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17 O variation in Solar System materials expressed in terms of the difference between the highest and lowest values for each major meteorite group (range). Abbreviations: C chon: carbonaceous chondrites; E chon: enstatite chondrites; O chon: ordinary chondrites; Prim achon: primitive achondrites (Ur: ureilites, A-L: acapulcoitelodranite suite, Br: brachinites, W: winonaites); Planets (L: lunar rocks, M: martian meteorites, T: terrestrial high He-olivines); Diff achon: differentiated achondrites (ED: eucrites and diogenites, MP: main-group pallasites, Me: mesosiderites, An: angrites, Au: aubrites). Full data and references: Table S1.
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A number of distinct methodologies are available for determining the oxygen isotope composition of minerals and rocks, these include laser-assisted fluorination, secondary ion mass spectrometry (SIMS) and UV laser ablation. In this review we focus on laser-assisted fluorination, which currently achieves the highest levels of precision available for...
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... For most applications, Vienna Standard Mean Ocean Water (VSMOW) is used as a reference point defining the origin (Lin et al., 2010) and to anchor the terrestrial fractionation line (TFL; Clayton & Mayeda, 1984). We illustrate bulk meteorite compositions in Figure 6 (data from various sources, e.g., Greenwood et al., 2017Greenwood et al., , 2020and references therein). For isotopically heterogeneous materials such as chondrites, the use of secondary ion mass spectrometry (SIMS) to investigate grain-scale variations in threeoxygen isotope ratios has also generated a significant body of lower precision data, including for forsteritic olivine in enstatite chondrites (Weisberg et al., 2010(Weisberg et al., , 2021. ...
... Data are presented in delta-notation (δ 18 O and Δ 17 O), that is, per mille (‰) variations relative to VSMOW and the Terrestrial Fractionation Line (TFL). Enstatite chondrite chondrule compositions are given by black squares (Clayton et al., 1991;Clayton & Mayeda, 1985;Tanaka & Nakamura, 2017) and all bulk meteorites are in gray squares (Greenwood et al., 2017(Greenwood et al., , 2020; and references therein). Major meteorite groups are indicated either by a line showing the average Δ 17 O of achondrites (from Greenwood et al., 2017) or the general areas indicated for chondrites. ...
... Enstatite chondrite chondrule compositions are given by black squares (Clayton et al., 1991;Clayton & Mayeda, 1985;Tanaka & Nakamura, 2017) and all bulk meteorites are in gray squares (Greenwood et al., 2017(Greenwood et al., , 2020; and references therein). Major meteorite groups are indicated either by a line showing the average Δ 17 O of achondrites (from Greenwood et al., 2017) or the general areas indicated for chondrites. Lower precision compositions of forsteritic olivine in enstatite chondrites (Weisberg et al., 2010(Weisberg et al., , 2021 are given by a two-dimensional probability distribution plot with contours at 5% intervals of total peak height. ...
The occurrence of forsteritic olivine in EH enstatite chondrites is indicative of bulk disequilibrium. In MgO‐rich magmatic systems, forsterite can either crystallize as a liquidus phase or be produced during peritectic melting of enstatite. Because diffusion of divalent cations through forsterite is relatively rapid, it records peak melting (i.e., chondrule‐forming events) and is also sensitive to subsequent metamorphism in the EH chondrite parent body. Here, we report the major and minor element geochemistry of olivine in EH chondrites across petrologic types 3 and 4. In all cases, olivine meets the technical definition of forsterite (>90 mole% Mg 2 SiO 4 ). For unequilibrated EH chondrites, minor elements identify CaO‐Al 2 O 3 ‐TiO 2 ‐rich (refractory forsterite), MnO‐rich (“LIME” forsterite), and FeO‐bearing (forsteritic olivine) endmember components, the latter with Cr 2 O 3 ‐rich and Cr 2 O 3 ‐poor varieties. At higher petrologic type, minor element concentrations become restricted and compositions approach pure forsterite, while grain sizes reduce strongly with peak metamorphic temperatures. These changes reflect diffusive equilibration with enstatitic groundmass and dissolution reaction with free silica. The global geochemical distribution of forsteritic olivine in EH chondrites is, perhaps unexpectedly, more similar to those in low‐FeO type I chondrules and associated objects in carbonaceous chondrites (CCs), rather than equivalent objects in ordinary (H, L, LL), low‐FeO (or HH), or Kakangari (K) chondrites. Among achondrites, there is similarity between pure forsterite in aubrites and EH4 chondrites arising due to subsolidus equilibration in both settings, while Cr 2 O 3 ‐poor forsteritic olivine in EH3 and CCs is similar to magnesian xenocrystic olivine in angrites. This might reflect CaO‐rich and SiO 2 ‐poor magmatic sources across multiple early solar system reservoirs.
