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Dynamic models of the protoplanetary disk indicate there should be large-scale material transport in and out of the inner Solar System, but direct evidence for such transport is scarce. Here we show that the ε50Ti-ε54Cr-Δ17O systematics of large individual chondrules, which typically formed 2 to 3 My after the formation of the first solids in the Solar System, indicate certain meteorites (CV and CK chondrites) that formed in the outer Solar System accreted an assortment of both inner and outer Solar System materials, as well as material previously unidentified through the analysis of bulk meteorites. Mixing with primordial refractory components reveals a “missing reservoir” that bridges the gap between inner and outer Solar System materials. We also observe chondrules with positive ε50Ti and ε54Cr plot with a constant offset below the primitive chondrule mineral line (PCM), indicating that they are on the slope ∼1.0 in the oxygen three-isotope diagram. In contrast, chondrules with negative ε50Ti and ε54Cr increasingly deviate above from PCM line with increasing δ18O, suggesting that they are on a mixing trend with an ordinary chondrite-like isotope reservoir. Furthermore, the Δ17O-Mg# systematics of these chondrules indicate they formed in environments characterized by distinct abundances of dust and H2O ice. We posit that large-scale outward transport of nominally inner Solar System materials most likely occurred along the midplane associated with a viscously evolving disk and that CV and CK chondrules formed in local regions of enhanced gas pressure and dust density created by the formation of Jupiter. [ABSTRACT FROM AUTHOR]

High-precision bulk aluminum-magnesium isotope measurements of calcium-aluminum-rich inclusions ( CAIs) from CV carbonaceous chondrites in several laboratories define a bulk 26Al-26Mg isochron with an inferred initial 26Al/27Al ratio of approximately 5.25 × 10−5, named the canonical ratio. Nonigneous CV CAIs yield well-defined internal 26Al-26Mg isochrons consistent with the canonical value. These observations indicate that the canonical 26Al/27Al ratio records initial Al/Mg fractionation by evaporation and condensation in the CV CAI-forming region. The internal isochrons of igneous CV CAIs show a range of inferred initial 26Al/27Al ratios, (4.2-5.2) × 10−5, indicating that CAI melting continued for at least 0.2 Ma after formation of their precursors. A similar range of initial 26Al/27Al ratios is also obtained from the internal isochrons of many CAIs (igneous and nonigneous) in other groups of carbonaceous chondrites. Some CAIs and refractory grains (corundum and hibonite) from unmetamorphosed or weakly metamorphosed chondrites, including CVs, are significantly depleted in 26Al. At least some of these refractory objects may have formed prior to injection of 26Al into the protosolar molecular cloud and its subsequent homogenization in the protoplanetary disk. Bulk aluminum and magnesium-isotope measurements of various types of chondrites plot along the bulk CV CAI isochron, suggesting homogeneous distribution of 26Al and magnesium isotopes in the protoplanetary disk after an epoch of CAI formation. The inferred initial 26Al/27Al ratios of chondrules indicate that most chondrules formed 1-3 Ma after CAIs with the canonical 26Al/27Al ratio. [ABSTRACT FROM AUTHOR]

