High-precision Mg isotope measurements of terrestrial and extraterrestrial material by HR-MC-ICPMS—implications for the relative and absolute Mg isotope composition of the bulk silicate Earth
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High-precision Mg isotope measurements of terrestrial and extraterrestrial material by HR-MC-ICPMS—implications for the relative and absolute Mg isotope composition of the bulk silicate Earth. / Bizzarro, Martin; Paton, Chad; Larsen, Kirsten Kolbjørn; Schiller, Martin; Trinquier, Anne Marie-Pierre Emilie; Ulfbeck, David Garf.
In: Journal of Analytical Atomic Spectrometry, Vol. 26, No. 3, 2011, p. 565-577.Research output: Contribution to journal › Journal article › Research › peer-review
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T1 - High-precision Mg isotope measurements of terrestrial and extraterrestrial material by HR-MC-ICPMS—implications for the relative and absolute Mg isotope composition of the bulk silicate Earth
AU - Bizzarro, Martin
AU - Paton, Chad
AU - Larsen, Kirsten Kolbjørn
AU - Schiller, Martin
AU - Trinquier, Anne Marie-Pierre Emilie
AU - Ulfbeck, David Garf
PY - 2011
Y1 - 2011
N2 - We report novel methods for the chemical purification of Mg from silicate rocks by ion-exchange chromatography, and high-precision analysis of Mg-isotopes by high-resolution multiple collector inductively coupled plasma source mass spectrometry (HR-MC-ICPMS). Using these methods, we have measured the relative and absolute Mg-isotope composition of a number of terrestrial and extraterrestrial materials, including international reference rock standards as well as pure Mg standards, olivine crystals separated from a mantle-derived spinel lherzolite (J12 olivine), one enstatite chondrite, a martian shergottite and sea water samples. Repeated analyses of terrestrial and extraterrestrial samples demonstrate that it is possible to routinely measure the relative Mg-isotope composition of silicate materials with an external reproducibility of 2.5 and 20 ppm for the m26Mg* and m25Mg values, respectively (m notation is the per 106 deviation from a reference material). Analyses of bulk mantle-derived rocks as well as a martian shergottite and an enstatite chondrite define a restricted range in m25Mg of ¿120 ¿ 28 ppm (2sd) relative to the DSM-3 reference standard (m25,26Mg 1/4 0), suggesting that the Mg-isotope composition of inner solar system bulk planetary materials is uniform within the resolution of our analyses. We have determined the absolute Mg-isotope composition of the J12 olivine, two CI chondrites as well as the DSM-3 and Cambridge-1 reference standards usinga mixed 26Mg-24Mg double-spike. The differences between the absolute 25Mg/24Mg ratios of the various materials analyzed relative to the DSM-3 standard are in excellent agreement with results obtained by the sample-standard bracketing method. Based on the averages obtained for the J12 olivine separates, we estimate the absolute Mg-isotope composition for Earth’s mantle – and hence that of the bulk silicate Earth – to be 25Mg/24Mg 1/4 0.126896 ¿ 0.000025 and 26Mg/24Mg 1/4 0.139652 ¿ 0.000033. Given the restricted range of m25Mg obtained for bulk planetary material by the sample-standard bracketing technique and the excellent agreement between the data obtained by the relative and absolute methods, we propose that these new values represent the absolute Mg-isotope composition of the bulk inner solar system. Using the absolute Mg-isotope composition of the J12 olivine, we calculate the isotopic abundances of Mg as 24Mg 1/4 0.789548 ¿ 0.000026, 25Mg 1/4 0.100190 ¿ 0.000018, and 26Mg 1/4 0.110261 ¿ 0.000023. Based on this result, we have calculated an atomic weight for Mg of 24.305565 ¿ 0.000045,which is marginally heavier than previous estimates but a factor of 10 more precise.
AB - We report novel methods for the chemical purification of Mg from silicate rocks by ion-exchange chromatography, and high-precision analysis of Mg-isotopes by high-resolution multiple collector inductively coupled plasma source mass spectrometry (HR-MC-ICPMS). Using these methods, we have measured the relative and absolute Mg-isotope composition of a number of terrestrial and extraterrestrial materials, including international reference rock standards as well as pure Mg standards, olivine crystals separated from a mantle-derived spinel lherzolite (J12 olivine), one enstatite chondrite, a martian shergottite and sea water samples. Repeated analyses of terrestrial and extraterrestrial samples demonstrate that it is possible to routinely measure the relative Mg-isotope composition of silicate materials with an external reproducibility of 2.5 and 20 ppm for the m26Mg* and m25Mg values, respectively (m notation is the per 106 deviation from a reference material). Analyses of bulk mantle-derived rocks as well as a martian shergottite and an enstatite chondrite define a restricted range in m25Mg of ¿120 ¿ 28 ppm (2sd) relative to the DSM-3 reference standard (m25,26Mg 1/4 0), suggesting that the Mg-isotope composition of inner solar system bulk planetary materials is uniform within the resolution of our analyses. We have determined the absolute Mg-isotope composition of the J12 olivine, two CI chondrites as well as the DSM-3 and Cambridge-1 reference standards usinga mixed 26Mg-24Mg double-spike. The differences between the absolute 25Mg/24Mg ratios of the various materials analyzed relative to the DSM-3 standard are in excellent agreement with results obtained by the sample-standard bracketing method. Based on the averages obtained for the J12 olivine separates, we estimate the absolute Mg-isotope composition for Earth’s mantle – and hence that of the bulk silicate Earth – to be 25Mg/24Mg 1/4 0.126896 ¿ 0.000025 and 26Mg/24Mg 1/4 0.139652 ¿ 0.000033. Given the restricted range of m25Mg obtained for bulk planetary material by the sample-standard bracketing technique and the excellent agreement between the data obtained by the relative and absolute methods, we propose that these new values represent the absolute Mg-isotope composition of the bulk inner solar system. Using the absolute Mg-isotope composition of the J12 olivine, we calculate the isotopic abundances of Mg as 24Mg 1/4 0.789548 ¿ 0.000026, 25Mg 1/4 0.100190 ¿ 0.000018, and 26Mg 1/4 0.110261 ¿ 0.000023. Based on this result, we have calculated an atomic weight for Mg of 24.305565 ¿ 0.000045,which is marginally heavier than previous estimates but a factor of 10 more precise.
U2 - 10.1039/c0ja00190b
DO - 10.1039/c0ja00190b
M3 - Journal article
VL - 26
SP - 565
EP - 577
JO - Journal of Analytical Atomic Spectrometry
JF - Journal of Analytical Atomic Spectrometry
SN - 0267-9477
IS - 3
ER -
ID: 33806689