# Multi-isotope (N, O, Ti, and Cr) study of C1 and CM -like clasts-Probing unsampled C1 material

Markus Patzek, Yogita Kadlag, Miriam Rüfenacht, Evelyn Füri, Andreas

Pack, Addi Bischoff, Harry Becker, Robbin Visser, Timm John, Maria

Schönbächler

► To cite this version:

Markus Patzek, Yogita Kadlag, Miriam Rüfenacht, Evelyn Füri, Andreas Pack, et al. Multi-isotope (N, O, Ti, and Cr) study of C1 and CM -like clasts-Probing unsampled C1 material. Meteoritics and Planetary Science, 2025, 10.1111/maps.14343. hal-05020796

HAL Id: hal-05020796

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# Multi-isotope (N, O, Ti, and Cr) study of C1 and CM-like clasts—Probing unsampled C1 material

Markus PATZEK<sup>1*</sup>, Yogita KADLAG<sup>2,3</sup>, Miriam RÜFENACHT<sup>4</sup>, Evelyn FÜRI<sup>5</sup>, Andreas PACK<sup>6</sup>, Addi BISCHOFF<sup>1</sup>, Harry BECKER<sup>2</sup>, Robbin VISSER<sup>2</sup>, Timm JOHN<sup>2</sup>, and Maria SCHÖNBÄCHLER<sup>4</sup>

<sup>1</sup>Institut für Planetologie, University of Münster, Münster, Germany

<sup>2</sup>Freie Universität Berlin, Institut für Geologische Wissenschaften, Berlin, Germany

<sup>3</sup>Physical Research Laboratory, Ahmedabad, Gujarat, India

<sup>4</sup>Institute of Geochemistry and Petrology, ETH Zurich, Zurich, Switzerland

<sup>5</sup>Université de Lorraine, CNRS, CRPG, Nancy, France

<sup>6</sup>Universität Göttingen, Geowissenschaftliches Zentrum, Göttingen, Germany

*Correspondence

Markus Patzek, Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, Münster D-48149, Germany.

Email: markus.patzek@uni-muenster.de

(Received 26 February 2025; revision accepted 14 March 2025)

**Abstract**—A multi-element isotope (N, O, Ti, and Cr) study was conducted on C1 and CM-like clasts hosted in achondrites and chondrite breccias to understand the genesis of these chondritic clasts. The mineralogy, O, and N isotopes confirm that CM-like clasts in howardites and polymict eucrites closely resemble CM chondrite-like material. The O and Cr isotope composition of C1 clasts in CR chondrites overlaps with those of CR chondrites, implying either formation in a similar nebular environment or resemblance to local CR material that underwent more extensive in situ alteration. Notably, these clasts are less enriched in <sup>15</sup>N than bulk CR chondrites. In contrast, C1 clasts in ureilites are enriched in <sup>15</sup>N relative to the Earth's atmosphere by ~100‰ setting them apart from any other known solar system material. They display elevated <sup>17</sup>O and <sup>18</sup>O values and lie along the CCAM line. In addition, a C1 clast from an ureilite represents the most <sup>54</sup>Cr-enriched and <sup>50</sup>Ti-depleted endmember among the carbonaceous chondrites. Altogether, these isotopic characteristics suggest that C1 clasts in ureilites represent material not sampled by any known meteorite group. Overall, this study highlights the presence of primitive, isotopically distinct materials in the early outer solar system, some of which were transported to the inner solar system to the accretion region of the host parent bodies.

## INTRODUCTION

Compositional information on primitive material from the outer solar system has been limited to data from comets, interplanetary dust, and volatile-rich meteorite groups such as the Murray-type (CM) and the Ivuna-type (CI) chondrites. Additional individual meteorites such as Flensburg, Tarda, Tagish Lake, and Kaidun (Bischoff et al., 2021; Marrocchi et al., 2021; Schrader et al., 2024) and samples returned from carbonaceous C-type asteroids by recent sample return missions such as Hayabusa2 and

OSIRIS-REx (e.g., Lauretta et al., 2024; Watanabe et al., 2017) hint that a greater diversity of chemical and isotopic composition exists. CM chondrites are a group of mostly brecciated carbonaceous chondrites whose components have undergone varying degrees of aqueous alteration (e.g., Lentfort et al., 2021; Rubin et al., 2007). CI chondrites are considered chemically the most “primitive” rocks in the solar system because their bulk chemical composition (except for the highly volatile elements and Li, Be, and B) is similar to that of the solar photosphere (e.g., Anders & Grevesse, 1989; Barrat
et al., 2012; Lodders, 2003). Conversely, all CI chondrites were heavily modified by aqueous alteration and brecciation on their parent body(ies) (Alfing et al., 2019; Morlok et al., 2006; Tomeoka & Buseck, 1988), which strongly affected their mineralogy (type 1; e.g., CI1).

Chondrites are a mixture of diverse materials (e.g., chondrules, matrix, refractory inclusions, metals, and sulfides) with different groups displaying unique oxygen and nucleosynthetic isotope variations in different elements (Clayton et al., 1991; Clayton & Mayeda, 1999; Trinquier et al., 2007; Warren, 2011). These compositions reflect mixing and perhaps thermochemical processing as a function of time and/or space in the solar nebula (e.g., Ek et al., 2020; Schneider et al., 2023; Trinquier et al., 2009; Williams et al., 2020). The distinct nucleosynthetic isotope composition of carbonaceous and noncarbonaceous meteorites, first reported by Trinquier et al. (2007) and Leya et al. (2008) based on Cr and Ti isotope variations in planetary materials, presumably results from the spatial separation of materials in the outer and the inner solar system within the first few Ma after formation of the solar system (Kruijer et al., 2017; Lichtenberg et al., 2021). According to the nucleosynthetic compositions in various elements (e.g., Ni, Cr, Ti, Ca, Zr, Mo, Ru, Pd, etc.; Akram et al., 2015; Budde et al., 2016; Dauphas et al., 2010; Ek et al., 2020; Kruijer et al., 2017; Leya et al., 2008; Nanne et al., 2019; Qin et al., 2010; Rüfenacht et al., 2023; Schiller et al., 2014; 2018; Steele et al., 2012; Trinquier et al., 2007; Zhang et al., 2011) and their abundance in C and H (e.g., Alexander et al., 2012; Vacher et al., 2020), the parent bodies of carbonaceous chondrites—including CI and CM chondrites—likely formed in orbits beyond Jupiter (Warren, 2011). These outer solar system materials are characterized by a different mix of presolar phases, as evidenced by an excess of neutron-rich isotopes produced by supernovae and deficits in s-process isotopes (e.g., Mezger et al., 2020), although the exact supernova type is still debated: While Nittler et al. (2018) suggested that carriers of ⁵⁴Cr excesses in bulk meteorites were produced by type Ia supernovae or in electron-capture supernovae, Hartogh et al. (2022) suggested type II supernovae as alternative sources. Calcium-aluminum-rich inclusions (CAIs) as well as amoeboid olivine aggregates (AOAs), which occur in many carbonaceous chondrite groups, show coupled variations in the neutron-rich isotopes, such as ⁵⁴Cr and ⁵⁰Ti, whereas the inverse array of ⁵⁴Cr-⁵⁰Ti variations is observed in bulk carbonaceous chondrites (Burkhardt et al., 2019; Jansen et al., 2024; Rüfenacht et al., 2023; Torrano et al., 2023, 2024; Trinquier et al., 2009). The origin of these different systematics is debated, but is likely linked to variable proportions of the CI chondrite-like matrix and refractory phases such as chondrules and refractory inclusions (Hellmann et al., 2023). Overall, mass-independent O (Δ¹⁷O, which is

defined as $Δ^{17}O = δ^{17}O - 0.528 × δ^{18}O$) and the nucleosynthetic isotope compositions of various elements serve as a powerful tool for deciphering genetic relationships between different meteorite groups because these compositions are distinct between meteorite groups but virtually homogeneous within a meteorite (e.g., Rüfenacht et al., 2023), with few exceptions as, for example, ⁵⁴Cr in Ryugu when small sample amounts are analyzed (e.g., Yokoyama et al., 2023). Recent work based on Fe nucleosynthetic isotope data (e.g., Hopp et al., 2022) and Te stable isotope data (Hellmann et al., 2023; Morton et al., 2024) indicates that a mixture of ubiquitous CI-like dust (different to the here studied clasts) incorporated into carbonaceous chondrites together with a more refractory component (e.g., chondrules) can account for the observed isotopic signatures of bulk carbonaceous chondrites (Marrocchi, Piralla, et al., 2023; Morton et al., 2024; Spitzer et al., 2024).

Clast material texturally and mineralogically similar to CI chondrites occurs not only in various known brecciated carbonaceous (CM, CR, and CH groups) and ordinary chondrites (H and L groups) but also in noncarbonaceous achondrites such as howardites, eucrites, and diogenites (HEDs) and ureilites (e.g., Bischoff et al., 2018; Bonal, Huss, Krot, & Nagashima, 2010; Bonal, Huss, Krot, Nagashima, Ishii, & Bradley, 2010; Briani et al., 2009, 2012; Patzek, Bischoff, et al., 2018; Van Kooten et al., 2016, 2017; and references therein; Goodrich et al., 2021; Kerraouch et al., 2021; Lee et al., 2025; Liu et al., 2020). Given that these phyllosilicate-dominated clasts are present in various inner and outer solar system materials, they have the potential to provide important constraints on the composition and transport dynamics of material across the early solar system. Texturally and mineralogically, the clasts are similar to each other (Briani et al., 2012; Gounelle et al., 2003; Patzek, Bischoff, et al., 2018; Zolensky et al., 1996): All clasts are dominated by a fine-grained matrix of intimately intergrown serpentine [(Mg, Fe)₃Si₂O₅(OH)₄] and saponite [Ca₀.₂₅(Mg,Fe)₃((Si,Al)₄O₁₀)(OH)₂ × n(H₂O)] with interstitially embedded organic matter of varying composition and structures. Spherulitic and framboidal magnetite (e.g., Figure 1), lath-shaped pyrrhotite, and abundant grains of olivine and pyroxene occur besides rare carbonate grains (calcite, dolomite, and breunnerite). Refractory inclusions are absent (Patzek, Bischoff, et al., 2018), but some clasts can contain chondrules and/or metal grains (e.g., Bonal, Huss, Krot, & Nagashima, 2010; Bonal, Huss, Krot, Nagashima, Ishii, et al., 2010; Patzek, Bischoff, et al., 2018; Van Kooten et al., 2017).

