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Improvement in matrix correction of δ18O analysis by SIMS for … · 2015-06-08 · ˚(Ca) + c Ca˛ Mn STDs: Sps-4, Sps-3, UWPp-1 Bias Mn = a Mn ˚(Mn)2 + b Mn ˚(Mn) + c Mn STDs:

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Text of Improvement in matrix correction of δ18O analysis by SIMS for … · 2015-06-08 · ˚(Ca) + c...

  • ReferencesIckert, R.B., Stern, R.A., 2013. Matrix Corrections and Error Analysis in High-Precision SIMS 18O/16O Measurements of Ca–Mg–Fe Garnet. Geostand. Geoanalytical Res. 37, 429–448. doi:10.1111/j.1751-908X.2013.00222.xKita, N.T., Ushikubo, T., Fu, B., Valley, J.W., 2009. High precision SIMS oxygen isotope analysis and the effect of sample topography. Chem. Geol. 264, 43–57.Martin, L.A.J., Rubatto, D., Crépisson, C., Hermann, J., Putlitz, B., Vitale-Brovarone, A., 2014. Garnet oxygen analysis by SHRIMP-SI: Matrix corrections and application to high-pressure metasomatic rocks from Alpine Corsica. Chem. Geol. 374-375, 25–36.

    doi:10.1016/j.chemgeo.2014.02.010Page, F.Z., Kita, N.T., Valley, J.W., 2010. Ion microprobe analysis of oxygen isotopes in garnets of complex chemistry. Chem. Geol. 270, 9–19.Raimondo, T., Clark, C., Hand, M., Cliff, J., Harris, C., 2012. High-resolution geochemical record of fluid-rock interaction in a mid-crustal shear zone: a comparative study of major element and oxygen isotope transport in garnet. J. Metamorph. Geol. 30,

    255–280. doi:10.1111/j.1525-1314.2011.00966.xVielzeuf, D., Champenois, M., Valley, J.W., Brunet, F., Devidal, J.L., 2005. SIMS analyses of oxygen isotopes: Matrix effects in Fe–Mg–Ca garnets. Chem. Geol. 223, 208–226. doi:http://dx.doi.org/10.1016/j.chemgeo.2005.07.008

    SummaryMagnitude of the matrix correction for Cr concentration is 1.9‰ at 13.4wt.% Cr2O3The 2SD of residual after this matrix correction applied (0.33‰) is better than the value if we simply apply the XGrs correction with all standards (0.75‰)Matrix correction scheme for pyralspite garnet needs only 7 calibration standardsBiases of pyralspite garnets are well described by sum of the biases derived from each component (Ca, Mn, Fe2+)

    Cr-pyrope

    XCr

    0.0 0.1 0.2 0.3 0.4

    0.0

    0.5

    1.0

    1.5

    2.0

    2.5

    Bias

    rel.

    to U

    WG

    -2 [‰

    ]

    0.0 0.2 0.4 0.6 0.8 1.02

    1

    0

    1

    2

    3

    XGrs

    Bias

    rel.

    to U

    WG

    -2 [‰

    ]

    For Cr-pyrope garnets, after applying the correction based on grossular content, the calibration curve for Cr-pyrope garnets using new standards reveals that the magnitude of the matrix correction for Cr concentration is ~ 1.9‰ at 13.4 wt.% Cr2O3 (XCr = 0.394). XCr is defined by Cr/(Al+Ti+Fe3++Cr). XGrs is end-member (grossular) propostions.

