An unusual chondritic xenolith was found in two sequentially prepared thin sections of a sample from the Krymka (LL3.2) chondrite. The xenolith has a rounded, slightly deformed shape of about 5 mm in apparent diameter and is partially surrounded by a double rim made of an inner fine-grained silicate-rich rim and an outer sulfide-rich rim. The xenolithic inclusion is characterized by partially equilibrated mineral constituents, a recrystallized chondritic texture with relic chondrules, and a high abundance of CAIs (0.11 vol%). Within the core of the xenolith, olivine and low-Ca pyroxene are the most abundant mineral phases, and randomly analyzed grains by grid analysis revealed mean compositions of Fa9.8 +/- 5.5 and Fs7.2 +/- 4.4Wo2.9 +/- 2.2 for olivine and low-Ca pyroxene, respectively. Within the entire clast, a feldspar-normative mesostasis is embedding all constituents, indicating partial melting of the xenolith, probably during impact metamorphism. Thus, the xenolithic clast is very likely an impact melt rock. Infrared (IR) spectroscopic studies revealed the dominance of olivine and low-Ca pyroxene in the obtained spectra from the fine-grained silicate-rich rim of the xenolith. Oxygen isotope analyses by SIMS show that, in the three-oxygen isotope diagram, most individual olivine grains from the xenolith plot within the field of bulk ordinary chondrites and their chondrules, except for three olivines: Two grains from the xenolith's core (Delta 17O = -1.6 +/- 0.5 parts per thousand and -2.4 +/- 0.5 parts per thousand) and one olivine from the rim (Delta 17O = -6.5 +/- 0.4 parts per thousand) show significant 16O enrichments. The chondritic impact melt rock studied here clearly demonstrates that this xenolithic clast formed prior to the Krymka parent body accretion within another pre-existing chondritic parent body. While previous studies have discussed a potential late-stage accretion of large Krymka constituents, the components within the apparent first-generation parent body experienced thermal annealing, and, subsequently, the xenolith suffered partial melting due to a shock event that probably caused this fragment to be ejected from its first-generation parent body.

Refractory inclusions [Ca,Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs)] in unmetamorphosed chondrites (petrologic type <= 3.0) have typically uniform O-16-rich solar-like compositions. The origin of oxygen-isotope heterogeneity within individual refractory inclusions from weakly metamorphosed (petrologic type > 3.0) chondrites remains controversial. It may reflect (i) condensation from a nebular gas having variable O-isotope composition, (ii) gas-solid or gas-melt O-isotope exchange with this gas, and/or (iii) O-isotope exchange with an O-16-depleted aqueous fluid in the host chondrite parent bodies. Here, we present the mineralogy, petrology and O-isotope compositions of refractory inclusions (12 CAIs and 2 AOAs) from the Rumuruti-type (R) chondrites of petrologic type 3 - Northwest Africa (NWA) 753, NWA 1471, and Dhofar 1123. The CAIs and AOAs are extensively altered: melilite is completely replaced by secondary minerals; perovskite is largely replaced by ilmenite; spinel and olivine are enriched in FeO. The polymineralic refractory inclusions have heterogeneous O-isotope compositions: Delta O-17 ranges from similar to-25 parts per thousand to similar to 5 parts per thousand (2 sigma = +/-similar to 2 parts per thousand). The only exception is a spinel-hibonite inclusion having uniform O-16-depleted composition (Delta O-17 similar to -14 parts per thousand). Hibonite, most ferroan spinel, and some olivine and Al,(Ti)-diopside grains in Rumuruti-type chondrite (RC) fragments of low petrologic type (3.15 - 3.2) retained their initial Delta O-17 values, which, however, range from -25 parts per thousand to similar to -14 parts per thousand, suggesting variations in O-isotope composition of nebular gas in the CAI-forming region. Most Al,Ti-diopside and some olivine and spinel grains in RC refractory inclusions are O-16-depleted compared to minerals most resistant to O-isotope exchange (hibonite and spinel) that retained their original compositions. The most O-16-depleted compositions of Al,Ti-diopside and ferroan olivine have Delta O-17 of similar to +5 parts per thousand that is similar to Delta O-17 of the aqueously formed grossular and ferroan olivine. We infer that the O-16-depleted Al,Ti-diopside, olivine, and spinel in isotopically heterogeneous refractory inclusions experienced post-formation O-isotope exchange with aqueous fluids in the RC parent asteroid(s).

