# Hybrid accretion of carbonaceous chondrites by radial transport across the
Jupiter barrier

Elishevah van Kooten Centre for Star and Planet Formation and Globe Institute,
University of Copenhagen
DK-1350 Copenhagen, Denmark  Université de Paris, Institut de Physique du
Globe de Paris
CNRS UMR 7154, 1 rue Jussieu, 75238 Paris, France  Martin Schiller Centre for
Star and Planet Formation and Globe Institute, University of Copenhagen
Øster Voldgade 5-7, DK-1350 Copenhagen, Denmark  Frédéric Moynier  Université
de Paris, Institut de Physique du Globe de Paris
CNRS UMR 7154, 1 rue Jussieu, 75238 Paris, France  Anders Johansen  Lund
Observatory, Department of Astronomy and Theoretical Physics, Lund University
Sölvegatan 27, SE-221 00 Lund, Sweden  Centre for Star and Planet Formation
and Globe Institute, University of Copenhagen
DK-1350 Copenhagen, Denmark  Troels Haugbølle  Centre for Star and Planet
Formation and Globe Institute, University of Copenhagen
DK-1350 Copenhagen, Denmark  Niels Bohr Institute, University of Copenhagen
DK-2100 Copenhagen, Denmark  Martin Bizzarro Centre for Star and Planet
Formation and Globe Institute, University of Copenhagen
DK-1350 Copenhagen, Denmark  Université de Paris, Institut de Physique du
Globe de Paris
CNRS UMR 7154, 1 rue Jussieu, 75238 Paris, France

###### Abstract

Understanding the origin of chondritic components and their accretion pathways
is critical to unravel the magnitude of mass transport in the protoplanetary
disk, the accretionary history of the terrestrial planet region and, by
extension, its prebiotic inventory. Here, we trace the heritage of pristine
components from the relatively unaltered CV chondrite Leoville through their
mass-independent Cr and mass-dependent Zn isotope compositions. Investigating
these chondritic fractions in such detail reveals an onion-shell structure of
chondrules, which is characterized by 54Cr- and 66Zn-poor cores surrounded by
increasingly 54Cr- and 66Zn-rich igneous rims and an outer coating of fine-
grained dust. This is interpreted as a progressive addition of 54Cr- and 66Zn-
rich, CI-like material to the accretion region of these carbonaceous
chondrites. Our findings show that the observed Cr isotopic range in
chondrules from more altered CV chondrites is the result of chemical
equilibration between chondrules and matrix during secondary alteration. The
54Cr-poor nature of the cores of Leoville chondrules implies formation in the
inner Solar System and subsequent massive outward chondrule transport past the
Jupiter barrier. At the same time, CI-like dust is transferred inwards. We
propose that the accreting Earth acquired CI-like dust through this mechanism
within the lifetime of the disk. This radial mixing of chondrules and matrix
shows the limited capacity of Jupiter to act as an efficient barrier and
maintain the proposed non-carbonaceous and carbonaceous chondrite dichotomy
over time. Finally, also considering current astrophysical models, we explore
both inner and outer Solar System origins for the CV chondrite parent body.

mass transport — chondrules — Earth’s accretion — protoplanetary disk

††journal: ApJ

##  1 Introduction

Chondrites are fragments of primitive planetesimals and represent sedimentary
agglomerates comprising the Solar System’s oldest and least altered planetary
building blocks. They primarily consist of three components, namely
chondrules, matrix and less abundant refractory inclusions, which represent
the first formed solids in the protoplanetary disk (Connelly et al., 2012).
Chondrules are spherical objects believed to have formed from melting of free-
floating dust agglomerates during transient heating events in the disk. The
matrix present in chondrites is thought to consist of relatively fine-grained,
unaltered material that surrounds the other chondrite components.
Collectively, chondrites and their components provide a unique time window
into the early evolution of the gaseous protoplanetary disk when the planets
accreted their main masses. These objects are typically divided into non-
carbonaceous (NC) and carbonaceous (CC) chondrites, and it has been suggested
that the former accreted in the terrestrial planet region (i.e., sunward of
Jupiter), whereas the latter accreted in the accretion region of gas giant
planets. This divergent heritage of chondrites is based on the relatively
volatile-rich nature of CC, the distribution of chondritic components in the
chondrite groups and their distinct isotope systematics relative to NC (Budde
et al., 2016; Warren, 2011).

The proposed early establishment of such a dichotomy through the rapid
accretion of Jupiter (Kruijer et al., 2017) implies limited or no chemical
and/or isotopic exchange between the NC and CC reservoirs. This model is in
line with the proposed elemental and isotopic complementarity between
chondrules and matrix, which suggests that chondrite components are
genetically linked and formed from a common disk reservoir. Both the
complementarity (Hezel & Palme, 2010) and the dichotomy model do not allow for
mass transport in the protoplanetary disk, but view planetary accretion within
a more static environment, where planetary building blocks are sampled within
the direct vicinity of the accreting object. The assumed absence of
significant mass transport between the inner terrestrial planet accretion
region and the outer Solar System is inconsistent with recent isotopic
evidence indicating protracted accretion of volatile-rich matter to the
terrestrial planets during the lifetime of the protoplanetary disk (Schiller
et al., 2020, 2018). In detail, the nucleosynthetic Ca and Fe isotope
composition of the Earth requires mixing between an inner Solar System derived
endmember and a CI-like endmember from the outer Solar System. CI (Ivuna-type)
chondrites are volatile-rich (i.e., rich in water and organics) meteorites
closely matching the composition of the solar photosphere and consist mainly
of fine-grained dust (i.e., matrix). Although it has been postulated that a
sharp Mo isotopic dichotomy exists between inner and outer Solar System
objects (Budde et al., 2016), the observation that Earth falls in between NC
and CC trends (Budde et al., 2019) appears to contradict the view that these
two reservoirs existed in the inner and outer Solar System, respectively, and
maintained isolation from each other. This observation has been interpreted as
evidence for an outer Solar System origin for the Moon-forming impactor, which
was admixed to Earth’s mantle during a giant impact. However, this hypothesis
is unlikely since the Moon and Earth are isotopically nearly identical for
most elements (Mastrobuono-Battisti et al., 2015; Zhang et al., 2012).
Alternatively, the Mo isotope composition of Earth may reflect progressive
admixing of volatile-rich matter to the inner Solar System as inferred from
the terrestrial Fe and Ca nucleosynthetic compositions. A better understanding
of the extent of mass transport between the NC and CC reservoirs is critical
to elucidate Earth’s accretion history, including the nature of volatiles and
prebiotic molecules delivered to our planet. For example, in a model of
limited mass transport between the inner and outer Solar System, delivery of
abundant prebiotic molecules such as complex organic compounds critical to
life occurs by stochastic processes late in the history of the terrestrial
planets. In contrast, progressive inward mass transport of outer Solar System
material during the disk lifetime raises the possibility that the delivery of
prebiotic molecules to the terrestrial planets is a natural consequence of
their main accretion phase, rather than a stochastic coincidence.

Recent astronomical observations of young protoplanetary disks and planet
formation simulations suggest that the growth of rocky planets occurs by the
highly efficient mechanism of pebble accretion, that is, the accretion of
millimeter- to centimeter-sized particles onto planetesimal seeds during the
$\sim$5 Myr protoplanetary disk lifetime (Johansen et al., 2015, 2021). In the
inner Solar System, this process is believed to be driven by the accretion of
mm-sized chondrules. Both the petrology and individual Pb-Pb ages of
chondrules (Bollard et al., 2017) indicate that these objects experienced
multiple melting events. For example, igneous rims surrounding chondrule cores
in CV (Vigarano-type) chondrites record the accretion of additional dust to
the chondrules followed by a heating event that likely post-dates the melting
of the corresponding cores (Rubin & Wasson, 1987; van Kooten & Moynier, 2019).
Moreover, chondrules are often characterized by fine-grained dust rims (FGRs),
which surround the igneous rims and represent an addition of even more
pristine dust to the chondrule system. Thus, individual chondrules are time-
sequenced samples that can provide insights into the secular composition and
isotopic evolution of disk solids that accreted to planets. In particular, the
onion-shell structure of a chondrule and its rims can be regarded as a
miniature planet and its feeding zones. Thus, by sampling the individual
accretion layers of the chondrule system, it is possible to reconstruct the
flux of material in the early Solar System during the time when the
terrestrial planets acquired their main mass.

Here, we have sampled chondrule cores and their igneous rims, as well as their
fine-grained dust rims and more coarse-grained intra-chondrule matrix (ICM)
from the relatively unaltered CV3.1 chondrite Leoville. The aim is to
investigate their genetic heritage and volatile related processes through
mass-independent Cr isotope and mass-dependent Zn isotope systematics,
respectively. In detail, nucleosynthetic Cr isotope signatures have been used
on bulk chondrites and chondrules in the past to trace the origin of their
precursor materials within the protoplanetary disk (Olsen et al., 2016;
Trinquier et al., 2007; van Kooten et al., 2016; Warren, 2011), whereas Zn
isotopes have been used as a probe for evaporation and condensation processes
of chondrites and chondrules (Luck et al., 2005; Pringle et al., 2017; van
Kooten & Moynier, 2019). Hence, combining these isotope systems will provide
us with useful information regarding the formation location and corresponding
thermodynamic conditions of various chondritic components as well as the
degree and direction of their inferred mass transport. CV chondrites have been
chosen for this study because of the large size of their components relative
to other carbonaceous chondrites, which allows for detailed sampling. We show
that from such a detailed investigation of one of the least altered CV
chondrites, a completely new picture emerges for the accretion history of the
CV chondrite parent body that impacts our understanding of the accretion
history of terrestrial planets.

##  2 Results

###  2.1 The petrology and compositions of Leoville fractions

We have investigated the petrology and elemental composition of Leoville
fractions using high resolution back scattered electron images, elemental
maps, laser ablation and inductively coupled plasma mass spectrometry (ICPMS)
analyses (for a detailed description see Appendix B and Table A1 and A2) in
this and previous studies (van Kooten et al., 2019; van Kooten & Moynier,
2019). Our data demonstrate that Leoville, classified as a reduced CV3.1
chondrite (Bonal et al., 2016), is one of the least altered CV chondrites
(Fig. 1 versus Fig. 2) when compared to other CV chondrites such as Vigarano
(CV3.1-3.4) and Allende (CV3.6). Here, we focus on chondrules with simple
core-igneous rim pairs (Fig. 1, Fig. 6). All chondrules are surrounded by FGRs
and the space between the FGRs is occupied by ICM, which includes chondrule
fragments and larger sulfide and metal grains. We note that for more altered
CV chondrites such as Vigarano and Allende, these two types of matrix become
indistinguishable (Fig. 2). The fluid-assisted thermal metamorphism results in
a coarsening and dehydration of the entire matrix towards a homogeneous
texture of phyllosilicates and larger grains of anhydrous Ca-rich pyroxene.
This alteration begins with the leaching of siderophile elements from the
oxidized/sulfurized metal into the matrix and modification of the chondrule
mesostasis (Fig. 2B) and concludes with the larger-scale elemental exchange
between chondrules and matrix (Fig. 2D and Fig. 2F). Furthermore, we observe a
transfer of a sulfur-rich matrix to the production of sulfide grains in the
chondrules (Fig. 2E, van Kooten & Moynier, 2019). The pristine Leoville
chondrite overall lacks these alteration features and, thus, by focusing on
this chondrite, we can be confident that the chondrules and their rims record
primary chemical and isotopic information.