    Fitting Parameters

    a b cRSS Max Offset 2SD of Residual

    Ca

    Mn

    Fe2+

    XGrs(Page et al., 2010)

    -0.4597 2.5982 -0.8602 7.41 -1.24 0.81

    8.02 -1.26 0.76

    0.81 -0.41 0.33

    4.69 -0.90 0.75

    -0.2196 0.7083 -0.0015

    -0.3677 0.4509 -0.1125

    -0.6101 8.826 -1.2758

    Summary table of �tting paramters and statistics of matrix correction 

    Ca [pfu]0.0 0.5 1.0 1.5 2.0 2.5

    Resi

    dual

    Bia

    s [‰

    ]

    -1.5

    -1.0

    -0.5

    0.0

    0.5

    1.0

    1.5

    ±0.3‰

    Fe2+ [pfu]0.0 0.5 1.0 1.5 2.0 2.5

    Resi

    dual

    Bia

    s [‰

    ]

    -1.5

    -1.0

    -0.5

    0.0

    0.5

    1.0

    1.5

    Fe2+

    Mn [pfu]

    Resi

    dual

    Bia

    s [‰

    ]

    0.0 0.5 1.0 1.5 2.0 2.5-1.5

    -1.0

    -0.5

    0.0

    0.5

    1.0

    1.5

    Mn

    Ca [atoms per formula unit: pfu]

    Bias

    rel.

    to U

    WG

    -2 [‰

    ]

    0.0 0.5 1.0 1.5 2.0 2.5-2

    -1

    0

    1

    2Ca

    13-62-2713-62-2913-63-1913-63-20

    13-63-2113-63-442B394ADK-5

    94ADK-7Alm-1Alm-2Alm-3

    Alm-4AlmCMGAlmSEBal509

    Beta114GrsQuGrsSEPyp-2

    Pyp-3Pyp-4Pyp-5PypAA

    PypAKPypDMPypMMR 53

    Sps-3Sps-4SpsSEUWG-2

    UWPp-1Yx

    XGrs

    Bias

    rel.

    to U

    WG

    -2 [‰

    ]

    0 0.2 0.4 0.6 0.8 1.0-2

    -1

    0

    1

    2

    3XGrs fitting

    Results

    Calibration curves were fitted by selected three standards (marked by circle outside of symbols). Matrix corrections were applied step-by-step (Ca => Mn => Fe2+). Inset figure shows simple XGrs cali-bration curve with all garnet standards. Blue curved line in the third plot (Fe2+) shows fitting curve with all standards. There is no significant difference between blue (all standards) and red (3 stan-dards). This correction scheme was evaluated using the measured offset of corrected δ18O from δ18OTrue value for all other garnet standards (excluding the 7 calibration standards). The 2 standard deviation (2SD) of the residual after Ca correction was 0.81‰. After the Mn correction was performed, the 2SD of the residual was down to 0.76‰; the final residual after the Fe2+ correction was 0.33‰.

    Residual Bias [‰] = δ18OTrue

    1000 -1

    δ18OCorrected1000 -1

    -1 ×1000

    Bias relative to UWG-2 [‰] = δ18OUWG-21000 -1

    δ18OMeasured1000 -1

    -1 ×1000

    Ca STDs: GrsSE, R-53, UWPp-1BiasCa = aCa∙(Ca)2 + bCa∙(Ca) + cCa 

    Mn STDs: Sps-4, Sps-3, UWPp-1BiasMn = aMn∙(Mn)2 + bMn∙(Mn) + cMn

    STDs: Alm-4, UWG-2, UWPp-1BiasFe2+ = aFe2+∙(Fe

    2+)2 + bFe2+∙(Fe2+) + cFe2+

    BiasTotal = BiasCa + BiasMn + BiasFe2+

    Fe2+Alm (Fe2+)

    Pyp (Mg)

    Sps (Mn)

    Grs (Ca)

    13-63-19

    PypAAPypAK

    PypMM13-62-29

    13-62-27

    13-63-20

    13-63-44

    AlmSEAlmCMG

    2B3

    Beta114

    Bal509

    13-63-21

    SpsSE

    Yx

    94ADK-5

    94ADK-7Alm-1

    Alm-2Alm-3Pyp-3

    Pyp-4

    Pyp-5

    PypDM

    GrsQu

    Pyp-2 UWG-2

    R-53

    Sps-3

    Sps-4

    GrsSE

    UWPp-1

    Alm-4

    Correction SchemePyralspite and grossular garnets are calibrated with each end-member composition (Ca/Mg+Ca: grossular-pyrope, Mn/Mg+Mn: spessartine-pyrope and Fe2+/Mg+Fe2+: almandine-pyrope) instead of XGrs. Each calibration curve was fitted by a quadratic equation with three standards (near both end-members and an intermediate composition). A pyrope standard (UWPp-1) was used for all calibrations and thus a total of 7 standards were used for this matrix correction (Ca: GrsSE, R-53, UWPp-1; Mn: Sps-3, Sps-4, UWPp-1; Fe: Alm-4, UWG-2, UWPp-1).

