A comparison of metallographic cooling rate methods used in meteorites

Herpfer, M. A.; Larimer, J. W.; Goldstein, Joseph I.

doi:10.1016/0016-7037(94)90387-5

Cited by 57 publications

(45 citation statements)

References 30 publications

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“…This could be consistent with IAB irons cooling at depth in their parent body, whereas winonaites were formed nearer to the surface and cooled more quickly. This suggestion is consistent with the faster metallographic cooling rate found for Winona (200°C/ Myr; Kothari et al, 1981) compared to IAB irons (10 -50°C/ Myr; Herpfer et al, 1994). The lower limit for the age of Mount Morris (Wisconsin) is considerably less than the lowest IAB age and may represent heating due to impact.…”

Section: Comparison Of Ages Of Winonaites and Silicate Inclusions In supporting

confidence: 77%

“…It is therefore informative to compare 39 Ar- 40 Ar ages of the three winonaites we dated with 39 Ar- 40 Ar ages (Niemeyer, 1979) and K- 40 Ar ages (Bogard et al, 1968) reported for silicate inclusions from several IAB iron meteorites. The 39 Ar- 40 Ar ages for IABs must be reduced by a factor of 0.988, however, to correct for a subsequent change in age of the Saint Séverin flux/age monitor originally used (Herpfer et al, 1994 (Crabb and Anders, 1981), the earth, the sun, and average carbonaceous chondrites (AVCC). C1 is a planetary composition derived by Pepin (1991). sions in IABs.…”

Section: Comparison Of Ages Of Winonaites and Silicate Inclusions In mentioning

confidence: 99%

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A petrologic and isotopic study of winonaites: evidence for early partial melting, brecciation, and metamorphism

Benedix

McCoy

Keil

et al. 1998

Geochimica et Cosmochimica Acta

114

213

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Section: Comparison Of Ages Of Winonaites and Silicate Inclusions In supporting

confidence: 77%

Section: Comparison Of Ages Of Winonaites and Silicate Inclusions In mentioning

confidence: 99%

A petrologic and isotopic study of winonaites: evidence for early partial melting, brecciation, and metamorphism

Benedix

McCoy

Keil

et al. 1998

Geochimica et Cosmochimica Acta

114

213

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“…42, 4.38, 4.35, and 4.34 Gyr. In their consideration of Niemeyer's data, Herpfer et al (1994) adopted a St. Severin age of 4.373 Ϯ 0.030 Gyr, the average of these four new analyses. This is the St. Severin age we used to correct the Netschaëvo and Weekeroo Station Ar-Ar ages reported in Table 2.…”

Section: Appendixmentioning

confidence: 99%

Chronology and petrology of silicates from IIE iron meteorites: evidence of a complex parent body evolution

Bogard

Garrison

McCoy

2000

Geochimica et Cosmochimica Acta

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Abstract-IIE iron meteorites contain silicate inclusions the characteristics of which suggest a parent body similar to that of H-chondrites. However, these silicates show a wide range of alteration, ranging from Netschaëvo and Techado, the inclusions of which are little altered, to highly differentiated silicates like those in Kodaikanal, Weekeroo Station, and Colomera, which have lost metal and sulfur and are enriched in feldspar. We find these inclusions to show varying degrees of shock alteration. We made 39 Ar-40 Ar age determinations of Watson, Techado, Miles, Colomera, and Sombrerete. Watson has an Ar-Ar age of 3.677 Ϯ 0.007 Gyr, similar to previously reported ages for Kodaikanal and Netschaëvo. We suggest that the various determined radiometric ages of these three meteorites were probably reset by a common impact event. The space exposure ages for these three meteorites are also similar to each other and are considerably younger than exposure ages of other IIEs.39 Ar ages inferred for the other four meteorites analyzed are considerably older than Watson and are: Techado ϭ 4.49 Ϯ 0.01 Gyr, Miles ϭ 4.405 Ϯ 0.012 Gyr, Colomera ϭ 4.470 Ϯ 0.010 Gyr, and Sombrerete ϭ 4.541 Ϯ 0.0012 Gyr. These ages are in fair agreement with previously reported Rb-Sr isochron ages for Colomera and Weekeroo Station. Although several mechanisms to form IIE meteorites have been suggested, it is not obvious that a single mechanism could produce a suite of meteorites with very different degrees of silicate differentiation and with isotopic ages that differ by Ͼ0.8 Gyr. We suggest that those IIEs with older isotopic ages are a product of partial melting and differentiation within the parent body, followed by mixing of silicate and metal while both were relatively hot. Netschaëvo and Watson may have formed by this same process or by impact mixing ϳ4.5 Gyr ago, but their isotopic ages may have been subsequently reset by shock heating. Kodaikanal apparently is required to have formed more recently, in which case impact melting and differentiation seems the only viable process. We see no compelling reasons to believe that IIE silicate and metal derived from different parent bodies or that the parent body of IIEs was the same as that of H-chondrites.