The nature of isotopic differences between 'normal' Ca,Al-rich inclusions (CAIs) characterized by the canonical initial Al-26/Al-27 ratio [(Al-26/Al-27)(0)] of similar to 5 x 10(-5) and the anomalous refractory inclusions characterized by the significantly lower (Al-26/Al-27)(0), < similar to 3 x 10(-6), which include PLACs (platy hibonite crystals), PLAC-like inclusions, and some corundum-, hibonite-, and grossite-rich CAIs, remains controversial. The Al-26-poor inclusions may have formed earlier, prior to 'normal' CAIs, and recorded heterogeneous distribution of Al-26 in the CAI-forming region, or they may have formed after nearly complete decay of Al-26, similar to >4 Myr later than the canonical CAIs. Here we present the first high precision multi-isotopic (O, Mg, Ca, and Ti) study of refractory inclusions (RIs) in the EH(a)3 enstatite chondrite Sahara 97072 using in situ SIMS measurements. Our study revealed the presence of two isotopically distinct populations of CAIs in this meteorite: 'normal' CAIs and PLAC-like inclusions. The 'normal' CAIs composed of spinel, Al,Ti-diopside, +/- hibonite, and secondary minerals, most likely replacing melilite, have solar-like Delta O-17 of similar to-23 parts per thousand, similar to the canonical (Al-26/Al-27)(0), and no resolvable nucleosynthetic isotope anomalies in Ca and Ti. The PLAC-like inclusions composed of hibonite, corundum, and +/- Al,Ti-pyroxene have Delta O-17 of similar to-19 parts per thousand, no resolvable excess of radiogenic Mg-26, and large nucleosynthetic isotope anomalies in Ti and Ca: one inclusion has positive anomalies in Ti-50 (835 epsilon) and Ca-48 (685 epsilon), whereas another one has negative anomalies in Ti-50 (-116 epsilon), Ti-46 (-112 epsilon), Ca-48 (-284 epsilon). We infer that (i) PLAC-like inclusions formed in an isotopically heterogeneous reservoir in which Ca-48 and Ti-50 were coupled but both isotopes were decoupled from Ti-46 suggesting different carrier phases for Ca-48 + Ti-50 and Ti-46. (ii) 'Normal' CAIs formed in a reservoir with uniform distribution of Ca and Ti isotopes, possibly reflecting increasing homogenization of this region with time due to evaporation/condensation, mixing and aggregation of isotopically anomalous grains present in the protosolar molecular cloud. (iii) The observed differences in Delta O-17 of 'normal' and PLAC-like CAIs indicate their formation in nebular reservoirs with distinct O-isotope compositions, which could have resulted from evaporation of disk regions with different dust/gas ratios, assuming that dust and gas had different Delta O-17 values, possibly inherited from the protosolar molecular cloud. (iv) The Al-26-poor PLAC-like inclusions predate formation of 'normal' CAIs with the canonical (Al-26/Al-27)(0) supporting heterogeneous distribution of Al-26 in the CAI-forming region at the earliest stages of the protoplanetary disk evolution. This heterogeneity may have resulted from heterogeneous distribution of Al-26 in the protosolar molecular cloud or from thermal processing of presolar grains having different abundances of live Al-26 which were present in the molecular cloud with uniform distribution of Al-26/Al-27 ratio at the canonical level. We conclude that Al-26-Mg-26 systematics have a limited significance for the chronology of refractory inclusions.

