Isotopic Measurements with the Cameca ims 1280 Ion

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* • 26 Al-26 Mg systematics* • 60 Fe-60 Ni systematics* • 53 Mn-53 Cr systematics • Carbon isotopes • Nitrogen isotopes • Hydrogen isotopes • Isotope ratio imaging (scanning ion imaging)

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

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), Mc. Keegan et al. (2005, LPSC 36, 2077).

Oxygen Isotopes in FUN CAIs DH 8 (Type B), Allende Normal CAIs from CR chondrites KT-1 (Type B), NWA 779 Makide et al. (2008) Krot et al. (2008)

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 Wisc. SIMS Laboratory

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.

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

26 Al-26 Mg Systematics Compact Type A CAI, 2 -A 1 from Kaba (CV 3) 26 Mg* (‰) (26 Al/27 Al)0=(4. 95± 0. 62)x 10 -5 26 Mg)0= -0. 47± 0. 76 27 Al/24 Mg Nagashima et al. (2007)

26 Al-26 Mg 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 26 Mg* using appropriate fractionation law • Use appropriate standards to correct for relative sensitivities of Al and Mg

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

Mass Fractionation of Magnesium Makide et al. (2008)

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?

26 Al-26 Mg: Standards • Isotopically characterized, matrix-matched standards for Mg isotopes to determine instrumental and intrinsic mass fractionation and to identify 26 Mg* – 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

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

60 Fe-60 Ni Systematics: Sulfides in Unequilibrated Ordinary Chondrites Krymka 60 Ni/61 Ni 26. 5 25. 5 24. 5 23. 5 22. 5 0 4 8 56 Fe/61 Ni 12 (x 106) (60 Fe/56 Fe)0 = (1. 81± 0. 72) x 107 Tachibana and Huss (2003) 16

60 Fe-60 Ni Systematics: Pyroxene Chondrules in Unequilibrated Ordinary Chondrites Tachibana et al. (2006) (60 Fe/56 Fe)0 = (2. 2~3. 7) x 10 -7

60 Fe-60 Ni Systematics: Porphyritic Chondrules in UOCs 60 Ni/61 Ni 23. 6 23. 4 23. 2 23. 0 0 0. 2 0. 4 0. 6 0. 8 1. 0 1. 2 56 Fe/61 Ni (x 106) (60 Fe/56 Fe)0 = (1. 7 ± 1. 1) x 10 -7 Huss et al. (2007) Semarkona SMK 3 -6 Tachibana et al. (2007)

60 Fe-60 Ni 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