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Frederic Moynier – One of the best experts on this subject based on the ideXlab platform.

  • the iron isotope composition of enstatite meteorites implications for their origin and the metal sulfide fe isotopic fractionation factor
    Geochimica et Cosmochimica Acta, 2014
    Co-Authors: Kun Wang, Frederic Moynier, Paul S Savage
    Abstract:

    Abstract Despite their unusual chemical composition, it is often proposed that the enstatite chondrites represent a significant component of Earth’s building materials, based on their terrestrial similarity for numerous isotope systems. In order to investigate a possible genetic relationship between the Fe isotope composition of enstatite chondrites and the Earth, we have analyzed 22 samples from different subgroups of the enstatite meteorites, including EH and EL chondrites, aubrites (main group and Shallowater) and the Happy Canyon impact melt. We have also analyzed the Fe isotopic compositions of separated (magnetic and non-magnetic) phases from both enstatite chondrites and Achondrites. On average, EH3–5 chondrites (δ56Fe = 0.003 ± 0.042‰; 2 standard deviation; n = 9; including previous literature data) as well as EL3 chondrites (δ56Fe = 0.030 ± 0.038‰; 2 SD; n = 2) have identical and homogeneous Fe isotopic compositions, indistinguishable from those of the carbonaceous chondrites and average terrestrial peridotite. In contrast, EL6 chondrites display a larger range of isotopic compositions (−0.180‰  Enstatite Achondrites (aubrites) also exhibit a relatively large range of Fe isotope compositions: all main group aubrites are enriched in the light Fe isotopes (δ56Fe = −0.170 ± 0.189‰; 2 SD; n = 6), while Shallowater is, isotopically, relatively heavy (δ56Fe = 0.045 ± 0.101‰; 2 SD; n = 4; number of chips). We take this variation to suggest that the main group aubrite parent body formed a discreet heavy Fe isotope-enriched core, whilst the Shallowater meteorite is most likely from a different parent body where core and silicate material remixed. This could be due to intensive impact-induced shearing stress, or the ultimate destruction of the Shallowater parent body. Analysis of separated enstatite meteorite mineral phases show that the magnetic phase (Fe metal) is systematically enriched in the heavier Fe isotopes when compared to non-magnetic phases (Fe hosted in troilite), which agrees with previous experimental observations and theoretical calculations. The difference between magnetic and non-magnetic phases from enstatite Achondrites provides an equilibrium metal–sulfide Fe isotopic fracfractionation factor of Δ56Femetal–troilite = δ56Femetal − δ56Fetroilite of 0.129 ± 0.060‰ (2 SE) at 1060 ± 80 K, which confirms the predictions of previous theoretical calculations.

  • the iron isotope composition of enstatite meteorites implications for their origin and the metal sulfide fe isotopic fractionation factor
    Geochimica et Cosmochimica Acta, 2014
    Co-Authors: Kun Wang, Frederic Moynier, Paul S Savage
    Abstract:

    Abstract Despite their unusual chemical composition, it is often proposed that the enstatite chondrites represent a significant component of Earth’s building materials, based on their terrestrial similarity for numerous isotope systems. In order to investigate a possible genetic relationship between the Fe isotope composition of enstatite chondrites and the Earth, we have analyzed 22 samples from different subgroups of the enstatite meteorites, including EH and EL chondrites, aubrites (main group and Shallowater) and the Happy Canyon impact melt. We have also analyzed the Fe isotopic compositions of separated (magnetic and non-magnetic) phases from both enstatite chondrites and Achondrites. On average, EH3–5 chondrites (δ56Fe = 0.003 ± 0.042‰; 2 standard deviation; n = 9; including previous literature data) as well as EL3 chondrites (δ56Fe = 0.030 ± 0.038‰; 2 SD; n = 2) have identical and homogeneous Fe isotopic compositions, indistinguishable from those of the carbonaceous chondrites and average terrestrial peridotite. In contrast, EL6 chondrites display a larger range of isotopic compositions (−0.180‰  Enstatite Achondrites (aubrites) also exhibit a relatively large range of Fe isotope compositions: all main group aubrites are enriched in the light Fe isotopes (δ56Fe = −0.170 ± 0.189‰; 2 SD; n = 6), while Shallowater is, isotopically, relatively heavy (δ56Fe = 0.045 ± 0.101‰; 2 SD; n = 4; number of chips). We take this variation to suggest that the main group aubrite parent body formed a discreet heavy Fe isotope-enriched core, whilst the Shallowater meteorite is most likely from a different parent body where core and silicate material remixed. This could be due to intensive impact-induced shearing stress, or the ultimate destruction of the Shallowater parent body. Analysis of separated enstatite meteorite mineral phases show that the magnetic phase (Fe metal) is systematically enriched in the heavier Fe isotopes when compared to non-magnetic phases (Fe hosted in troilite), which agrees with previous experimental observations and theoretical calculations. The difference between magnetic and non-magnetic phases from enstatite Achondrites provides an equilibrium metal–sulfide Fe isotopic fracfractionation factor of Δ56Femetal–troilite = δ56Femetal − δ56Fetroilite of 0.129 ± 0.060‰ (2 SE) at 1060 ± 80 K, which confirms the predictions of previous theoretical calculations.

  • Nature of volatile depletion and genetic relationships in enstatite chondrites and aubrites inferred from Zn isotopes
    Geochimica et Cosmochimica Acta, 2011
    Co-Authors: Frederic Moynier, Randal Paniello, Matthieu Gounelle, Francis Albarède, Pierre Beck, Frank Podosek, B. Zanda
    Abstract:

    Enstatite meteorites include the undifferentiated enstatite chondrites and the differentiated enstatite Achondrites (aubrites). They are the most reduced group of all meteorites. The oxygen isotope compositions of both enstatite chondrites and aubrites plot along the terrestrial mass fractionation line, which suggests some genetic links between these meteorites and the Earth as well. For this study, we measured the Zn isotopic composition of 25 samples from the following groups: aubrites (main group and Shallowater), EL chondrites, EH chondrites and Happy Canyon (impact-melt breccia). We also analyzed the Zn isotopic composition and elemental abundance in separated phases (metal, silicates, and sulfides) of the EH4, EL3, and EL6 chondrites. The different groups of meteorites are isotopically distinct and give the following values (parts per thousand): aubrite main group (-7.08 < delta Zn-66

Paul S Savage – One of the best experts on this subject based on the ideXlab platform.

  • the iron isotope composition of enstatite meteorites implications for their origin and the metal sulfide fe isotopic fractionation factor
    Geochimica et Cosmochimica Acta, 2014
    Co-Authors: Kun Wang, Frederic Moynier, Paul S Savage
    Abstract:

    Abstract Despite their unusual chemical composition, it is often proposed that the enstatite chondrites represent a significant component of Earth’s building materials, based on their terrestrial similarity for numerous isotope systems. In order to investigate a possible genetic relationship between the Fe isotope composition of enstatite chondrites and the Earth, we have analyzed 22 samples from different subgroups of the enstatite meteorites, including EH and EL chondrites, aubrites (main group and Shallowater) and the Happy Canyon impact melt. We have also analyzed the Fe isotopic compositions of separated (magnetic and non-magnetic) phases from both enstatite chondrites and Achondrites. On average, EH3–5 chondrites (δ56Fe = 0.003 ± 0.042‰; 2 standard deviation; n = 9; including previous literature data) as well as EL3 chondrites (δ56Fe = 0.030 ± 0.038‰; 2 SD; n = 2) have identical and homogeneous Fe isotopic compositions, indistinguishable from those of the carbonaceous chondrites and average terrestrial peridotite. In contrast, EL6 chondrites display a larger range of isotopic compositions (−0.180‰  Enstatite Achondrites (aubrites) also exhibit a relatively large range of Fe isotope compositions: all main group aubrites are enriched in the light Fe isotopes (δ56Fe = −0.170 ± 0.189‰; 2 SD; n = 6), while Shallowater is, isotopically, relatively heavy (δ56Fe = 0.045 ± 0.101‰; 2 SD; n = 4; number of chips). We take this variation to suggest that the main group aubrite parent body formed a discreet heavy Fe isotope-enriched core, whilst the Shallowater meteorite is most likely from a different parent body where core and silicate material remixed. This could be due to intensive impact-induced shearing stress, or the ultimate destruction of the Shallowater parent body. Analysis of separated enstatite meteorite mineral phases show that the magnetic phase (Fe metal) is systematically enriched in the heavier Fe isotopes when compared to non-magnetic phases (Fe hosted in troilite), which agrees with previous experimental observations and theoretical calculations. The difference between magnetic and non-magnetic phases from enstatite Achondrites provides an equilibrium metal–sulfide Fe isotopic fractionation factor of Δ56Femetal–troilite = δ56Femetal − δ56Fetroilite of 0.129 ± 0.060‰ (2 SE) at 1060 ± 80 K, which confirms the predictions of previous theoretical calculations.

  • the iron isotope composition of enstatite meteorites implications for their origin and the metal sulfide fe isotopic fractionation factor
    Geochimica et Cosmochimica Acta, 2014
    Co-Authors: Kun Wang, Frederic Moynier, Paul S Savage
    Abstract:

    Abstract Despite their unusual chemical composition, it is often proposed that the enstatite chondrites represent a significant component of Earth’s building materials, based on their terrestrial similarity for numerous isotope systems. In order to investigate a possible genetic relationship between the Fe isotope composition of enstatite chondrites and the Earth, we have analyzed 22 samples from different subgroups of the enstatite meteorites, including EH and EL chondrites, aubrites (main group and Shallowater) and the Happy Canyon impact melt. We have also analyzed the Fe isotopic compositions of separated (magnetic and non-magnetic) phases from both enstatite chondrites and Achondrites. On average, EH3–5 chondrites (δ56Fe = 0.003 ± 0.042‰; 2 standard deviation; n = 9; including previous literature data) as well as EL3 chondrites (δ56Fe = 0.030 ± 0.038‰; 2 SD; n = 2) have identical and homogeneous Fe isotopic compositions, indistinguishable from those of the carbonaceous chondrites and average terrestrial peridotite. In contrast, EL6 chondrites display a larger range of isotopic compositions (−0.180‰  Enstatite Achondrites (aubrites) also exhibit a relatively large range of Fe isotope compositions: all main group aubrites are enriched in the light Fe isotopes (δ56Fe = −0.170 ± 0.189‰; 2 SD; n = 6), while Shallowater is, isotopically, relatively heavy (δ56Fe = 0.045 ± 0.101‰; 2 SD; n = 4; number of chips). We take this variation to suggest that the main group aubrite parent body formed a discreet heavy Fe isotope-enriched core, whilst the Shallowater meteorite is most likely from a different parent body where core and silicate material remixed. This could be due to intensive impact-induced shearing stress, or the ultimate destruction of the Shallowater parent body. Analysis of separated enstatite meteorite mineral phases show that the magnetic phase (Fe metal) is systematically enriched in the heavier Fe isotopes when compared to non-magnetic phases (Fe hosted in troilite), which agrees with previous experimental observations and theoretical calculations. The difference between magnetic and non-magnetic phases from enstatite Achondrites provides an equilibrium metal–sulfide Fe isotopic fractionation factor of Δ56Femetal–troilite = δ56Femetal − δ56Fetroilite of 0.129 ± 0.060‰ (2 SE) at 1060 ± 80 K, which confirms the predictions of previous theoretical calculations.

Kun Wang – One of the best experts on this subject based on the ideXlab platform.