... The combination in ALs of a near-chondritic composition largely undepleted in incompatible elements and textural evidence for subsolidus recrystallization with limited melting is the hallmark of a primitive achondrite group. ALs are thought to represent a single, distinct parent body from known meteorites based on their unique oxygen isotope compositions and abundances of volatiles, lithophile, and siderophile elements (Greenwood et al., 2012(Greenwood et al., , 2017Keil & McCoy, 2018). ...
Primitive achondrites like the acapulcoites‐lodranites (AL) clan are meteorites that formed on bodies in the process of forming a metallic core, providing a unique window into how early solar system processes transformed unmelted material into differentiated bodies. However, the size and structure of the parent body of ALs and other primitive achondrites are largely unknown. Paleomagnetism can establish the presence or absence of a metallic core by looking for evidence of a dynamo field. We conducted a magnetic study of the Acapulco acapulcoite to determine its ferromagnetic minerals and their recording properties. This is the first detailed rock magnetic and first paleomagnetic study of a primitive achondrite group. We determined that metal inclusions inside silicate grains consist of two magnetic minerals, kamacite and tetrataenite, which have robust recording properties. However, the mechanisms and timing by which these minerals acquired any natural remanent magnetization are unknown. Despite this, Acapulco has not been substantially remagnetized since arriving on Earth and therefore should retain a record dating to 4.55 billion years ago. Future studies could characterize this record by using high‐resolution magnetometry measurements of individual populations of grains and developing an understanding of how and when they became magnetized. Our discovery of tetrataenite in ALs provides the first mineralogical evidence for slow cooling [<∼5–10 × 10³°C per million years (Ma⁻¹)] of the AL parent body at low temperatures (∼320°C). Its presence suggests the AL parent body is unlikely to have been catastrophically disrupted at AL peak temperatures (∼1,200°C) without subsequent reaccretion.
... The Δ 17 O isotopic value is − 0.078 ± 0.019 ‰ (2SD, n = 2) and the Ɛ 54 Cr value is − 0.60 ± 0.32 (2SD, n = 6). Such isotopic compositions are consistent with other angrites ( Fig. 1; Greenwood et al., 2017;Vaci et al., 2021;Rider-Stokes et al., 2023), confirming the previous classification based on the mineralogical features of NWA 12774 (Gattacceca et al., 2020). ...
... Aubrites are the group of achondrites that most closely matches the O (Greenwood et al., 2017) and nucleosynthetic (e.g., Ca, Ti, Cr, Ni; Burkhardt et al., 2019; references therein) isotopic composition of the Earth -Moon system. Aubrites are considered to have formed under highly reducing conditions (about 5 to 7 log units below the iron -wüstite (IW) oxygen fugacity buffer; Righter et al., 2006), potentially indicating their formation in the innermost portion of the solar protoplanetary disk (Kallemeyn and Wasson, ever, there is petrologic and geochemical evidence that there was subsolidus redistribution of trace elements, potentially linked to thermal metamorphism (Barrat et al., 2016;Okada et al., 1988). ...
Aubrites and enstatite chondrites (ECs) are isotopically similar to the Earth and therefore may resemble the primary materials that accreted to form our planet. Recent bulk H elemental and isotopic analyses of ECs and the Norton County aubrite suggest that enstatite-rich materials are H-rich and may represent a significant source of terrestrial water, with measured values of 3000±2000 μg/g H 2 O and 5300±900 μg/g H 2 O in the bulk and enstatite fractions of Norton County (Piani et al., Science, 2020). Here, we present a detailed investigation of in situ H 2 O concentrations in enstatite, diopside, forsterite, and plagioclase from a suite of main group aubrites, including Norton County, and Shallowater. We find that enstatite (4±2 μg/g H 2 O), diopside (4.8±0.5 μg/g H 2 O), and forsterite (5±3 μg/g H 2 O) have similar H 2 O concentrations, and all are significantly lower than plagioclase (24±3 μg/g H 2 O). We combine our in situ analyses of H 2 O contents with equilibrium partition coefficients and bulk mineralogies to estimate the bulk H 2 O content of our samples. We compare these first order estimates with bulk volatile analyses conducted using sample pyrolysis and find that the previous bulk H 2 O analyses of aubrites predominantly reflect terrestrial contamination and alteration. If our conclusion that the reported bulk H 2 O analyses of Norton County primarily reflect terrestrial contamination and alteration extends to bulk analyses of ECs, then EC-like material may not be a significant source of terrestrial water. Our results support the hypothesis that thermal metamorphism, melting, and differentiation leads to efficient desiccation of planetesimals relative to chondrites, and that differentiated planetesimals contributed, at most, trace amounts to Earth's water budget.