Despite the similar mineralogy and alteration temperatures of CI-like clasts in ureilites and CI1 chondrites, their bulk D/H ratios and the δ³⁴S of sulfides are distinct from each other (Patzek et al., 2019, 2020;
<figure><img src="image_2.png" /></figure>

FIGURE 1. Backscattered electron images of (a) a small Cl clast in the polymict ureilite Dar al Gani (DaG) 164 showing the typical mineralogy including framboidal magnetite (mag), pyrrhotite (po), and accessory phosphate (phos) embedded within a fine-grained, phyllosilicate-rich matrix, (b) a CM-like clast in the polymict eucrite Northwest Africa (NWA) 7542. Abundant type I chondrules (chd) and fragments of those (dark gray) occur occasionally surrounded by accretionary rims and abundant lumps of a tochilinite-cronstedtite intergrowth (TCI), (c) a Cl clast in the polymict ureilite DaG 319 showing similar mineralogy compared to that shown in panel a including additional sulfide (sulf), and (d) a CM-like clast from polymict eucrite NWA 7542 with typical CM-like mineralogy including chondrules of various types surrounded by fine-grained rims, TCI clumps and various sulfides all embedded within a matrix consisting of an intergrowth of fine-grained phyllosilicates with fine sulfides and TCIs.

Visser et al., 2018, 2019). Although CI-like clasts and CI1 chondrites did not experience temperatures above ~100°C during their alteration episode(s) excluding an excessive loss of H (Visser et al., 2018), the CI-like clasts in ureilites are enriched in D by up to 3000‰ relative to VSMOW (Patzek et al., 2020). The D enrichments in the clasts are not solely due to a high abundance of organic matter, but were also attributed to a D-rich water component residing in the phyllosilicate-rich matrix (Patzek et al., 2020). This indicates the incorporation of large quantities of D-rich ices that formed at greater heliocentric distance than those sampled by other aqueously altered carbonaceous chondrites (Aikawa & Herbst, 2001; Drouart et al., 1999). The incorporation of material from different isotopic reservoirs is also evidenced by the generally lighter δ³⁴S signature of pyrrhotite in CI-like clasts in ureilites compared to that in CI1 chondrites (average of ~-1.04 ± 0.32‰ vs. ~+1.12 ± 0.23‰; Visser et al., 2019). Based on these isotopic differences compared to CI1 chondrites, the CI-like clasts in various meteorite groups are better referred to as Cl clasts, and we will maintain this distinction in the following.

Here, we present N, O, Ti, and Cr isotope data of Cl and CM-like clasts from ureilites, CR chondrites, and HED

meteorites (howardites, eucrites, and diogenites) and combine these new data with previous results from other isotopic systems (Patzek et al., 2019, 2020; Patzek, Pack, et al., 2018; Visser et al., 2018, 2019, 2020) to evaluate their implications for the diversity of carbonaceous chondrites and early solar system processes. Such multi-isotope analyses are key for improving our understanding of genetic relationships (N, O, Cr, and Ti) between different meteorite groups and for understanding the distribution of presolar carrier phases, for example, Cr and Ti, in different regions of the solar nebula. Furthermore, variations in nucleosynthetic isotope compositions of Cr and Ti in the clasts and comparison with the existing data on meteorites allow us to assess their accretion time scales and evolutionary history, and by coupling these data with O and N isotopic signatures, we can trace the nature of the accreting material.

## METHODS

### Samples

The analyzed samples were manually extracted from host meteorite chips as bulk pieces. This was done by
sawing meteorite chips of ~5 mm thickness followed by examination using optical and low-vacuum scanning electron microscopy to locate potential clasts and identify the clast type (i.e., C1 or CM-like) based on textural characteristics and preliminary mineral chemistry (see e.g., Patzek, Bischoff, et al., 2018; Patzek, Pack, et al., 2018). Care was taken to select clasts with typical mineralogical and petrographic features consistent with those described in detail by Patzek, Bischoff, et al. (2018) and Patzek, Pack, et al. (2018) to ensure generation of a consistent data set. The meteorite chips were then either broken or sawed next to the clasts, and the surrounding host material was progressively removed with a dissection needle. The outer fraction of the fragments was scratched and removed using plastic tweezers to avoid contamination in case of metal isotope analysis. Given the required mass for isotope analyses of N (0.02–0.7 mg), O (1–3 mg), Cr (2–4 µg), and Ti (0.5–1 µg) and the varying abundance of these elements, it was not feasible to obtain data for all isotope systems from each investigated clast. For an overview, the analyzed isotope systems and clasts are provided in Table 1. Nitrogen and O isotope analyses were carried out on different fragments of the same clast, whereas Cr and Ti isotopes were analyzed from the same dissolution.

## Nitrogen Isotopes and Noble Gases

Nitrogen and noble gases (Ne and Ar; see Supporting information) were extracted from the clasts by CO₂ laser heating and analyzed using the Noblesse HR (Nu Instruments) multicollector noble gas mass spectrometer at CRPG’s noble gas facility. Clast fragments weighing between 0.024 and 0.682 mg in mass were placed into different pits of the laser chamber, which was baked at 100°C overnight under ultra-high vacuum to remove any adsorbed terrestrial gases. Each sample was heated individually for 3 min in two temperature steps (at minimum laser power and until melting). The extracted gas fraction was split into two calibrated volumes for specific nitrogen and noble gas purifications. N was purified in a Pyrex and quartz glass line using a CuO furnace cycled between 723 and 1173 K and a U-shaped cold trap held at 93 K (see Humbert et al., 2000 for details). Prior to expanding the purified gas into the mass spectrometer, the amount of molecular N was adjusted by volume dilution in a volume-calibrated purification line to match the pressure of an air standard, which was purified using the same procedure. N₂ abundances and isotope ratios were determined at a trap current of 150 µA in multicollection mode at mass 28 (¹⁴N¹⁴N) on Fa2 with a 10¹¹Ω resistor, mass 29 (¹⁴N¹⁵N) on Fa1 with a 10¹²Ω resistor, and mass 30 (¹⁵N¹⁵N) on IC0. Given

that the ¹²C¹⁶O peak is partially separated from that of ¹⁴N₂, the analytical procedure consisted of measuring the ¹²C¹⁶O signal prior to measuring the ¹²C¹⁶O + ¹⁴N₂ and ¹³C¹⁶O + ¹⁵N¹⁴N signals. Following data acquisition, which comprised 25 measurement cycles, the ¹⁴N₂ and ¹⁵N¹⁴N signals were obtained by correcting for the CO and laser chamber blank (i.e., <0.5% for most samples and extraction steps) contributions. Repeat analyses (n = 109) of air standards yielded a ¹⁴N¹⁴N / ¹⁴N¹⁵N ratio of 137.94 ± 0.07, that is, a reproducibility of 0.5‰. Nitrogen isotope data are reported as δ¹⁵N values relative to air in permil (‰; Equation 1):

$$ \delta^{15}\text{N} = \left[ \frac{\left( \frac{^{15}\text{N}}{^{14}\text{N}} \right)_{\text{Sample}} - 1}{\left( \frac{^{15}\text{N}}{^{14}\text{N}} \right)_{\text{Standard}}} \right] \times 1000 \quad (1) $$

Average N₂ abundances and isotope ratios obtained for several fragments of the studied clasts are reported in Table 1. Heating steps for which the blank contribution to the measured gas abundances represents ≥30% are not reported. A full table including details on the Ne, Ar, and additional N data can be found in Table S7.

## Oxygen Isotopes

Oxygen isotope data have been obtained from 1 to 3 mg of sample material (Table 1). The samples were weighed and loaded on an Ni sample holder and stored in a desiccator for 12 h at 50°C to remove adsorbed moisture. Samples were reacted in a BrF₅ atmosphere using a CO₂ laser following the method described in Pack et al. (2016). The released gas was purified along a custom-built purification line and introduced into a Thermo MAT253 gas source isotope ratio mass spectrometer in dual inlet mode with simultaneous detection of m/z 32, 33, and 34 for the different isotope combinations (i.e., ¹⁶O¹⁶O, ¹⁷O¹⁶O, and ¹⁸O¹⁶O). The separated ion beams of masses 32, 33, and 34 were collected in Faraday cups attached to amplifiers with the resistances of 3 × 10⁸Ω, 3 × 10¹¹Ω, and 1 × 10¹¹Ω, respectively, on feedback resistors. For each sample, ~40 cycles were measured with a total measurement time of ~45 min. The Δ¹⁷O is reported relative to a reference line with a slope of 0.528 (Equation 2)

$$ \Delta^{17}\text{O} = 1000 \times \ln(10^{-3} \times \delta^{17}\text{O}_{\text{VSMOW}} + 1) - 0.528 \quad (2) \\ \times 1000 \times \ln(10^{-3} \times \delta^{18}\text{O}_{\text{VSMOW}} + 1) $$