Figure 1: Back scattered electron images and Mg-Ca-Al-S (red-green-blue-
yellow) elemental maps from Leoville (CV3.1) chondrules and matrix. A)
depicting various components of Leoville, including 1) chondrule core with a
barred olivine texture (sample Ach4), 2) metal/sulfide rim around the core, 3)
igneous rim with forsterite, low-Ca pyroxene and abundant metal/sulfide
grains, 4) a fine-grained dust rim and 5) the intra-chondrule matrix. B)
Elemental map of A), where yellow reflects the sulfides. The bright blue grain
in the upper right corner is a CAI. C) Close-up of A), in which the
distinction between a FGR and ICM is highlighted. D) An Al-rich chondrule
(sample Bch6) with a single olivine grain and pyroxenes, surrounded by a metal
rim and a FGR. The distinction between FGR and ICM is highlighted. E)
Elemental map of D). F) Close-up of D), which highlights the borders between
three FGRs and the ICM. For more images of Leoville components sampled in this
study, see the Appendix B.  Figure 2: Back scattered electron images and Mg-
Ca-Al-S (red-green-blue-yellow) elemental maps from Vigarano (CV3.1-3.4) and
Allende (CV$>$3.6) chondrules and matrix. Vigarano contains more and less
altered areas. A) shows a more altered area with a barred type I chondrule
with mineralogical zonation. The FGR surrounding the chondrule is altered near
the chondrule boundary where exchange of among others Fe-Mg occurs. B)
Elemental map of A). C) Close-up of A). D) Chondrule from Allende. In the
surrounding coarse-grained matrix, the distinction between FGR and ICM cannot
be made because of secondary alteration. E) Elemental map of Allende
chondrules, where the alteration of the chondrules is reflected by the
transfer of sulfides to the chondrule cores and the alteration of the coarse-
grained matrix is visible. The green grains in the matrix are recrystallized
Ca-pyroxenes. F) Another chondrule from Allende where the rim of the chondrule
is significantly altered through Fe-Mg elemental exchange.

###  2.2 Cr isotope signatures of Leoville components

We have measured the Cr isotope compositions of 11 ICM fragments as well as
one FGR (Appendix A for detailed methods, Table LABEL:tab:CrZn, Fig. 3), which
have also been analyzed for their Zn isotope compositions on the same
aliquots. Given that the average thickness of the FGRs is $\sim$100 $\upmu$m,
which is comparable to that of the microdrill bits, it was not possible to
sample additional FGRs without contamination from surrounding materials.
However, we note that the chemical composition of the FGRs in Leoville and in
similarly unaltered sections of Vigarano are identical and, as such, the
obtained isotope compositions of the FGRs are likely representative of CV
chondrites in general (van Kooten et al., 2019). All errors reported here are
2SD. We distinguish between clean and contaminated (chondrule fragments
present) ICM (see Appendix B). We show that the average $\upepsilon$54Cr value
of the clean ICM (0.70$\pm$0.37 ‱) is indistinguishable from that of our bulk
CV chondrite value of 0.81$\pm$0.28 ‱ and averaged literature values of
0.86$\pm$0.06 ‱. The 55Mn/52Cr ratios (0.59$\pm$0.24) and $\upepsilon$53Cr
(53Cr being the decay product of 53Mn with a half-life of 3.74 Myr) signatures
(0.20$\pm$0.51 ‱) of the clean ICM are also consistent with a bulk CV
chondrite signature. The contaminated ICM is more variable and ranges between
–2.20$\pm$0.35 ‱ and 0.51$\pm$0.23 ‱, with most $\upepsilon$54Cr values being
negative (Table LABEL:tab:CrZn). The FGR has a $\upepsilon$54Cr value of
1.26$\pm$0.32 ‱, which is within error of the CI chondrite value of
1.54$\pm$0.30 ‱ measured in this study and literature values (Qin et al.,
2010; Schiller et al., 2014; Trinquier et al., 2007). Moreover, its
$\upepsilon$53Cr signature (0.24$\pm$0.12 ‱) and 55Mn/52Cr ratio of 0.86 also
correspond to CI chondrites (Qin et al., 2010; Shukolyukov & Lugmair, 2006;
van Kooten et al., 2020). The type I chondrule cores have an average
$\upepsilon$54Cr of –0.58$\pm$0.16 ‱ (n = 13, 2SD), with a range between
–1.00$\pm$0.30 ‱ and –0.09$\pm$0.30 ‱. This overlaps with the range of
previous individual CV chondrule Cr isotope analyses ($\upepsilon$54Cr =
–0.79$\pm$0.10 to 2.01$\pm$0.10 ‱; Olsen et al., 2016), but the distribution
of the $\upepsilon$54Cr values and the average obtained for the Leoville
chondrules is not in agreement with previous datasets (Kadlag et al., 2019;
Olsen et al., 2016; Williams et al., 2020). In detail, the average
$\upepsilon$54Cr values of the Leoville chondrule cores is significantly more
negative than for Vigarano chondrules ($\upepsilon$54Cr = 0.26$\pm$0.28 ‱, n =
10; Olsen et al., 2016), NWA 3118 ($\upepsilon$54Cr = 0.77$\pm$0.28 ‱, n = 6;
Olsen et al., 2016) and bulk Allende chondrules ($\upepsilon$54Cr =
0.90$\pm$0.28 ‱, n = 100; Kadlag et al., 2019). The $\upepsilon$53Cr
signatures of the chondrule cores are –0.20$\pm$0.09 ‱, within error of the
solar system initial $\upepsilon$53Cr value of –0.18 ‱ (Göpel et al., 2015),
and the cores have an average 55Mn/52Cr ratio of 0.20$\pm$0.14. The five
igneous rims have higher $\upepsilon$54Cr values with an average of
0.10$\pm$0.24 ‱ and ranging between –0.46$\pm$0.30 and 0.22$\pm$0.30 ‱. The
$\upepsilon$54Cr value of each individual chondrule rim is higher than that of
the corresponding core (Table LABEL:tab:CrZn). The $\upepsilon$53Cr signatures
of rims vary little and average –0.32$\pm$0.11 ‱ despite exhibiting variable
55Mn/52Cr ratios between 0.10 and 0.77. Finally, we have measured two bulk
chondrules (i.e., core with igneous rim) with $\upepsilon$54Cr values of
0.02$\pm$0.40 ‱ and 0.09$\pm$0.18 ‱ and two Al-rich chondrules with
$\upepsilon$54Cr values of –1.30$\pm$0.11 ‱ and 1.63$\pm$0.30 ‱.

Table 1: Mass-independent Cr and mass-dependent Zn isotope data of Leoville components and reference materials. For Cr isotope analyses, in case of samples measured on multiple filaments, the error is taken as the 2SD of the weighted mean is taken, otherwise the error reflects the external reproducibility of the measurements taken from the standards (30 ppm [2SD] on $\upepsilon$54Cr). WM = weighted mean. *Data from van Kooten & Moynier (2019). The row ‘aliquots’ for the standards reflects the number of aliquots processed through chemistry (Appendix A for detailed explanation). FGR = fine-grained rim and ICM = intra chondrule matrix.  |  |  $\updelta$66Zn |  $\upepsilon$54Cr |  $\upepsilon$53Cr
---|---|---|---|---
Reference materials | Aliquots |  |  |  |  |  |  |  |  |
NWA 12523 (CV bulk) | 3 | 0.27* |  ± |  0.19 | 0.81 |  ± |  0.28 | 0.04 |  ± |  0.42
Ivuna (CI bulk) | 5 |  |  |  | 1.50 |  ± |  0.23 | 0.15 |  ± |  0.06
PCC1 | 2 |  |  |  | 0.12 |  ± |  0.09 | -0.01 |  ± |  0.08
BHVO2 | 1 | 0.34* |  ± |  0.08 | -0.03 |  |  | 0.02 |  |
Leoville chondrules | Fraction |  |  |  |  |  |  |  |  |
Bch3 | Al-rich core |  |  |  | 1.63 |  ± |  0.30 | 0.25 |  ± |  0.15
Bch6 | Al-rich core | 0.10 |  ± |  0.12 | -1.30 |  ± |  0.11 | -0.08 |  ± |  0.25
Ach1 | core | -0.94 |  ± |  0.12 | -0.63 |  ± |  0.49 | -0.11 |  ± |  0.09
Ach7 | core |  |  |  | -0.83 |  ± |  0.39 | -0.38 |  ± |  0.32
Ach8 | core |  |  |  | -0.85 |  ± |  0.30 | -0.36 |  ± |  0.15
Ach4 | core |  |  |  | -0.65 |  ± |  0.30 | -0.11 |  ± |  0.15
Ach9 | core |  |  |  | -0.63 |  ± |  0.30 | -0.03 |  ± |  0.15
Bch7 | core |  |  |  | -0.72 |  ± |  0.30 | -0.31 |  ± |  0.15
Ach10 | core |  |  |  | -0.44 |  ± |  0.30 | -0.16 |  ± |  0.15
Bch1 | core |  |  |  | -0.50 |  ± |  0.30 | 0.02 |  ± |  0.15
Bch2 | core |  |  |  | -0.14 |  ± |  0.30 | -0.1 |  ± |  0.15
C1 | core | -0.77 |  ± |  0.19 | -0.09 |  ± |  0.30 | -0.38 |  ± |  0.15
C2 | core | -0.77 |  ± |  0.19 | -1.00 |  ± |  0.30 | -0.42 |  ± |  0.15
C3 | core | -0.90 |  ± |  0.19 | -0.46 |  ± |  0.30 | -0.67 |  ± |  0.15
C5 | core | -0.72 |  ± |  0.19 | -0.72 |  ± |  0.30 | -0.33 |  ± |  0.15
C6 | core | -0.77 |  ± |  0.19 |  |  |  |  |  |
Ach2 | core+rim | 0.15 |  ± |  0.12 | 0.09 |  ± |  0.18 | -0.12 |  ± |  0.38
Ach3 | core+rim | -0.06 |  ± |  0.12 | 0.02 |  ± |  0.40 | -0.16 |  ± |  0.20
C1 | rim | -0.14 |  ± |  0.12 | 0.17 |  ± |  0.30 | -0.28 |  ± |  0.15
C2 | rim | -0.11 |  ± |  0.12 | -0.41 |  ± |  0.30 | -0.36 |  ± |  0.15
C3 | rim | -0.04 |  ± |  0.12 | -0.14 |  ± |  0.30 | -0.26 |  ± |  0.15
C5 | rim | 0.23 |  ± |  0.12 | -0.13 |  ± |  0.30 | -0.33 |  ± |  0.15
C6 | rim | 0.01 |  ± |  0.12 | -0.03 |  ± |  0.30 | -0.39 |  ± |  0.15
Leoville matrix |  |  |  |  |  |  |  |  |  |
Ach1mx | IC mx | -0.02 |  ± |  0.12 | 0.47 |  ± |  0.28 | -0.17 |  ± |  0.04
Ach2mx | IC mx | -0.02 |  ± |  0.12 | -0.51 |  ± |  0.33 | -0.11 |  ± |  0.09
Ach3mx | IC mx | -0.26 |  ± |  0.12 | 0.51 |  ± |  0.23 | 0.15 |  ± |  0.05
Ach7mx | IC mx | -0.19 |  ± |  0.12 | 0.92 |  ± |  0.11 | 0.26 |  ± |  0.11
Bmx1 | ICmx | 0.21 |  ± |  0.12 | -0.21 |  ± |  0.40 | 0.14 |  ± |  0.17
Bmx2 | IC mx | 0.14 |  ± |  0.12 | -0.17 |  ± |  0.30 | -0.17 |  ± |  0.15
Bmx3 | IC mx | -0.43 |  ± |  0.12 | -2.20 |  ± |  0.39 | 0.12 |  ± |  0.07
Leo2ch1mx1 | IC mx | -0.09 |  ± |  0.12 | 0.68 |  ± |  0.30 | 0.28 |  ± |  0.15
Leo2ch1mx2 | IC mx | -0.09 |  ± |  0.12 | 0.73 |  ± |  0.30 | 0.42 |  ± |  0.15
Leo2ch2mx | IC mx | -0.60 |  ± |  0.12 | -0.08 |  ± |  0.30 | 0.59 |  ± |  0.15
Leo2ch3mx | IC mx | -0.29 |  ± |  0.12 | -0.47 |  ± |  0.30 | 0.16 |  ± |  0.15
Ch1mx | FGR | 0.14 |  ± |  0.12 |  |  |  |  |  |
Ch2mx | FGR | 0.24 |  ± |  0.12 | 1.26 |  ± |  0.32 | 0.24 |  ± |  0.12
cores (WM) |  | -0.84 |  ± |  0.10 | -0.58 |  ± |  0.16 | -0.20 |  ± |  0.09
rims (WM) |  | -0.01 |  ± |  0.18 | -0.11 |  ± |  0.26 | -0.32 |  ± |  0.07
FGR |  | 0.24 |  ± |  0.12 | 1.26 |  ± |  0.32 | 0.24 |  ± |  0.12
ICM (clean) |  | -0.10 |  ± |  0.14 | 0.70 |  ± |  0.37 | 0.20 |  ± |  0.51
Figure 3: $\upepsilon$54Cr values from Leoville components (A) Data from Table
LABEL:tab:CrZn, where the dark blue circles reflect the Al-rich chondrules,
solid green shows the Leoville chondrule cores, solid green with light green
rim are the two bulk chondrules sampled (including core and rim), open green
circles are the chondrule rims, blue diamonds reflect the clean ICM and the
yellow diamond represents the FGR. We also show the range of OC chondrules
(shaded green area, Bollard et al., 2019), the CV bulk $\upepsilon$54Cr value
and the $\upepsilon$54Cr value for CI chondrites. All errors reflect the 2SD
external reproducibility of the measurements. A density distribution is shown
at the bottom for the chondrule cores and rims. B) $\upepsilon$54Cr weighted
averages for chondrule populations from Leoville (CV3.1), Vigarano (CV3.1-3.4,
Olsen et al., 2016), NWA 3118 (CV3.6, Olsen et al., 2016) and Allende
(CV$>$3.6, Kadlag et al., 2019).