Abstract: High precision SIMS 26Al–26Mg isotope analyses were performed for a pristine Type B1 CAI Leoville 3535-1 on multiple mineral phases that include aluminum-rich zoned melilite mantle (Åk20–Åk60), magnesium-rich melilite (Åk70), fassaite, spinel and anorthite in the core. The data yield a well-defined internal isochron with an inferred initial 26Al/27Al ratio of (5.002±0.065)×10−5, which is lower than those of bulk CAIs and pristine fine-grained CAIs. Assuming homogeneous distribution of 26Al in the early solar system, Leoville 3535-1 formed ∼50ka after the time corresponding to the bulk CAI isochron. One anorthite analysis near the grain boundary adjacent to melilite shows sub-μm-scale heterogeneous magnesium distribution, though the 26Al–26Mg data plot on the isochron regression. Thus, the internal 26Al–26Mg system of the CAI remained closed since the last melting event that crystallized anorthite. High precision magnesium isotope analyses of magnesium-rich minerals (fassaite, magnesium-rich melilite, and spinel) show a small amount of scatter from the regression line (∼0.1‰) beyond analytical uncertainties. Most spinel and some fassaite data are systematically displaced below and above the regression line, respectively. It is likely that spinel remained unmelted at the time of the last melting event, while fassaite and anorthite crystallized from a partial melt. The regression line made by fassaite and anorthite data shows an initial 26Al/27Al ratio indistinguishable from that using all data. Mass dependent fractionation of magnesium isotopes in spinel is the same as those in melilite and fassaite (δ25Mg∼5‰), indicating that magnesium isotope fractionation, presumably from evaporative magnesium loss, predated the last melting event. Thus a majority of the CAI appears to have escaped magnesium isotope exchange with nebular gas during the last melting event, except for the outer rim of the melilite mantle that shows slightly lower δ25Mg values. The 26Al–26Mg systematics of this Leoville Type B CAI suggest it experienced a final melting event at ∼50ka after the initial Al–Mg fractionation event. This may correspond to melting during the active protostar stage (known as “Class I”), during which sporadic high temperature heating events repeatedly affected refractory solids in the solar nebula. [Copyright &y& Elsevier]

Abstract: Calcium-, aluminum-rich inclusions (CAIs) are often enriched in the heavy isotopes of magnesium and silicon relative to bulk solar system materials. It is likely that these isotopic enrichments resulted from evaporative mass loss of magnesium and silicon from early solar system condensates while they were molten during one or more high-temperature reheating events. Quantitative interpretation of these enrichments requires laboratory determinations of the evaporation kinetics and associated isotopic fractionation effects for these elements. The experimental data for the kinetics of evaporation of magnesium and silicon and the evaporative isotopic fractionation of magnesium is reasonably complete for Type B CAI liquids (Richter F. M., Davis A. M., Ebel D. S., and Hashimoto A. (2002) Elemental and isotopic fractionation of Type B CAIs: experiments, theoretical considerations, and constraints on their thermal evolution. Geochim. Cosmochim. Acta 66, 521–540; Richter F. M., Janney P. E., Mendybaev R. A., Davis A. M., and Wadhwa M. (2007a) Elemental and isotopic fractionation of Type B CAI-like liquids by evaporation. Geochim. Cosmochim. Acta 71, 5544–5564.). However, the isotopic fractionation factor for silicon evaporating from such liquids has not been as extensively studied. Here we report new ion microprobe silicon isotopic measurements of residual glass from partial evaporation of Type B CAI liquids into vacuum. The silicon isotopic fractionation is reported as a kinetic fractionation factor, α Si, corresponding to the ratio of the silicon isotopic composition of the evaporation flux to that of the residual silicate liquid. For CAI-like melts, we find that α Si =0.98985±0.00044 (2σ) for 29Si/28Si with no resolvable variation with temperature over the temperature range of the experiments, 1600–1900°C. This value is different from what has been reported for evaporation of liquid Mg2SiO4 (Davis A. M., Hashimoto A., Clayton R. N., and Mayeda T. K. (1990) Isotope mass fractionation during evaporation of Mg2SiO4. Nature 347, 655–658.) and of a melt with CI chondritic proportions of the major elements (Wang J., Davis A. M., Clayton R. N., Mayeda T. K., and Hashimoto A. (2001) Chemical and isotopic fractionation during the evaporation of the FeO–MgO–SiO2–CaO–Al2O3–TiO2–REE melt system. Geochim. Cosmochim. Acta 65, 479–494.). There appears to be some compositional control on α Si, whereas no compositional effects have been reported for α Mg. We use the values of α Si and α Mg, to calculate the chemical compositions of the unevaporated precursors of a number of isotopically fractionated CAIs from CV chondrites whose chemical compositions and magnesium and silicon isotopic compositions have been previously measured. [Copyright &y& Elsevier]