The uncertainty (2 SD, denoted by 2σ hereafter) in the Δ¹⁷O values was 0.015‰ for a single measurement. The δ¹⁷O and δ¹⁸O values are reported in permil (‰) on the VSMOW scale.
<table><caption>TABLE 1. Nitrogen, O, Cr, and Ti isotope compositions and $^{55}$Mn/$^{52}$Cr ratios of analyzed C1 clasts and CM-like clasts found in ureilites, CR chondrites, and HED meteorites. $\delta^{15}$N, $\delta^{17}$O, $\delta^{18}$O, and $\Delta^{17}O$ are given in $\%e$ relative to VSMOW and air in the case of N. Chromium isotopes are reported in $\epsilon$ (10$^4 \times$ deviation from the NIST 3112a reference material). Nitrogen concentration and N2 abundances, and $\delta^{15}N$ are reported as averages and SD based on individual analyses (see full table in Supporting information). Titanium isotopes are reported in $\epsilon$ (10$^4 \times$ deviation from the ETH in-house Ti wire standard) and uncertainty is 2SD. Also shown are new data for some carbonaceous chondrites and terrestrial reference materials. Weight is given in mg for O, N, and Cr + Ti analyses.</caption><thead><tr><th>Sample</th><th>Weight (O)</th><th>δ<sup>18</sup>O (%)</th><th>δ<sup>17</sup>O (%)</th><th>Δ<sup>17</sup>O (%)</th><th>Weight (N)</th><th>δ<sup>15</sup>N (%)</th><th>[N] (ppm)</th><th>Weight (Cr + Ti)</th><th>δ<sup>53</sup>Cr</th><th>δ<sup>58</sup>Cr</th><th>Mn/Cr</th><th>n (Cr)</th><th>δ<sup>46</sup>Ti/<sup>47</sup>Ti</th><th>δ<sup>38</sup>Ti/<sup>47</sup>Ti</th><th>δ<sup>30</sup>Ti/<sup>47</sup>Ti</th><th>n (Ti)</th></tr></thead><tbody><tr><td colspan="16"><strong>C1 clasts (ureilites)</strong></td></tr><tr><td>DaG 1064-A</td><td>2.3</td><td>12.60 ± 0.20</td><td>7.74 ± 0.20</td><td>1.10 ± 0.015</td><td></td><td></td><td></td><td>1.690</td><td>0.65 ± 0.05</td><td>2.84 ± 0.22</td><td>3.75 ± 0.15</td><td>3</td><td>-0.02 ± 0.25</td><td>0.03 ± 0.09</td><td>0.33 ± 0.12</td><td>10</td></tr><tr><td>DaG 164C</td><td>1.002</td><td>12.57 ± 0.20</td><td>7.92 ± 0.20</td><td>1.29 ± 0.015</td><td>0.452</td><td>104.3 ± 7.4</td><td>1043</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>DaG 164X-01</td><td>1.064</td><td>12.14 ± 0.20</td><td>7.42 ± 0.20</td><td>1.02 ± 0.015</td><td>0.682</td><td>95.8 ± 3.6</td><td>217</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>DaG 164X-03</td><td>0.745</td><td>11.79 ± 0.20</td><td>7.10 ± 0.20</td><td>0.89 ± 0.015</td><td></td><td></td><td></td><td>-23.7 ± 26.0</td><td>3-30</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td colspan="16"><strong>Ureilites<sup>a,b</sup></strong></td></tr><tr><td colspan="16"><strong>C1 clasts (CR chondrites)</strong></td></tr><tr><td>Afer 059-A</td><td>1.3</td><td>2.52 ± 0.20</td><td>-0.37 ± 0.20</td><td>-1.70 ± 0.015</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Afer 311-A</td><td>2.1</td><td>8.21 ± 0.20</td><td>2.83 ± 0.20</td><td>-1.49 ± 0.015</td><td>0.458</td><td>107.3 ± 18.0</td><td>661</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Afer 311-C</td><td>1.7</td><td>9.16 ± 0.20</td><td>3.28 ± 0.20</td><td>-1.54 ± 0.015</td><td>0.442</td><td>98.9 ± 13.2</td><td>497</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Afer 097</td><td>0.719</td><td>6.89 ± 0.20</td><td>1.60 ± 0.20</td><td>-2.03 ± 0.015</td><td></td><td></td><td></td><td>1.630</td><td>0.32 ± 0.06</td><td>1.29 ± 0.27</td><td>0.78 ± 0.04</td><td>5</td><td></td><td></td><td></td><td></td></tr><tr><td>Afer 139<sup>c</sup></td><td>-/-</td><td>5.60</td><td>0.99</td><td>-1.96</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Afer 114<sup>c</sup></td><td>-/-</td><td>3.39</td><td>-0.81</td><td>-2.60</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td colspan="16"><strong>CR chondrites<sup>a</sup></strong></td></tr><tr><td colspan="16"><strong>CM-like clasts (HEDs)</strong></td></tr><tr><td>NWA 7542-A</td><td></td><td></td><td></td><td></td><td>0.373</td><td>22.3 ± 1.2</td><td>574</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>NWA 7542-B</td><td>1.227</td><td>7.92 ± 0.20</td><td>1.85 ± 0.20</td><td>-2.32 ± 0.015</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>NWA 7542-G</td><td>2.01</td><td>9.20 ± 0.20</td><td>2.83 ± 0.20</td><td>-2.01 ± 0.015</td><td>0.399</td><td>11.8 ± 0.9</td><td>472</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>NWA 8736-A</td><td>1.019</td><td>5.51 ± 0.20</td><td>-0.26 ± 0.20</td><td>-3.16 ± 0.015</td><td>0.440</td><td>8.6 ± 0.7</td><td>510</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>NWA 6695-B</td><td>1.802</td><td>7.36 ± 0.20</td><td>0.90 ± 0.20</td><td>-2.97 ± 0.015</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>PRA 04402-A</td><td>1.609</td><td>6.42 ± 0.20</td><td>1.31 ± 0.20</td><td>-2.07 ± 0.015</td><td></td><td></td><td></td><td>-50 to +20</td><td>0.05-1.3</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td colspan="16"><strong>HED<sup>a,b</sup></strong></td></tr><tr><td colspan="16"><strong>Reference samples</strong></td></tr><tr><td>Allende #1</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td colspan="16"><strong>(CV3)</strong></td></tr><tr><td>Allende #2<sup>c</sup></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td colspan="16"><strong>(Flensburg (Clung))</strong></td></tr><tr><td>Murchison</td><td></td><td></td><td></td><td></td><td>0.414</td><td>30.9 ± 1.3</td><td>811</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td colspan="16"><strong>(CM2)</strong></td></tr><tr><td>Ivuna (Cl)</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Orgueil<sup>d</sup> (Cl)</td><td></td><td></td><td></td><td></td><td>0.233</td><td>46 ± 6.8</td><td>1170</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>UBN<sup>e</sup></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>BHVO<sup>2c</sup></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>NIST processed</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table>

<sup>a</sup>Cr isotope and Mn/Cr data from Dreibus and Wänke (1980); Weisberg et al. (1993); Dreibus et al. (1997); Trinquier et al. (2007, 2008); Qin et al. (2010); Yamakawa et al. (2010).

<sup>b</sup>$\delta^{15}$N and [N] data from Grewal (2022); Grady and Pillinger (1988); Grady and Wright (2003); Grady et al. (1985). For some values, ranges are given from literature.

<sup>c</sup>Previous data from our working group by Endress et al. (1994); DaG = Dar al Gani; NWA = Northwest Africa; PRA = Mount Pratt.

<sup>d</sup>Cr and O isotope data are derived from different aliquots.

<sup>e</sup>Reference data from Kadlag et al. (2021). See Table S8 for details.
## Titanium Isotopes

Titanium isotope analyses were performed by adopting the procedure described in Rüfenacht et al. (2023) using Bio-RAD AG1-X8 resins in a three-stage column procedure. The procedural yield was >90%, and the blank of the total chemical procedure was ~1.4 ng Ti. This corresponds to a blank contribution of <0.07% for the analyses (Table 1). The Ti isotope measurements were carried out on a Thermo Scientific Neptune Plus multicollector inductively coupled plasma mass spectrometer (MC-ICPMS) at ETH Zurich. For instrumental mass bias corrections, Ti isotopic data were normalized to $^{49}$Ti/$^{47}$Ti ratio of 0.749766 (Niederer et al., 1985) using the exponential law. Samples were bracketed with an in-house Ti wire standard from Alfa Aesar (Williams et al., 2021). Measurements were done in medium resolution. To ascertain accuracy and reproducibility, repeated analyses of the same sample solution were performed on three different days, together with repeated measurements of the terrestrial standard rock BHVO-2 and a bulk CM2 chondrite (Jbilet Winselwan). The Ti isotope data are reported in $\epsilon$ notation (Equation 3):

$$ \epsilon^{i} \text{Ti} = \left[ \frac{\left( \frac{i^{\prime} \text{Ti}}{47 \text{Ti}} \right)_{\text{Sample}} - 1}{\left( \frac{i^{\prime} \text{Ti}}{47 \text{Ti}} \right)_{\text{standard}}} \right] \times 10^{4}, i = 46, 48, 50 \quad (3) $$

## Chromium Isotopes

Separated fragments of clasts were inspected under a binocular microscope (the photographs of the fragments are included in the Supporting information) and crushed in an agate mortar. Homogeneous powders of clasts were weighed precisely (weights of Acfer 311-C, Dar al Gani (DaG) 1064-A, and Northwest Africa (NWA) 7542-G were 1.63, 1.69, and 1.79 mg, respectively) and dissolved in a 4:1 mixture of HF: HNO$_3$ (4 mL HF and 1 mL HNO$_3$) in Parr bombs. Digestion solutions were split into three parts; the first aliquot (16% of the digestion solution) was used to determine $^{55}$Mn/$^{52}$Cr ratios, the second aliquot was used to determine precise Cr isotope compositions (75% of the digestion solution), and the third aliquot (9% of the digestion solution) was used to determine major and trace element abundances. The Ti cut from the ion exchange separation was used for subsequent Ti isotope analyses.

The $^{55}$Mn/$^{52}$Cr ratio was determined by the standard addition method. A detailed description of the sample preparation and methods for Cr isotope analysis is given in Kadlag et al. (2019, 2021). Uncertainties on $^{55}$Mn/$^{52}$Cr

ratios were <5% ($2\sigma$) for all samples. Results of the Cr isotopic composition and the Mn/Cr ratios are given in Table 1. The separation of Cr from matrix elements removes mainly interfering elements such as Fe, Ti, and V and major matrix elements such as Mg, Mn, Al, Na, and Si. Purification of Cr was achieved by a two-step separation on anion and cation exchange columns using the procedure from Kadlag et al. (2019). The Cr fraction was collected from the anion exchange resin in 6 M HCl along with other matrix elements. The Cr yield after separation is >90%.