###  2.3 The Zn isotope compositions of Leoville components

We have measured the Zn isotope compositions of 11 ICM fragments (see Appendix
A for detailed methods). Previous measurements of Leoville matrix include two
FGRs (Table LABEL:tab:CrZn, Fig. 7, van Kooten & Moynier, 2019). Both
$\updelta$66Zn values determined for FGRs are indistinguishable (0.14$\pm$0.12
‰ and 0.24$\pm$0.12 ‰) and form an average of 0.19$\pm$0.14‰. ICM samples are
generally lighter with values ranging between –0.43$\pm$0.12 ‰ and
0.14$\pm$0.12 ‰. Samples regarded as representing pure ICM return an average
$\updelta$66Zn composition of –0.10$\pm$0.14 ‰, whereas contamination results
in more variable $\updelta$66Zn values that also push the average to a lighter
average value of –0.15$\pm$0.44 ‰. We can relate these variations to
chondrule/CAI contaminations or heterogeneities of the matrix. The positive
endmember $\updelta$66Zn value of the ICM (0.14$\pm$0.12 ‰) coincides with a
large sulfide grain in the Bmx2 sample, whereas the more negative
$\updelta$66Zn values correlate with observed chondrule contaminations.
Collectively, pure ICM has a light Zn isotope composition relative to the FGRs
and to the bulk CV chondrite and the heaviest FGR (Ch2mx, Table
LABEL:tab:CrZn) has a $\updelta$66Zn value that is within error of CV and CI
bulk chondrites. In addition to the matrix, we have sampled a large fraction
of a chondrule core and two whole chondrules (i.e., combined core and igneous
rim) to verify the Zn isotope compositions reported for singularly small
samples from Leoville chondrules (van Kooten & Moynier, 2019). These chondrule
cores are very Zn-depleted and previous data was obtained on only 1-5 ng of
Zn, thus, involving large blank contributions of about 20 %. The Zn isotope
analyses of a larger Leoville chondrule core (10 ng Zn) in this study shows
that, after blank correction, the large core composition ($\updelta$66Zn =
–0.94$\pm$0.12 ‰) is indistinguishable from the previous measurements
($\updelta$66Zn = –0.81$\pm$0.18 ‰, van Kooten & Moynier, 2019). Moreover, the
bulk chondrule compositions measured here are in agreement with previous
analyses of Allende bulk chondrules (Pringle et al., 2017). Furthermore, we
analyzed an Al-rich chondrule, which in contrast to the other chondrule cores
has a positive $\updelta$66Zn value of 0.10$\pm$0.12 ‰.

Figure 4: Plot of mass-independent $\upepsilon$54Cr versus mass-dependent
$\updelta$66Zn values of Leoville components, reflecting their potential
heritage and precursor materials. The averaged isotope compositions of
chondrule cores and rims (bigger spheres) are also shown. The spheres
represent chondrules, the squares reflect bulk chondrites (grey = CV) and the
diamonds represent the matrix. A mixing line is drawn with CI chondrites (Cr =
2590 ppm and Zn = 310 ppm, Lodders, 2003) and Leoville chondrule cores (Cr =
3000 ppm and Zn = 50 ppm) as endmembers. We note that the curvature of the
mixing line is mostly dependent on the estimated Zn content of the chondrule
cores (including metal rim), which is currently unknown. The tick marks
represent fractions of 0.1. Notably, most Leoville components fall on this
mixing line, including the chondrule rims, the ICM, the CV bulk and the FGR.
The clean ICM is a mixture between CI-like material, chondrules and CAIs. This
suggests that variations in $\updelta$66Zn are not only related to volatile
loss processes, but are also related to their precursor materials. The Al-rich
chondrule Bch6 and one ICM sample do not fall on this mixing line, suggesting
that some of this material has FUN-CAIs as precursor, rather than canonical
CAIs.).

##  3 Discussion

###  3.1 The effect of secondary alteration

Prior to making an attempt to understand the origin of chondritic components
through their (nucleosynthetic) isotope systematics, it is of critical
importance to recognize the effects of elemental and isotopic exchange between
these components during secondary alteration (e.g., thermal metamorphism
and/or aqueous alteration). Although the use of nucleosynthetic isotopes is
often perceived as providing a means to assess the heritage of precursor
materials to thermally processed chondritic components independent of
secondary processes, this method is not assumption free. Notably, isotopic
fractionation occurs during elemental exchange between chondritic components
and the magnitude and kinetics of this fractionation are subject to the redox
conditions, fluid composition and temperature of alteration. Given that
alteration typically is a low temperature process where equilibrium processes
dominate, the resulting mass-dependent isotope fractionation is not
necessarily appropriately accounted for by the typical kinetic mass
fractionation laws applied to correct stable isotope data obtained by mass
spectrometry. Indeed, mass-dependent isotope fractionation at low-temperature
conditions such as experienced during moderate secondary alteration on
carbonaceous chondrite parent bodies theoretically and empirically result in
large isotopic variations. Especially for the redox-sensitive chromium,
extreme fractionations up to 7 ‰ (at 298 K, per 1 amu) have been predicted
(Schauble et al., 2004). Since for every 0.1 ‰ of fractionation can generate a
potential bias on the mass-independent $\upepsilon$54Cr of 0.04, the total
effect of inappropriately corrected equilibrium isotope fractionation between
chondritic components can potentially result in epsilon-level shifts in the
$\upepsilon$54Cr value (Schiller et al., 2014; van Kooten et al., 2017). Given
that Cr is highly mobile even at the most early stages of alteration, which is
highlighted by the fact that the chromium content and distribution in olivine
phenocrysts from ordinary and CV chondrite chondrules has been used to
determine the degree of thermal metamorphism (Grossman & Brearley, 2005),
reinforces that extreme caution is needed when utilizing the Cr isotope
composition of individual chondrules and matrix to make inferences about their
genetic relationships.

What is unambiguous from our Cr isotope measurements of the Leoville chondrule
cores is that their $\upepsilon$54Cr values are significantly lower than those
reported for chondrules from more altered CV chondrites. With increasing
degree of thermal metamorphism (Leoville $<$ Vigarano $<$ NWA 3118 $\sim$
Allende) the average chondrule $\upepsilon$54Cr value approaches that of the
bulk CV chondrite (Fig. 3). This suggests that the Cr isotope signatures of
chondrules and matrix are progressively homogenized during thermal
metamorphism. The major implications of these results are that 1) the
previously reported range of $\upepsilon$54Cr values is to some extent the
result of secondary alteration (Kadlag et al., 2019; Olsen et al., 2016), 2)
the $\upepsilon$53Cr values from chondrules used for isochrons in the Mn-Cr
decay system need to be reassessed according to their level of alteration (Zhu
et al., 2019) and 3) other isotope systems such as Fe, W and Mo that are
redox-sensitive may also need to be revisited. For example, stable Fe isotope
variations between chondrules and matrix from the moderately altered CM
chondrite Murchison have been interpreted in favor of chondrule-matrix
complementarity (Hezel et al., 2018). Furthermore, complementary mass-
independent isotope variations of W and Mo have been proposed between
chondrule and matrix from the altered CV chondrite Allende (Budde et al.,
2016). We suggest that the Leoville chondrule cores, igneous rims and matrix
provide accurate constraints on the origin and formation mechanisms of these
components through their Cr and Zn isotope signatures, respectively. We note,
however, that even Leoville is not completely unaltered as some of its metal
is sulfurized (van Kooten et al., 2019). A detailed investigation of the CV
chondrite metal (isotope) composition may improve our understanding of the
contribution of metal to the total mass balance of the carbonaceous chondrites
and the effect of oxidation on the composition of the matrix (van Kooten et
al., 2019). For example, leaching of the metal by oxidation can bring
siderophile elements such as W and Mo into the matrix and sulfurization can
concentrate Zn in secondary products.

###  3.2 The origin of CV chondrite components

The first order observation emerging from our work is that the chondrule-rim
systems in the pristine Leoville CV chondrite span a range of 54Cr
compositions that is similar to that observed for the Solar System’s planets
and asteroidal bodies, namely from ureilite-like to CI-like signatures. The
onion-ring like structure of individual chondrules record an increasingly
54Cr-rich composition from core to outer rim. This observation firmly
establishes that NC and CC material coexisted in space and time, which has far
reaching implications for understanding mass transport processes and the
origin of chondritic components that we discuss below.