  • the iron isotope composition of enstatite meteorites implications for their origin and the metal sulfide fe isotopic fractionation factor
    Geochimica et Cosmochimica Acta, 2014
    Co-Authors: Kun Wang, Frederic Moynier, Paul S Savage
    Abstract:

    Abstract Despite their unusual chemical composition, it is often proposed that the enstatite chondrites represent a significant component of Earth’s building materials, based on their terrestrial similarity for numerous isotope systems. In order to investigate a possible genetic relationship between the Fe isotope composition of enstatite chondrites and the Earth, we have analyzed 22 samples from different subgroups of the enstatite meteorites, including EH and EL chondrites, aubrites (main group and Shallowater) and the Happy Canyon impact melt. We have also analyzed the Fe isotopic compositions of separated (magnetic and non-magnetic) phases from both enstatite chondrites and Achondrites. On average, EH3–5 chondrites (δ56Fe = 0.003 ± 0.042‰; 2 standard deviation; n = 9; including previous literature data) as well as EL3 chondrites (δ56Fe = 0.030 ± 0.038‰; 2 SD; n = 2) have identical and homogeneous Fe isotopic compositions, indistinguishable from those of the carbonaceous chondrites and average terrestrial peridotite. In contrast, EL6 chondrites display a larger range of isotopic compositions (−0.180‰  Enstatite Achondrites (aubrites) also exhibit a relatively large range of Fe isotope compositions: all main group aubrites are enriched in the light Fe isotopes (δ56Fe = −0.170 ± 0.189‰; 2 SD; n = 6), while Shallowater is, isotopically, relatively heavy (δ56Fe = 0.045 ± 0.101‰; 2 SD; n = 4; number of chips). We take this variation to suggest that the main group aubrite parent body formed a discreet heavy Fe isotope-enriched core, whilst the Shallowater meteorite is most likely from a different parent body where core and silicate material remixed. This could be due to intensive impact-induced shearing stress, or the ultimate destruction of the Shallowater parent body. Analysis of separated enstatite meteorite mineral phases show that the magnetic phase (Fe metal) is systematically enriched in the heavier Fe isotopes when compared to non-magnetic phases (Fe hosted in troilite), which agrees with previous experimental observations and theoretical calculations. The difference between magnetic and non-magnetic phases from enstatite Achondrites provides an equilibrium metal–sulfide Fe isotopic fractionation factor of Δ56Femetal–troilite = δ56Femetal − δ56Fetroilite of 0.129 ± 0.060‰ (2 SE) at 1060 ± 80 K, which confirms the predictions of previous theoretical calculations.

  • the iron isotope composition of enstatite meteorites implications for their origin and the metal sulfide fe isotopic fractionation factor
    Geochimica et Cosmochimica Acta, 2014
    Co-Authors: Kun Wang, Frederic Moynier, Paul S Savage
    Abstract:

    Abstract Despite their unusual chemical composition, it is often proposed that the enstatite chondrites represent a significant component of Earth’s building materials, based on their terrestrial similarity for numerous isotope systems. In order to investigate a possible genetic relationship between the Fe isotope composition of enstatite chondrites and the Earth, we have analyzed 22 samples from different subgroups of the enstatite meteorites, including EH and EL chondrites, aubrites (main group and Shallowater) and the Happy Canyon impact melt. We have also analyzed the Fe isotopic compositions of separated (magnetic and non-magnetic) phases from both enstatite chondrites and Achondrites. On average, EH3–5 chondrites (δ56Fe = 0.003 ± 0.042‰; 2 standard deviation; n = 9; including previous literature data) as well as EL3 chondrites (δ56Fe = 0.030 ± 0.038‰; 2 SD; n = 2) have identical and homogeneous Fe isotopic compositions, indistinguishable from those of the carbonaceous chondrites and average terrestrial peridotite. In contrast, EL6 chondrites display a larger range of isotopic compositions (−0.180‰  Enstatite Achondrites (aubrites) also exhibit a relatively large range of Fe isotope compositions: all main group aubrites are enriched in the light Fe isotopes (δ56Fe = −0.170 ± 0.189‰; 2 SD; n = 6), while Shallowater is, isotopically, relatively heavy (δ56Fe = 0.045 ± 0.101‰; 2 SD; n = 4; number of chips). We take this variation to suggest that the main group aubrite parent body formed a discreet heavy Fe isotope-enriched core, whilst the Shallowater meteorite is most likely from a different parent body where core and silicate material remixed. This could be due to intensive impact-induced shearing stress, or the ultimate destruction of the Shallowater parent body. Analysis of separated enstatite meteorite mineral phases show that the magnetic phase (Fe metal) is systematically enriched in the heavier Fe isotopes when compared to non-magnetic phases (Fe hosted in troilite), which agrees with previous experimental observations and theoretical calculations. The difference between magnetic and non-magnetic phases from enstatite Achondrites provides an equilibrium metal–sulfide Fe isotopic fractionation factor of Δ56Femetal–troilite = δ56Femetal − δ56Fetroilite of 0.129 ± 0.060‰ (2 SE) at 1060 ± 80 K, which confirms the predictions of previous theoretical calculations.