Precise determination of the Cr isotope ratios was carried out on a Triton TIMS at the Freie Universität Berlin. Approximately 1–2 µg pure Cr from each sample was loaded on two to three single Re filaments along with silica gel and boric acid, and most filament loads were measured twice. Each measurement consisted of 28 blocks and 20 cycles (8 s integration time). Baseline, peak center, and amplifier rotation were performed after every 7th block. Reported values are the averages of three to four measurements for each sample (see Table S5 for details). The average values of $^{53}$Cr/$^{52}$Cr and $^{54}$Cr/$^{52}$Cr of the NIST 3112a reference material are 0.1134558 and 0.0282106, respectively. A constant $^{50}$Cr/$^{52}$Cr = 0.051859 was assumed to correct instrumental mass fractionation (Shields et al., 1966). $\epsilon^{i}$Cr is defined as the ratio of the isotope i to $^{52}$Cr relative to that of NIST 3112a (Equation 4):

$$ \epsilon^{i} \text{Cr} = \left[ \frac{\left( \frac{i^{\prime} \text{Cr}}{52 \text{Cr}} \right)_{\text{Sample}} - 1}{\left( \frac{i^{\prime} \text{Cr}}{52 \text{Cr}} \right)_{\text{NIST 3112a}}} \right] \times 10^{4}, i = 53, 54 \quad (4) $$

## RESULTS

### Trace Element Inventory of C1 and CM-Like Clasts

The CI-normalized REE concentrations of two C1 clasts show a nearly chondritic pattern when considering analytical uncertainties (Table 2; Figure 2). In contrast, the CM-like clast NWA 7542G shows enrichments in La to Eu and Tm up to 4× CI and a slight decrease from light to heavy REE. The REE concentrations of the C1 clasts Acfer 311-C and DaG 1064A show less pronounced features, except for a slightly positive Eu anomaly. The C1 clast DaG 1064A is enriched in Mn (2.5× CI) and Ti (4.5× CI) relative to CI, whereas the CM-like clast NWA 7542-G is only enriched in Ti. Abundances in the C1 clast Acfer 311-C are also chondritic for the above-mentioned elements. The major elements and REE concentrations of Flensburg analyzed in this work are consistent with the published values for most elements (Bischoff et al., 2021; Figure 2).
<table><caption>TABLE 2. Concentrations of the rare earth elements (REE) and selected major and minor elements given in µg g⁻¹ (REE) and wt% (major and minor elements), respectively.</caption><thead><tr><th></th><th colspan="2">Acfer 311-C (C1b)</th><th colspan="2">DaG 1064-A (C1a)</th><th colspan="2">NWA 7542-G (CM-like)</th><th colspan="2">Flensburg (Clung)</th></tr></thead><tbody><tr><td>Mn</td><td>0.20</td><td>±0.01</td><td>0.63</td><td>±0.01</td><td>0.17</td><td>±0.01</td><td>0.156</td><td>±0.001</td></tr><tr><td>Cr</td><td>0.30</td><td>±0.01</td><td>0.20</td><td>±0.01</td><td>0.29</td><td>±0.01</td><td>0.295</td><td>±0.00</td></tr><tr><td>Fe</td><td>23.07</td><td>±0.01</td><td>17.68</td><td>±0.01</td><td>20.38</td><td>±0.01</td><td>18.88</td><td>±0.08</td></tr><tr><td>Mg</td><td>11.72</td><td>±0.01</td><td>9.42</td><td>±0.01</td><td>8.54</td><td>±0.01</td><td>10.60</td><td>±0.10</td></tr><tr><td>Ni</td><td>1.44</td><td>±0.02</td><td>0.98</td><td>±0.01</td><td>1.09</td><td>±0.02</td><td>1.27</td><td>±0.02</td></tr><tr><td>Ti</td><td>0.06</td><td>±0.02</td><td>0.21</td><td>±0.02</td><td>0.13</td><td>±0.02</td><td>0.05</td><td>±0.01</td></tr><tr><td>Al</td><td>1.00</td><td>±0.02</td><td>0.48</td><td>±0.02</td><td>0.68</td><td>±0.02</td><td>1.17</td><td>±0.02</td></tr><tr><td>La</td><td>0.286</td><td>±0.017</td><td>0.178</td><td>±0.016</td><td>0.795</td><td>±0.015</td><td>0.330</td><td>±0.020</td></tr><tr><td>Ce</td><td>0.695</td><td>±0.124</td><td>0.424</td><td>±0.117</td><td>3.071</td><td>±0.133</td><td>0.790</td><td>±0.030</td></tr><tr><td>Pr</td><td>0.112</td><td>±0.006</td><td>0.067</td><td>±0.006</td><td>0.379</td><td>±0.005</td><td>0.122</td><td>±0.004</td></tr><tr><td>Nd</td><td>0.524</td><td>±0.058</td><td>0.364</td><td>±0.055</td><td>1.737</td><td>±0.051</td><td>0.610</td><td>±0.020</td></tr><tr><td>Sm</td><td>0.175</td><td>±0.019</td><td>0.099</td><td>±0.011</td><td>0.582</td><td>±0.015</td><td>0.200</td><td>±0.010</td></tr><tr><td>Eu</td><td>0.093</td><td>±0.007</td><td>0.054</td><td>±0.007</td><td>0.267</td><td>±0.007</td><td>0.080</td><td>±0.003</td></tr><tr><td>Gd</td><td>0.222</td><td>±0.028</td><td>0.137</td><td>±0.025</td><td>0.340</td><td>±0.024</td><td>0.470</td><td>±0.010</td></tr><tr><td>Tb</td><td>0.040</td><td>±0.008</td><td>0.026</td><td>±0.008</td><td>0.061</td><td>±0.007</td><td>0.052</td><td>±0.001</td></tr><tr><td>Dy</td><td>0.286</td><td>±0.043</td><td>0.171</td><td>±0.039</td><td>0.370</td><td>±0.038</td><td>0.344</td><td>±0.003</td></tr><tr><td>Ho</td><td>0.064</td><td>±0.008</td><td>0.040</td><td>±0.007</td><td>0.072</td><td>±0.007</td><td>0.076</td><td>±0.002</td></tr><tr><td>Er</td><td>0.180</td><td>±0.017</td><td>0.112</td><td>±0.012</td><td>0.208</td><td>±0.011</td><td>0.221</td><td>±0.004</td></tr><tr><td>Tm</td><td>0.029</td><td>±0.001</td><td>0.020</td><td>±0.002</td><td>0.125</td><td>±0.002</td><td>0.035</td><td>±0.001</td></tr><tr><td>Yb</td><td>0.213</td><td>±0.029</td><td>0.133</td><td>±0.027</td><td>0.336</td><td>±0.027</td><td>0.213</td><td>±0.002</td></tr><tr><td>Lu</td><td>0.029</td><td>±0.006</td><td>0.018</td><td>±0.004</td><td>0.027</td><td>±0.003</td><td>nd</td><td>nd</td></tr></tbody></table>

Note: Uncertainties are given as 1SD.

Abbreviation: nd, no data.

<figure><img src="image_3.png" /><figcaption>FIGURE 2. CI-normalized REE and selected major element concentrations of C1 clasts, CM-like clasts, and Flensburg (Bischoff et al., 2021) in the order of their 50% condensation temperature. REE concentrations of C1 clasts are nearly chondritic, whereas the CM-like clast is enriched in elements from Nd to Eu and in Tm and shows a pattern similar to group II CAIs. C1 clast DaG 1064-A has elevated Mn and Ti concentrations. The light red band represents the range of values in the CM chondrite Paris (Hewins et al., 2014). Bulk CI chondrites values used for normalization are from Lodders (2003).</figcaption></figure>

## Nitrogen, Oxygen, Titanium, and Chromium Isotopes of C1 and CM-Like Clasts

Four C1 clasts from different pieces of the paired CR chondrite Acfer-El Djouf (Bischoff, Palme, Ash,

et al., 1993; Endress et al., 1994) were analyzed for their O isotope composition; out of these, two clasts from Acfer 311 were selected for N isotope analyses and one for Cr isotope analyses. The C1 clast Acfer 059-A has an ¹⁶O-enriched O isotope composition compared to the
other three C1 clasts from the paired CR chondrites. The O isotope data of C1 clasts in CR chondrites range from 2.5‰ to 9.2‰ in δ¹⁸O and -0.4‰ to 3.3‰ in δ¹⁷O. Additional data obtained by our group include two clasts from Acfer 139 and Acfer 114 yielding 5.6‰ and 3.4‰ in δ¹⁸O and 1‰ and -0.8‰ in δ¹⁷O, respectively (Endress et al., 1994). The N concentration ranges from 405 to 870 ppm and the δ¹⁵N value varies between 85.7‰ and 131.3‰ for various clast fragments (Table S8; Figure 4). The average δ¹⁵N value for the two C1 clasts is 98.9 ± 13.2‰ (Table 1; Table S8). The C1 clast Acfer 311-C has ε⁵³Cr and ε⁵⁴Cr values of 0.32 ± 0.06 and 1.29 ± 0.27, respectively (Table 1; Figures 5 and 6). Its ⁵⁵Mn/⁵²Cr ratio is 0.78 ± 0.04. Due to low Ti concentrations, no Ti isotope data are available for C1 clasts in CR chondrites.

Four C1 clasts from two different polymict ureilites show a range in δ¹⁸O and δ¹⁷O from 11.8‰ to 12.6‰ and 7.1‰ to 7.9‰, respectively, plotting along the carbonaceous chondrite anhydrous mixing line (CCAM; Figure 3a). Two different C1 clasts in DaG 164 are enriched in ¹⁵N by 97‰–104‰ and their N concentration ranges from 200 to 1000 ppm (Table 1 and Table S8; Figure 4). The average δ¹⁵N value for the two analyzed C1 clasts is 100.1 ± 1.9‰ (Table 1; Table S8). The C1 clast DaG 1064-A has ε⁵³Cr and ε⁵⁴Cr values of 0.65 ± 0.05 and 2.84 ± 0.22, respectively (Table 1; Figures 5 and 6) and an ⁵⁵Mn/⁵²Cr ratio of 3.75 ± 0.15. The same clast is enriched in ε⁵⁰Ti by 0.33 ± 0.12 (2 SD) relative to the Earth (Table 1).