In detail, the $\upepsilon$54Cr values of Leoville chondrule cores define a
relatively narrow and negative range compared to previous measurements (Kadlag
et al., 2019; Olsen et al., 2016). Interestingly, the range of
$\upepsilon$54Cr values of the cores corresponds to that of inner Solar System
materials, such as eucrites, angrites, ordinary chondrites (Trinquier et al.,
2007) and ureilites ($\upepsilon$54Cr = –0.91$\pm$0.15 ‱; Zhu et al., 2020b)
of which the latter are suggested to represent an endmember composition of
planetary bodies that accreted in the terrestrial planet region (Schiller et
al., 2018). The ureilite parent body likely formed $<$1 Myr after CAI
formation (van Kooten et al., 2017) and its low bulk $\upepsilon$54Cr value is
interpreted to reflect: 1) a formation location in the asteroid belt before
injection of 54Cr-rich material into the protoplanetary disk (Goodrich et al.,
2015) or 2) formation close the Sun, where its $\upepsilon$54Cr value is the
result of removal of the 54Cr-rich carrier, perhaps via thermal processing,
from the dust (Larsen et al., 2011). However, since astrophysical models of
injection of supernova-derived dust to the disk show a very low probability of
explaining the high abundance of supernova-derived, short-lived radionuclides
(and by extension 54Cr) (Ouellette et al., 2010), it is more likely that the
low $\upepsilon$54Cr values of the chondrules reflect a formation location
close to the protosun. Either way, the Cr isotope composition of Leoville
chondrule cores establishes that these objects initially originated in the
terrestrial planet formation region as opposed to the outer Solar System,
which is characterized by positive $\upepsilon$54Cr values (van Kooten et al.,
2016). The oxygen isotope systematics of the least altered CV chondrite
chondrules support relatively dry conditions during their final melting event
(Hertwig et al., 2018), in agreement with an inner Solar System origin of
these chondrules. Furthermore, the Zn isotope compositions of the chondrule
cores are remarkably similar (Table LABEL:tab:CrZn, van Kooten & Moynier,
2019). Zn stable isotope fractionation during chondrule formation is thought
to occur either through volatile loss from the chondrule or partitioning of Zn
to the metal/sulfide melt and subsequent metal-silicate separation. Hence, our
data suggest a very similar formation mechanism for these chondrules from the
same spatiotemporal reservoir. Exceptions from this are the Al-rich chondrules
Bch6 and Bch3. Al-rich chondrules are thought to have formed from CAI-like
precursor materials (Zhang et al., 2014), which have very negative
$\updelta$66Zn values (Luck et al., 2005). In agreement with the presence of a
CAI precursor, Bch3 has a very high $\upepsilon$54Cr value (Zn isotope
composition not measured). Bch6 is distinct from this in that it has both the
lowest $\upepsilon$54Cr value measured here and a positive $\updelta$66Zn
value, unlike the more typical type I chondrules (Fig. 4) and contrary to the
prediction based on a CAI-precursor. However, it is also possible that Bch6
inherited a FUN-CAI precursor, which exhibit very negative $\upepsilon$54Cr
values (Holst et al., 2013).

The igneous rims have higher $\updelta$66Zn and $\upepsilon$54Cr values
compared to the chondrule cores. These rims are thought to represent
chondritic dust that is thermally processed during transient heating events in
the disk prior to accretion onto chondrule cores as volatile depleted
forsterite-bearing grains (van Kooten & Moynier, 2019). Subsequently, the
grains react with surrounding volatile-rich gas, which progressively enriches
the igneous rims in heavy Zn isotopes as well as moderately volatile elements.
This results in a near-chondritic elemental composition of the igneous rims,
as well as forsterite relict grains overgrown by low-Ca pyroxene co-existing
with troilite/metal assemblages. Based solely on the Zn isotope data igneous
rims may have formed concurrently to chondrule cores. However, the 54Cr-
enrichment of the rims suggests that they reflect a separate and less
energetic heating events than those that formed chondrule cores. During this
second heating event, increasingly 54Cr-rich material was added to the
chondrule growing reservoir. The higher $\upepsilon$54Cr signature of
chondrule rims relative to their cores cannot result from inappropriately
corrected mass-dependent equilibrium isotope fractionation, since estimated
temperatures of igneous rim formation by sintering (T $<$ 1000-1200 K; Jones
et al., 2018; Rubin & Wasson, 1987) are too high to cause significant
fractionation during gas-melt interaction between CrO (liquid) in chondrule
silicates and CrO2 (gas) and the expected fractionation is predicted to result
in a lighter final silicate (Sossi et al., 2018). Hence, the 54Cr enrichment
of the rims over the cores must be the product of addition of 54Cr-rich
material to the chondrule forming reservoir. This also implies that the stable
isotope enrichment in 66Zn is not necessarily the product of gas-melt
interaction, but may also reflect a change in the chemical nature of the
precursor materials. The presence of the igneous rims reflects reheating of
chondrules at relatively low temperatures in a less energetic disk environment
with lower gas densities, which could have been in 1) an older disk and/or 2)
at larger orbital distances. The fine-grained dust rims that accreted around
the chondrules have a very homogeneous CI-like chemical composition (van
Kooten et al., 2019) and corresponding high $\upepsilon$54Cr and
$\updelta$66Zn values. We note that even though we only measured the Cr
isotope composition of a single FGR, the mass balance of all CV components
requires FGRs to have CI-like Cr isotope signatures since chondrules and
intra-chondrule matrix have similar or lower $\upepsilon$54Cr values than bulk
CV chondrites and addition of refractory solids is insufficient to explain the
bulk value (Appendix C). Collectively, the nucleosynthetic Cr isotope
systematics of the FGRs agree with being derived from pristine CI-like dust
and mass-dependent Zn isotope systematics suggest that the FGRs did not
experience significant volatile gain or loss. This is in agreement with the
model that matrix and chondrules are not complementary to each other (van
Kooten et al., 2019). Rather, our Cr isotope data suggest that the CV
chondrite reservoir was increasingly enriched in CI-like dust from the outer
Solar System.

Finally, the Cr isotope composition of the pure intra-chondrule matrix is
indistinguishable from that of bulk CV chondrites (Fig. 3), whereas the Zn
isotope composition is typically lighter. This appears to be the result of
addition of CAI-like material to the ICM (Fig. 4). Overall, petrological and
isotopic characteristics suggest that the ICM represents a mixture of
chondrule, CAI and matrix fragments. The visually ‘contaminated’ ICM including
chondrule fragments typically has more negative Cr and Zn isotope values, with
one of the matrix samples being significantly more negative than the
chondrules. Similar to the Al-rich chondrule Bch6, this may be the result of
addition of FUN-CAI-like material. Collectively, the nature of the ICM implies
that this material is not by itself a primary nebular product but reflects a
mixture of all CV chondrite components. This, in turn, indicates that the CV
ICM is a parent body feature that formed during accretion and physical erosion
of the CV chondrite components. Hence, although the fine-grained dust within
the ICM may still retain some primary features (Haenecour et al., 2018), the
overall composition is not primary and this material should not be used as
such.

###  3.3 Massive outward transport of inner Solar System chondrules

The current paradigm proposes that carbonaceous chondrites, including CV
chondrites, formed in the outer Solar System, beyond the accretion region of
Jupiter. Convincing arguments in favor of this model include the petrologic
and isotopic dichotomy of bulk NCs and CCs (e.g., Mo, O, Cr, Ca, Ti; Budde et
al., 2016; Schiller et al., 2018; Warren, 2011). Additionally, previous Cr
isotope measurements of individual CV chondrules have been interpreted to
indicate that CV chondrites accreted in a spatially distinct reservoir from
inner Solar System materials (Olsen et al., 2016). At face value, our results
suggest that CV chondrites do not contain outer Solar System derived
chondrules but represent hybrid bodies consisting of inner Solar System
chondrule cores and outer Solar System derived CI-like dust. If CV chondrites
are representative of other chondrule-bearing carbonaceous chondrites, this
implies that chondrules did not form beyond the accretion region of Jupiter.
The exception from this are the metal-rich carbonaceous chondrites (i.e., CR,
CB and CH), for which the chondrules contain exclusively 54Cr-rich outer Solar
System signatures. These chondrites likely formed beyond the accretion region
of the gas giants (van Kooten et al., 2020). Hence, the major chondrule-
forming factory may have been restricted to the inner Solar System such that
outer Solar System chondrules only represent a minority of objects, perhaps
formed by impacts (i.e., CH and CB, Krot et al., 2005), bow shocks (i.e., CR,
(Morris et al., 2012; van Kooten et al., 2016)), or in the vicinity of the
giant planets (Bodénan et al., 2020).

Previous studies have proposed that CC chondrules are the product of outer
Solar System precursor dust mixed to various degrees with 54Cr-rich refractory
inner Solar System grains such as spinels and/or another unknown carrier
(Gerber et al., 2017; Williams et al., 2020). In this model, CC chondrules are
generally viewed as outer Solar System products with an incorporated ‘nugget
effect’. In detail, CC chondrule formation is suggested to be in situ (i.e.,
where the CC chondrites accreted) and ascribed to mixing, agglomeration and
subsequent heating of inner and outer Solar System dust. If correct, this
model predicts that a range of 54Cr values should be observed for CV
chondrules. Although a compositional range has been reported for altered CV
chondrites such as Allende and NWA 3118, we attribute this observation to
secondary alteration (Fig. 3). Our data based on the pristine Leoville CV
chondrite firmly establishes that chondrule cores are 54Cr-depleted and, as
such, cannot have formed from outer Solar System precursors. An important
implication of our results is that massive outward transport of inner Solar
System chondrules to the accretion regions of carbonaceous chondrites must
have taken place during the early evolution of the protoplanetary disk (Fig.
5, model 2). Thus, outward mass transport was not limited to refractory
inclusions and $\upmu$m-sized dust but also included the most abundant
chondrite component, namely chondrules.

The U-corrected Pb-Pb age dating of inner Solar System chondrules support the
hypothesis that these objects formed early and contemporaneously (Bollard et
al., 2017; Connelly et al., 2012). Indeed, absolute chronology of individual
ordinary chondrite chondrules indicate that the bulk of these objects formed
within 1 Myr of Solar System formation. As discussed above, Leoville chondrule
cores were likely formed in the inner Solar System and presumably in the
accretion region of ureilites, relatively close to the protosun. Cr, O and Zn
isotope data of the most unaltered CV chondrule cores suggest that these
components formed from a single population (Hertwig et al., 2018, this study).
This is in agreement with the model of thermal processing, where the precursor
material of these cores consisted of 54Cr-depleted thermally processed dust
complementary to the 54Cr-rich gas from which the CV CAIs originally condensed
(Larsen et al., 2011). Hence, similar to ordinary chondrite chondrules, the
formation of CV chondrules may have overlapped with that of CAIs and was
restricted to the first Myr of Solar System formation (Bollard et al., 2017;
Connelly et al., 2012). We note that individual Pb-Pb ages of CV chondrules
are rare and only exist for the moderately altered Allende (Connelly et al.,
2012), which agreeably have ages indistinguishable from CAI formation. These
age-dated Allende chondrules were selected based on their low degree of
alteration and coincidentally also have negative 54Cr isotope signatures
relative to Earth, in agreement with our results and interpretations.

Outward mass transport of solids is modeled to be most efficient in the
earliest evolutionary stage of the protoplanetary disk, either via stellar and
disk outflows or, alternatively, during viscous expansion of the disk (Shu et
al., 1996; Cuzzi et al., 2003; Ciesla, 2007, 2010; Haugbølle et al., 2019).
Thus, outward mass transport of inner Solar System chondrules to the outer
Solar System likely occurred prior to the formation of Jupiter, that is,
within the first Myr of disk evolution. Once CV chondrules were transported
and stored at the pressure trap created by a planetary gap opened by Jupiter,
the chondrule cores were coated by a progressive addition of CI-like dust
(Fig. 5, model 2). The chondrules probably experienced brief heating events
that formed the igneous rims in the outer Solar System. Finally, after the
last coating of fine-grained dust, the CV chondrules grinded together within
rubble pile asteroids located at Jupiter’s pressure trap (Eriksson et al.,
2020), thereby forming a second generation of dust: the intra-chondrule
matrix. These products cemented together forming the CV chondrites.
Importantly, Jupiter’s pressure trap does not prevent fine-grained dust to be
transported through the gap (Haugbølle et al., 2019; Weber et al., 2018). This
implies that if coating of chondrules by CI-like dust occurred beyond
Jupiter’s orbit, the same process was experienced by chondrules present in the
terrestrial planet region. Hence, if Earth indeed accreted its main mass
through pebble accretion, and specifically by chondrules (Johansen et al.,
2015), Earth would have been progressively enriched by CI-like material (Fig.
5, model 2). This is in agreement with the Fe isotopic data that predict a
significant part of Earth’s mass should be CI-like (Schiller et al., 2020).
Although the formation of Jupiter may have aided the storage of significant
amounts of mm-sized solids such as inner Solar System chondrules and
refractory inclusion beyond its orbit, Jupiter did not prevent the mass
transfer of outer Solar System CI-like dust to the inner Solar System. Thus,
in contrast to current belief, the early formation of Jupiter had limited
impact on the compositional gradient that exist between inner and outer Solar
System bodies.