Calcium, aluminum-rich inclusions (CAIs) are the oldest solids dated that formed in the solar system. Most CAIs in unmetamorphosed chondritic meteorites (chondrites; petrologic type ≤3.0) have uniform solar-like ^16 O-rich compositions (Δ ^17 O ∼ −24‰) and a high initial ^26 Al/ ^27 Al ratio [( ^26 Al/ ^27 Al) _0 ] of ∼(4–5) × 10 ^−5 , consistent with their origin in a gas of approximately solar composition during a brief (<0.3 Ma) epoch at the earliest stage of our solar system. The nature of O-isotope heterogeneity in CAIs (Δ ^17 O range from ∼−24 up to ∼+5‰) from weakly metamorphosed chondrites (petrologic type >3.0) remains an open issue. This heterogeneity could have recorded fluctuations of O-isotope composition of nebular gas in the CAI-forming region and/or postcrystallization O-isotope exchange of CAI minerals with aqueous fluids on the chondrite parent asteroids. To obtain insights into possible processes resulting in this heterogeneity, we investigated the mineralogy, rare-earth element abundances, and O- and Mg-isotope compositions of a CAI from the CO3.1 chondrite Dar al Gani 083. This concentrically zoned inclusion has a Zn-hercynite core surrounded by layers of (from core to edge) grossite, spinel, melilite, and Al-diopside. The various phases have heterogeneous Δ ^17 O (from core to edge): −2.2 ± 0.6‰, −0.9 ± 2.1‰, −13.7 ± 2.1‰, −2.6 ± 2.3‰, and −22.6 ± 2.1‰, respectively. Magnesium-isotope compositions of grossite, spinel, melilite, and Al-diopside define an undisturbed internal Al–Mg isochron with ( ^26 Al/ ^27 Al) _0 of (2.60 ± 0.29) × 10 ^−6 . We conclude that the variations in Δ ^17 O of spinel and diopside recorded fluctuations in O-isotope composition of nebular gas in the CAI-forming region prior to injection and/or homogenization of ^26 Al at the canonical level. The ^16 O depletion of grossite and melilite resulted from O-isotope exchange with asteroidal fluid, which did not disturb Al–Mg isotope systematics of the CAI primary minerals.

Calcium-aluminum-rich inclusions (CAIs) commonly observed in chondritic meteorites are the oldest dated solids formed in the Solar System. Short-lived isotope chronologies (Al-26-Mg-26, Hf-182-W-182) suggest a similar to 2 Ma gap between the formation of CAIs and the accretion of the final chondrite parent bodies. One thin section, 3.27 cm(2) in size, of an ordinary chondrite NWA 3358 (H3.1) studied contains 52 refractory inclusions (CAIs and amoeboid olivine aggregates (AOAs)) comprising 0.14 % of its area, which is the highest abundance of refractory inclusions among non-carbonaceous chondrites containing on average similar to 0.009 area % of CAIs and AOAs. In combination with a low chondrule/matrix ratio of similar to 1.5, this makes NWA 3358 a unique ordinary chondrite. The aqueously-formed fayalites (Fa(>99)) in NWA 3358 have the inferred initial Mn-53/Mn-55 ratio of (5.56 +/- 0.44) x 10(-6) which is the highest measured value for secondary minerals in chondrites and corresponds to the formation time of similar to 1.0-1.5 Ma after CAIs. Based on the Mn-53-Cr-53 chronology of fayalite formation and the thermal modeling, we infer that the first-generation of an H chondrite parent body, similar to 6-12 km in diameter, accreted within 1.0 Ma after formation of CAIs, filling the gap of similar to 2 Ma between CAIs and the earliest chondrite parent bodies. This early accretion provides a possible mechanism of CAIs/AOAs storage in the inner solar nebula and could explain the high amount of refractory inclusions in NWA 3358. A later destruction of these first-generation bodies may also explain the presence of CAIs and chondrules of different ages within later formed chondrite parent bodies.

Calcium-aluminum-rich inclusions (CAIs) are highly refractory objects found in different chondrite groups and represent some of the oldest known solids of the Solar System. As such, CAIs provide key information regarding the conditions prevailing in the solar protoplanetary disk as well as subsequent mixing and transport processes. Many studies have investigated CAIs for their isotopic compositions and reported nucleosynthetic isotope anomalies in numerous elements, which are typically explained by the variable incorporation of isotopically highly anomalous presolar phases. However, with the exception of 54Cr-enriched nanospinels, the exact presolar phases responsible for the isotopic heterogeneities are yet to be identified. To address this issue, we here present in-situ Ti isotopic analyses obtained on a diverse set of CAIs from various CV3 chondrites. The in-situ measurements were performed by targeting individual mineral phases of 15 CAIs with laser-ablation mass spectrometry and indicate significant inter- and intra-CAI isotopic heterogeneity in the neutron-rich isotope 50Ti. This is particularly pronounced for primitive fine-grained CAIs, whereas coarse-grained CAIs, which have been subject to melting, exhibit smaller degrees of Ti isotopic heterogeneity. To further investigate this Ti isotopic heterogeneity, we additionally obtained Ti isotopic compositions of sequential acid leachates from two fine-grained and two coarse-grained CAIs derived from CV3 chondrites. In contrast to potential expectations from the first part of the study, we do not observe any significant intra-CAI Ti isotopic heterogeneity between the different leaching steps. The lack of intra-CAI Ti isotopic heterogeneity in the acid leachate samples of this study likely reflects that the leaching procedure is unable to efficiently separate the carriers of isotopically anomalous Ti in CAIs. By comparing the bulk CAI Ti isotope compositions with Ti isotope data for hibonite-rich objects from the literature, we find that the range of Ti isotope compositions recorded by CAIs from various chondrite groups can be accounted for by the averaging of hibonite grains. In turn, the variable Ti isotope compositions of hibonite grains can be explained by the averaging of isotopically diverse presolar grains present in the Sun's parental molecular cloud. This effect of averaging is statistically supported by the central limit theorem, and the concept has the potential to be useful for other isotopic systems.