Oxygen isotope data on five different CM-like clasts from four different HED meteorites were obtained (Table 1; Figure 3). The δ¹⁸O and δ¹⁷O values range from 5.5‰ to 9.2‰ and from -0.3‰ to 2.8‰, respectively. Nitrogen concentrations and isotope ratios (δ¹⁵N) in three different CM-like clasts range from ~472 to 574 ppm and from 8.6 ± 0.7‰ to 22.3 ± 1.2‰, respectively (Figure 4). The average δ¹⁵N value for the three CM-like clasts is 8.5 ± 2.9‰ (SD; Table 1; Table S7). The mean value of five analyses of ε⁵³Cr and ε⁵⁴Cr of the CM-like clast NWA 7542G yielded 0.27 ± 0.06 and 0.23 ± 0.13, respectively (Figure 5) with an ⁵⁵Mn/⁵²Cr ratio of 0.67 ± 0.04. The same clast has an ε⁵⁰Ti of 3.72 ± 0.31 (Table 1).

## Noble Gas (Ne, Ar) Data of C1 and CM-Like Clasts

Noble gas (Ne and Ar) isotope data were obtained from the same aliquots used for N isotope and concentration measurements. All data for ²⁰Ne and ³⁶Ar concentrations as well as the ²⁰Ne/²²Ne, ²¹Ne/²²Ne, and ³⁶Ar/³⁸Ar ratios for each heating step are reported in Table S8. In triple-Ne-isotope space (Figure 4c), the

<figure><img src="image_4.png" /></figure>

FIGURE 3. Oxygen isotope composition of (a) the CI chondrite Orgueil (black cross), C1 clasts from ureilites and CR chondrites and (b) CM-like clasts in different HEDs accompanied by literature data (Brearley & Prinz, 1992, a; Buchanan et al., 1993, b; Clayton & Mayeda, 1999, c; Schrader et al., 2011, d; van Drongelen et al., 2016, e; Goodrich et al., 2021, f; Greenwood et al., 2017, g; Ito et al., 2022, h; Greenwood et al., 2023, i; Hewins et al., 2014, j; Kimura et al., 2020; k) and additional data from MetBull. For reference, the CCAM and the terrestrial fractionation line (TFL) are shown. (a) C1 clasts in ureilites from this study (C1a, yellow squares) plot along the CCAM, whereas those from the CR chondrite (C1b, blue diamonds; including two data points from Endress et al., 1992) plot on a correlation line similar to that of bulk CR chondrites with a slope of ~0.7 (Weisberg et al., 1993). (b) CM-like clasts (red circles) plot close to bulk CM chondrites on a correlation line with a slope of ~0.7 (Clayton & Mayeda, 1999). Gray squares of C1 clasts in ureilites include mineralogically similar clasts from Almahata Sitta samples following the CCAM line, and mineralogically slightly different clasts depleted in ¹⁸O when compared to C1 clasts analyzed in this work.

studied clasts exhibit a spread between trapped “planetary” Ne (Ne-Q and Ne-A; Ott, 2014), carried by the so-called phase Q (e.g., Busemann et al., 2000) and
<figure><img src="image_5.png" /></figure>

FIGURE 4. (a) Nitrogen isotopic composition (δ¹⁵N in ‰) of the analyzed clasts in comparison with different chondrite groups, ureilites, and Ryugu samples (Alexander et al., 2012; Grady et al., 2002; Downes et al., 2015; Kerridge et al., 1985; Murty et al., 2010; Piani et al., 2021 and reference therein; Hashizume et al., 2024; Okazaki et al., 2022). The results for Murchison (red cross) and Ivuna (black triangle) from this study overlap with published data for CM and CI chondrites and those of Ryugu (black circles), respectively. C1 clasts in CR chondrites (blue diamonds) are less enriched in ¹⁵N when compared to bulk CR chondrites. (b) Nitrogen concentration (wt%) of analyzed clasts. (c) Isotopic composition (²⁰Ne/²²Ne versus ²¹Ne/²²Ne) of neon extracted from fragments of the chondritic clasts, the CM chondrite Murchison, and the CI chondrite Ivuna. The isotopic signatures of solar neon, different meteoritic neon endmembers (A, B, Q), and cosmogenic neon are shown for comparison (Moreira, 2013, and references therein). Cosmogenic neon is produced by spallation reactions during irradiation by cosmic rays in space and is not a primordial component.

<figure><img src="image_6.png" /></figure>

FIGURE 5. (a) ε⁵⁴Cr-Δ¹⁷O diagram of C1 clasts in the polymict ureilites DaG 1064 and CR chondrite Acfer 311, and a CM-like clast in the polymict eucrite NWA 7542. Additionally, analyses of Orgueil, Flensburg, Allende, and Ryugu are shown. For reference, the data for host meteorites of the clasts (HEDs, ureilites) and a suite of carbonaceous chondrites are given (Clayton and Mayeda, 1996; Trinquier et al., 2007). Also, literature data for C1 clasts in the Almahata Sitta (AhS) meteorite obtained by Goodrich et al. (2018, 2021) are given for reference. Ti data on Flensburg are from Bischoff et al. (2021). Cr and Ti data are from Yokoyama et al. (2022, 2023) and weighted mean O isotope data for Ryugu are taken from Greenwood et al. (2023). (b) ε⁵⁴Cr-²⁰Ti diagram of C1 clasts in the polymict ureilites DaG, and a CM-like clast in the polymict eucrite NWA 7542. Exemplary, Earth, Moon, EC, HEDs, and ureilites are given as examples for noncarbonaceous meteorites (NC) and plot along a correlation line that intercepts the carbonaceous chondrite (CC) field. CC meteorites define their own array with a defined slope. C1 clast DaG 1064-A extends this array to lower ε⁵⁰Ti and higher ε⁵⁴Cr values—even more extreme than those of CI chondrites.

various presolar components, and cosmogenic Ne produced by galactic cosmic rays. C1 clasts from CR chondrites appear to contain a higher proportion of planetary Ne, whereas C1 clasts from ureilites and CM-like clasts show generally higher ²¹Ne/²²Ne ratios and plot closer to the cosmogenic endmember. The ³⁶Ar/³⁸Ar ratio is less diagnostic but aligns with the presence of Ar-Q (Wieler et al., 1992).
<figure><img src="image_7.png" /><figcaption>FIGURE 6. Variation of ε<sup>53</sup>Cr with the Mn/Cr ratio of different bulk chondrites, the C1 clast Acfer 311-C, the C1 clast DaG 1064-A, the CM-like clast NWA 7542-G, and the Flensburg C1<sub>ung</sub>. White circles are selected literature values for CM chondrites (*Kadlag et al., 2019; Trinquier et al., 2008; Göpel et al., 2015). White triangles are literature values for CI chondrites (**Kadlag et al., 2019 and Trinquier et al., 2008). White squares are literature values for Ryugu (***Yokoyama et al., 2022, 2023). Note that C1 clast DaG 1064-A is off scale as indicated by the arrow. The dashed line represents the isochron defined by components of Orgueil and the solid line is the bulk chondrite isochron from Trinquier et al. (2008) with the uncertainty interval highlighted in gray. Error bars are 2 s.</figcaption></figure>

DISCUSSION

Comparison of CM-Like Clasts to CM Chondrites

The δ¹⁵N values and N concentrations of the analyzed CM-like clasts are within the range observed for CM chondrites (e.g., Alexander et al., 2012; Broadley et al., 2022; Füri & Marty, 2015; Kerridge, 1985; Pearson et al., 2006; Vacher et al., 2020) and also overlap with those of the analyzed Murchison sample (Figure 4; Table 1). The slight variation between different fragments of the same clast (e.g., Table S7) can be attributed to the heterogeneity of the N carrier phases (e.g., abundance and distribution of organic matter, presolar phases and nitrides; e.g., Pearson et al., 2006) and the very small sample size analyzed here. Contamination by surrounding host material is unlikely to have affected the N measurements given its generally low N concentration of less than 10 ppm (Grady et al., 1997; Grady & Wright, 2003; Mahajan et al., 2019). The Ne isotopic compositions of the clasts record a contribution from cosmogenic ²¹Ne produced by spallation (Figure 4c) but show no detectable contribution from implanted solar wind, suggesting that the clast material has not been part of the regolith at the upper surface of their parent body(ies) for an extended period.

Oxygen isotope data of CM-like clasts analyzed in
this work overlap with literature data of CM-like clasts
from different meteorites (e.g., Buchanan et al., 1993; van

Drongelen et al., 2016) and CM chondrites in general
(Clayton & Mayeda, 1999; Figure 3b). Overall, these O
isotope data define a correlation line with a slope of
~0.84. Scatter around the correlation line indicates small
variations within the CM chondrite group. Data obtained
in this study define a relatively small range in δ¹⁸O of
~3.7‰ (~5.5‰–9.2‰) compared to bulk CM
chondrites, which span a range of ~10.2‰ (~1.2–11.5‰)
in δ¹⁸O. According to the correlation of the O isotopic
composition (here mainly the δ¹⁸O value) and the overall
degree of aqueous alteration (Clayton & Mayeda, 1999;
Hewins et al., 2014; Kimura et al., 2020), the CM-like
clasts record an intermediate degree of aqueous alteration
relative to the other CM chondrites. However, previous
studies have shown that some clasts (e.g., in Elephant
Moraine (EET) 87513; fig. 2 in Patzek, Bischoff,
et al., 2018) and CM chondrites are breccias consisting of
lithologies with variable degrees of aqueous alteration
similar to what has been observed in CM bulk rocks (e.g.,
Bischoff et al., 2017; Kerraouch et al., 2021; Lentfort
et al., 2021; Lindgren et al., 2013; Metzler et al., 1992;
Zolensky et al., 1997, 2015). Three clasts studied by
Patzek, Bischoff, et al. (2018) and Patzek, Pack,
et al. (2018) have been classified using the Rubin
et al. (2007) scheme to be of petrologic subtype
CM2.2–CM2.8 (see Lentfort et al., 2021).