Figure 5: Schematic representation of a protoplanetary disk showing two
chondrite accretion scenarios, with Jupiter as a barrier separating NC and CC
(model 2) and without Jupiter (model 1). At t$<$1 Myr, CV (pink spheres) and
OC chondrule cores (red spheres) form in the inner Solar System in different
oxidizing environments. OC chondrules form close to the water ice sublimation
front, where they rapidly accrete FGRs (Krot et al., 1997) within the ice line
in a high dust-to-gas region (Ida and Guillot, 2016). CV chondrule cores and
CAIs are transported outwards to (model 2) beyond Jupiter’s accretion region
at 3-5 AU or (model 1) outside the ice line, but within Jupiter’s initial core
accretion region at $>$30 AU (Öberg & Wordsworth, 2019). CR chondrules (blue
spheres) form beyond the gas giant orbits (van Kooten et al., 2020). Earth’s
initial feeding zone consists of CV-like type I chondrules surrounded by metal
rims and with ureilitic Cr isotope signatures. This is the metal that forms
Earth’s core and leaves the mantle depleted in Fe (Schiller et al., 2020).
Model 1: At t$<$2 Myr, CV CAIs and chondrules accrete CI-like FGRs outside of
the stagnant water ice line (see text for further details) and grow to form
planetesimals (Ros & Johansen, 2013). CAIs and other mm-sized to cm-sized
objects are caught in the rapid pile-up of material in planetesimals and a
significant fraction of these objects do not pass the ice line barrier. In
both models: At t$<$3 Myr, as the accretion of NC and CCs is finalized, the
ice line migrates further inwards and the chondrules in Earth’s feeding zone
can accrete CI-like dust rims. These dust rims accrete to Earth’s final mass
during pebble accretion and result in the Earth having a CI-like Fe isotopic
composition of its mantle (Schiller et al., 2020). The metal-rich carbonaceous
chondrites accrete beyond Saturn’s (model 2) or Jupiter’s (model 1) orbit.

###  3.4 A potential inner Solar System accretion region for CV chondrites?

The previous section assumed Jupiter to pose as a barrier that prevented the
macroscopic components from the CC (i.e., chondrules and CAIs) from drifiting
into the inner Solar System and, based on this assumption, that all
carbonaceous chondrites accreted beyond the orbit of Jupiter. However,
considering our new results and the latest developments in astrophysical
models, we explore whether the accretion region of CV chondrites and, by
extension, that of other CCs is required to be in the outer Solar System.
Focusing solely on the Cr isotope compositions of unaltered CV chondrite
components, then it is not necessary to accrete CV chondrites in the outer
Solar System. Indeed, the observation that the 54Cr-poor compositions of the
CV chondrule cores are mantled by increasingly more 54Cr-rich rims is
consistent with the progressive addition of CI-like material to an inner Solar
System accretion region. If this is correct, then the other physicochemical
constraints on the formation regions of NCs versus CCs should be met as well.
Specifically, the observed isotopic and petrological dichotomy between these
chondrite groups needs to be accounted for. For this purpose, we compare
constraints from ordinary chondrites (NC) to those of CV chondrites (CC).

The make-up of ordinary chondrites may not be very different from CV
chondrites. The sizes (Friedrich et al., 2015) and Cr isotope compositions of
OC chondrules overlap with those of CV chondrule cores (Fig. 3). Oxygen
isotope analyses of the least altered OC and CV chondrules suggest that these
chondrules formed in different disk reservoirs and/or at different times. The
$\Delta^{17}$O values of Semarkona, Bishunpur and Krymka (LL3.00-3.1; Kita et
al., 2010) chondrules define a narrow range of $\sim$0.7 ‰, whereas Kaba
chondrules (CV3.1ox) have $\Delta^{17}$O values below the terrestrial
fractionation line and on the PCM slope between –8 and –4 ‰ (Hertwig et al.,
2018), although a fraction of OC chondrules has $\Delta^{17}$O values similar
to CV chondrules (Hertwig et al., 2018). A plausible interpretation of the
$\Delta^{17}$O systematics of OC chondrules is that these objects originated
in an oxidizing environment, where 16O-depleted gas interacted with silicate
dust of similar isotope composition further away from the protosun.
Alternatively, the relatively high $\Delta^{17}$O values of OC chondrules
reflect a higher silicate/dust ratio in the chondrule forming region (Tenner
et al., 2015). Such environments are predicted to exist at the sublimation
front of the water ice line (Fig. 5, model 1), which would have been located
near the current asteroid belt at the time of ordinary chondrite accretion
(Dodson-Robinson et al., 2009). Given that our 54Cr isotope data indicate an
inner Solar System origin for CV chondrules, a possibility is that the lower
$\Delta^{17}$O values of these objects reflects a formation region sunwards of
the OC chondrule forming region (Fig. 5, model 1). Within the FGRs of OCs,
microchondrules are observed that match the petrology and oxygen isotope
systematics of their host chondrules (Dobrică & Brearley, 2016; Krot et al.,
1997). Therefore, the accretion of fine-grained dust around these chondrules
must have been practically concurrent with chondrule formation in OCs and,
hence, also occurred near the water ice line (Fig. 5, model 1). These early
formed mm-sized chondrules and their rims would have drifted sunward until
they encountered either a physical trap (i.e., a pressure bump) or a region of
increased pebble density (i.e., a pile up zone) to store/accrete them, since
the relatively rapid rate of inward radial drift would not allow them to
remain in the disk long enough to form planetesimals otherwise (Desch et al.,
2017). A pile-up of pebbles has been theorized to exist at the sublimation
front of the water ice line by accumulation of deaccelerating sublimated
silicates, which are piled-up to form regions of high dust-to-gas ratios and,
finally, gravitationally collapse to form planetesimals (Ida & Guillot, 2016).
Collectively, this would suggest early formation of OC chondrules and rapid
accretion of their parent bodies. This is in agreement with the modelled
accretion ages of ordinary chondrites $<$1.8 Myr after CAI formation (earlier
if assuming a heterogeneous distribution of 26Al, Appendix D) (Doyle et al.,
2015).

The final accretion region of CV chondrites and, by extension, other CCs is
inferred to be outwards from the ordinary chondrite accretion region, since
the CV parent bodies accreted later (Doyle et al., 2015) and contain a larger
fraction of pristine CI-like matrix. Materials that are initially transported
outwards invariably drift inwards towards the central star unless they can
overcome the radial drift barrier, usually by decoupling from the gas by
changing the solid-to-gas ratio in the disk (Gonzalez et al., 2017). Although
various so-called ‘pressure traps’ have been proposed in the past (i.e., long-
lived vortices etc.), the most popular barrier to separate NCs from CCs is
invoked by the opening of a gap associated with giant planet formation
(Kruijer et al., 2017). In detail, the lack of CAIs in the terrestrial
accretion region and the distinct isotopic make-up of concurrently accreting
NCs versus CCs is attributed to the formation of Jupiter and the resulting
separation of reservoirs (Haugbølle et al., 2019). The isotopic dichotomy is
also observed for the iron meteorites that are linked to NCs and CCs by their
Mo isotope signatures (Kruijer et al., 2017). The Hf-W model ages of these
irons and the chondrites suggest that a barrier should have been in place at
$<$1 Myr after CAI formation. However, a potential problem with using Jupiter
as a barrier is that its chemical composition does not allow its core to have
formed at the proposed location of 3–5 AU. In fact, an initial accretion
location at $>$30 AU is inferred from the position of N2 and noble gas ice
lines as well as the asymmetry in its two populations of Trojan asteroids
(Öberg & Wordsworth, 2019; Pirani et al., 2019). This early and distal
accretion is followed by $\sim$2 Myr of migration until final accretion of its
envelope at 5 AU. If Jupiter formed at $>$30 AU, this requires that CAIs and
chondrules were transported outwards to such distances, which has been
proposed to occur through jets and outflows (Haugbølle et al., 2019) or by
outward turbulent diffusion (Ciesla, 2007). In the former scenario, CAIs that
are not accreted by the protosun are ejected as part of the outflow and either
lost to the interstellar medium or distributed in the protostellar envelope as
part of the entrainment and mixing of envelope and jet material (Haugbølle et
al., 2019). They then return to the protoplanetary disk during the general
accretion of the envelope in the protostellar phases on a timescale of 500 kyr
(Haugbølle et al., 2019). In outward diffusion models developed by Ciesla
(2007) and later models including particle growth during transport (Misener et
al., 2019), materials can be exchanged over a radial span of 5–20 AU on
timescales of only $\sim$105 yr. Misener et al. (2019) suggest that a barrier
must be in place within these spatiotemporal parameters to prevent mixing
between NC and CC reservoirs. Therefore, if CAIs are transported radially by
viscous spreading, either Jupiter did not originate at $>$30 AU or Jupiter is
not the cause for the NC – CC dichotomy.

An alternative possibility to Jupiter is that the water ice line acted as the
barrier that separates the NC and CC reservoirs. Ice lines have been proposed
to initiate rapid pile-ups of materials that form planetesimals and are
related to the sublimation (Ida & Guillot, 2016) and condensation (Drazkowska
& Alibert, 2017; Hyodo et al., 2019; Schoonenberg & Ormel, 2017; Schoonenberg
et al., 2018) of ice. In detail, while on the inside of the ice line an
increased solid-to-dust ratio is related to the deacceleration of sublimated
particles, the outside of the ice line is defined by outward diffusion and
condensation of water and resulting streaming instabilities. As we outline
below, certain feasible disk models allow for the ice line to remain
relatively stagnant and positioned within the asteroid belt throughout the
accretion timescales of chondrite parent bodies (assuming internal heating of
the disk, Béthune & Latter, 2020). During the lifetime of the protoplanetary
disk, the accretion rate to the central star is expected to decline (Hartmann
et al., 1998) and, as the gas density decreases, the water ice line migrates
inwards. As a result, within a $<$3 Myr period the ice line is expected to be
around 1 AU in most disk models (Dodson-Robinson et al., 2009; Oka et al.,
2011). CV chondrites have modelled accretion ages of $<$2.6 Myr after CAI
formation (Doyle et al., 2015) (earlier depending on the distribution of 26Al
in the disk, Appendix D) and, thus, the separation of macroscopic NC and CC
components is expected to last at least that long. Hence, if the water ice
line indeed acted as barrier, the rate of inward migration must have been slow
enough to accommodate this separation. The speed of ice line migration is
highly dependent on the accretion rate onto the central star. This rate is
highest during the class I stage (105 yrs) where the protostar is embedded in
the molecular cloud and the protoplanetary disk is replenished through infall
from the envelope (Hartmann & Kenyon, 1996). During this stage, FU Orionis
type outbursts can shift the ice line far outwards, with retention rates of
10-100s yrs. The accretion rate declines over time/with disk age, but this
decline is not proven to be constant and the uncertainty on its progression is
more than an order of magnitude (Hartmann et al., 1998; Li & Xiao, 2016).
Indeed, for some stars the accretion rate may still be 10-8 $M_{\odot}$/y
after 3 Myr, which would suggest that the water ice line could be relatively
stagnant during that time. Recent models also show that the position of the
ice line is dependent on other disk parameters, such as the radial
distribution of the turbulent viscosity parameter $\upalpha$ in the disk and
the growth rate of chondrules into asteroids (Kalyaan & Desch, 2019). These
parameters influence the balance between the outward diffusion of water vapor
and the growth of icy pebbles outside of the ice line. These models show that
it is possible to form the distribution of water-poor and water-rich asteroids
in situ in the asteroid belt (Alexander et al., 2012), without a need for the
scattering of asteroids by a Grand Tack (Walsh et al., 2011) or for the
fossilization of the water ice line through the formation of Jupiter
(Morbidelli et al., 2016). This ice line fossilization was invoked to prevent
icy particles from populating the terrestrial planet region (Morbidelli et
al., 2016). If Jupiter indeed formed at large orbital distances, we consider
the possibility that chondrite parent bodies formed in situ at their current
positions in the asteroid belt and were chemically separated via the water ice
line that remained stagnant for a period $<$2.6 Myr. The efficiency of this
chemical separation depends on the relative accretion timescales of NC and CC
as well as the rate of planetesimal accretion at the ice line. It is likely
that at least some material will pass through the ice line. For example,
chondrules have been found in enstatite chondrites with an outer Solar System
Cr isotope signature (Zhu et al., 2020a) and rare CAIs in ordinary chondrites
have similar oxygen isotope systematics as those found in CC (Huss et al.,
2001).