    The bias for unknowns are calculated as follows:

    Step-by-Step calibration:Calibration is applied to standards in the following steps.Biases were calculated as alphas, and subsequently converted back to value in δ-notation [‰].

    all standardsthree standards

    Session on 6/24/2014

    Garnet: (X2+)3(Y3+)2(SiO3)4

    AlmandinePyrope

    SpessartineGrossular

    AndraditeUvarovite

    FeMgMnCaCaCa

    AlAlAlAlFeCr

    X2+ Y3+

    Pyralspite

    Ugrandite

    InstrumentPrimary HV

    Primary BeamBeam Size

    Sample HVPresputtering

    DTFA ScanCounting TimeCycle Number

    Entrance SlitContrast Aperture

    Field ApertureEnergy Slit

    MRPDetectors

    CAMECA IMS 128010 kV~2.1 nA10-µm-10kV10 secON80 sec20 cycles120 µm400 µm4000 µm40 eV2200 (16O, 18O), 5000 (16O1H)3FCs (16O, 16O1H, 18O)

    Instrument & Analytical condition

    For SIMS analysis, normal procedures were followed: 10-µm spot size, 2 Faraday cups, 3.5 min/spot (Kita et al., 2009). We also measured 16O1H with the axial Faraday cup to monitor the OH count rate. All analyses were carried out at WiscSIMS Laboratory, University of Wisconsin-Madison.

    Standard Mineral !18OTrue !18OMeas SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO CaO F Total Si Ti Al Cr Fe3+ Fe2+ Mn Mg Ca F OHvacancy (VIII) Alm Pyp Sps Grs And Uvar CaTi FluoGrs HydroGrs

    PypDM Pyrope 5.6 -0.8 43.3 0.0 24.6 0.0 1.9 0.0 28.1 0.2 98.1 2.99 0.00 2.00 0.00 0.03 0.08 0.00 2.89 0.01 2.8 96.7 0.1 0.4 0.0 0.0 0.013-63-19 Pyrope 5.9 -0.3 41.4 0.1 22.7 0.6 10.0 0.4 19.8 3.8 98.8 2.98 0.00 1.93 0.04 0.07 0.54 0.02 2.13 0.30 18.0 71.4 0.8 9.4 0.3 0.2 0.0

    PypAA Pyrope 5.5 0.1 42.3 0.1 21.7 2.0 9.0 0.4 19.4 4.9 99.8 3.03 0.01 1.83 0.11 0.00 0.54 0.02 2.08 0.38 17.8 68.9 0.8 11.7 0.0 0.7 0.0PypAK Pyrope 5.5 0.0 41.9 0.1 22.2 1.2 11.8 0.4 17.8 4.6 100.0 3.03 0.00 1.89 0.07 0.00 0.71 0.02 1.91 0.36 23.7 63.6 0.8 11.4 0.0 0.4 0.0