... ‰; Bunch et al., 2005), while the maingroup pallasite's average D 17 O is −0.187±0.016‰ (Greenwood et al., 2017). These data suggest that Zinder, despite its NC origin, is also not directly related to main-group pallasites. ...
Complex interelement trends among magmatic IIIF iron meteorites are difficult to explain by fractional crystallization and have raised uncertainty about their genetic relationships. Nucleosynthetic Mo isotope anomalies provide a powerful tool to assess if individual IIIF irons are related to each other. However, while trace-element data are available for all nine IIIF irons, Mo isotopic data are limited to three samples. We present Mo isotopic data for all but one IIIF irons that help assess the genetic relationships among these irons, together with new Mo and W isotopic data for Fitzwater Pass (classified IIIF), and the Zinder pallasite (for which a cogenetic link with IIIF irons has been proposed). After correction for cosmic-ray exposure, the Mo isotopic compositions of the IIIF irons are identical within uncertainty and confirm their belonging to carbonaceous chondrite-type (CC) meteorites. The mean Mo isotopic composition of Group IIIF overlaps those Groups IIF and IID, but a common parent body for these groups is ruled out based on distinct trace element systematics. The new Mo isotopic data do not argue against a single parent body for the IIIF irons, and suggest a close genetic link among these samples. By contrast, Fitzwater Pass has distinct Mo and W isotopic compositions, identical to those of some non-magmatic IAB irons. The Mo and W isotope data for Zinder indicate that this meteorite is not related to IIIF irons, but belongs to the non-carbonaceous (NC) type and has the same Mo and W isotopic composition as main-group pallasites.
... However, a portion of the achondrites remains ungrouped. They represent the products of material that experienced variable levels of differentiation and they presumably come from different bodies with respect to those ascribed to the existing meteorite groups of achondrites (Mittlefehldt, 2014;Greenwood et al., 2017). ...
... However, even if Al Huwaysah 010 shows similar oxygen isotope values of the brachinites (δ 17 O = 2.31‰, δ 18 O = 4.73‰, and Δ 17 O = À0.15‰, Greenwood et al., 2017), the composition of some mineral phases is different when compared with the same phases occurring in the brachinites (Day et al., 2012;Grady et al., 2014;Greenwood et al., 2017;Mittlefehldt et al., 2003). ...
... However, even if Al Huwaysah 010 shows similar oxygen isotope values of the brachinites (δ 17 O = 2.31‰, δ 18 O = 4.73‰, and Δ 17 O = À0.15‰, Greenwood et al., 2017), the composition of some mineral phases is different when compared with the same phases occurring in the brachinites (Day et al., 2012;Grady et al., 2014;Greenwood et al., 2017;Mittlefehldt et al., 2003). ...
Al Huwaysah 010 is an ungrouped achondrite meteorite, recently referred to as a brachinite‐like meteorite. This meteorite, showing a fine‐grained assemblage of low‐Ca pyroxene and opaque phases, is strongly reduced in comparison to other reduced brachinites. The occurrence of some tiny plates of graphite and oldhamite in this meteorite suggests that a partial melt residue has experienced a further reduction process. Olivine, the most abundant phase, is compositionally homogeneous (Fo 83.3 ) as well as the clinopyroxene (En 45.5 Fs 10.8 Wo 43.7 ) and the plagioclase (Ab 69.5 ). Orthopyroxene (En 85.4 Fs 13.9 Wo 0.7 ) also occurs but only in a fine intergrowth. Other accessory phases are Fe metal grains (Ni‐free or Cr‐bearing Fe‐Ni alloy), troilite, chlorapatite, pentlandite (as inclusions in chromite). The sample shows two different closure temperatures: the highest (≈900°C) is determined via the olivine–chromite intercrystalline geothermometer and the lowest temperature (≈520°C) is determined via the pyroxene‐based intracrystalline geothermometer. These temperatures may represent, respectively, the closure temperature associated with the formation and a subsequent impact event excavating the sample from the parental body. The visible to near‐infrared (VNIR) reflectance spectra of Al Huwaysah 010 exhibit low reflectance, consistent with the presence of darkening components, and weak absorptions indicative of olivine and pyroxene. Comparing the spectral parameters of Al Huwaysah 010 to potential parent bodies characterized by olivine–pyroxene mineralogy, we find that it falls within the field previously attributed to the SIII type asteroids. These results lead us to classify the Al Huwaysah 010 meteorite as the most reduced brachinite, whose VNIR spectral features show strong affinities with those of SIII asteroids.