##  4 Conclusions

Our detailed Cr and Zn isotope investigation of the relatively unaltered
carbonaceous chondrite Leoville and its components sheds light on the origin
and mass transport of chondrules and matrix in the protoplanetary disk. The
first order observation emerging from our work is that Leoville’s chondrule-
rim systems span a range of 54Cr compositions that is similar to that observed
for the Solar System’s planets and asteroidal bodies, namely from ureilite-
like to CI-like signatures. The onion-ring structure of individual chondrules
record an increasingly 54Cr- and 66Zn-rich composition from the chondrule core
to the outer rim. These data show that the observed Cr isotopic range in
chondrules from more altered CV chondrites is the result of chemical
equilibration between chondrules and matrix during secondary alteration. We
propose two scenarios that could account for the hybrid isotopic nature of CV
chondrites, subject to the radial distance at which Jupiter originated. First,
if proto-Jupiter opened a disk gap within $<$1 Myr after CAI formation at 3-5
AU, CV chondrite accretion is best explained by massive outward transport of
chondrules combined with an inward flux of CI-like dust. These components were
then trapped beyond Jupiter and cemented together. In this interpretation, the
CI-like fine grained dust that accreted to the CV chondrules was also
transferred inwards across the gap and into the terrestrial planet region.
Bidirectional transport of chondrules in outflows outwards and fine grained
matrix strongly coupled to the accreting gas inwards take in to account the
full dynamics in the protosolar environment, and nuances the view of Jupiter
as an efficient barrier for solids in the NC and CC reservoirs. Second, since
our data do not require an outer Solar System accretion region for CV
chondrites, we consider an alternative model in which the water ice line,
rather than Jupiter, acted as a barrier between NC and CC reservoirs. This
consideration is rationalized by recent models that propose Jupiter originated
from beyond 30 AU. Indeed, a range of astrophysical conditions within the
protoplanetary disk allow for a relatively stagnant ice line within the
timeframe of chondrite accretion. However, this scenario requires further
verification via numerical simulations that explore the efficiency of ice line
pile-ups as well as the transport and retention time of refractory solids
within the protoplanetary disk. Finally, we note that astrophysical models
show that water-rich planetesimals at the ice line may accrete rapidly,
independent of the role of Jupiter in modulating mass transport between the
inner and outer Solar System. This implies that two populations of CCs should
exist. The first one formed beyond Jupiter and contains chondrules and CAIs.
The second one, if all chondrules and CAIs were blocked by Jupiter, contains
only fine-grained dust coated by ice. Hence, CI chondrites, with their unique
petrology relative to other CCs, could have formed at the ice line within
Jupiter’s orbit.

We thank Alexander Krot for valuable discussion on oxygen isotope systematics
in chondrules. This project has received funding from the European Union’s
Horizon 2020 research and innovation programme under the Marie Skłodowska-
Curie Grant Agreement No 786081 to E.K. F.M. acknowledges funding from the
European Research Council under the H2020 framework program/ERC grant
agreement no. 637503 (Pristine) and financial support of the UnivEarthS Labex
program at Sorbonne Paris Cité (ANR-10-LABX- 0023 and ANR-11-IDEX-0005-02).
Parts of this work were supported by IPGP multidisciplinary PARI program, and
by Region Île-de-France SESAME Grant no. 12015908. M.S. acknowledges funding
from the Villum Fonden (no. 00025333). Additional financial support for this
project was provided by Carlsberg Foundation (CF18-1105), the Danish National
Research Foundation (DNRF97) and the European Research Council (ERC Advanced
Grant Agreement, no. 833275-DEEPTIME) to M.B. A.J. was supported by ERC
Consolidator Grant 724 687-PLANETESYS.

##  Appendix A Materials and methods

###  A.1 Samples

In this study, we have analyzed the Cr and Zn isotope composition, as well as
the elemental composition of a total of 37 fractions from the Leoville CV3.1
chondrite, which is a find that belongs to the reduced subgroup of CV
chondrites. This CV chondrite was selected based on its low degree of
secondary alteration relative to other CV chondrites (Bonal et al., 2016).
Even though the Leoville chondrite experienced some terrestrial weathering in
the form of calcium carbonate and Fe-oxide veins throughout the sample (Abreu
& Brearley, 2005), the boundaries of these veins are sharp, and care was taken
to avoid these areas. We sampled a total of 11 matrix areas: 3 areas consist
of purely intra-chondrule matrix, 5 samples contain a mixture of fine-grained
dust rims and ICM and another 2 samples are sampled from only the FGRs. In
addition to these samples, we have measured the Cr isotope composition of an
FGR previously analyzed for its Zn isotope composition (van Kooten & Moynier,
2019). Likewise, we have analyzed the Cr isotope signatures of 5 chondrule
cores (porphyritic olivine type) and 5 corresponding igneous rims, also
previously measured for their Zn isotope composition (van Kooten & Moynier,
2019). We have sampled an additional 14 chondrules, 11 of which do not contain
igneous rims and 2 of them being Al-rich chondrules. We note that part of
these samples have been previously analyzed for their composition by laser
ablation inductively coupled plasma mass spectrometry (van Kooten et al.,
2019) or by inductively coupled plasma quadrupole mass spectrometry (van
Kooten & Moynier, 2019). The Leoville fractions were extracted by New Wave
micromill with tungsten carbide drill bits at the Institute de Physique du
Globe de Paris (IPGP) and thereafter transferred to clean Savillex beakers.
The diameter of the drill spots was 150 µm and care was taken not to drill too
deep ($<$200 $\upmu$m) to avoid contamination from surrounding materials. This
typically resulted in $\sim$100-500 $\upmu$g of material. During drilling, all
drillspots were carefully examined under a plain-light microscope and spots
where contamination was suspected were discarded. Before and after drilling,
back scattered electron (BSE) images of the sampled areas were taken to verify
the nature of the sampled materials. This was done using the Zeiss EVO MA10
scanning electron microscope (SEM) at IPGP. In addition to BSE images, we have
also made elemental maps of the selected areas (Figs. 1 and 6).

Figure 6: Back scattered electron images and Mg-Ca-Al-S elemental maps of
chondrules sampled in this study, along with the drill locations (red
circles). The orange circles represent matrix locations.

###  A.2 Digestion and purification

All extracted samples were first digested in concentrated mixtures of 1:1
HNO3/HF acids using PARR bombs at temperatures of 210 ∘C for 48 hours, to
ensure complete digestion of potential refractory minerals located in the
Leoville fractions. The samples were then dried down and taken up in aqua
regia to dissolve fluorides formed during the first digestion step. The
Leoville fractions were taken up in 200 $\upmu$l 1.5M HBr and 5 % of the
aliquot was saved for elemental composition analyses by Agilent 7900 ICP-Q-MS
at IPGP. The samples were first eluted on a 100 $\upmu$l AG1X8 (200–400 mesh)
anion resin using 1.5M HBr to separate all elements from Zn, which was
subsequently eluted in 0.5M HNO3 (van Kooten & Moynier, 2019). This
purification step was repeated to ensure the complete removal of all
impurities from the Zn cut. The final Zn cut was between 5-15 ng for all
Leoville fractions and the procedural blank was $<$0.2 ng. The first HBr cut
eluted from the anion resin was saved for further Cr purification. The second
HBr cut of the repeat column was not added to the first cut, since it contains
a negligible amount of Cr (0.3 wt.% of the total). These aliquots were dried
down and taken up in 230 $\upmu$l 2M HNO3 and 20 $\upmu$l concentrated H2O2.
The samples were left at room temperature for $>$1 week to ensure complete
speciation of Cr to Cr3+. Similar to the Zn purification method (van Kooten &
Moynier, 2019), an adjusted Cr column chromatography was developed to
accommodate the small sample sizes of $\sim$100 $\upmu$g ($\sim$30 ng Cr).
This involves a two-in-one column procedure that is fast (3 hours cleaning, 3
hours elution), produces low blanks ($<$0.2 ng Cr) and avoids the risk of
losing these small samples by repeated dry-down and take-up of acids. In
detail, two columns are stacked on top of each other, with a TOGDA column (250
$\upmu$l resin volume) on top of a biorad AG50X8 (200–400 mesh) cation (1 ml
resin volume). The samples are loaded on the top column in their pretreatment
solution of 2M HNO3/H2O2 and are subsequently eluted with 1 ml of 2M HNO3,
thereby efficiently retaining Ca on the resin. This elute drops directly onto
a preconditioned cation column and, after removing the top column, an
additional 750 $\upmu$l of 2M HNO3 are added. The total elution of 2 ml 2M
HNO3 on the cation ensures the separation of Na and K. We note that the
separation of Cr and matrix elements is also achieved by eluting the latter
with a 2M HNO3/HF solution. However, we describe the procedure here to include
the further separation of Na$\pm$K (2 ml 2M HNO3), Fe—Ti—V—Al (5 ml 1M HF) and
Mg—Ni—Mn (22 ml 1M HNO3) for future analyses. The final elution of Cr is
preceded by a last clean-up of Fe, Ti and V in 3 ml 1M HF (to avoid
interferences on the Cr signal by TIMS) and is done using 10 ml of 6M HCl. The
total recovery of Cr is $>$95 %, which has been tested using various rock
compositions, including BHVO-2, PCC1, bulk CV and CI chondrites. After
chemistry, the dried Zn- and Cr-cuts are finally taken up in 7M HNO3 and are
heated to 140 ∘C for $>$24 hours before isotope analyses.

###  A.3 Neptune Plus MC-ICPMS and Triton TIMS

Zinc isotopes (64Zn, 66Zn, 68Zn) were measured using a Thermo Scientific
Neptune Plus Multi-Collector Inductively-Coupled-Plasma Mass-Spectrometer (MC-
ICPMS) at IPGP and the analytical setup was done according to van Kooten &
Moynier (2019). BHVO-2 and CV bulk chondrite standards were measured alongside
the samples to provide an estimate of the accuracy and reproducibility of the
analyses within each session. The samples were bracketed by the JMC-Lyon
standard and the data are reported in the delta notation as permil deviations
from the standard ($\updelta$66Zn = [[66Zn/64Znsmp]/[66Zn/64Znstd]-1] $\times$
1000). The mass-dependent relationship between the $\updelta$66Zn and
$\updelta$68Zn data are shown in Fig. 7.