David W. Mittlefehldt – One of the best experts on this subject based on the ideXlab platform.

  • Appendix: Meteorites – A Brief Tutorial
    Reviews in Mineralogy & Geochemistry, 2008
    Co-Authors: David W. Mittlefehldt
    Abstract:

    There are four broad categories of meteorites—chondrites, Achondrites, irons and stony irons. These are subdivided into meteorite groups, the basic unit of meteorite classification. Although no formal guideline is in place for the minimum number of meteorites needed to define a group, common practice is that there should be five or more members in a group. A defined meteorite group is thought to be derived from a single asteroid. However, some groups are genetically related and are derived from a common parent asteroid. Chondrites are primitive stony meteorites; rocks whose compositions are little changed since their formation in the solar nebula. There are fourteen defined groups of chondrites, and they make up the vast majority of meteorites falling to Earth in the current epoch. Achondrites are stony meteorites of two broad types. Some are primitive materials like chondrites, but most are the products of igneous differentiation. There are ten defined groups of Achondrites, of which seven are differentiated types. Irons are also the products of asteroidal differentiation, having crystallized from metallic melts separated from chondritic precursors. There are thirteen defined groups of iron meteorites. Stony-irons are also differentiated materials, and both the rocky and metallic phases were formed by igneous processes on asteroids. There are two defined groups of stony-iron meteorites. In addition to those that fit into groups, there are many meteorites that are unique, or for which there are less than five examples. These ungrouped meteorites make up a substantial fraction of meteorites recovered to date.

  • Acapulco- and Lodran-like Achondrites: Petrology, geochemistry, chronology, and origin
    Geochimica et Cosmochimica Acta, 1996
    Co-Authors: David W. Mittlefehldt, Marilyn M. Lindstrom, Donald D. Bogard, Daniel H. Garrison, Stephen W. Field
    Abstract:

    We have performed petrologic and geochemical studies of five primitive Achondrites: ALHA81187 and ALHA81261 (Acapulco-like), EET 84302 (transitional, but Acapulco-like), and LEW 88280 and MAC 88177 (Lodran-like). We have also performed 39Ar-40Ar chronology on ALHA81187, ALHA81261, and EET 84302. LEW 88280 and MAC 88177 contain more ferroan olivines, orthopyroxenes, clinopyroxenes, and chromites than do the Acapulco-like Achondrites. Plagioclase is present in only ALHA81187, ALHA81261, and EET 84302. Its composition does not track that of the mafic silicates; EET 84302, with the most calcic plagioclase, contains olivine and pyroxene with an mg# intermediate between ALHA81187 and ALHA81261. Similarly, spinels in EET 84302 have the same mg# as those in ALHA81187, while pyroxenes in the former are more ferroan than in the latter. Acapulco-like Achondrites have Sm/Sc ratios between 0.8–1.5 times H chondrites, and Na/Sc ratios are between 0.81.0 times H chondrites, indicating that silicate partial melts have not been lost from these rocks. Siderophile and chalcophile elements are fractionated and show a trend of increasing Ir/Ni ratios with decreasing Se/Co ratios. This variation is consistent with fractionation by partial melting in the Fe-Ni-S system. EET 84302 is very depleted in Se and troilite is a accessory phase, indicating essentially total loss of the low temperature Fe-Ni-S melt. In contrast, the Lodran-like Achondrites are depleted in the highly incompatible lithophile elements relative to more compatible elements: Sm/Sc ratios are 0.2−0.7 times and Na/Sc ratios are 0.04–0.18 times H chondrites. These data are consistent with a model for formation of the Lodran-like Achondrites as partial melting residues. However, the low Ir/Ni and high Se/Co ratios in two Lodran-like Achondrites suggest the metal + troilite in these rocks is dominated by the low melting fraction in the Fe-Ni-S system. This metal + troilite was added to the silicates after partial melting depleted them in a basaltic fraction. The Ar-Ar release spectra yield good plateau ages of 4.507 ± 0.024 Ga (ALHA81187), 4.511 ± 0.007 Ga (ALHA81261), and 4.519 ± 0.017 Ga (EET 84302), in good agreement with previously determined Ar-Ar ages for other Acapulco-like Achondrites. Together, the Ar-Ar ages demonstrate that metamorphism on the Acapulco-Lodran parent body occurred 4.51 ± 0.02 Ga ago, roughly 50 Ma after its formation. The geochemical and petrologic evidence on the Acapulco- and Lodran-like Achondrites suggest that heating on the parent body was localized and heterogeneous in space and time. The parent body was probably not subjected to parent body-wide magmatism, in contrast to the case for 4 Vesta and the HED meteorites.

Ian A. Franchi – One of the best experts on this subject based on the ideXlab platform.

  • The Tafassasset primitive achondrite: Insights into initial stages of planetary differentiation
    Geochimica et Cosmochimica Acta, 2012
    Co-Authors: K. G. Gardner-vandy, Dante S. Lauretta, Richard C. Greenwood, Timothy J. Mccoy, M. Killgore, Ian A. Franchi
    Abstract:

    Abstract Tafassasset is an exceptional meteorite that has been linked to both the CR chondrites and the primitive Achondrites. Because previous evidence suggests it might be a primitive achondrite from a known chondrite type, we have undertaken a study of the petrology, geochemistry, and formation history of the meteorite. Tafassasset is predominantly FeO-rich olivine (∼58%) yet contains abundant Fe,Ni-metal (∼10 vol.%) and sulfide (∼3 vol.%). Other phases include high- and low-Ca pyroxene, plagioclase, chromite, and phosphate. It has a recrystallized texture, containing equigranular grains that often meet at 120° triple junctions. There are no relict chondrules in the thin sections examined, although they have been reported previously. Electron microprobe analyses reveal homogeneous olivine (Fa 28.6 ), both low-and high-Ca pyroxene (Fs 23.6 Wo 3.7 and Fs 12.2 Wo 39.3±1 ), a range of plagioclase composition (An 23–47 ), Fe,Ni-metal (with 5.3–36.6 wt.% Ni and 0.1–0.8 wt.% Co), troilite, chromite, and Ca–phosphate. Bulk composition analyses reveal two chips depleted in refractory lithophile and some siderophile elements compared to CI chondrites. Exceptions are enrichments in Fe, Ni and Co. A third chip is essentially chondritic in bulk composition. Different stones of the meteorite have slightly different oxygen isotope composition, yet all lie in the CR chondrite trend with one in the acapulcoite–lodranite field. Thermodynamic calculations show that Tafassasset equilibrated at a temperature above the Fe,Ni–FeS eutectic and at an oxygen fugacity of ∼IW-1. The texture, heterogeneous distribution of mineral phases, plagioclase composition, two-mineral closure temperatures, and bulk composition all provide evidence that Tafassasset partially melted on its parent body. A comparison with the CR chondrites, the brachinites, and two anomalous Achondrites indicates that Tafassasset is most similar to ungrouped primitive Achondrites Lewis Cliff (LEW) 88763 and Divnoe, and to the brachinites in overall petrography, modal mineralogy, mineral compositions, oxidation state, and bulk composition. The comparison also excludes the possibility that Tafassasset formed by partial melting of a CR chondrite. Tafassasset is a primitive achondrite and likely evolved on a parent body that experienced incomplete melting, never reached isotopic homogeneity, and was from the same oxygen isotopic reservoir as the CR chondrite parent body.

