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Secondary fluorescence effects in microbeam analysis and their impacts on geospeedometry and geothermometry

Borisova, Anastassia Y. and Zagrtdenov, Nail R. and Toplis, Michael J. and Donovan, John J. and Llovet, Xavier and Asimow, Paul D. and de Parseval, Philippe and Gouy, Sophie (2018) Secondary fluorescence effects in microbeam analysis and their impacts on geospeedometry and geothermometry. Chemical Geology, 490 . pp. 22-29. ISSN 0009-2541. https://resolver.caltech.edu/CaltechAUTHORS:20180509-104511407

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Abstract

Characteristic and bremsstrahlung X-ray emission during electron-specimen interactions in electron microprobe (EPMA) and scanning electron microscope (SEM) instruments causes secondary fluorescence X-ray effects from adjacent (boundary) phases. This is well-known, yet the impact of such effects in microbeam analysis of natural mineral-hosted inclusions and adjacent to mineral-mineral and mineral-glass boundaries are frequently neglected, especially in geospeedometry and geothermometry applications. To demonstrate the important influence of the secondary fluorescence effect on the measured concentration of elements and its consequences for geochemical applications, we consider the effect of mineral-mineral and mineral-glass boundaries in microanalysis of Cr, Zr and Ti both experimentally, using electron probe measurements on cold-pressed material couples, and computationally, using the software suite “CalcZAF/Standard” and its Graphical User Interface (GUI) for the semi-analytical model FANAL (Llovet et al., 2012). We demonstrate, for example, that apparent Cr contents of the order of ~3000 to 5000 ppm in chromite-hosted glass inclusions at 6 μm from the inclusion boundary can be entirely due to secondary fluorescence in the Cr-rich host phase. Because the spatial gradient in secondary fluorescence-induced X-ray emission superficially resembles a diffusion profile, we emphasize the need to quantitatively correct for such effects in any geospeedometry application involving measurement of diffusion profiles adjacent to grain boundaries with large concentration contrasts. We also provide a scheme for estimating analytical errors related to the secondary fluorescence effect when applying geothermometers such as Ti-in-zircon, Ti-in-quartz (TitaniQ) and Zr-in-rutile. Temperature estimates based on trace Ti, Zr and Cr contents in minerals and glasses affected by secondary fluorescence in nearby phases (e.g., rutile, zircon and chromite) can be severely overestimated, in some cases by hundreds of degrees Celsius.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.chemgeo.2018.05.010DOIArticle
ORCID:
AuthorORCID
Asimow, Paul D.0000-0001-6025-8925
Additional Information:© 2018 Published by Elsevier B.V. Received 21 November 2017, Revised 16 March 2018, Accepted 7 May 2018, Available online 9 May 2018. A.Y.B. thanks Nadezhda Sushchevskaya, Michel Pichavant, Didier Beziat, Jim Webster, and Sebastian Meffre for providing glass and mineral samples. A.Y.B. thanks Sebastian Meffre for providing unpublished data on reference zircons (e.g., Mud Tank zircon). This work has been supported by ISIFoR (ADERA 450710) grant to A.Y.B. in 2017–2018.
Funders:
Funding AgencyGrant Number
ISIFoRADERA 450710
Subject Keywords:Secondary fluorescence effects; EMPA; SEM; Microanalysis of Cr, Zr and Ti; Ti-in zircon, Ti-in quartz (TitaniQ) and Zr-in rutile geothermometers; Mineral saturation, geospeedometry
Record Number:CaltechAUTHORS:20180509-104511407
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20180509-104511407
Official Citation:Anastassia Y. Borisova, Nail R. Zagrtdenov, Michael J. Toplis, John J. Donovan, Xavier Llovet, Paul D. Asimow, Philippe de Parseval, Sophie Gouy, Secondary fluorescence effects in microbeam analysis and their impacts on geospeedometry and geothermometry, Chemical Geology, Volume 490, 2018, Pages 22-29, ISSN 0009-2541, https://doi.org/10.1016/j.chemgeo.2018.05.010. (http://www.sciencedirect.com/science/article/pii/S0009254118302304)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:86308
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:09 May 2018 20:46
Last Modified:03 Oct 2019 19:42

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