    PypMM Pyrope 5.3 0.1 41.6 0.9 21.2 0.0 13.3 0.4 17.8 4.3 99.6 3.03 0.05 1.82 0.00 0.03 0.78 0.02 1.93 0.34 25.5 62.8 0.8 10.5 0.2 0.0 0.313-62-29 Pyrope 7.4 -0.4 40.5 0.4 21.7 0.2 16.6 0.4 16.2 3.0 99.0 3.00 0.02 1.90 0.01 0.05 0.98 0.03 1.78 0.24 32.3 58.9 0.9 7.5 0.2 0.0 0.113-62-27 Pyrope 6.5 0.2 40.0 0.3 22.2 0.1 17.0 0.4 13.2 6.0 98.9 2.99 0.01 1.95 0.01 0.03 1.04 0.02 1.47 0.48 34.5 48.9 0.7 15.5 0.2 0.1 0.113-63-20 Pyrope 6.1 0.6 40.2 0.3 22.3 0.0 15.3 0.3 12.9 8.0 99.3 2.99 0.01 1.95 0.00 0.04 0.92 0.02 1.43 0.64 30.5 47.6 0.6 20.7 0.4 0.0 0.113-63-44 Pyrope 6.4 0.7 40.1 0.2 22.3 0.1 14.4 0.3 12.0 9.7 99.0 3.00 0.01 1.96 0.00 0.02 0.88 0.02 1.33 0.77 29.3 44.3 0.6 25.3 0.2 0.1 0.1

    AlmSE Almandine 8.3 -1.6 37.5 0.0 21.2 0.0 34.5 0.2 6.4 0.3 100.1 2.96 0.00 1.97 0.00 0.10 2.18 0.01 0.75 0.03 73.4 25.2 0.4 0.9 0.0 0.0 0.0AlmCMG Almandine 7.5 -1.1 38.3 0.0 21.1 0.0 32.6 1.1 6.3 1.1 100.6 3.00 0.00 1.95 0.00 0.03 2.10 0.07 0.74 0.09 70.0 24.6 2.4 2.9 0.1 0.0 0.0

    2B3 Almandine 6.9 0.5 36.5 0.0 19.5 0.0 31.4 1.8 0.7 9.0 98.8 2.98 0.00 1.88 0.00 0.16 1.99 0.12 0.08 0.79 66.7 2.7 4.1 24.4 2.0 0.0 0.0Beta114 Almandine 9.3 -1.0 38.3 0.0 21.5 0.0 29.4 0.7 7.9 2.2 100.0 2.98 0.00 1.97 0.00 0.07 1.83 0.05 0.92 0.18 61.6 30.8 1.6 5.8 0.2 0.0 0.0Bal509 Almandine 12.3 -0.9 39.3 0.0 22.2 0.0 25.3 0.3 11.7 1.2 100.0 2.98 0.00 1.98 0.00 0.06 1.54 0.02 1.32 0.10 51.7 44.4 0.6 3.2 0.1 0.0 0.0

    UWG-2 Almandine 5.8 0.0 39.8 0.1 22.0 0.0 21.4 0.4 10.8 5.2 99.7 3.01 0.00 1.97 0.00 0.01 1.35 0.03 1.22 0.42 44.7 40.4 0.9 13.9 0.1 0.0 0.013-63-21 Almandine 4.6 1.2 38.7 0.4 21.4 0.0 19.7 0.3 6.7 11.7 98.9 2.99 0.02 1.95 0.00 0.03 1.25 0.02 0.77 0.97 41.5 25.7 0.7 31.4 0.4 0.0 0.4

    SpsSE Spessartine 5.4 -0.9 35.7 0.1 20.2 0.0 3.1 39.7 0.0 0.1 98.9 2.98 0.01 1.99 0.00 0.04 0.17 2.81 0.00 0.01 5.7 0.1 94.0 0.2 0.0 0.0 0.0GrsSE Grossular 3.8 2.8 38.9 0.4 21.9 0.0 1.4 0.7 0.0 35.0 98.3 2.98 0.02 1.98 0.00 0.00 0.08 0.04 0.00 2.88 2.7 0.0 1.4 94.5 0.2 0.0 1.1

    R-53 Grossular 5.3 2.4 39.8 0.4 22.0 0.0 8.8 0.1 5.1 22.7 98.9 3.02 0.03 1.97 0.00 0.00 0.56 0.01 0.57 1.85 18.7 19.2 0.3 61.0 0.0 0.0 0.892W-1 Andradite -0.3 39.6 0.5 19.8 0.0 4.4 0.2 0.4 34.9 99.6 3.01 0.03 1.78 0.00 0.14 0.14 0.01 0.04 2.85 4.7 1.3 0.3 85.6 6.7 0.0 1.310691 Andradite 0.2 39.4 0.7 19.5 0.0 4.5 0.1 0.5 34.7 99.4 3.02 0.04 1.75 0.00 0.14 0.15 0.01 0.05 2.84 4.8 1.8 0.3 84.5 6.8 0.0 1.8

