques- Carmes, C (2002) Decomposition of wavelength dispersive X-Ray spectra. J Res Natl Inst Stand Technol 107, 509–529.Google Scholar
Reno, BL, Piccoli, PM, Brown, M & Trouw, RAJ (2012). In situ monazite (U–Th)–Pb ages from the Southern Brası Brazil: Constraints on the high-temperature retrograde evolution of HP granulites. J Metamorph Geol 30, 81–112.Google Scholar
Scott, VD & Love, G (1983). Quantitative Electron-Probe Microanalysis. New York, NY: Wiley.Google Scholar
Self, PG, Norrish, K, Milnes, AR, Graham, J & Robinson, B (1990). Holes in the background in XRS. X-Ray Spectrom 19, 59–61.Google Scholar
Simmons, WB & Heinrich, EW (1980). Rare-Earth pegmatites of the South Platte District, Colorado. Colorado Geol Surv Resource Series 11, 138.Google Scholar
Smith, DGW, Gold, CM & Tomlinson, DA (1975). The atomic number dependence of the X-ray continuum intensity and the practical calculation of background in energy dispersive electron microprobe analysis. X-Ray Spectrom 4, 149–156.Google Scholar
Smith, DGW & Reed, SJB (1981). The calculation of background in wavelength-dispersive electron microprobe analysis. X-Ray Spectrom 10, 198–202.Google Scholar
Sommerfeld, A (1931). Über die Beugung und Bremsung der Elektronen. Ann Phys 403, 257–330.Google Scholar
Spear, FS, Pyle, JM & Cherniak, DJ (2009). Limitations of chemical dating of monazite. Chem Geol 266, 218–230.Google Scholar
Stern, RA & Rayner, NM (2003). Ages of several xenotime megacrysts by ID-TIMS: Potential reference materials for ion microprobe U-Pb geochronology. Geol Surv Canada, Curr Res 2003-F1, 7.Google Scholar
Suzuki, K & Kato, T (2008). CHIME dating of monazite, xenotime, zircon and polycrase: Protocol, pitfalls and chemical criterion of possibly discordant age data. Gondwana Res 14, 569–586.Google Scholar
Trincavelli, J, Limandri, S, Carreras, A & Bonetto, R (2008). Experimental method to determine the absolute efficiency curve of a wavelength dispersive spectrometer. Microsc Microanal 14, 306–314.Google Scholar
Tucker, RD, Krogh, TE & Råheim, A (1990). Proterozoic evolution and age-province boundaries in the central part of the Western Gneiss Region, Norway: Results of U-Pb dating of accessory minerals from Trondheimsfjord to Geiranger. Geol Assoc Canada Spec Paper 38, 149–173.Google Scholar
Williams, ML, Jercinovic, MJ, Goncalves, P & Mahan, KH (2006). Format and philosophy for collecting, compiling, and reporting microprobe monazite ages. Chem Geol 225, 1–15.Google Scholar
Williams, ML, Jercinovic, MJ & Hetherington, CJ (2007). Microprobe monazite geochronology: Understanding geologic processes by integrating composition and chronology. Ann Rev Earth Planet Sci 35, 137–175.Google Scholar
Supplementary material: File

Allaz et al. supplementary material

Allaz et al. supplementary material 1

Download Allaz et al. supplementary material(File)
File 3.7 MB