Abstract: We have conducted systematic investigations of formation age, chemical compositions, and mineralogical characteristics of ferromagnesian chondrules in Yamato-81020 (CO3.05), one of the most primitive carbonaceous chondrites, to get better understanding of the origin of chemical groups of chondrites. The 26Al–26Mg isotopic system were measured in fourteen FeO-poor (Type I), six FeO-rich (Type II) and two aluminum-rich (Al-rich) chondrules using a secondary ion mass spectrometer. Excesses of 26Mg in plagioclase (1.0–13.5‰) are resolved with sufficient precision (mostly 0.4–6.6‰ at 2σ level) in all the chondrules studied except one. Chemical zoning of Mg and Na in plagioclase were investigated in detail in order to evaluate the applicability of 26Al–26Mg chronometer. We conclude that the Al–Mg isotope system of the chondrules in Y-81020 have not been disturbed by parent-body metamorphism and can be used as chronometer assuming homogeneous distribution of 26Al. Assuming an initial 26Al/27Al ratio of 5×10−5 in the early solar system, 26Al–26Mg ages were found to be 1.7–2.5Ma after CAI formation for Type I, 2.0–3.0Ma for Type II and 1.9 and 2.6Ma for Al-rich chondrules. The formation ages of ferromagnesian chondrules in Y-81020 are in good agreement with those of L and LL (type 3.0–3.1) chondrites in the literature, which indicates that common chondrules in the CO chondrite were formed contemporaneously with those in L and LL chondrites. The concurrent formation of chondrules of CO and L/LL chondrites suggests that the chemical differences between CO and L/LL chondrites might be caused by spatial separation of chondrule formation environments in the protoplanetary disk. [Copyright &y& Elsevier]

We measured oxygen isotope ratios of 16 silicate fragments from seven aerogel tracks (turnip-like type B tracks 77, 149, 172, 191, and 220; carrot-like type A tracks 22 and 175) of the comet 81P/Wild 2 collector from NASA's Stardust mission using secondary ion mass spectrometry. Thirteen were prepared by ultramicrotomy; three from track 220 were prepared by sputtering resin blocks using a SIMS Kohler beam, a new procedure aiming to mine as many cometary particles encased in aerogel/resin as possible. Combining new and literature results, we recognized that most silicate fragments of individual type B tracks have diverse mineralogy but consistent mass-independent fractionation of oxygen isotopes (Δ17O = δ17O − 0.52 × δ18O). These observations suggest that their impactors are loosely bound aggregates of unequilibrated materials originating mainly from similar protoplanetary disk regions, resembling the cluster IDP U2-20-GCA. Furthermore, silicate fragments from type A track 22 have almost identical mineralogy and Δ17O values, confirming that its impactor is a single chondrule-like fragment. The terminal particle of type A track 175 is pure forsterite with Δ17O of ∼ –23 ‰. Six iron-rich fragments of this study have positive oxygen isotope ratios (Δ17O∼ +2 ‰) and ordinary chondrite chondrule-like olivine compositions. Together with five similar fragments in the literature, a unique population (Mg# ≤ 86) of Wild 2 fragments that resemble chondrules from the inner solar system (O-E-R) chondrites or the outer solar system CH-CB chondrites was identified. The remaining 16O-poor Wild 2 fragments are Mg# ≥ 79 silicates with Δ17O ∼ –2 ‰ and a small amount of Mg# ≤ 79 silicates with Δ17O ∼ 0 ‰, which are most consistent with CR chondrite chondrules. Thus, we conclude that in addition to the possible major source of CR chondrite chondrule-like materials, the inner solar system or CH-CB chondrule-like materials are a minor component of comet Wild 2, like the cluster IDP U2-20-GCA. [ABSTRACT FROM AUTHOR]