    MexGrs Andradite 10.6 5.4 39.9 0.4 19.2 0.0 3.3 0.5 0.7 35.7 99.6 3.03 0.02 1.72 0.00 0.17 0.04 0.03 0.08 2.90 1.4 2.5 1.0 85.6 8.5 0.0 1.0AF749A Andradite -1.2 39.3 0.6 18.4 0.0 6.4 0.3 0.3 34.5 99.7 3.01 0.03 1.66 0.00 0.25 0.16 0.02 0.04 2.83 5.3 1.2 0.5 79.4 12.0 0.0 1.6

    92LEW2 Andradite -1.5 6.1 35.5 0.0 1.1 0.0 27.6 0.1 0.0 32.1 96.5 3.01 0.00 0.11 0.00 1.86 0.09 0.01 0.00 2.91 2.9 0.1 0.2 5.6 91.1 0.0 0.192LEW7 Andradite -1.6 6.2 35.6 0.1 1.3 0.0 27.2 0.1 0.0 32.0 96.4 3.02 0.00 0.13 0.00 1.82 0.11 0.01 0.01 2.91 3.5 0.2 0.2 6.5 89.4 0.0 0.2

    92LEW10 Andradite -1.2 5.4 37.1 0.7 9.0 0.0 17.1 0.2 0.1 33.2 97.4 3.01 0.04 0.87 0.00 1.03 0.14 0.01 0.02 2.89 4.5 0.6 0.4 42.3 50.2 0.0 2.192LEW8 Andradite -0.9 5.3 36.8 0.9 9.4 0.0 16.7 0.2 0.2 33.2 97.4 2.99 0.05 0.90 0.00 1.01 0.12 0.01 0.03 2.88 4.0 0.8 0.4 43.4 48.7 0.0 2.694ADK-5 Almandine 5.2 0.4 38.9 0.1 22.0 0.0 24.4 1.1 6.7 7.0 100.3 3.00 0.00 2.00 0.00 0.00 1.57 0.07 0.77 0.58 52.5 25.8 2.3 19.3 0.0 0.0 0.094ADK-7 Almandine 6.4 -0.1 39.8 0.1 22.4 0.0 21.9 0.5 11.2 4.1 99.9 3.00 0.00 1.99 0.00 0.00 1.38 0.03 1.26 0.33 46.1 41.9 1.0 11.0 0.0 0.0 0.0UWPp-1 Pyrope 6.3 -0.7 43.7 0.0 25.1 0.0 6.1 0.0 24.7 1.1 100.7 3.00 0.00 2.03 0.00 0.00 0.35 0.00 2.53 0.08 11.8 85.5 0.1 2.6 0.0 0.0 0.0

    GrsQu Grossular 3.9 2.4 39.8 0.2 22.4 0.0 1.6 0.8 0.0 34.5 99.4 3.02 0.01 2.00 0.00 0.00 0.10 0.05 0.00 2.81 3.4 0.1 1.6 94.3 0.0 0.0 0.6Yx Pyrope 5.6 -0.2 40.9 0.5 22.7 0.0 13.6 0.4 16.0 5.3 99.4 3.00 0.03 1.95 0.00 0.00 0.83 0.02 1.74 0.42 27.6 57.7 0.8 13.6 0.0 0.0 0.2