The early solar system was a dynamic period during which the formation of early solids set into motion the process of planet building. Although both astrophysical observations and theoretical modeling demonstrate the presence of widespread transport of material, we lack concrete quantitative constraints on timings, distances, and mechanisms thereof. To trace these transport processes, one needs objects of known early formation times and these objects would need to be distributed throughout parent bodies with known accretion times and distances. Generally, these criteria are met by "regular" (i.e., non-fractionated and unidentified nuclear and excluding hibonite-rich) Ca-Al-rich inclusions (CAIs) as these objects formed very early and close to the young Sun and contain distinctive nucleosynthetic isotope anomalies that permit provenance tracing. However, nucleosynthetic isotopic signatures of such refractory inclusions have so far primarily been analyzed in chondritic meteorites that formed within similar to 4 AU from the Sun. Here, we investigate Ti isotopic signatures of four refractory inclusions from the ungrouped carbonaceous chondrite WIS 91600 that was previously suggested to have formed beyond similar to 10 AU from the Sun. We show that these inclusions exhibit correlated excesses in Ti-50 and Ti-46 and lack large Ti isotopic anomalies that would otherwise be indicative of more enigmatic refractory materials with unknown formation ages. Instead, these isotope systematics suggest the inclusions to be genetically related to regular CAIs commonly found in other chondrites that have a broadly known formation region and age. Collectively, this implies that a common population of CAIs was distributed over the inner similar to 10 AU within similar to 3.5 Myr, yielding an average (minimum) speed for the transport of millimeter-scale material in the early solar system of similar to 1 cm s(-1).

MS‐MU‐012, a 15.5 g clast from the Almahata Sitta polymict ureilite, is the first known plagioclase‐bearing main group ureilite. It is a coarse‐grained (up to 4 mm), equilibrated assemblage of 52% olivine (Fo 88), 13% orthopyroxene (Mg# 89.2, Wo 4.5), 11% augite (Mg# 90.2, Wo 37.3), and 14% plagioclase (An 68), plus minor metal and sulfide. The plagioclase grains have been secondarily remelted and internally recrystallized, but retain primary external morphologies. Melt inclusions occur in olivine. Rounded chadocrysts of olivine and orthopyroxene are enclosed in augite grains. In terms of texture, mineralogy, major and minor element mineral compositions, and oxygen isotopes, MS‐MU‐012 is virtually identical to the archetypal Hughes‐type main group ureilites, with the significant addition of primary plagioclase. We conclude that MS‐MU‐012 formed as a cumulate in a common lithologic unit with the Hughes‐type ureilites. Based on reconstructed compositions of melts trapped in olivine, orthopyroxene, and augite in the Hughes‐type samples, we infer that the parent magma of the Hughes unit originated as a late melt in the incremental melting of the ureilite parent body (UPB), near the end of the melting sequence, but was not completely extracted from the mantle like earlier melts and was emplaced in an intrusive body. MELTS calculations indicate that olivine began to crystallize at ~1260 °C, followed shortly thereafter by co‐crystallization of orthopyroxene and augite. Plagioclase began to crystallize at ~1170–1180 °C. Graphite was buoyant in the melt and became heterogeneously distributed in flotation cumulates. Residual silicate liquid was extracted from the cumulate pile and could have crystallized to form the “labradoritic melt lithology” (with plagioclase of An ~68‐35), which is partially preserved as clasts in polymict ureilites. The final equilibration temperature recorded by the Hughes unit was ~1140–1170 °C, just before catastrophic disruption of the UPB. MS‐MU‐012 provides a critical missing link in the differentiation history of this asteroid.