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“…Referring to literature data on Ni-based cooling rates is a precarious business because the estimated cooling rates have changed to a large extent over the years (Saikumar and Goldstein, 1988). Even today, there are unexplainable differences in the rates between different researchers (Herpfer et al, 1994). I decided to mainly use the data set compiled by Wood (1 979) because it is the largest data set.…”

Section: Cooling Ratesmentioning

confidence: 99%

Ion probe measurements of carbon and nitrogen in iron meteorites

Sugiura

1998

Meteorit & Planetary Scien

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Abstract-Carbon and nitrogen distributions in iron meteorites, their concentrations in various phases, and their isotopic compositions in certain phases were measured by secondary ion mass spectrometry (SIMS).Taenite (and its decomposition products) is the main carrier of C, except for IAB iron meteorites, where graphite and/or carbide (cohenite) may be the main carrier. Taenite is also the main carrier of N in most iron meteorites unless nitrides (carlsbergite CrN or roaldite (Fe,Ni)4N) are present. Carbon and N distributions in taenite are well correlated unless carbides and/or nitrides are exsolved.There seem to be three types of C and N distributions within taenite.(1) These elements are enriched at the center of taenite (convex type). (2) They are enriched at the edge of taenite (concave type). (3) They are enriched near but some distance away from the edge of taenite (complex type). The first case (1) is explained as equilibrium distribution of C and N in Fe-Ni alloy with M-shape Ni concentration profile. The second case (2) seems to be best explained as diffusion controlled C and N distributions. In the third case (3), the interior of taenite has been transformed to the a phase (kamacite or martensite). Carbon and N were expelled from the a phase and enriched near the inner border of the remaining y phase. Such differences in the C and N distributions in taenite may reflect different cooling rates of iron meteorites.Nitrogen concentrations in taenite are quite high approaching 1 wt% in some iron meteorites. Nitride (carlsbergite and roaldite) is present in meteorites with high N concentrations in taenite, which suggests that the nitride was formed due to supersaturation of the metallic phases with N. The same tendency is generally observed for C (ie., high C concentrations in taenite correlate with the presence of carbide and/or graphite).Concentrations of C and N in kamacite are generally below detection limits.Isotopic compositions of C and N in taenite can be measured with a precision of several permil. Isotopic analysis in kamacite in most iron meteorites is not possible because of the low concentrations. The C isotopic compositions seem to be somewhat fractionated among various phases, reflecting closure of C transport at low temperatures. A remarkable isotopic anomaly was observed for the Mundrabilla (IIICD anomalous) meteorite. Nitrogen isotopic compositions of taenite measured by SIMS agree very well with those of the bulk samples measured by conventional mass spectrometry.

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A comparison of metallographic cooling rate methods used in meteorites

Cited by 57 publications

References 30 publications

A petrologic and isotopic study of winonaites: evidence for early partial melting, brecciation, and metamorphism

A petrologic and isotopic study of winonaites: evidence for early partial melting, brecciation, and metamorphism

Chronology and petrology of silicates from IIE iron meteorites: evidence of a complex parent body evolution

Ion probe measurements of carbon and nitrogen in iron meteorites

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