Abstract: Experimental data are reported on Mg diffusion in plagioclase crystals with a range of anorthite content ( ), at temperatures between 800 and 1150 °C. Oriented and polished single crystals of anorthite ( ), labradorite ( ), andesine ( ) and oligoclase ( ) were each embedded in powered source material enriched in natural MgO or 25MgO and suspended in a furnace at constant temperature. Diffusion profiles in quenched samples were measured from the polished surface using SIMS depth profiling. The diffusion coefficient does not depend significantly on the Mg concentration gradient, and little anisotropy is observed between the b and c directions in labradorite. Diffusion coefficients increase systematically with decreasing , and the entire data set is described by , where R is the gas constant, T is absolute temperature, and the diffusion coefficient D is in /s. 26Al–26Mg ages in albite-rich plagioclase are much more easily reset than in anorthite, with closure temperatures up to 120–150 K lower. [Copyright &y& Elsevier]

Abstract: Highly precise and accurate ion microprobe analyses of oxygen three-isotope ratios in chondrules from the Acfer 094, one of the most primitive carbonaceous chondrites, show that chondrules preserve evidence for oxygen isotope heterogeneity in chondrule-forming regions of the solar nebula. Identical Δ17O values in most minerals and glass within each chondrule indicate that the oxygen isotope ratio in chondrule melt did not change during or after crystallization. Nearly half of the chondrules studied contain small amounts of olivine grains that have an oxygen isotope anomaly relative to other minerals and glass in the same chondrule. Most chondrules in Acfer 094 can be classified into two oxygen isotope groups (Δ17O∼−2‰ and Δ17O∼−5‰) indicating that the final melting of chondrules occurred within two distinct oxygen isotope reservoirs, probably representing the local protoplanetary disk immediately before planetesimal formation. One of these reservoirs (Δ17O∼−2‰) is observed from chondrules in other carbonaceous chondrites and from crystalline silicates in comet Wild 2, suggesting that crystalline silicates formed in an oxygen isotope reservoir of Δ17O∼−2‰ were widely distributed in the outer asteroid belt and throughout the outer solar nebula. Oxygen three-isotope ratios of minerals in chondrules from Acfer 094 are distributed along a newly defined Primitive Chondrule Minerals (PCM) line, which has slope ∼1 [δ17O=(0.987±0.013)×δ18O−(2.70±0.11)] and intersects the terrestrial fractionation line at δ18O=5.8±0.4‰. These data are distinct from, and plot between, the CCAM, and Young and Russell lines. The PCM line is interpreted to represent the mixing trend of extreme oxygen isotope reservoirs in the early solar system that were the primary oxygen isotope reservoir of solids that accreted to form planets including the Earth. [Copyright &y& Elsevier]

Abstract: We report 53Mn–53Cr and 26Al–26Mg isotopic data, obtained by in-situ SIMS analysis, for feldspathic clasts in polymict ureilites DaG 319 and DaG 165. The analyzed clasts belong to the “albitic lithology,” the most abundant population of indigenous feldspathic materials in polymict ureilites, and are highly fractionated igneous assemblages of albitic plagioclase, Fe-rich pyroxenes, phosphates, ilmenite, silica, and Fe(Mn, K, P, Ti)-enriched glass. Glass in DaG 165 clast 19 has extremely high and variable 55Mn/52Cr ratios (500–58,000) and shows correlated 53Cr excesses up to ∼1500‰, clearly indicating the presence of live 53Mn at the time of formation. The slope of the well-correlated isochron defined by glass and pyroxenes from this clast corresponds to (53Mn/55Mn)=(2.84±0.10)×10−6 (2σ). Data for less 55Mn/52Cr-enriched glasses from DaG 319 clast B1, as well as phosphates from several other clasts, are consistent with this isochron. The 53Mn/55Mn ratio obtained from the isochron implies that these clasts are 0.70±0.18Ma younger than the D''Orbigny angrite, corresponding to the absolute age of 4563.72±0.22Ma. Plagioclase in DaG 319 clast B1 has a fairly constant 27Al/24Mg ratio of ∼900 and shows resolvable 26Mg excesses of ∼2‰. The slope of the isochron defined by pyroxene and plagioclase in this clast is (3.0±1.1)×10−7 (2σ), corresponding to a time difference of 5.4 (−0.3/+0.5)Ma after CAI (assuming the canonical initial 26Al/27Al ratio of 5×10−5) and an age 0.5 (−0.3/+0.5)Ma younger than D''Orbigny. Its absolute age (relative to D''Orbigny) is 4563.9 (+0.4/−0.5)Ma, in agreement with the 53Mn–53Cr age from clast 19. These data provide the first high-precision age date, ∼5.4Ma after CAI, for ureilites, giving a minimum estimate for the age of differentiation of their parent asteroid. Interpretation of this age for the thermal and physical history of that asteroid depends on a number of currently unknown or model-dependent parameters, including its size, bulk composition, and oxidation state, and the petrologic relationship between the feldspathic clasts and main group ureilites. [Copyright &y& Elsevier]