... The oxygen isotope compositions of bulk angrites have previously been reported as displaying a high level of homogeneity, particularly with regard to 17 O excess (Δ 17 O), indicating that all the currently identified angritic meteorites originated from a single parent body and probably underwent early isotopic homogenization in a global magma ocean 8,9 . Although many angrites display limited evidence of shock deformation, indicating that the APB was not affected by multiple impact events 10 , it has been suggested that the quenched angrites may represent impact melts 11,12 . ...
... We collected high-precision, oxygen three-isotope data on bulk-rock samples from nine angrites, encompassing all petrologic subgroups ( Supplementary Fig. 1), using laser-assisted fluorination following established procedures 9,15 . In addition, separated olivine and groundmass fractions from A 881371, A 12209 and NWA 12320 were also analysed for their oxygen isotopic compositions. ...
Angrite meteorites are thought to represent ancient basaltic igneous rocks that formed inward of Jupiter’s orbit on the basis of their isotopic parameters such as ε⁵⁰Ti, ε⁵⁴Cr and Δ¹⁷O in addition to Fe/Mn ratios of pyroxene. New bulk oxygen isotope measurements of nine angrites, and of olivine ‘xenocrysts’ and groundmass fractions from three quenched angrites, however, reveal clear isotopic disequilibrium, implying an impact melt origin. Groundmass fractions from Asuka 12209, Asuka 881371 and Northwest Africa 12320 quenched angrites demonstrate an average Δ¹⁷O value of −0.003 ± 0.020‰. Here, excluding the bulk value and all groundmass fractions of Northwest Africa 12320, which is contaminated by an impactor, we determine a new well constrained average Δ¹⁷O value for the angrite parent body (−0.066 ± 0.016‰). Microstructural investigations of Northwest Africa 12320 reveal the presence of both fully recrystallized and undeformed olivine xenocrysts, indicating that some xenocrysts underwent high-temperature processes. These results suggest that angrites bear signatures of impact-driven isotopic mixing, possibly in response to early giant planet migration. The evidence for impact mixing raises doubts about the utility of quenched angrites as a suitable Pb–Pb isotopic anchor, which in turn has consequences for accurately defining the timeline of other Solar System events.
... Stony meteorites that have undergone differentiation are called achondrites. Some achondrites (such as howardites, eucrites, diogenites, and angrites) exhibit igneous textures (e.g., Stolper, 1975); they are usually enriched in incompatible lithophile elements and homogeneous in isotope compositions (e.g., Mittlefehldt, 2014;Greenwood et al., 2017). These igneous achondrites are generally thought to be formed by magma crystallization, although whether such magmas represent extracted melts from partially molten mantles or residual liquids of entirely molten mantles Nicklas et al., 2022). ...
Primitive achondrites represent residual mantle material of planetesimals from which up to 20% partial melts were extracted. Melting experiments on chondritic compositions suggest that melts produced by <~20% partial melting are rich in silica and alkali elements. Such melts are highly viscous (>~10^3 Pa.s), and percolation models predict that they would only migrate negligible distances over timescales of 1–10 Myr. After these timescales, a planetesimal would either be melted into a magma ocean by radiogenic heating from 26Al, if it formed early; or it would cool below solidus, if it formed relatively late. However, melt migration is also controlled by permeability, which could be high for aggregates of rock boulders (compared to those of mineral grains). Specifically, the theory of planet formation suggests that collisions occurred frequently between planetesimals in the early solar system. These collisions may have shattered the planetesimals into fragments with sizes of meters to tens of meters, which would have accreted gravitationally into one or more daughter bodies. We develop a model to investigate melt migration in “rubble-pile” planetesimals; in particular, the melt exchange between partially molten rock boulders and the void space between them. The results suggest that, with typical properties of primitive achondrite materials at the conditions of low-degree partial melting, melts may have been squeezed into the voids between boulders, and migrated rapidly through these channels. Therefore, primitive achondrites may record melt migration in rubble-pile bodies reaccreted from fragments of partially molten planetesimals.