On October 7, 2008, the asteroid 2008 TC3 exploded as it entered the Earth’s atmosphere, producing significant dust (in the atmosphere) and delivering thousands of stones in a strewn field in Sudan, collectively known as the Almahata Sitta (AhS) stones. About 600 fragments were officially recovered in 2008 and 2009. Further rocks were collected since the fall event by local people. From these stones, 249 were classified at the Institut für Planetologie in Münster (MS) known as MS‐xxx or MS‐MU‐xxx AhS subsamples. Most of these rocks are ureilitic in origin (168; 67%): 87 coarse‐grained ureilites, 60 fine‐grained ureilites, 15 ureilites with variable texture/mineralogy, four trachyandesites, and two polymict breccias. We identified 81 non‐ureilitic fragments, corresponding to 33% of the recovered samples studied in Münster. These included chondrites, namely 65 enstatite chondrites (43 EL; 22 EH), 11 ordinary chondrites (OC), one carbonaceous chondrite, and one unique R‐like chondrite. Furthermore, three samples represent a unique type of enstatite achondrite. Since all AhS stones must be regarded as individual specimens independent from each other, the number of fresh ureilite and enstatite chondrite falls in our meteorite collections has been increased by several hundred percent. Overall, the samples weigh between <1 and 250 g and have a mean mass of ~15 g. If we consider—almost 15 years after the fall—the mass calculations, observations during and after the asteroid entered the atmosphere, the mineralogy of the C1 stones AhS 91A and AhS 671, and the experimental work on fitting the asteroid spectrum (e.g., Goodrich et al., 2019; Jenniskens et al., 2010; Shaddad et al., 2010), the main portion of the meteoroid was likely made of the fine‐grained (carbonaceous) dust and was mostly lost in the atmosphere. In particular, the fact that C1 materials were found has important implications for interpreting asteroid 2008 TC3's early spectroscopic results. Goodrich et al. (2019) correctly suggested that if scientists had not recovered the “water‐free” samples (e.g., ureilites, enstatites, and OC) from the AhS strewn field, 2008 TC3 would have been assumed to be a carbonaceous chondrite meteoroid. Considering that the dominating mass of the exploding meteoroid consisted of carbonaceous materials, asteroid 2008 TC3 cannot be classified as a polymict ureilite; consequently, we state that the asteroid was a polymict carbonaceous chondrite breccia, specifically a polymict C1 object that may have formed by late accretion at least 50–100 Ma after calcium–aluminum‐rich inclusions.

Understanding the genetic relationship between different chondritic components will help to decipher their origin and dynamical evolution within the protoplanetary disk. Here, we obtain insight into these processes by acquiring O-isotope data from 17 Al-rich chondrules from unequilibrated ordinary chondrites (OCs, petrologic type <= 3.2) and four Al-rich chondrules from the CO3.1 carbonaceous chondrite Dar al Gani (DaG) 083. These particular kinds of chondrules are of special interest, as it is suggested that their precursors may have contained refractory material related to Ca,Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs). The four investigated Al-rich chondrules from the CO3.1 chondrite Dar al Gani 083 consist of olivine, low-Ca pyroxene, Ca pyroxene, and spinel phenocrysts embedded in mostly Na-rich glassy mesostasis. Two chondrules have a homogeneous O-isotopic composition and two are heterogeneous in their O-isotopic composition. One chondrule contains relict spinel grains with a Delta O-1(7) value of -24.3 +/- 1.3 parts per thousand indicative of O-16-rich precursor refractory material, similar to constituents of CAIs and AOAs. The presence of CAI-like precursors for the Al-rich chondrules from CO chondrites is consistent with their previously reported presence of Ti-50 excesses (Ebert et al., 2018). The Al-rich chondrules in the ordinary chondrites studied consist of olivine, low-Ca pyroxene, Ca pyroxene, and, occasionally, spinel phenocrysts embedded in mostly Na-rich glassy mesostasis. Hibonite is present in one Al-rich chondrule. The vast majority of these chondrules have heterogeneous O-isotopic compositions: Chondrule glasses are O-1(6)-depleted compared to chondrule phenocrysts; the Delta O-17 values of the former approach those of aqueously formed fayalite and magnetite grains in type 3 OCs, +5 parts per thousand, We infer that the chondrule glasses experienced O-isotope exchange with an aqueous fluid on the OC parent asteroids. Chondrule phenocrysts, like spinel, olivine, low-Ca pyroxene, and Ca pyroxene, were not affected by this isotope exchange and preserved their initial O-isotope compositions. The phenocrysts within individual chondrules have similar Delta O-17, whereas the inter-chondrule Delta O-17 values range from -4.5 to +1.4 parts per thousand, i.e., they are in general O-1(6) enriched relative to the majority of ferromagnesian type I and type II porphyritic chondrules in OCs having Delta O-17 of similar to +1 parts per thousand. Because no relict grains were identified in the Al-rich chondrules from ordinary chondrites, the original O-isotopic composition of the refractory precursor material remains unknown. Additional detailed Na measurements within olivine grains show no major changes in the Na content of the chondrule melt during their crystallization. This implies either that the Na was part of the precursor material or that the Na was enriched in the chondrule melt/glass after crystallization of the olivines. (C) 2022 Elsevier Ltd. All rights reserved.