We have performed in situ analyses of Li-Be-B and Al-Mg isotope systematics, and abundances of rare earth elements (REEs) in two Ca-Al-rich inclusions (CAIs) from the Ornans-like carbonaceous chondrite Yamato-81020 (CO3.05). The present CO CAIs are depleted in ultra-refractory heavy REEs (group II REE pattern), suggesting condensation of these CAIs or their precursors from the solar nebula. Initial 26Al/27Al ratios, (26Al/27Al) 0 , of these CO CAIs are found to be (4.8 ± 0.5) × 10–5 and (4.9 ± 0.3) × 10–5 (95% confidence), indicating their contemporaneous formation with a majority of CAIs from Vigarano-like carbonaceous (CV) chondrites. Melilite grains in the present CO CAIs show clear excesses in 10B, ranging from ∼370 to ∼4300‰ relative to the chondritic B isotopic composition, which are correlated well with 9Be/11B ratios. The correlation indicates in situ decay of 10Be in the present CO CAIs and yields initial 10Be/9Be ratios, (10Be/9Be) 0 , for the individual CAIs of (2.9 ± 0.6) × 10–3 and (2.2 ± 1.0) × 10–3 (95% confidence), which are significantly greater than the average (10Be/9Be) 0 = ∼0.7 × 10–3 recorded in CAIs from CV chondrites. The apparent variation in (10Be/9Be) 0 between the CO and CV CAIs, despite having indistinguishable (26Al/27Al) 0 of ∼5 × 10–5, provides evidence for heterogeneous distribution of 10Be in the CAI forming-regions at the very beginning of the Solar System. The elevated (10Be/9Be) 0 and group II REE patterns in the CO CAIs may reflect that compared with the CV CAIs having unfractionated REEs the present CO CAIs have formed closer to the Sun where 10Be was produced more efficiently through solar cosmic ray irradiation caused by solar flares. Alternatively, if the present CO CAIs and CV CAIs formed in the same region, and 26Al was distributed homogeneously at the CAI-forming region, our results indicate that solar cosmic ray fluxes at the forming region have fluctuated by a factor of six within a short duration (∼0.2 million years) inferred from the Al-Mg chronology. [ABSTRACT FROM AUTHOR]