    Alm-1 Almandine 4.8 -0.5 39.7 0.0 22.4 0.0 23.5 0.9 11.1 2.6 100.1 3.00 0.00 2.00 0.00 0.00 1.48 0.06 1.25 0.21 49.5 41.6 1.9 7.0 0.0 0.0 0.0Alm-2 Almandine 7.4 -1.2 38.1 0.0 21.5 0.0 29.8 3.8 6.1 0.8 100.1 3.00 0.00 2.00 0.00 0.00 1.96 0.26 0.71 0.07 65.4 23.8 8.6 2.2 0.0 0.0 0.0Alm-3 Almandine 13.5 -1.1 38.0 0.0 21.5 0.0 32.3 1.1 5.7 1.5 100.1 3.00 0.00 2.00 0.00 0.00 2.13 0.07 0.67 0.13 71.2 22.2 2.4 4.2 0.0 0.0 0.0Alm-4 Almandine 11.2 -1.1 37.7 0.0 21.3 0.0 32.3 1.7 4.5 2.3 99.8 3.00 0.00 2.00 0.00 0.00 2.15 0.12 0.54 0.20 71.7 17.9 3.9 6.6 0.0 0.0 0.0Pyp-2 Almandine 7.6 -1.8 37.3 0.0 21.2 0.0 36.0 0.4 3.8 1.3 100.0 3.00 0.00 2.00 0.00 0.00 2.41 0.02 0.45 0.11 80.4 15.1 0.8 3.7 0.0 0.0 0.0Pyp-3 Almandine 7.6 -1.7 37.8 0.0 21.3 0.0 34.0 1.1 4.9 1.0 100.2 3.00 0.00 2.00 0.00 0.00 2.26 0.08 0.58 0.08 75.2 19.4 2.6 2.8 0.0 0.0 0.0Pyp-4 Pyrope 7.5 0.1 40.1 0.1 22.6 0.0 19.1 0.5 13.0 4.1 99.6 3.00 0.00 1.99 0.00 0.00 1.19 0.03 1.45 0.33 39.8 48.3 1.0 10.8 0.0 0.0 0.0Pyp-5 Almandine 7.6 -1.7 37.7 0.0 21.3 0.0 35.1 0.2 4.7 1.2 100.1 3.00 0.00 1.99 0.00 0.00 2.34 0.01 0.55 0.10 77.9 18.4 0.4 3.3 0.0 0.0 0.0Sps-3 Spessartine 5.3 0.1 38.3 0.1 21.6 0.0 1.5 32.0 5.4 1.9 100.8 3.00 0.01 1.99 0.00 0.00 0.10 2.12 0.62 0.16 3.3 20.8 70.6 5.3 0.0 0.0 0.0Sps-4 Spessartine 6.8 -0.5 36.3 0.2 20.6 0.0 1.9 40.4 0.0 0.6 99.9 2.99 0.01 2.00 0.00 0.00 0.13 2.82 0.00 0.05 4.3 0.1 94.0 1.7 0.0 0.0 0.0

    U-194-09 Cr-Pyrope 5.3 0.7 41.1 0.0 18.7 6.8 7.4 0.5 18.8 6.2 99.5 3.00 0.00 1.61 0.39 0.00 0.45 0.03 2.04 0.48 15.0 68.0 0.9 12.9 0.0 3.1 0.0U-33-10 Cr-Pyrope 5.4 0.6 41.6 0.1 18.4 7.8 7.0 0.4 19.7 5.7 100.6 2.99 0.01 1.56 0.44 0.00 0.42 0.02 2.12 0.44 14.1 70.5 0.7 11.4 0.0 3.2 0.0U-98-10 Cr-Pyrope 5.1 1.3 40.0 0.8 12.3 13.4 7.1 0.3 17.6 7.8 99.4 3.01 0.05 1.09 0.79 0.01 0.43 0.02 1.97 0.63 14.2 64.4 0.7 11.6 0.1 8.4 0.5