On July 15, 2021, a huge fireball was visible over Poland. After the possible strewn field was calculated, the first and so far only sample, with a mass of 350 g, was discovered 18 days after the fireball event. The Antonin meteorite was found August 3, 2021, on the edge of a forest close to a dirt road near Helenow, a small suburb of the city of Mikstat. The rock is an ordinary chondrite breccia and consists of equilibrated and recrystallized lithologies. The boundaries between different fragments are difficult to detect, and the lithologies are of petrologic type 5 and type 4. The rock is moderately shocked (S4) and contains local impact melt areas and thin shock veins. The low‐Ca pyroxene and olivine are equilibrated (Fs20.6 and Fa24.0, respectively), typical of L chondrites. The L chondrite classification is also supported by O isotope data and the results of bulk chemical analysis. The Ti isotope characteristics confirm that Antonin is related to the noncarbonaceous (NC) meteorites. One of the studied thin sections shows an unusual metal–chondrule assemblage, perhaps indicating that the metal in the chondrite is heterogeneously distributed, which is, however, not clearly visible in the element abundances.

CM chondrites are complex impact (mostly regolith) breccias, in which lithic clasts show various degrees of aqueous alteration. Here, we investigated the degree of alteration of individual clasts within 19 different CM chondrites and CM‐like clasts in three achondrites by chemical analysis of the tochilinite‐cronstedtite‐intergrowths (TCIs; formerly named “poorly characterized phases”). To identify TCIs in various chondritic lithologies, we used backscattered electron (BSE) overview images of polished thin sections, after which appropriate samples underwent electron microprobe measurements. Thus, 75 lithic clasts were classified. In general, the excellent work and specific criteria of Rubin et al. (2007) were used and considered to classify CM breccias in a similar way as ordinary chondrite breccias (e.g., CM2.2‐2.7). In BSE images, TCIs in strongly altered fragments in CM chondrites (CM2.0‐CM2.2) appear dark grayish and show a low contrast to the surrounding material (typically clastic matrix), and can be distinguished from TCIs in moderately (CM2.4‐CM2.6) or less altered fragments (CM2.7‐CM2.9); the latter are bright and have high contrast to the surroundings. We found that an accurate subclassification can be obtained by considering only the “FeO”/SiO 2 ratio of the TCI chemistry. One could also consider the TCIs’ S/SiO 2 ratio and the metal abundance, but these were not used for classification due to several disadvantages. Most of the CM chondrites are finds that have suffered terrestrial weathering in hot and cold deserts. Thus, the observed abundance of metal is susceptible to weathering and may not be a reliable indicator of subtype classification. This study proposes an extended classification scheme based on Rubin’s scale from subtypes CM2.0‐CM2.9 that takes the brecciation into account and includes the minimum to maximum degree of alteration of individual clasts. The range of aqueous alteration in CM chondrites and small spatial scale of mixing of clasts with different alteration histories will be important for interpreting returned samples from the OSIRIS‐REx and Hayabusa 2 missions in the future.

