0.1

1

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100000

10 100 1000 10000

HSE

(n

g/g

)

Ir (ng/g)

Pt slope (low Ir): 0.5639 Pt slope (high Ir): 0.173

Ru slope (low Ir): 0.3469 Ru slope (high Ir): 0.3469

Pd slope (low Ir): -0.023 Pd slope (high Ir): -0.045

Os slope (low Ir): 0.7495 Os slope (high Ir): 1.4064

Re slope (low Ir): 0.8345 Re slope (high Ir): 1.1574

J. Dietderich advised by R. J. Walker

DISCUSSION INTRODUCTION

MODELING FRACTIONAL CRYSTALLIZATION OF GROUP IIAB IRON METEORITES

CONCLUSION

REFERENCES

RESULTS

ANALYTICAL METHODS

0.01

0.1

1

10

100

Re Os Ir Ru Pt Pd

Sam

ple

/CI

FilomenaFilomena (dup)

0.01

0.1

1

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Re Os Ir Ru Pt Pd

Sam

ple

/CI

Santa Luzia

Santa Luzia (dup)

0.01

0.1

1

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Re Os Ir Ru Pt Pd

Sam

ple

/CI

0.01

0.1

1

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1000

Re Os Ir Ru Pt Pd

Sam

ple

/CI

Navajo Old Woman

Filomena Filomena (dup)

Lombard Smithsonian Iron

Mount Joy Bilibino

Coahuila * Sikote Alin *

Negrillos Bennett County

Гpecck Gressk Old Woman A

Sao Juliao de Moreira Sikhote-Alin

Santa Luzia Santa Luzia (duplicate)

Derrick Peak

0.01

0.1

1

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-500 1500

Re

(n

g/g

)

Pd (ng/g) Experimental

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-500 1500

Re

(n

g/g

)

Pd (ng/g) Slope

0.1

1

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1000 10000 100000

Re

(n

g/g

)

Ru (ng/g)

0.01

0.1

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100000

0.1 100 100000

Re

(n

g/g

)

Ir (ng/g)

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100 1000 10000 100000

Pt/

Os

Pt (ng/g)

0

0.05

0.1

0.15

0.2

0.25

0.1 10 1000

Re

/Os

Re (ng/g)

Liquid High Ir Solid High Ir Data High Ir

Liquid Low Ir Solid Low Ir Data Low Ir

Starting Comp. Liquid Starting Comp. Solid

The IIAB irons are fragments of metallic core from an astroidal parent body. Through the use of the isotope dilution, concentrations of the HSE Re, Os, Ir, Ru, Pt, and Pd were measured in group IIAB iron meteorites to better understand the systematics of core formation and crystallization in the parent body that these meteorites sample. As the core formed, different concentrations of HSE crystallized out of the melt depending on starting concentrations, melt compatibility, and the presence of S & P. These variations in abundances were measured and used to create a model to explore the fractional crystallization path of IIAB iron meteorites. I hypothesized that modified previous models for IIAB irons would be sufficient to model Re, Os, Ir, Ru, and Pt, yet insufficient to model Pd. This is because Pd exhibits incompatible tendencies, while the other HSE favor the solid.

A sample suite was selected that spanned the range of available Ni weight percent. The samples were then prepared to be dissolved and then weighed. Spike quantities were calculated based on previous work with IIAB iron meteorites Os and Ir abundances . After combining the samples, spikes, and acid mixture in Carius tubes, the tubes were sealed and heated at 240oC for a 24-hour period. Once the samples cooled, Os extraction was done by using carbon tetrachloride. The Os cut was purified by microdistillation and then run on the thermal ionization mass spectrometer (TIMS). The remaining five HSE were separated by column chemistry into three cuts (Re-Ru, Pt-Ir, and Pd), and then run on the inductively coupled plasma-mass spectrometer (ICP-MS). Both the TIMS and ICP-MS provided isotopic ratio measurements that were used in isotope dilution calculations resulting in the HSE concentrations to be used in the modeling process. The analytical uncertainty and sample heterogeneity were scrutinized throughout the experimentation. The analytical uncertainty was most influential for the samples with high Ir concentrations, while the sample heterogeneity was the most influential for samples with low Ir concentrations.

Using an initial 17 wt% S , the D0 for Ir, and the equation from Chabot, incremental D coefficients were calculated. The Ir D coefficients, correlation slopes, and equation from Chabot and Jones, were used to calculate the incremental DHSE coefficients. The D coefficients were then used to calculate expected concentrations throughout the process of crystallization. This provided solid and liquid track data for the HSE. Initial abundances were then changed so to situate the collected data between the solid and liquid tracks. The resulting estimated initial abundances of HSE in the molten core were normalized and plotted versus sample data. This showed higher enrichment of Re, Os, Ir, Ru, and Pt in relation to Pd.

Log-log plot of Ir versus other HSE (above) • Trendlines for high and low Ir samples • Slopes calculated for both high

and low Ir samples

Abundance plot (left) • CI chondrite normalized data from data table +

unpublished data

The techniques used were effective and yielded precise concentration measurements . These measurements were used to create a viable model for the fractional crystallization of the group IIAB iron meteorites. The Re, Os, Ru, Ir, and Pt were explained by slightly altering previous IIAB models, and the same model was less sufficient to explain the Pd data. This confirmed my hypothesis, that due to the unique workings of Pd, previous modeling could not be used to explain Pd in group IIAB irons. While the new split high/low Ir model helps to better understand the systematics of IIAB core crystallization, I feel that perhaps a more successful model may be possible by building in a function that allows the liquid and solid tracks of crystallization to be deviated without having to start and stop the model.

Chabot N. and Jones J. The parameterization of solid metal-liquid metal partitioning of siderophile elements. Meteoritics & Planetary Science. October 01, 2003;38(10):1425-1436. Chabot N. Sulfur contents of the parental metallic cores of magmatic iron meteorites. Geochimica et Cosmochimica Acta. September 01, 2004;68(17):3607-3618. Cook D. Pt-Re-Os systematics of group IIAB and IIIAB iron meteorites. Geochimica et Cosmochimica Acta. March 01, 2004;68(6):1413-1431. Jones J. Fractional crystallization of iron meteorites; constant versus changing partition coefficients. Meteoritics. May 01, 1994;29(3):423-426. Morgan J. Rhenium-osmium concentration and isotope systematics in group IIAB iron meteorites. Geochimica et Cosmochimica Acta. June 01, 1995;59(11):2331-2344. Wasson J. Formation of IIAB iron meteorites. Geochimica et Cosmochimica Acta. February 01, 2007;71(3):760-781.

The above data table contains concentration data and combined uncertainties.