The CM-like clast NWA 7542-G exhibits ε⁵⁴Cr
isotope composition between values of HED meteorites
and typical CM chondrites (Figure 5). We attribute this
either to significant contamination of this CM-like clast with its polymict eucrite host or, alternatively, to a contribution of $^{54}$Cr-depleted FUN-CAI material, or a combination of both processes. In the following, we discuss the evidence for these different options.

The separation of CM-like clast material with optically light-colored chondrules from a light-colored HED-host can result in uncertainty regarding the purity of the clast material. Quantification of the permissible contamination using the O- and Cr-isotope compositions of the CM-like clast NWA 7542-G by eucritic material with typical $\varepsilon^{53}$Cr and Mn/Cr ratios (average $\varepsilon^{53}$Cr $\approx$ 0.69‰; average $^{55}$Mn/$^{52}$Cr $\approx$ 2.2; Trinquier et al., 2008) suggests a maximum contamination with $\sim$10% eucritic material that results in much higher $\varepsilon^{53}$Cr values than those observed. In addition, this clast exhibits a slightly larger $\varepsilon^{50}$Ti excess than bulk CM chondrites, precluding contamination by the eucritic host with negative $\varepsilon^{50}$Ti values.

The elevated concentrations (up to 4x CI) of Ti, La to Eu, and Tm in the CM-like clast NWA 7542-G indicate that it contains CAI material with a group II REE pattern (i.e., Figure 2). Since normal CAIs in carbonaceous chondrites commonly show a positive $\varepsilon^{54}$Cr and $\varepsilon^{50}$Ti anomaly, it is surprising that clast NWA 7542-G has a lower $\varepsilon^{54}$Cr than CM chondrites together with elevated REE concentrations. Possibly, sample NWA 7542-G contained “Fractionated and Unknown Nuclear Effects” (FUN)-CAI-like material that can show large negative $\varepsilon^{54}$Cr anomalies of up to $\sim$−150 (e.g., Papanastassiou & Brigham, 1989). Only a tiny contribution from such CAIs (with rather normal $\varepsilon^{50}$Ti of 9) are sufficient to lower the bulk $\varepsilon^{54}$Cr of the analyzed clast. However, FUN-CAIs (with a negative $\varepsilon^{54}$Cr anomaly) are rare compared to “common” CAIs with varying element abundances and variable enrichments in $^{54}$Cr, $^{53}$Cr, and/or $^{50}$Ti (e.g., Holst et al., 2013). The high Eu concentration of NWA 7542-G is not typical for group II REE patterns, but might reflect contamination by the host eucrite as cumulate eucrites are enriched in Eu (up to $10 \times$ CI; e.g., Barrat et al., 2000). Thus, the $\varepsilon^{54}$Cr value, the group II REE pattern, and the elevated Eu concentrations might reflect mixing between CM-like material with a small contribution from FUN-CAI-like material and a slight contamination by the eucrite host.

The $\varepsilon^{50}$Ti value of NWA 7542-G is slightly enriched when compared to that of CM chondrites (i.e., $\sim$3.7 versus $\sim$2.6 to 3.5, respectively), but can be explained by the previously discussed presence of FUN-CAI-like material and the introduction of local and extreme heterogeneities. Alternatively, hibonite grains that are common in CM chondrites are able to introduce similar extreme Ti isotope heterogeneities (e.g., Kööp et al., 2018).

Overall, a genetic link between CM-like clasts and CM chondrites is implied by various similarities such as (1) the

mineralogy and texture with typical tochilinite–cronstedtite intergrowth (TCI), abundant chondrules, carbonates, accretionary rims, and the appropriate sulfide mineralogy (e.g., Lentfort et al., 2021; Rubin et al., 2007); (2) The S isotope composition of sulfides (Visser et al., 2019); (3) the D/H ratio (Patzek et al., 2020); and (4–5) the N and O isotope signatures, as demonstrated in this study (Table 1). The Cr and Ti isotope signatures are likely contaminated by the host eucrite material and a potential FUN-CAI-like material with a positive $\varepsilon^{50}$Ti.

## Comparison of C1 Clasts in CR Chondrites to Their Host

C1 clasts in CR chondrites are often referred to as “dark inclusions” (Bischoff, Palme, Ash, et al., 1993; Endress et al., 1994; Weisberg et al., 1993). They reach sizes of up to several millimeters, and previous studies reported slight differences in their mineralogy compared to the matrix of CR chondrites of petrologic type 2 and 1 (Bischoff, Palme, Ash, et al., 1993; Endress et al., 1994). These observations were confirmed by the clasts analyzed in this work. The O isotope ratios in the studied C1 clasts are, however, comparable to those of bulk CR chondrites (Figure 3; Clayton & Mayeda, 1999; Endress et al., 1994; Schrader et al., 2011, 2014). The CR chondrites define a correlation line with a slope of $\sim$0.7 in a three-oxygen isotope plot, where samples having experienced a higher degree of aqueous alteration are more enriched in $^{17}$O and $^{18}$O, plotting further to the top-right. Although the correlation line based solely on the C1 clasts in CR chondrites implies a different slope compared to that of CR chondrites, this difference is likely influenced by heterogeneity in the alteration conditions and/or the O isotopic composition of the water. The $\varepsilon^{54}$Cr isotope data obtained on the C1 clast Acfer 311-C are indistinguishable from bulk CR-type material (Figure 5). Thus, the Cr isotope data imply a genetic relationship between the C1 clasts in CR chondrites and their host CR chondrites, indicating a likely common origin, although their alteration conditions and/or the isotopic composition of the altering water were slightly different. Elemental and isotopic equilibration between the clasts and their CR chondrite hosts is highly unlikely, as evidenced by the observations from other aqueously altered samples, such as CM chondrite breccias, which retain elemental and isotopic differences between different lithologies (e.g., Lentfort et al., 2021; Verdier-Paoletti et al., 2019). However, the $\delta^{15}$N isotope compositions of the C1 clasts Acfer 311-A and -C are at or below the lower end of the range observed in CR chondrites (which record $\delta^{15}$N values >150‰; Figure 4a; e.g., Alexander et al., 2013; Pearson et al., 2006), and their N concentrations are lower than reported in the literature (Figure 4b). Since the Acfer CR chondrites
were subject to terrestrial alteration, as indicated by
abundant rust and other FeOOH phases infiltrating the
rock (e.g., Kallemeyn et al., 1994), the N isotopic
compositions and concentrations of the clasts (i.e., that of
the OM) might have been modified, as shown in previous
studies (e.g., Alexander et al., 2007), resulting in a lower
δ¹⁵N composition and reduced N concentrations,
compared to CR chondrites by leaching of organic
materials. Alternatively, the isotopic signature of the N
reservoir sampled by the two clasts might have been
distinct from that of the accretion region of the CR
chondrite parent bodies.

Since the texture of CR chondrites indicates limited
brecciation, the C1 clasts might be a primary component
within the accretion region of CR chondrites. This
implies that the clasts may have been aqueously altered
prior to their accretion by the CR chondrites parent
body(ies) (e.g., Weisberg et al., 1993), but within the same
reservoir. Despite having fewer chondrules, the clasts and
the CR chondrites have very similar ε⁵⁴Cr composition.
Considering the rather young mean chondrule age of
3.6 Ma after CAI for CR chondrites (Hf-W chronometer;
Budde et al., 2018), the CR chondrite parent body did not
accrete prior to ~4 Ma (Schrader et al., 2017). Thus, the
alteration of C1 clasts in an earlier parent body, prior to
the accretion of the CR chondrite parent body but within
the same region is a possibility (Bischoff, 1998). For
instance, Bischoff et al. (2021) showed that the C1
chondrite Flensburg contains carbonates, which formed
less than 3 Ma after CAIs clearly showing that aqueous
alteration processes were active in the solar system at this
early time. Weisberg et al. (1993) suggested that the
existence of C1 clasts in CR chondrites is most likely
explained by more intense aqueous alteration on the CR
parent body invoking later brecciation by impacts and
lithification. However, the texture of CR chondrites is less
brecciated than that of CM chondrites (e.g., Lentfort
et al., 2021) with generally unbrecciated chondrules and a
similar size of clasts and chondrules, which is unexpected,
if an origin with impact-related brecciation mixing, and
re-lithification on the same parent body is considered.
Therefore, we argue that the mixing/accretion
mechanisms of the CM and CR breccias might be
fundamentally different from each other, for example,
CM chondrites are regolith breccias that formed and
were aqueously altered on a parent body, whereas CR
chondrites are accretionary breccias that formed by the
agglomeration of dust, pre-existing mineral and rock
fragments, chondrules, and ice in space. Although dating
of carbonates in a different C1 clast and carbonates in the
matrix of CR chondrite Renazzo did not show any age
difference between them, this specific clast could have
been formed roughly at the same time as Renazzo (Jilly-
Rehak et al., 2017).

In summary, the C1 clasts in the CR chondrite share
a similar nucleosynthetic ⁵⁴Cr signature and O isotope
signature with their host material. These clasts likely
represent more strongly altered CR material that accreted
in the same region as the CR chondrite parent body(ies)
and were accreted alongside the other CR chondrite
components. This would be in line with matrix-rich CR
chondrites such as Al Rais, Grosvenor Mountains (GRO)
95577, or Bells (e.g., Marrocchi, Rigaudier, et al., 2023).