The Cr-isotope composition of all samples was measured by thermal ionization
mass spectrometry (Triton TIMS) at the Centre for Star and Planet Formation
(StarPlan, Denmark). Chromium isotope analyses were conducted using a hybrid
method of total evaporation and standard-sample bracketing technique fully
described in van Kooten et al. (2016). Samples typically contained 30–100 ng
Cr and were measured on W-filaments with 15–30 ng per filament. Considering
potential analytical biases related to the processing of such small sample
sizes, we have thoroughly tested this method using different rock standards
that encompass the chemical compositions of the various Leoville fractions.
This included the Cr purification of five individual 100 $\upmu$g (total
sample) aliquots of the CI chondrite Ivuna (representing the matrix), which
were measured on five individual filaments and yield an average
$\upepsilon$54Cr value of 1.50$\pm$0.23 ‱ (the epsilon notation reflects the
parts per thousand deviation of the mass bias corrected xCr/52Cr ratio from
the SRM 979 standard, where x = 53 or 54). We also processed three aliquots of
100 $\upmu$g each from the bulk CV chondrite NWA 12523 as well as two aliquots
from the PCC1 geological standard (serving as analogues for bulk chondrules),
which yield average $\upepsilon$54Cr values of 0.81$\pm$0.28 and 0.12$\pm$0.09
‱, respectively. Hence, we show that such small fractions ($\sim$30 ng Cr) can
be successfully measured with an external reproducibility of $<$30 ppm (2SD).
Finally, as a last test to verify our TIMS results, we have put another,
larger ($\sim$2 $\upmu$g Cr) aliquot of same digestion used for TIMS analyses
of the CV chondrite NWA 12523 through the same chemistry and measured the Cr
isotope composition by MC-ICPMS (StarPlan). In addition, we were able to run
the largest chondrule sample LeoBch4 by TIMS as well as MC-ICPMS. The MC-ICPMS
analyses yield $\upepsilon$54Cr values that are indistinguishable from the
TIMS data (CV: 0.92±0.12 ‱, LeoBch4: 0.26$\pm$0.30 ‱ [TIMS: 0.18$\pm$0.30 ‱
]).

Figure 7: Zn isotope analyses of Leoville matrix and chondrule fractions,
showing $\updelta$66Zn versus $\updelta$68Zn values. The solid line reflects
the mass-dependent relationship between both isotope ratios.

##  Appendix B Petrology and compositions of Leoville fractions

We have carefully examined the petrological fabric of all fractions before
subjecting them to microdrill extraction and have, thus, managed to sample a
wide range of compositions and textures that together reflect the entirety of
material accreted to form the CV chondrites (Fig. 1). Firstly, the chondrules
of Leoville are typically between 1-3 mm in diameter and consist dominantly of
porphyritic olivine textures. Approximately 10 vol.% of the chondrules have
barred olivine textures, 50 vol.% contain relatively fine-grained olivine-
pyroxene igneous rims with abundant metal and sulfide and about 30 vol.%
contain mineralogical zonation of increasing pyroxene or olivine towards the
chondrule core rim relative to the feldspathic mesostasis. Most chondrules
contain one or more metal/sulfide rims around their primary or secondary cores
and the surface area of these rims often surpasses that of the cores (Fig. 1,
Fig. 6). About 5 vol.% of all chondrules in our thick section of Leoville are
Al-rich (i.e., $>$10 wt.% of Al2O3). Secondly, all chondrules are surrounded
by fine-grained dust rims (FGRs), which are typically between 100 and 300
$\upmu$m in diameter. The space between the FGRs is occupied by a more coarse-
grained matrix (ICM: intra-chondrule matrix), which includes chondrule
fragments and larger sulfide and metal grains.

We provide the major and minor element compositions of Leoville chondrules,
rims and matrices in Table A1. Since the compositions are derived from
solutions obtained through HF acid digestion, the exclusion of Si in these
measurements prevented element normalization and, hence, we discuss only
element ratios. Foremost, these ratios can be used to compare laser ablation
(LA) ICPMS derived compositions of Leoville fractions (van Kooten et al.,
2019) to microdrill extracted aliquots and potential contaminations related to
this technique. For example, the sampling of various types of matrix presents
great difficulties due to the small size of the areas relative to the drill
tip. While LA analyses of the FGRs show this matter to be CI-like, these
drilled areas may include contaminations from surrounding chondrules and/or
CAIs. As a result, of the ten attempts to sample these FGRs, only one proved
successful. The matrix composition of Ch2 is the only sample with a near-solar
Al/Mg ratio of 0.12 and a super-chondritic Fe/Mg ratio of 3.4, which is
indicative of pristine CV chondrite FGRs (van Kooten et al., 2019). Other
matrix samples have either higher Al/Mg ratios (indicative of CAI
contamination), and/or lower Fe/Mg ratios (from chondrule contamination).
These fractions have either been designated ‘contaminated’ or ‘clean’ ICM,
depending on the visual inspection of the drill holes. Two of the sampled
chondrules are Al-rich chondrules, based on their high Al/Mg, Ca/Mg and Na/Mg
ratios.

##  Appendix C Mass balance calculations of CV chondrite components

We outline here the mass balance of relatively unaltered CV chondritic
components using the Cr isotope data from Leoville chondrules, igneous rims,
Al-rich chondrules, fine-grained dust rims, intra-chondrule matrix and CAIs
(Table A3). We note that this mass balance is subject to the errors of the Cr
isotope measurements and the estimations of the modal abundances of the
components. We have calculated the bulk CV $\upepsilon$54Cr value in a
scenario where all matrix, including FGRs, have a $\upepsilon$54Cr composition
similar to the average ICM ($\upepsilon$54Cr = 0.7 ‱). We note that although
the values of Al-rich chondrules may be widely variable (Table
LABEL:tab:CrZn), possibly due to incorporation of different CAI- and FUN-CAI-
like precursors, their total budget is estimated to be $<$1 vol.% of all
chondrules (Zhang et al., 2019) and is thus insignificant for the calculated
bulk chondrule $\upepsilon$54Cr value, which is around –0.5 ‱. The bulk CV
chondrite value including only chondrules and matrix is then estimated to be
$\sim$0 ‱, assuming both components have similar Cr contents ($\sim$3000 ppm).
CAIs and AOAs have much lower Cr contents ($\sim$200 ppm) and although
their$\upepsilon$54Cr values are high (6.8 and 5.4 ‱, respectively; Larsen et
al., 2011), the mass balance of chondrules, matrix and CAIs shows that the
final calculated bulk $\upepsilon$54Cr value is $<$0.1 ‱ (Table A3). It is
currently unknown what the contribution of the metal (not related to the
chondrules) to the Cr isotope budget is. Leaching experiments of Leoville show
that the metal may have a negative $\upepsilon$54Cr signature (Trinquier et
al., 2007). Hence, the mass balance of all CV chondrite components suggests
that the CI-like $\upepsilon$54Cr value measured for the FGR in this study is
likely applicable to all FGRs and is required to get a bulk CV chondrite value
of 0.8 ‱.

Table 2: Mass balance calculations of CV chondritic components and their $\upepsilon$54Cr values. The bulk CV $\upepsilon$54Cr value ($<$0.1) is calculated as if all matrix had the composition of the average ICM. The measured CV bulk value (0.8) is the measured $\upepsilon$54Cr value.  Component | Modal abundance (vol.%) |  $\upepsilon$54Cr
---|---|---
Chondrule core | 75 | } 45a | -0.6 | } -0.5 | } 0
Chondrule rim | 25 | -0.1
Al-rich chondrules | <1c |  $\sim$0?
FGR | 50 | } 40a | 1.3 | } 0.7d
ICM | 50 | 0.7
CAIs/AOAs |  | 10a | 6.8 |  | 6.8
metalb |  | <5 | ? |  |
Bulk |  | 100 | 0.8 |  | <0.1

##  Appendix D Implications from potential 26Al heterogeneity in the
protoplanetary disk

Variations in $\upmu^{26}$Mg* (the decay product of 26Al) between bulk Solar
System materials and individual components such as chondrules have been
interpreted to reflect 26Al (Bollard et al., 2017; Larsen et al., 2011; Olsen
et al., 2016; van Kooten et al., 2016, 2017, 2020; Schiller et al., 2015;
Connelly & Bizzarro, 2018; Connelly et al., 2017; Larsen et al., 2016) and Mg
isotope heterogeneity (Budde et al., 2018; Wasserburg et al., 2012).
Typically, the accretion timescales of chondrites, achondrites and their
parent bodies are modelled assuming a homogeneous and canonical distribution
of 26Al. However, if the interpretation of a reduced 26Al reservoir for
chondrites is correct (Larsen et al., 2011; Schiller et al., 2015), then
accretion of chondrites was more rapid than assuming a canonical 26Al/27Al
ratio.

