Abstract
We present in situ microanalyses of Fe3+/ΣFe in mantle-derived kaersutites as measured by electron probe microanalysis (EMP) based on the “self absorption induced FeLα peak shift” method. The EMP results are not in agreement with bulk (wet chemistry) data. The heterogeneities revealed for some kaersutite megacrysts, when comparing bulk and EMP Fe3+/ΣFe results, cannot explain the differences with the EMP measurements. It is thus proposed that any EMP overestimation of Fe3+/ΣFe results from a beam-induced dehydrogenation and a subsequent oxidation of Fe2+ to Fe3+ according to the known relation: Fe2+ + OH- = Fe3+ + O2- + 1/2 H2. To demonstrate this phenomenon, H losses were measured by secondary ion mass spectrometry (SIMS) after EMP irradiation at different beam currents on two amphiboles with 1.1 and 1.7 wt% H2O, respectively. In both amphiboles, H losses were observed under high beam currents (240 and 100 nA). No dehydrogenation is observed under lower beam currents for the 1.1 wt% H2O amphibole, but still occurs, down to at least 50 nA, for the amphibole with the greatest H2O contents. Amphiboles with low H2O contents (below ~0.5 H+) are less affected by beam damage. For amphiboles with higher H2O contents, the electron beam current density should be reduced with consideration given to the resulting high statistical errors.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Hydrothermal synthesis of hematite spherules and jarosite: Implications for diagenesis and hematite spherule formation in sulfate outcrops at Meridiani Planum, Mars
- Concentric slow cooling of a low-P–high-T terrane: Evidence from 1600–1300 Ma mica dates in the 1780–1700 Ma Black Hills Orogen, South Dakota, U.S.A.
- Monazite ages from carbonatites and high-grade assemblages along the Kambam Fault (Southern Granulite Terrane, South India)
- Forward modeling of the effects of mixed volatile reaction, volume diffusion, and formation of submicroscopic exsolution lamellae on calcite-dolomite thermometry
- A low-temperature phase diagram for ilmenite-rich compositions in the system Fe2O3-FeTiO3
- Dehydrogenation of kaersutitic amphibole under electron beam excitation recorded by changes in Fe3+/ΣFe: An EMP and SIMS study
- Protonation in germanium equivalents of ringwoodite, anhydrous phase B, and superhydrous phase B
- Andreyivanovite: A second new phosphide from the Kaidun meteorite
- The crystal chemistry of whitlockite and merrillite and the dehydrogenation of whitlockite to merrillite
- Single-crystal elastic properties of (Mg0.987,Fe0.013)O to 9 GPa
- Stoichiometry of synthetic ulvöspinel single crystals
- Thermal behavior and structural transformation in the chabazite-type zeolite willhendersonite, KCaAl3Si3O12·5H2O
- The kinetics and mechanisms of schwertmannite transformation to goethite and hematite under alkaline conditions
- Crystal chemistry of the mixed-layer sequence talc–talc-smectite–smectite from submarine hydrothermal vents
- Crystal chemical and structural characterization of fibrous tremolite from Susa Valley, Italy, with comments on potential harmful effects on human health
- Thermodynamic properties of CaTh(PO4)2 synthetic cheralite
- A computational study of order-disorder phenomena in Mg2TiO4 spinel (qandilite)
- Mineralogical characterization of silica sinters from the El Tatio geothermal field, Chile
- Influence of multi-electron excitation on EXAFS spectroscopy of trivalent rare-earth ions and elucidation of change in hydration number through the series
- Pressure-induced over-hydration and water ordering in gismondine: A synchrotron powder diffraction study
- 57Fe Mössbauer study of the oxidation state of iron in stilpnomelane from granite pegmatites in Poland
- Constraints on structural models of ferrihydrite as a nanocrystalline material
- Pb+ irradiation of synthetic zircon (ZrSiO4): Infrared spectroscopic investigation
- Equation of state and crystal structure of a new germanate post-titanite phase
- Synthetic hypersilicic Cl-bearing mica in the phlogopite-celadonite join: A multimethodical characterization of the missing link between di- and tri-octahedral micas at high pressures
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