    U-L33-10 Cr-Pyrope 5.3 0.5 41.7 0.1 18.3 7.7 7.0 0.4 19.7 5.7 100.6 3.00 0.01 1.56 0.44 0.00 0.42 0.02 2.11 0.44 14.1 70.5 0.7 11.4 0.0 3.2 0.1U-163-01 Cr-Pyrope 40.8 1.4 15.0 9.3 7.8 0.3 18.8 6.3 99.7 3.01 0.08 1.31 0.54 0.00 0.48 0.02 2.06 0.50 15.6 67.4 0.7 11.0 0.0 4.6 0.7U-84-09 Cr-Pyrope 5.3 0.9 41.3 0.1 17.4 8.9 7.1 0.4 18.7 6.8 100.4 3.00 0.00 1.49 0.51 0.00 0.43 0.02 2.02 0.53 14.3 67.5 0.7 13.0 0.0 4.4 0.0

    Sps-5 F-Spessartine 3.3 -1.0 32.3 0.0 20.5 0.0 2.9 40.9 0.0 0.5 3.6 100.9 2.61 0.00 1.95 0.00 0.20 0.00 2.80 0.00 0.05 0.93 0.64 0.39 0.0 0.1 98.2 0.1 0.1 0.0 0.0 0.8 0.6New

    sta

    ndar

    ds

    Alm+Sps

    Pyp Grs

    PypDM13 63 19PypAAPypAKPypMM13 62 2913 62 27

    13 63 2013 63 44AlmSEAlmCMG2B3Beta114Bal509

    UWG 213 63 21SpsSEGrsSER 53

    UWPp 1GrsQuYx94ADK 594ADK 7Alm 1

    Alm 2Alm 3Alm 4Pyp 2Pyp 3Pyp 4

    Pyp 5Sps 3Sps 4Sps 5

    Alm

    Pyp Sps

    New Standards

    Garnet standards

    In this study, we introduce 22 new garnet standards in addition to the current 27 garnet standards (Page et al., 2010). We report 16 low-Ca pyralspite garnets (3 pyropes, 9 almandines, 2 spessartines, 1 fluorine-bearing spessartine and 1 grossular) including intermediate compositions between pyrope and spessartine that were lacking in the composition range of our previous suite of garnet standards. In addition, 6 Cr-pyrope standards were added to evaluate the effect of Cr on the matrix correction. We evaluated the homogeneity of chemical composition and δ18O of all new garnet standards by EPMA and SIMS. The δ18OTrue values were calibrated by laser fluorination.

    Stable isotope analysis by SIMS requires a large suite of matching standards for minerals that show complex solid-solution. There is no theoretical basis for extrapolating composition and samples are generally bracketed by the cation composition of standards. For oxygen isotope analysis of pyralspite garnets, a matrix correction based on grossular (Ca) component (XGrs) has been proposed (Page et al., 2010). This simple correction scheme has been generally accepted (Ickert and Stern, 2013; Martin et al., 2014; Raimondo et al., 2012) and can be described with a quadratic curve. However, we observed significant dispersion (>0.5‰) in the low-Ca, near end-member, pyralspite garnets such as pyrope (Mg), almandine (Fe2+) and spessartine (Mn) in recent garnet sessions. While there are some correction schemes that consider these components (Ickert and Stern, 2013; Martin et al., 2014; Vielzeuf et al., 2005), these corrections used a linear fit and/or single component and cannot explain the observed dispersions of low-Ca pyralspite garnets.

    In this study, we added new garnet standards that were lacking in the composition range of our previous suite of garnet standards and applied three different matrix correction using quadratic equations. We applied matrix corrections based on 7 garnets (selected as calibration standards) to 27 other garnet standards (including 12 new garnet standards) to evaluate the quality of the matrix correction. In addition, we also added new Cr-pyrope garnet standards, to evaluate the effect of Cr on the matrix correction. The effect of Cr has not previously been studied systematically for matrix correction.

    Introduction

    Improvement in matrix correction of δ18O analysis by SIMS for pyralspite and Cr-pyrope garnetsKouki Kitajima1,2 ([email protected]), Ariel Strickland1, Michael J. Spicuzza1 and John W. Valley1,2

    1 WiscSIMS, Department of Geoscience, University of Wisconsin Madison, Madison, WI, 53706. 2 NASA Astrobiology Institute, Department of Geoscience, University of Wisconsin-Madison, Madison, WI, 53706