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Table 3: Elemental compositions and ratios of Leoville drilled fractions by ICP-Q-MS (see Appendix A for details). Concentrations are given in ppb together with the relative standard deviation (RSD%). | Cores | ICM | FGR
---|---|---|---
| Ach3 | Ach1 | Bch6 | Ach7 | Ach2 | Bmx1 | Bmx2 | Bmx3 | Ach7mx | Ach1mx | Ach2mx | Ach3mx | Ch2mx
Li | 0.02 |  $\pm$42 | 0.04 |  $\pm$23 | 0.06 |  $\pm$18 | 0.04 |  $\pm$17 | 0.04 |  $\pm$27 | 0.04 |  $\pm$19 | 0.04 |  $\pm$12 | 0.05 |  $\pm$9 | 0.05 |  $\pm$4 | 0.05 |  $\pm$8 | 0.05 |  $\pm$9 | 0.04 |  $\pm$9 | 0.020 |  $\pm$4
Na | 4.3 |  $\pm$3 | 6.2 |  $\pm$3 | 15.1 |  $\pm$1 | 2.2 |  $\pm$5 | 8.6 |  $\pm$1 | 2.9 |  $\pm$4 | 4.4 |  $\pm$7 | 3.9 |  $\pm$8 | 16.9 |  $\pm$2 | 3.0 |  $\pm$11 | 5.5 |  $\pm$6 | 4.2 |  $\pm$7 | 3.7 |  $\pm$4
Mg | 1097 |  $\pm$0.4 | 484 |  $\pm$0.1 | 91 |  $\pm$0.4 | 610 |  $\pm$0.3 | 708 |  $\pm$0.1 | 90 |  $\pm$1.1 | 138 |  $\pm$0.2 | 131 |  $\pm$0.2 | 321 |  $\pm$0.9 | 124 |  $\pm$0.2 | 148 |  $\pm$0.8 | 82 |  $\pm$0.3 | 83.6 |  $\pm$2
Al | 34.7 |  $\pm$2 | 71.7 |  $\pm$1 | 58.6 |  $\pm$2 | 11.0 |  $\pm$1 | 62.0 |  $\pm$1 | 7.9 |  $\pm$4 | 11.4 |  $\pm$2 | 15.2 |  $\pm$2 | 31.7 |  $\pm$2 | 12.7 |  $\pm$3 | 15.5 |  $\pm$4 | 9.9 |  $\pm$3 | 8.3 |  $\pm$2
P | 4.1 |  $\pm$28 | 4.6 |  $\pm$32 | 18.5 |  $\pm$11 | 5.2 |  $\pm$53 | 4.1 |  $\pm$70 | 5.5 |  $\pm$43 | 6.7 |  $\pm$20 | 2.2 |  $\pm$68 | 4.0 |  $\pm$28 | 7.5 |  $\pm$25 | n.d. | 5.9 |  $\pm$45 | n.d.
K | 4.5 |  $\pm$4 | 3.8 |  $\pm$6 | 6.1 |  $\pm$9 | 3.5 |  $\pm$12 | 3.6 |  $\pm$6 | 3.2 |  $\pm$15 | 4.3 |  $\pm$46 | 4.1 |  $\pm$49 | 2.4 |  $\pm$91 | 2.3 |  $\pm$84 | 1.6 |  $\pm$127 | n.d. | n.d.
Ca | 32.9 |  $\pm$7 | 68.9 |  $\pm$3 | 43.8 |  $\pm$7 | 14.3 |  $\pm$3 | 64.1 |  $\pm$4 | 9.6 |  $\pm$17 | 13.3 |  $\pm$8 | 15.5 |  $\pm$12 | 33.9 |  $\pm$3 | 12.4 |  $\pm$11 | 17.6 |  $\pm$6 | 12.1 |  $\pm$5 | 8.4 |  $\pm$7
Ti | 2.3 |  $\pm$6 | 3.4 |  $\pm$4 | 1.6 |  $\pm$13 | 0.7 |  $\pm$6 | 3.1 |  $\pm$4 | 0.3 |  $\pm$13 | 0.6 |  $\pm$13 | 0.8 |  $\pm$13 | 1.7 |  $\pm$6 | 0.5 |  $\pm$22 | 0.8 |  $\pm$3 | 0.4 |  $\pm$24 | 0.3 |  $\pm$31
V | 0.38 |  $\pm$2 | 0.23 |  $\pm$4 | 0.56 |  $\pm$1 | 0.19 |  $\pm$3 | 0.34 |  $\pm$2 | 0.05 |  $\pm$6 | 0.07 |  $\pm$8 | 0.07 |  $\pm$2 | 0.18 |  $\pm$0.5 | 0.07 |  $\pm$2 | 0.08 |  $\pm$3 | 0.04 |  $\pm$8 | 0.05 |  $\pm$0.5
Cr | 7.2 |  $\pm$0.7 | 5.0 |  $\pm$0.3 | 6.0 |  $\pm$0.5 | 5.1 |  $\pm$0.7 | 11.7 |  $\pm$0.6 | 2.5 |  $\pm$1.2 | 3.8 |  $\pm$0.6 | 3.4 |  $\pm$1.2 | 8.3 |  $\pm$0.1 | 3.5 |  $\pm$1.0 | 4.2 |  $\pm$1.2 | 2.1 |  $\pm$1.4 | 2.5 |  $\pm$2
Mn | 2.0 |  $\pm$0.9 | 1.3 |  $\pm$1.3 | 1.1 |  $\pm$2.4 | 0.8 |  $\pm$2.4 | 1.8 |  $\pm$1.0 | 1.3 |  $\pm$1.1 | 1.9 |  $\pm$2.3 | 2.1 |  $\pm$1.1 | 5.0 |  $\pm$0.5 | 1.8 |  $\pm$0.8 | 2.1 |  $\pm$2.9 | 1.8 |  $\pm$0.6 | 1.6 |  $\pm$2
Fe | 169 |  $\pm$0.6 | 79 |  $\pm$0.4 | 163 |  $\pm$0.3 | 304 |  $\pm$0.2 | 584 |  $\pm$0.2 | 204 |  $\pm$0.6 | 262 |  $\pm$0.1 | 274 |  $\pm$0.5 | 590 |  $\pm$0.4 | 260 |  $\pm$0.3 | 249 |  $\pm$0.7 | 241 |  $\pm$0.2 | 280.0 |  $\pm$1
Co | 0.8 |  $\pm$1.5 | 0.4 |  $\pm$1.9 | 0.8 |  $\pm$0.6 | 0.6 |  $\pm$1.0 | 2.4 |  $\pm$1.4 | 0.6 |  $\pm$1.1 | 1.0 |  $\pm$1.4 | 0.6 |  $\pm$2.8 | 0.9 |  $\pm$0.9 | 0.6 |  $\pm$1.4 | 0.9 |  $\pm$1.5 | 0.5 |  $\pm$1.1 | 0.6 |  $\pm$0.5
Ni | 8.3 |  $\pm$0.4 | 1.9 |  $\pm$1.6 | 20.0 |  $\pm$0.7 | 3.9 |  $\pm$0.5 | 48.3 |  $\pm$0.3 | 11.5 |  $\pm$0.7 | 15.5 |  $\pm$0.9 | 19.2 |  $\pm$0.7 | 14.2 |  $\pm$1.4 | 13.9 |  $\pm$1.0 | 15.6 |  $\pm$1.3 | 9.2 |  $\pm$1.3 | 10.9 |  $\pm$1
Cu | 0.09 |  $\pm$3 | 0.31 |  $\pm$1 | 0.24 |  $\pm$2 | 0.05 |  $\pm$4 | 0.35 |  $\pm$1 | 0.11 |  $\pm$3 | 0.16 |  $\pm$4 | 0.15 |  $\pm$1 | 0.15 |  $\pm$2 | 0.13 |  $\pm$3 | 0.15 |  $\pm$1 | 0.09 |  $\pm$4 | n.d.
Zn | 0.04 |  $\pm$28 | 0.19 |  $\pm$16 | 0.42 |  $\pm$3 | 0.01 |  $\pm$49 | 0.09 |  $\pm$11 | 0.07 |  $\pm$34 | 0.13 |  $\pm$9 | 0.13 |  $\pm$13 | 0.25 |  $\pm$7 | 0.13 |  $\pm$7 | 0.27 |  $\pm$4 | 0.11 |  $\pm$3 | 0.29 |  $\pm$5
Rb | 0.016 |  $\pm$47 | 0.014 |  $\pm$54 | 0.019 |  $\pm$37 | 0.013 |  $\pm$57 | n.d. | n.d. | 0.016 |  $\pm$23 | 0.017 |  $\pm$22 | 0.013 |  $\pm$30 | 0.015 |  $\pm$24 | 0.017 |  $\pm$22 | 0.010 |  $\pm$37 | n.d.
Sr | 0.024 |  $\pm$2 | 0.059 |  $\pm$3 | 0.059 |  $\pm$2 | 0.014 |  $\pm$4 | 0.064 |  $\pm$2 | 0.005 |  $\pm$9 | 0.008 |  $\pm$7 | 0.032 |  $\pm$3 | 0.026 |  $\pm$4 | 0.013 |  $\pm$4 | 0.014 |  $\pm$4 | 0.008 |  $\pm$7 | 0.008 |  $\pm$5
Sn | 0.23 |  $\pm$12 | 0.09 |  $\pm$33 | 0.24 |  $\pm$20 | 0.12 |  $\pm$21 | 0.08 |  $\pm$30 | 0.15 |  $\pm$20 | 0.12 |  $\pm$12 | 0.11 |  $\pm$15 | 0.10 |  $\pm$15 | 0.09 |  $\pm$14 | 0.08 |  $\pm$16 | 0.05 |  $\pm$19 |  |
Sb | 0.19 |  $\pm$4 | 0.15 |  $\pm$5 | 0.23 |  $\pm$3 | 0.17 |  $\pm$5 | 0.14 |  $\pm$5 | 0.18 |  $\pm$4 | 0.19 |  $\pm$0.5 | 0.18 |  $\pm$3 | 0.17 |  $\pm$2 | 0.16 |  $\pm$3 | 0.14 |  $\pm$0.5 | 0.13 |  $\pm$4 |  |
Ba | n.d. | 0.02 |  $\pm$4 | 0.06 |  $\pm$14 | n.d. | 0.01 |  $\pm$10 | n.d. | 0.01 |  $\pm$49 | 0.15 |  $\pm$4 | 0.01 |  $\pm$25 | 0.10 |  $\pm$4 | 0.01 |  $\pm$48 | 0.01 |  $\pm$34 | 0.01 |  $\pm$10
Fe/Mg | 0.15 |  $\pm$0.7 | 0.16 |  $\pm$0.4 | 1.79 |  $\pm$0.5 | 0.50 |  $\pm$0.4 | 0.83 |  $\pm$0.3 | 2.26 |  $\pm$1.3 | 1.90 |  $\pm$0.2 | 2.09 |  $\pm$0.5 | 1.84 |  $\pm$0.9 | 2.09 |  $\pm$0.3 | 1.68 |  $\pm$1.0 | 2.94 |  $\pm$0.3 | 3.35 |  $\pm$1.9
27Al/24Mg | 0.04 |  $\pm$2 | 0.19 |  $\pm$1 | 0.81 |  $\pm$2 | 0.02 |  $\pm$1 | 0.11 |  $\pm$1 | 0.11 |  $\pm$4 | 0.10 |  $\pm$2 | 0.14 |  $\pm$2 | 0.12 |  $\pm$2 | 0.13 |  $\pm$3 | 0.13 |  $\pm$4 | 0.15 |  $\pm$3 | 0.12 |  $\pm$3
55Mn/52Cr | 0.33 |  $\pm$1 | 0.31 |  $\pm$1 | 0.21 |  $\pm$2 | 0.19 |  $\pm$2 | 0.18 |  $\pm$1 | 0.64 |  $\pm$2 | 0.58 |  $\pm$2 | 0.74 |  $\pm$2 | 0.72 |  $\pm$1 | 0.62 |  $\pm$1 | 0.60 |  $\pm$3 | 1.00 |  $\pm$2 | 0.51 |  $\pm$2

Table 4: Overview table of analyses carried out for samples used in this study. BSE = back scattered electron images, maps = elemental maps from SEM, LA = laser ablation ICPMS and WA = wet analyses by ICP-Q-MS or HR-ICPMS (see Appendix A for detailed explanation). Analyses were done in this study [*], by van Kooten et al. (2019) [1] or by van Kooten & Moynier (2019) [2]. | BSE | maps | LA | WA | ref
---|---|---|---|---|---
Cores |  |  |  |  |
Ach1 | x | x |  |  | [*]
Ach7 | x |  |  |  | [*]
Bch6 | x | x | x |  | [1]
C1 | x |  |  | x | [2]
C2 | x |  |  | x | [2]
C3 | x |  |  | x | [2]
C5 | x |  |  | x | [2]
C6 | x |  |  | x | [2]
Bch1 | x | x |  | x | [*]
Bch2 | x | x |  | x | [*]
Bch3 | x | x |  | x | [*]
Bch4 | x | x |  | x | [*]
Bch7 | x | x |  | x | [*]
Ach4 | x |  |  | x | [*]
Ach8 | x | x |  | x | [*]
Ach9 | x |  |  | x | [*]
Ach10 | x | x |  | x | [*]
Core with rim |  |  |  |  |
Ach2 | x | x | x |  | [1]
Ach3 | x | x |  |  | [*]
Rims |  |  |  |  |
C1 | x | x |  | x | [2]
C2 | x | x |  | x | [2]
C3 | x | x |  | x | [2]
C5 | x | x |  | x | [2]
C6 | x | x |  | x | [2]
ICM |  |  |  |  |
Ach1mx | x | x |  | x | [*]
Ach2mx | x | x |  | x | [*]
Ach3mx | x | x |  | x | [*]
Ach7mx | x |  |  | x | [*]
Bmx1 | x |  |  | x | [*]
Bmx2 | x |  |  | x | [*]
Bmx3 | x |  |  | x | [*]
Leo2ch1mx1 | x |  |  |  | [*]
Leo2ch1mx2 | x |  |  |  | [*]
Leo2ch2mx | x |  |  |  | [*]
Leo2ch3mx | x |  |  |  | [*]
FGR |  |  |  |  |
C1 | x | x |  | x | [2]
C2 | x | x |  | x | [2]