C1 Clasts in Ureilites and CR Chondrites Compared to
CI Chondrites

A number of C1 clasts in ureilites have been described previously by various authors (Brearley & Jones, 1998; Brearley & Prinz, 1992; Goodrich et al., 2018, 2021; Ikeda et al., 2003; Prinz et al., 1987; Van Kooten et al., 2017). Brearley and Prinz (1992) reported the first O isotope data (i.e., Δ¹⁷O = 1.48‰) on a C1 clast in the polymict ureilite Nilpena and proposed an origin of this material as a late accreted veneer to the ureilitic parent body. In addition, these authors attributed the difference in O isotope composition between the C1 clast in Nilpena and C11 chondrites to aqueous alteration at lower water/rock ratios than in CI chondrites. Recently, Goodrich et al. (2021) published O isotope data (i.e., Δ¹⁷O = 1.6–1.8‰) on C1 fragments from the Almahata Sitta polymict breccia that define a linear correlation on a three-isotope diagram with a slope of ~0.95, overlapping with the carbonaceous chondrite anhydrous mineral line (CCAM; Figure 3; Clayton & Mayeda, 1977, 1989). However, the δ¹⁷O and δ¹⁸O of C1 clasts are different from C11 chondrites, which are more enriched in ¹⁸O relative to ¹⁷O. Sakamoto et al. (2007) reported a phase heavily enriched in ¹⁷O and ¹⁸O by up to 180‰, which plots along a line of slope 1, overlapping with the extension of the CCAM and PCM (primitive chondrule mineral line; Ushikubo et al., 2012). This so-called “cosmic symplectite” (COS) is thought to be a remnant of primordial ices containing O affected by self-shielding of CO in a dense molecular cloud (Clayton, 2002; Ireland, 2012; Lyons & Young, 2005).

The O isotope composition of the C1 clast in ureilites
analyzed here suggests that they might have incorporated
¹⁷O- and ¹⁸O-rich ices that originated from an O isotope
reservoir that formed through CO self-shielding and
photo dissociation (Ireland, 2012) and did not undergo
significant mass-dependent isotope fractionation. The
aqueous alteration of these clasts therefore did not lead
to a significant mass-dependent fractionation, which can
be explained by a low water/rock ratio during the
alteration of the C1 clasts in their parent body.

The ε⁵⁰Ti and ε⁵⁴Cr isotope data of the C1 clast in
the ureilite DaG 1064 clearly prove its different heritage
compared to CI chondrites (Figure 5b) and material
returned from Ryugu, which is CI-related but chemically
more pristine compared to CI chondrites because of
limited terrestrial alteration acting on it (e.g., Broadley
et al., 2023; Greenwood et al., 2023; Nakamura
et al., 2022; Yokoyama et al., 2023). The deviation from
the Δ¹⁷O-ε⁵⁴Cr array defined by other carbonaceous
chondrites toward high ε⁵⁴Cr (but not high Δ¹⁷O; c.f.
Figure 3a) is remarkable. We note that ε⁵⁴Cr in DaG
1064-A also differs from values of mineralogically similar
clasts in the Almahata Sitta (AhS) ureilite samples
published by Goodrich et al. (2018, 2021) (i.e., Figure 5;
DaG 1064-A with ε⁵⁴Cr = 2.84 ± 0.22‰ versus AhS with
ε⁵⁴Cr ≈ 1.84‰) and clasts from the ureilite DaG 319
(with ε⁵⁴Cr ranging from 1.30 ± 0.12 to 1.89 ± 0.11)
analyzed by Van Kooten et al. (2017). Since DaG 1064-A
has an ε⁵⁰Ti value of only ~0.5 (Figure 5b), it plots below
CI chondrites in an ε⁵⁴Cr-ε⁵⁰Ti diagram (Figure 5b),
extending the array defined by other carbonaceous
meteorites. This array mainly results from the admixture
of CAI-bearing carbonaceous chondrites and CI
chondrites (Figure 5b). The ε⁵⁴Cr-ε⁵⁰Ti data of DaG
1064-A and NWA 7542-G lie on the opposite extension
of this array. However, CAIs usually show enrichments
in both ε⁵⁴Cr and ε⁵⁰Ti (Torrano et al., 2023). The
ε⁵⁴Cr-ε⁵⁰Ti array of carbonaceous chondrites suggests the
presence of components with decoupled or inversely
coupled ε⁵⁴Cr-ε⁵⁰Ti carriers in the clasts.
Inversely correlated ε⁵⁴Cr-ε⁵⁰Ti compositions are also
observed for the leachates of Murchison (Burkhardt
et al., 2019), supporting the presence of such components
in the carbonaceous chondrites. The combination of the
low ε⁵⁰Ti value with the absence of CAIs and the O
isotopic composition that follows the CCAM might point
toward a formation region beyond that of the other CC
parent bodies, perhaps at a very large heliocentric
distance. Overall observations from multiple isotope
systems suggest that the clast DaG 1064-A is probably
sampling particular primitive and thermally unaltered
material, which is currently unsampled by individual
meteorites.

The δ¹⁵N values of 90‰–112‰ for C1 clasts in
ureilites fall between those of CR chondrites and those of
all other chondrite groups, but they are clearly higher
than the bulk δ¹⁵N of ureilites (Table 1). Contamination
of the clasts with surrounding ureilite host material is
unlikely. The N concentrations in ureilites are eight times
lower than those in the analyzed clasts (Table 1), so
significant contamination would be required to affect the
N isotope ratio. Such contamination, combined with
the elevated Cr concentrations in ureilitic pyroxene and
olivine (Berkley et al., 1980), would result in dramatically
lowered ε⁵⁴Cr, which is not observed. Consequently, the
N isotopic composition of the C1 clasts in ureilites
requires incorporation of ¹⁵N-rich material (ice and/or

organic matter) formed through specific processes within
the solar nebula or the interstellar medium. Such
processes may include photo dissociation, similar to that
proposed for mass-independent isotope fractionation of
O isotopes (Alexander et al., 2012; Broadley et al., 2022;
Füri & Marty, 2015; Kerridge, 1985; Pearson et al., 2006;
Vacher et al., 2020).

The ε⁵³Cr and the Mn/Cr ratio of C1 clast Acfer 311-C (CR chondrite) plots in between the isochron of components of Orgueil and the isochron defined by bulk carbonaceous chondrites, similar to other bulk rocks from the literature (Figure 6; Trinquier et al., 2008). The analyzed C1 clast DaG 1064-A is enriched in ⁵³Cr (0.65ε) when compared to other bulk carbonaceous chondrites at a very high ⁵⁵Mn/⁵²Cr ratio of 3.75 (Figure 6). The observed enrichment in ⁵³Cr is slightly less (<0.2ε) compared to that calculated from the ε⁵³Cr-Mn/Cr correlation of bulk chondrite isochron from the data in this study. It suggests that the clasts are either younger than chondrites or redistribution of Mn during aqueous alteration. Thus, while the ⁵³Mn-⁵³Cr system was disturbed, the high ⁵⁴Cr abundance conceivably may reflect the small-scale heterogeneity of presolar material enriched in ⁵⁴Cr and depleted in ⁵⁰Ti (e.g., Dauphas et al., 2010; Nittler et al., 2018; Qin et al., 2010; Trinquier et al., 2007, 2008; Yamakawa & Yin, 2014).

In summary, the C1 clasts in CR chondrites differ
from those in ureilites, and both differ from CI chondrites
and material from C-type asteroid Ryugu. The C1 clasts
from ureilites possess Cr and Ti isotope signatures that
extend the known range of carbonaceous chondrites,
potentially representing primordial building block
material that has not yet been sampled by individual
meteorites or sample return missions.

Diversity of C1 Material and Its Relevance

C1 clasts have been identified in a number of different meteorite groups including H, CH, and Rumuruti chondrites, as well as HEDs and ureilites (e.g., Bischoff, Palme, Schultz, et al., 1993; Briani et al., 2012; Greshake, 2014; Greshake et al., 2016) and analyzed for different isotope systems focusing on different aspects such as their formation, alteration history, and transportation. The available studies imply that C1 material was ubiquitous in the early solar system and hosted as clasts in meteoritic breccias: Zolensky et al. (2003) showed that a C1 clast in the H chondrite Zag is enriched in ¹⁷O and ¹⁸O compared to C1 clasts and CI chondrites analyzed here, however, having similar Δ¹⁷O when compared to C1 clasts in ureilites (Figure 7). It further contains organics with hotspots rich in D (up to 2300‰) and ¹⁵N (up to 700‰; Kebukawa et al., 2019). In a three-oxygen isotope diagram, the clast plots on a common slope ~0.52 line along with
<figure><img src="image_8.png" /></figure>

FIGURE 7. Three-oxygen isotope diagram showing data for individual C1 clasts in ureilites (C1a; this work and those from Brearley & Prinz, 1992 and Goodrich et al., 2021) in yellow; data for C1 clasts in CR chondrites (C1b) are shown in blue. The inset shows a larger range in δ¹⁷O and δ¹⁸O plotting the position of the solar wind (sun) and the cosmic symplectite (COS) as analyzed by Sakamoto et al. (2007). Oxygen isotope composition of a C1 clast in the H chondrite Zag is shown in green. It is enriched in ¹⁸O relative to ¹⁷O compared to the C1 clasts in ureilites and CR chondrites. Interestingly, a mass-dependent fractionation line (MDF, slope of ~0.52) connects the Zag clast with the array defined by the C1 clasts in ureilites and with data of C1 clast AhS 671 studied by Goodrich et al. (2021).

sample AhS 671 (mineralogically similar clasts in Almahata Sitta ureiltic material; Goodrich et al. (2019, 2021)), also overlapping with the clasts analyzed here, possibly implying mass-dependent O isotope fractionation from a common reservoir (Figure 7).

Gounelle et al. (2003, 2005) published petrologic characteristics and H isotope data on C1 clasts ("CR-microclasts") that are usually well below 500 µm in size. These data overlap with H isotope data on C1 clasts obtained by our group (Patzek et al., 2020) and are in the range of δD of CI chondrites. Based on petrologic data, Gounelle et al. (2003, 2005) and Patzek, Bischoff, et al. (2018) suggested that C1 clasts in HEDs differ from CI chondrites; however, N, O, Ti, and Cr isotope data for these clasts are not yet available. Such data are also unknown for a mineralogically different C1 clast in the R chondrite NWA 6828 described by Greshake (2014) and Greshake et al. (2016).