  • Oxygen isotope variation in primitive Achondrites: The influence of primordial, asteroidal and terrestrial processes
    Geochimica et Cosmochimica Acta, 2012
    Co-Authors: Richard C. Greenwood, Ian A. Franchi, J. M. Gibson, Gretchen Benedix
    Abstract:

    A detailed oxygen isotope study of the acapulcoites, lodranites, winonaites, brachinites and various related Achondrites has been undertaken to investigate the nature of their precursor materials. High levels of terrestrial alteration displayed by many of these samples have been mitigated by leaching in ethanolamine thioglycollate (EATG) solution. Due to their high metal and sulphide content, acapulcoite, lodranite and winonaite samples show much greater isotopic shifts during weathering than brachinites. As observed in previous studies, Antarctic weathered finds are displaced to lighter oxygen isotope compositions and non-Antarctic finds to heavier values. Leached primitive achondrite residues continue to show high levels of oxygen isotope heterogeneity. This variation is reflected in the 2σ error on group mean Δ17O values, which decrease in the following order: acapulcoite–lodranite clan > brachinites > winonaites. On an oxygen three-isotope diagram, the acapulcoite––lodranite clan define a limited trend with a slope of 0.61 ± 0.08 and an intercept of −1.43 ± 0.27 (R2 = 0.78). A broad positive correlation between Δ17O and olivine fayalite contents displayed by both acapulcoite and lodranite samples may be the result of early aqueous alteration and subsequent dehydration. Winonaites experienced a greater degree of differentiation than the acapulcoite–lodranite clan and define a distinct mass fractionation line, with a slope of 0.53 ± 0.01 and an intercept of −0.53 ± 0.04 (R2 = 1). A number of samples currently classified as acapulcoites (NWA 725, NWA 1052 and Dho 1222) have oxygen isotope compositions indicating that they are winonaites. The relatively high level of oxygen isotope heterogeneity displayed by the brachinites supports their designation as primitive Achondrites. A number of ungrouped olivine-rich Achondrites (Divnoe, NWA 4042, NWA 4363, NWA 4518, NWA 5400, Zag (b)) as well as the unique plagioclase-rich Achondrites GRA 06128 and GRA 06129 have similar oxygen isotope compositions to the brachinites. It remains unclear whether the brachinites and related olivine-rich Achondrites are from a single or multiple parent bodies. The primitive Achondrites and related samples represent material from at most only 18 parent bodies, compared to an estimated 65 for the iron meteorites. This suggests that asteroidal mantle material is underrepresented in the meteorite record. Early fragmentation of differentiated asteroids, followed by preferential destruction of their silicate-rich mantles, offers a possible explanation for this discrepancy. On an oxygen three-isotope diagram, primitive chondrule-bearing winonaites (Dho 1222, NWA 725, NWA 1052, NWA 1463, Mt. Morris (Wisconsin)) plot close to the Young & Russell (Y&R) slope 1 line, with more evolved samples extending away from it towards the CCAM line. A similar relationship is shown by the CR chondrites. The acapulcoite–lodranite clan plots between the slope 1 and CCAM lines. However, the precursor material to the clan may have had a composition close to the slope 1 line prior to parent body processing. These relationships support the view that primordial oxygen isotope variation in the early solar system is best represented by the slope 1 (Y&R) line.