... A correlated variation plot between ferrosilite (Fs) content of low-Ca pyroxene and fayalite (Fa) content of olivine in primitive achondrites is often used for this purpose. Criteria to distinguish winonaites from acapulcoites include: (i) highly reduced assemblage, among which typically Mg-rich olivine and Mg-rich pyroxene, as well as the presence of highly reduced accessory minerals such as alabandite, daubr eelite, and schreibersite; (ii) modal abundance of metal, troilite, and olivine; (iii) major element composition of pyroxene and chromite; (iv) bulk composition (Floss, 2000); and (v) oxygen isotopes Greenwood et al., 2012Greenwood et al., , 2017. Because the latter is not always measured to classify a meteorite (e.g., Keil & McCoy [2018] report that more than 50% of classified acapulcoites are lacking oxygen isotopic data), meteoriticists rely mostly on these mineralogy and chemistry criteria. ...
... Oxygen isotope analysis was performed at the Open University (OU), using an infrared laser-assisted fluorination system (Greenwood et al., 2017) on NWA 090. Oxygen was released from the sample (approximate weight of 2 mg) by heating in the presence of BrF5. ...
... This criterion has been argued to be the sole criterion that can accurately discriminate winonaites and acapulcoites (Li et al., 2011). As highlighted by Greenwood et al. (2012Greenwood et al. ( , 2017, samples need to be pretreated for the removal of terrestrial weathering products. The absence of EATG treatment produces consequent shift in oxygen isotopes. ...
The Northwest Africa (NWA) 090 meteorite, initially classified as an acapulcoite, presents petrological, chemical, and isotopic characteristics comparable to a group of seven primitive winonaites: Dhofar 1222, NWA 725, NWA 1052, NWA 1054, NWA 1058, NWA 1463, and NWA 8614. Five of these samples were previously classified as acapulcoites or ungrouped achondrites before being reclassified as winonaites based on their oxygen isotopic compositions. These misclassifications are indicative of the particular compositional nature of these primitive achondrites. All contain relict chondrules and a lower closure temperature of metamorphism of 820±20°C compared to other typical winonaites, as well as mineral elemental compositions similar to those of acapulcoites. The oxygen isotopic signature of these samples, d17 O of 1.18±0.17‰, d18O of 3.18±0.30‰, and D 17O of -0.47±0.02, is in fact resolvable from both acapulcoites and winonaites. We investigate the relationship between these eight primitive achondrites, typical winonaites, and acapulcoites, to redefine petrological, mineralogical, and geochemical criteria of primitive achondrite classification. Distinguishing between winonaites, acapulcoites, and this group of eight primitive achondrites can be unambiguously done using a combination of several mineralogical and chemical criteria. A combination of olivine fayalite content and FeO/ MnO ratio, as well as plagioclase potassium content allow us to separate these three groups without the absolute necessity of oxygen isotope analyses. NWA 090 as well as the other seven primitive achondrites, although related to winonaites, are most likely derived from a parent body distinct from winonaites and acapulcoites-lodranites, and define a new group of primitive achondrites that can be referred to as tissemouminites.
... The sample chamber configuration was also modified so that it could be removed from the fluorination line under vacuum and then opened within the nitrogen-filled glove box. The two-part chamber was made vacuum tight using a compression seal with a copper gasket and quick-release KFX clamp 6 . A 3-mm-thick BaF 2 window at the top of the chamber allowed simultaneous viewing and laser heating of samples. ...
... Oxygen isotopic compositions of Ryugu samples and carbonaceous chondritesNOTES All analyses this study except *from Ito et al.7 and ** from Greenwood et al.6 . $ mass was estimated based on measured 17% yield for particle C68 -see methods for further details. ...
The delivery of water to the inner Solar System, including Earth, is still a debated topic. A preferential role for hydrated asteroids in this process is supported by isotopic measurements. Carbonaceous chondrite (CC) meteorites represent our main source of information about these volatile-rich asteroids. However, the destruction of weaker materials during atmospheric entry creates a bias in our CC data. The return of surface materials from the C-type asteroid 162173 Ryugu by the Hayabusa2 spacecraft provides a unique opportunity to study high-porosity, low-density, primitive materials, unrepresented in the meteorite record. We measured the bulk oxygen isotope composition from four Ryugu particles and show that they most closely resemble the rare CI (CC Ivuna-type) chondrites, but with some differences that we attribute to the terrestrial contamination of the CI meteorites. We suggest that CI-related material is widespread among carbonaceous asteroids and a more important source of Earth’s water and other volatiles than its limited presence in our meteoritic collection indicates.