C1 clasts in CH chondrites have also been described by numerous authors (e.g., Bischoff, Palme, Schultz, et al., 1993; Bonal, Huss, Krot, & Nagashima, 2010; Bonal, Huss, Krot, Nagashima, Ishii, et al., 2010; Greshake et al., 2002; Van Kooten et al., 2016, 2017). Bonal, Huss, Krot, and Nagashima (2010) showed that C1 clasts in Isheyevo are enriched in ¹⁵N on a bulk scale relative to other solar system materials and contain N hotspots but no enrichment in D. A similar observation was made by Briani et al. (2009) on a xenolith in Isheyevo yielding δ¹⁵N signatures ranging from low values (~-300‰) to extremely high values (~+5000‰). Data by Van Kooten et al. (2016, 2017) reveal that C1 clasts in metal-rich CH chondrites are characterized by a deficit of ²⁶Mg relative to inner solar system materials, while they show a ⁵⁴Cr enrichment similar to that of CR chondrites.

Each of the aforementioned studies focused on a subset of clasts and/or isotope systems.
By combining conclusions drawn from N, O, H, S, Cr, and Ti isotopes (this work, Patzek, Bischoff, et al., 2018, Patzek, Pack, et al., 2018, Patzek et al., 2019; Visser et al., 2018, 2019), it is possible to distinguish between different groups of C1 material. Using O and H isotopes, Patzek et al. (2019, 2020) demonstrated that C1 clasts from ureilites, CR chondrites, and known CI chondrites sample distinct isotopic reservoirs. This finding is confirmed in the present work with C1 clasts in ureilites exhibiting unique isotopic signatures not observed in any other known solar system material.

C1 clasts hosted by polymict ureilites and CI chondrites, their closest analog in terms of mineralogy, are likely sampling different parent bodies. It is unlikely that a single C1 or CI parent body could account for the very distinct isotope signatures observed for the various types of C1 clasts, CI chondrites, or ungrouped C1 chondrites such as Flensburg (Bischoff et al., 2021). Based on data obtained here, C1 clasts in ureilites plot along the CCAM line, indicating that their parent bodies incorporated a relatively ¹⁷O- and ¹⁸O-rich water component, which seems to have undergone less mass-dependent O isotope fractionation than water in CM and CR chondrites (e.g., Figures 3a and 7). This absence of mass-dependent O isotope fractionation in C1 clasts in ureilites might result from alteration at very low water-rock ratios in small pebbles or bodies, where all the water is consumed during reaction with anhydrous minerals. This alteration must be rather fast and complete to prevent the formation of isotopically fractionated water reservoirs and maintain the ~1:1 ratio for ¹⁷O/¹⁶O and ¹⁸O/¹⁶O. For CM chondrites, various studies have proposed O isotope compositions of waters (Clayton & Mayeda, 1999; Fujiya, 2018). Fujiya (2018) concluded that, because ¹⁸O is enriched during fractionation relative to ¹⁷O in the CM fluids, the CM primordial water underwent at least one additional isotope fractionation process before altering the silicates in the CM parent bodies, which might have happened during the condensation of ice under Rayleigh conditions. Based on D/H ratios of the water component in CM chondrites, Piani et al. (2018) showed that the studied lithology in the CM chondrite breccia Paris was altered by a slightly different water when compared to other studied CM chondrites or CM lithologies, which has been shown for less altered CM chondrites as well and can be attributed to nebular hydration of amorphous silicates prior to accretion (Marrocchi, Rigaudier, et al., 2023). Alexander (2019) proposed that the mass-dependent fractionation of O isotopes of the water altering CMs and other carbonaceous chondrites is consistent with incomplete condensation of ice under Rayleigh conditions at low temperatures. However, this process would lead to an enrichment by only ~100‰ in δD, requiring D-rich water to explain the observed δD signatures of carbonaceous chondrites and of

the C1 clasts in ureilites (Patzek et al., 2019, 2020). The difference in δD between the CM chondrite Paris and other CM chondrites together with the isotopic composition of C1 clasts found in ureilites implies multiple sources and isotopic compositions of ices in the early solar system. This is further supported by the δ¹⁵N signature of the C1 clasts in ureilites, which plot between the N isotopic composition of CR and CM chondrites, demonstrating the existence of material with ¹⁵N enrichments intermediate between these two groups making these clasts unique among meteorites. Identification of the exact carrier phases responsible for these specific ¹⁵N enrichments would require a stepped heating approach with smaller temperature increments. Since the samples analyzed here were only measured in two steps, a definitive identification is not possible. The ¹⁵N enrichment likely results from a mixture of organics (SOM and IOM; e.g., Alexander et al., 2007), presolar grains, nitrides, and phase Q, which all have a distinct (and variable) ¹⁵N signatures as shown in studies of Ryugu samples and CI chondrites (e.g., Barosch et al., 2022; Gamblin et al., 2024; Grady et al., 2002; Matsumoto et al., 2024; Nguyen et al., 2023; Verchovsky, 2017).

Overall, several C1 clasts measured for Ti and Cr isotopes show excesses in ⁵⁴Cr and depletions in ⁵⁰Ti compared to other carbonaceous chondrites, despite being hosted in a ureilite, indicating mixing of outer and inner solar system materials, likely in the regolith of the ureilite parent body or alternatively on a second-generation rubble pile asteroid. Whether this mixing happened recently or in the early solar system is unclear. Additionally, these ureilite-hosted C1 clasts incorporated unfractionated ices as indicated by their O isotope composition. The parent body of these clasts likely accreted in the outer solar system where it incorporated ¹⁵N-enriched organics and a very low fraction of ⁵⁰Ti-enriched CAI-like material. The virtual absence of CAI-like material with Ti excesses and Cr depletion accreted by the parent body possibly implies formation in the far outer solar system.

In summary, these results point to a considerable diversity of C1 material in the early solar system that is preserved in brecciated meteorites, with the C1 clasts in ureilites being of special interest for understanding the evolution of material in the early solar system.

## CONCLUSIONS

The N, O, Ti, and Cr isotope results of C1 clasts in various groups of achondrite and chondrite breccias suggest that isotopically distinct primitive parent bodies existed in the outer part of the early solar system. Some of this material was later accreted by inner solar system objects such as the HED and ureilite parent bodies and
serves as a time capsule for the diversity of aqueously altered C1 material. The new mineralogical and isotopic data imply a large diversity in C1 material, distinct from C11 chondrites and Ryugu. Although C11 chondrites and samples returned from Ryugu have the closest affinities to the solar photosphere for all elements except the highly volatile ones, their O isotope composition requires isotope fractionation processes on the parent body(ies), likely occurring already in the disk or its molecular cloud precursor. This work shows that the water component altering the C1 clasts in ureilites has an O isotope composition that follows an ~slope-1 line (CCAM), which is distinct from those of other aqueously altered type 1 and 2 carbonaceous chondrites. This is consistent with ices formed from an ¹⁷O- and ¹⁸O-rich reservoir, possibly resulting from mass-independent isotope fractionation due to photodissociation and CO self-shielding in a dense molecular cloud or in the solar nebula. To explain the absence of mass-dependent O isotope fractionation, the alteration of the C1 clasts in ureilites must have occurred on small bodies at very low water/rock ratios and at relatively fast and quantitative reaction rates to hinder mass-dependent isotope fractionation. Nonetheless, the water/rock ratio must have been high enough to allow nearly complete hydration of the precursor material since these clasts are nearly free of anhydrous silicates. With their ¹⁵N enrichment of ~100%, the C1 clasts in ureilites bridge the gap between CR and CM chondrites, which implies a continuous ¹⁵N enrichment across these chondrite groups.

An analyzed C1 clast from the ureilite DaG 1064 provides an endmember composition for carbonaceous chondrites in the ε⁵⁴Cr-ε⁵⁰Ti space, demonstrating its unique characteristic and nearly closing the apparent gap in Ti isotopes between Earth (inner solar system materials) and carbonaceous chondrites from larger heliocentric distances. The isotopic compositions of additional types of clasts (i.e., those in HEDs and H chondrites) are still unknown and might further broaden the diversity of carbonaceous chondrite-like material in the early solar system.

*Acknowledgments*—U. Heitmann is thanked for skillful thin section preparation. We further acknowledge Thorsten Grund for keeping the SEM running, Maike Fischer, Dingsu Feng, and Dennis Kohl for maintenance and assistance during O isotope analyses. We thank Monika Feth and Daniel Wießner for support and assistance in the clean lab for Cr isotope work, and Laurent Zimmermann for help with noble gas analyses at CRPG. We acknowledge the Meteorite Working Group at the Johnson Space Center and Mike Zolensky for contributing samples. US Antarctic meteorite samples are recovered by the

Antarctic Search for Meteorites (ANSMET) program, which has been funded by NSF and NASA, and they are characterized and curated by the Department of Mineral Sciences of the Smithsonian Institution and the Astromaterials Curation Office at NASA Johnson Space Center. Associate editor Yves Marrocchi and two anonymous reviewers are thanked for providing suggestions and comments to improve this manuscript. This work is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—Project-ID 263649064—TRR 170 (subproject B05). MR and MS acknowledge funding from the NCCR PlanetS supported by the Swiss National Science Foundation under grants 51NF40_182901 and 51NF40_205606. E.F. was supported by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement no. 715028). This is TRR170 publication no. 228. Open Access funding enabled and organized by Projekt DEAL.

*Data Availability Statement*—The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.

*Editorial Handling*—Dr. Yves Marrocchi

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## SUPPORTING INFORMATION

Additional supporting information may be found in the online version of this article.

**Figure S1.** Microscopic picture of material of the extracted clast NWA 7542-G.

**Figure S2.** Microscopic picture of extracted clast DaG 1064-A.

**Figure S3.** Microscopic picture of extracted clast Acfer 311-C.

**Figure S4.** Major, minor, and trace element concentrations normalized to CI chondrites. REE sorted

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from La to Lu to emphasize the observable group II CAI pattern.

**Figure S5.** ε⁵⁴Cr vs. ε⁵³Cr standard data during the analytical session.

**Table S1.** Results of individual runs of the TIMS analyses for Cr isotopes.

**Table S2.** ⁵⁵Mn/⁵²Cr ratios of Orgueil and Ivuna from published literature.

**Table S3.** N and Ne-Ar elemental and isotopic analyses for individual clasts including all heating steps.