The nature of oxygen -isotope heterogeneity in refractory inclusions [Ca,Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs)] from weakly metamorphosed chondrites is one of the outstanding problems in cosmochemistry. To obtain insights into possible processes resulting in O -isotope heterogeneity of refractory inclusions, we investigated the min- eralogy, petrology, and oxygen isotopic compositions of six CAIs and two AOAs and aqueously formed fayalite grains within the matrix of the H3.1 chondrite Northwest Africa (NWA) 3358. Most of the refractory inclusions studied appear to be unmolten solar nebula condensates; some may have experienced partial melting and/or high -temperature annealing. The NWA 3358 refractory inclusions nearly completely avoided metasomatic alteration on the H-chondrite parent body: nephe- line grains replacing anorthite and/or melilite are either very minor or absent. Five out of eight refractory inclusions studied have heterogeneous O -isotope composition: A 17 O ranges from -- 25%0 to -3.5 ? 2%0 (2 r). This O -isotope heterogeneity appears to be mineralogically controlled with melilite and anorthite being systematically 16 O -depleted compared to hibonite, spinel, Al,Ti-diopside, and forsterite all having similar solar -like A 17 O of --24 ? 2%0. In contrast to NWA 3358 refractory inclusions, the previously studied AOAs and a fine-grained CAI from the LL3.00 chondrite Semarkona have uniform A 17 O of --25%0 (Itoh et al., 2007; McKeegan et al., 1998). Because the mineralogically-controlled O -isotope heterogeneity in refrac- tory inclusions from ordinary chondrites appears to correlate with petrologic type of a host meteorite experienced by aqueous alteration, we suggest O -isotope exchange in NWA 3358 CAIs and AOAs resulted from aqueous fluid -rock interaction on the H-chondrite parent asteroids. This is supported by the presence of 16 O -depleted anorthite (A 17 O - 3.5 ? 2%0) and aqueously formed fayalite similar depleted in 16 O (A 17 O - 4 ? 2%0). The A 17 O of NWA 3358 fayalite is comparable to that of magnetite and fayalite in Semarkona and other weakly metamorphosed L3 and LL3 chondrites (Choi et al., 1998; Doyle et al., 2015) suggesting similar A 17 O of aqueous fluids on the H, L, and LL chondrite parent asteroids. (C) 2020 Elsevier Ltd. All rights reserved.

Based on the high abundance of fine‐grained material and its dark appearance, NWA 11024 was recognized as a CM chondrite, which is also confirmed by oxygen isotope measurements. But contrary to known CM chondrites, the typical phases indicating aqueous alteration (e.g., phyllosilicates, carbonates) are missing. Using multiple analytical techniques, this study reveals the differences and similarities to known CM chondrites and will discuss the possibility that NWA 11024 is the first type 3 CM chondrite. During the investigation, two texturally apparent tochilinite–cronstedtite intergrowths were identified within two thin sections. However, the former phyllosilicates were recrystallized to Fe‐rich olivine during a heating event without changing the textural appearance. A peak temperature of 400–600 °C is estimated, which is not high enough to destroy or recrystallize calcite grains. Thus, calcites were never constituents of the mineral paragenesis. Another remarkable feature of NWA 11024 is the occurrence of unknown clot‐like inclusions (UCLIs) within fine‐grained rims, which are unique in this clarity. Their density and S concentration are significantly higher than of the surrounding fine‐grained rim and UCLIs can be seen as primary objects that were not formed by secondary alteration processes inside the rims. Similarities to chondritic and cometary interplanetary dust particles suggest an ice‐rich first‐generation planetesimal for their origin. In the earliest evolution, NWA 11024 experienced the lowest degree of aqueous alteration of all known CM chondrites and subsequently, a heating event dehydrated the sample. We suggest to classify the meteorite NWA 11024 as the first type 3 CM chondrite similar to the classification of CV3 chondrites (like Allende) that could also have lost their matrix phyllosilicates by thermal dehydration.