PLACs (platy hibonite crystals) and related hibonite-rich calcium-, aluminum-rich inclusions (CAIs; hereafter collectively referred to as PLAC-like CAIs) have the largest nucleosynthetic isotope anomalies of all materials believed to have formed in the solar system. Most PLAC-like CAIs have low inferred initial 26 Al/ 27 Al ratios and could have formed prior to injection or widespread distribution of 26 Al in the solar nebula. In this study, we report 26 Al– 26 Mg systematics combined with oxygen, calcium, and titanium isotopic compositions for a large number of newly separated PLAC-like CAIs from the Murchison CM2 chondrite (32 CAIs studied for oxygen, 26 of these also for 26 Al– 26 Mg, calcium and titanium). Our results confirm (1) the large range of nucleosynthetic anomalies in 50 Ti and 48 Ca (our data range from −70‰ to +170‰ and −60‰ to +80‰, respectively), (2) the substantial range of Δ 17 O values (−28‰ to −17‰, with Δ 17 O = δ 17 O − 0.52 × δ 18 O), and (3) general 26 Al-depletion in PLAC-like CAIs. The multielement approach reveals a relationship between Δ 17 O and the degree of variability in 50 Ti and 48 Ca: PLAC-like CAIs with the highest Δ 17 O (∼−17‰) show large positive and negative 50 Ti and 48 Ca anomalies, while those with the lowest Δ 17 O (∼−28‰) have small to no anomalies in 50 Ti and 48 Ca. These observations could suggest a physical link between anomalous 48 Ca and 50 Ti carriers and an 16 O-poor reservoir. We suggest that the solar nebula was isotopically heterogeneous shortly after collapse of the protosolar molecular cloud, and that the primordial dust reservoir, in which anomalous carrier phases were heterogeneously distributed, was 16 O-poor (Δ 17 O ⩾ −17‰) relative to the primordial gaseous (CO + H 2 O) reservoir (Δ 17 O < −35‰). However, other models such as CO self-shielding in the protoplanetary disk are also considered to explain the link between oxygen and calcium and titanium isotopes in PLAC-like CAIs. [ABSTRACT FROM AUTHOR]

We report oxygen, calcium, titanium and 26 Al– 26 Mg isotope systematics for spinel-hibonite inclusions (SHIBs), a class of calcium–aluminum-rich inclusions (CAI) common in CM chondrites. In contrast to previous studies, our analyses of 33 SHIBs and four SHIB-related objects obtained with high spatial resolution demonstrate that these CAIs have a uniform Δ 17 O value of approximately −23‰, similar to many other mineralogically pristine CAIs from unmetamorphosed chondrites (e.g., CR, CV, and Acfer 094). Five SHIBs studied for calcium and titanium isotopes have no resolvable anomalies beyond 3 σ uncertainties. This suggests that nucleosynthetic anomalies in the refractory elements had been significantly diluted in the environment where SHIBs with uniform Δ 17 O formed. We established internal 26 Al– 26 Mg isochrons for eight SHIBs and found that seven of these formed with uniformly high levels of 26 Al (a multi-CAI mineral isochron yields an initial 26 Al/ 27 Al ratio of ∼4.8 × 10 −5 ), but one SHIB has a smaller initial 26 Al/ 27 Al of ∼ 2.5 × 10 −5 , indicating variation in 26 Al/ 27 Al ratios when SHIBs formed. The uniform calcium, titanium and oxygen isotopic characteristics found in SHIBs with both high and low initial 26 Al/ 27 Al ratios allow for two interpretations. (1) If subcanonical initial 26 Al/ 27 Al ratios in SHIBs are due to early formation, as suggested by Liu et al. (2012), our data would indicate that the CAI formation region had achieved a high degree of isotopic homogeneity in oxygen and refractory elements before a homogeneous distribution of 26 Al was achieved. (2) Alternatively, if subcanonical ratios were the result of 26 Al– 26 Mg system resetting, the clustering of SHIBs at a Δ 17 O value of ∼−23‰ would imply that a 16 O-rich gaseous reservoir existed in the nebula until at least ∼0.7 Ma after the formation of the majority of CAIs. [ABSTRACT FROM AUTHOR]

Northwest Africa (NWA) 5492 and Grosvenor Mountains (GRO) 95551 are metal-rich chondrites having silicate (olivine and pyroxene) compositions that are more reduced than those in other metal-rich chondrites, such as the CH and CB chondrites. Additionally, sulfides in NWA 5492 and GRO 95551 are more abundant and not related to the metal, as in the CB chondrites. Average metal compositions in NWA 5492 and GRO 95551 are close to H chondrite metal. Oxygen isotope ratios of NWA 5492 and GRO 95551 components (chondrules and fragments) show a range of compositions with most having Δ 17 O values >0‰. Since there is no matrix component, their average chondrule + fragment oxygen isotopic compositions are considered to be representative of whole rock and (Δ 17 O values) are sandwiched between the values for enstatite (E) and ordinary (O) chondrites. These data argue for a close relationship between NWA 5492 and GRO 95551 and suggest that they are the first examples of a new type of metal-rich chondrite. Oxygen isotope ratios of chondrules in NWA 5492 and GRO 95551 show considerable overlap with chondrules in O, E and R chondrites, with average compositions indistinguishable from LL3 chondrules, suggesting considerable mixing between these Solar System materials during chondrule formation and/or that their precursors experienced similar formation environments and/or processes. Another characteristic shared between NWA 5492 and GRO 95551 and O, E and R chondrites is that they are all relatively dry (low abundances of hydrated minerals), compared to many C chondrites and have fewer, smaller CAIs than many C chondrites. (No CAIs were found in NWA 5492 or GRO 95551 but they contain rare Al-rich chondrules.) We suggest that O, E, R and the NWA 5492 and GRO 95551 chondrites are closely related Solar System materials. [ABSTRACT FROM AUTHOR]

