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Isotopic Measurements with the Cameca ims 1280 Ion Microprobe at the University of Hawai‘i

Isotopic Measurements with the Cameca ims 1280 Ion Microprobe at the University of Hawai‘i. Gary R. Huss, Kazu Nagashima, Sasha Krot, Kentaro Makide, and Lydie Bonal W. M. Keck Cosmochemistry Laboratory University of Hawai‘i at Manoa. Isotopic Systems Studied at UH. Oxygen isotopes*

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Isotopic Measurements with the Cameca ims 1280 Ion Microprobe at the University of Hawai‘i

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  1. Isotopic Measurements with the Cameca ims 1280 Ion Microprobe at the University of Hawai‘i Gary R. Huss, Kazu Nagashima, Sasha Krot, Kentaro Makide, and Lydie Bonal W. M. Keck Cosmochemistry Laboratory University of Hawai‘i at Manoa

  2. Isotopic Systems Studied at UH • Oxygen isotopes* • 26Al-26Mg systematics* • 60Fe-60Ni systematics* • 53Mn-53Cr systematics • Carbon isotopes • Nitrogen isotopes • Hydrogen isotopes • Isotope ratio imaging (scanning ion imaging)

  3. Oxygen Isotopes • CAIs from CR, CH, CV chondrites* • FUN CAIs from CV chondrites* • Carbonates from lithic clasts in Isheyevo • Type II chondrules from CR chondrites • Chondrules from CH and CB chondrites

  4. Oxygen Isotopes in FUN CAIs Data from Clayton et al. (1977, EPSL 34, 209), Clayton et al. (1977, GRL 4, 295), Lee et al. (1980, GRL 7, 493), Clayton et al. (1984, GCA 48, 535), McKeegan et al. (2005, LPSC 36, 2077).

  5. Oxygen Isotopes in FUN CAIs DH8 (Type B), Allende Normal CAIs from CR chondrites KT-1 (Type B), NWA 779 Makide et al. (2008) Krot et al. (2008)

  6. Oxygen Isotopes: Standards • Standards are critically important for calibrating instrumental mass fractionation (IMF) and determining accurate oxygen isotopic compositions • At UH, we have standards for • Olivines of several compositions • Spinel • Pyroxenes of several compositions • Quartz* • Garnet* • Calcite*, dolomite*, siderite* * Many of these generously provided by the WiscSIMS Laboratory

  7. Oxygen Isotopes: Standards • We need or are working on standards for • Melilite or melilite glass of several compositions • Ca-Al oxides • Wollastonite • Intermediate olivines • Tochilinite • Magnetite • Magnesite • When we develop a standard, we will try to prepare enough to share with other SIMS labs.

  8. 26Al-26Mg Systematics • CAIs from CR chondrites* • CAIs from CV chondrites* • FUN CAIs from CV chondrites • Chondrules from CR chondrites • Chondrules from ordinary chondrites

  9. 26Al-26Mg Systematics Compact Type A CAI, 2-A1 from Kaba (CV3) (26Al/27Al)0=(4.95±0.62)x10-5 26Mg* (‰) 26Mg)0= -0.47±0.76 27Al/24Mg Nagashima et al. (2007)

  10. 26Al-26Mg Systematics: Improving the Precision of the Isochron • High sensitivity of 1280 can improve precision • Employ multicollection where possible • Automated beam centering and careful measurement protocol improves reproducibility • Correct instrumental mass fractionation (IMF) and account for intrinsic mass fractionation separately • Correct IMF using standard-sample bracketing • Calculate 26Mg* using appropriate fractionation law • Use appropriate standards to correct for relative sensitivities of Al and Mg

  11. Al-Mg Sensitivity Factors Makide et al. (2008)

  12. Mass Fractionation of Magnesium Makide et al. (2008)

  13. Measuring of Mass Fractionation of Mg • Good statistical precision • Good sample preparation • Measure samples and standards with the same primary beam current and shape and with same measurement time. • Tight control over ion extraction and beam path in secondary ion mass spectrometer • Well-characterized, matrix-matched standards to estimate IMF and point-to-point variability • Demonstrated long-term reproducibility • Residual uncertainty: Do samples and standards behave in precisely the same way?

  14. 26Al-26Mg: Standards • Isotopically characterized, matrix-matched standards for Mg isotopes to determine instrumental and intrinsic mass fractionation and to identify 26Mg* • Assuming the published Mg composition for natural samples may not be enough • Matrix-matched standards for relative sensitivity factors • Complete suite for cosmochemistry should include • Spinel, hibonite, Ca-Al oxides • Olivines and pyroxenes of various compositions • Melilites of various compositions • Plagioclase (with Al/Mg ~ 100) • Glasses of different compositions

  15. 60Fe-60Ni Systematics • Sulfides from ordinary chondrites • Chondrules from ordinary chondrites* • Fayalite from CV chondrites • Chondrules from CR chondrites

  16. 60Fe-60Ni Systematics: Sulfides in Unequilibrated Ordinary Chondrites Krymka 26.5 25.5 24.5 23.5 22.5 60Ni/61Ni 0 4 8 12 16 56Fe/61Ni (x106) (60Fe/56Fe)0 = (1.81± 0.72) x10-7 Tachibana and Huss (2003)

  17. 60Fe-60Ni Systematics: Pyroxene Chondrules in Unequilibrated Ordinary Chondrites (60Fe/56Fe)0 = (2.2~3.7) x 10-7 Tachibana et al. (2006)

  18. 60Fe-60Ni Systematics: Porphyritic Chondrules in UOCs 23.6 23.4 23.2 23.0 60Ni/61Ni 0 0.2 0.4 0.6 0.8 1.0 1.2 56Fe/61Ni (x106) (60Fe/56Fe)0 = (1.7 ± 1.1) x10-7 Semarkona SMK3-6 Huss et al. (2007) Tachibana et al. (2007)

  19. 60Fe-60Ni Systematics: Next Steps • Improve precision of the data • Develop multicollection (in progress) • Higher transmission in secondary mass spectrometer • Brute force (measure longer) • Develop a complete suite of appropriate standards • Find better samples to measure

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