Introduction: Ca-Al-rich inclusions (CAIs) are refractory mineral assemblages and the oldest dated solids that formed inside the Solar System. Although their formation is generally tied to high-temperature processes occurring near the young Sun, they are found primarily in outer Solar System materials, including chondrites, interplanetary dust particles, and comets. This being the case, understanding the origin and subsequent distribution of CAIs promises insights into the earliest stages of the Solar System and the processes taking place therein. However, this endeavor is complicated by mineralogically, chemically, and isotopically different subtypes of refractory inclusions, such as hibonite-rich grains (e.g., PLACs & SHIBS), the enigmatic group of FUN-CAIs, and the more common ‘regular’ CAIs, whose relationships among one another are poorly constrained. In recent years, mass-independent isotope anomalies of nucleosynthetic origin have proven to be a powerful tool to constrain genetic links among extraterrestrial materials, as they trace distinctive signatures of the underlying source reservoir and are not easily overprinted. Until recently, however, nucleosynthetic isotope anomalies have been almost exclusively explored in (1) large-sized CAIs from CV chondrites (particularly from the widely available Allende meteorite) using high-precision mass spectrometry [1], or (2) in sub-mm-sized hibonite-rich grains from the Murchison CM2 chondrite employing far less precise in-situ analyses [e.g., 2-4]. Here we aim to address this issue by performing high-precision isotopic analyses of CAIs from CO and CM chondritic meteorites. Because these inclusions are considerably smaller compared to previously investigated CV CAIs, the element of interest needs to be present in weight percent levels, making titanium (Ti) an attractive target for the type of study. Additionally, Ti has five stable isotopes (46Ti, 47Ti, 48Ti, 49Ti, and 50Ti) which are formed in different nucleosynthetic environments and, hence, could provide additional information about the origin of nucleosynthetic isotope anomalies in CAIs. Samples and Methods: Twelve CAIs from five different CO3 chondrites (DaG 005, DaG 025, DaG 027, DaG 083, and NWA 2187) with diameters of several hundred μm and ten CAIs (most <300 μm) from the CM2 chondrite Jbilet Winselwan were selected for this study. Two inclusions from Jbilet Winselwan (termed ‘JW-4’ and ‘JW-7’) are of particular interest, as they consist of intergrown laths of hibonite and spinel, bearing mineralogical resemblance to the previously mentioned individual PLAC and SHIB crystals. All samples were identified and characterized using a JEOL 6610-LV SEM at the University of Münster, and subsequently removed using a New Wave Research Micro Mill [5]. After digestion, the samples were purified using a two-stage ion exchange chromatography following [6] and measured using the Neptune Plus MC-ICPMS in Münster, as outlined in [7]. Due to small sample sizes, solutions were measured at Ti concentrations between 50 and 100 ppb. When normalizing to 49Ti/47Ti to correct for mass bias, this results in a sub-ε analytical uncertainty for ε46Ti, ε48Ti, and ε50Ti. This is roughly a 100-fold increase in precision compared to in-situ methods, with which such small samples previously had to be investigated. Results: Titanium isotope compositions of the samples analyzed here are shown in Figures 1 and 2, along with literature data for 49 Allende CAIs from [8] and two CK CAIs from [9] in Figure 1. All investigated regular CAIs (i.e., excluding JW-4 and JW-7) from CO and CM chondrites exhibit resolved excesses in ε50Ti, and 17 out of 20 show positive isotope anomalies in ε46Ti. The vast majority of these CAIs plot within uncertainty of the correlation line defined by an array of 49 CAIs from the Allende meteorite, where ε46Ti= (0.162±0.03) × ε50Ti + (0.15±0.27) [8]. To our knowledge, CAI sample JW-6 has the lowest ε50Ti value ever reported for any regular CAI and appears to be the first such sample with a resolved deficit in ε46Ti (Figure 1). The two exceptional inclusions JW-4 (consisting largely of hibonite) and JW-7 (consisting largely of spinel) in contrast show highly anomalous Ti isotopic compositions and plot far away from the correlated array of regular CAIs (Figure 2).

The CM chondrites are generally complex impact breccias, in which lithic clasts and mineral fragments showing various degrees of aqueous alteration and possibly originating from different parent bodies are mixed together. The occurrence of CM-like clasts in other chondritic and achondritic meteorite breccias is also well-documented, however, reports on the occurrence of foreign clasts in CM chondrites are rare. In this study, we reinvestigated the white clast in the Murchison CM chondrite and demonstrate that the clast is not related to R chondrites as earlier suggested. In addition to the classification we discuss the origin and the history of its formation by studying several aspects like mineralogy, bulk chemistry, Rare Earth Elements (REE), oxygen isotopes, and the soluble organic compounds.