The Stardust spacecraft returned cometary samples that contain crystalline material, but the origin of the material is not yet well understood. We found four crystalline particles from comet 81P/Wild 2 that were apparently formed by flash-melting at a high temperature and are texturally, mineralogically, and compositionally similar to chondrules. Chondrules are submillimeter particles that dominate chondrites and are believed to have formed in the inner solar nebula. The comet particles show oxygen isotope compositions similar to chondrules in carbonaceous chondrites that compose the middle-to-outer asteroid belt. The presence of the chondrulelike objects in the comet suggests that chondrules have been transported out to the cold outer solar nebula and spread widely over the early solar system. [ABSTRACT FROM AUTHOR]

• Five out of 20 fragments (≥5 μm) in the giant cluster IDP U2-20GCA have chondrule-like textures. • Oxygen isotope systematics of crystalline silicate fragments are closest to Wild 2 particles and CR chondrite chondrules. • Four fragments likely sourced from the formation regions of ordinary, R, or CH-CB chondrite chondrules. Anhydrous interplanetary dust particles (IDPs) collected from Earth's stratosphere are the most primitive extraterrestrial materials that likely are the remnants of major building blocks of our solar system. While they probably originated from icy outer solar system comets, this hypothesis needs to be further verified via comparison with Wild 2 (a Jupiter-family comet) particles returned by the Stardust mission. Besides, the origins of their components can be further constrained by comparing with materials in primitive chondrite. Here we investigate the petrology and oxygen isotope systematics of 20 fragments extracted from a giant cluster IDP U2-20GCA. Fifteen are monomineralic or polymineralic fragments composed of olivine and/or pyroxene. Others are plagioclase/glass bearing fragments similar to barred-olivine chondrules, enstatite-rich chondrules, and Al-rich chondrules (ARC). They show a range of Mg# [mol% Mg/(Mg+Fe)] in olivine and pyroxene (99-75) and MnO and Cr 2 O 3 abundances in olivine that resemble Wild 2 particles. Individual fragments have relatively 16O-poor oxygen isotope ratios with δ 18 O and δ 17 O varying from − 6.2 ± 1.0 ‰ to 6.8 ± 1.9 ‰ and − 6.7 ± 2.6 ‰ to 5.3 ± 1.2 ‰ , respectively. Most fragments show Δ 17 O (= δ 17 O- 0.52 × δ 18 O) increasing from ∼ − 3 ‰ to ∼ 0 ‰ with decreasing Mg#, similar to those observed in Wild 2 particles and CR chondrite chondrules. Four fragments (including the ARC-like fragment) show oxygen isotope signatures of ordinary (O), R, or CH-CB chondrite chondrules. The similarities among the giant cluster IDP, Wild 2 particles, and primitive chondrite chondrules demonstrate (i) a cometary origin of anhydrous IDPs; (ii) the major source of crystalline silicates in comets is likely to be CR chondrite chondrule-like materials, while minor sources include O, R, or CH-CB chondrite chondrule-like materials. The conclusions support the hypothesis that anhydrous IDPs sampled extremely heterogeneous materials formed in wide solar system regions like Wild 2 particles. [ABSTRACT FROM AUTHOR]