Isabella Pignatelli
email: isabella.pignatelli@univ-lorraine.fr

Enrico Mugnaioli

Yves Marrocchi

Cronstedtite polytypes in the Paris meteorite

Keywords: cronstedtite, MDO polytypes, 3D electron diffraction, Paris meteorite

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Introduction

Cronstedtite is an iron-rich phyllosilicate whose layer is made of a tetrahedral (T) and an octahedral (O) sheet (T-O or 1:1 layer). The octahedral sheet is trioctahedral [START_REF] Bailey | Polytypism of trioctahedral 1:1 layer silicates[END_REF] meaning that all cation sites are occupied almost exclusively by iron (both Fe 2+ and Fe 3+ ), even if small amount of other cations such as Mg 2+ , Mn 2+ and Al 3+ have been reported [START_REF] Frondel | Polytypism in cronstedtite[END_REF][START_REF] Geiger | Crystal structure of cronstedtite-2H 2[END_REF]Hybler et al., 2002). Fe 3+ is also present in the tetrahedral sheet and this allows for discriminating cronstedtite from other Fe-bearing phyllosilicates, in particular greenalite. According to that, the general formula of cronstedtite is (Fe 2+ 3-x Fe 3+

x )(Si 2-x Fe 3+

x )O 5 (OH) 4 with 0 < x < 0.8 [START_REF] Geiger | Crystal structure of cronstedtite-2H 2[END_REF][START_REF] Smrčok | Refinement of the crystal structure of cronstedtite-3T[END_REF]Hybler et al., 2000[START_REF] Hybler | Refinement of the crystal structure of cronstedtite-2H 2[END_REF][START_REF] Kogure | Coexistence of two polytypic groups in cronstedtite from Lostwithiel England[END_REF].

From the structural point of view, the absence of interlayer cations makes the polytypism of cronstedtite, as well as of other T-O phyllosilicates, more complex than in micas because the adjacent layers can be stacked with a shift and/or rotation [START_REF] Bailey | Polytypism of trioctahedral 1:1 layer silicates[END_REF]. Twelve maximum degree of order (MDO) polytypes have been theoretically derived by [START_REF] Bailey | Polytypism of trioctahedral 1:1 layer silicates[END_REF] & Nuttall., 1963& Nuttall., , 1963;;[START_REF] Kogure | A HRTEM study of cronstedtite: determination of polytypes and layer polarity in trioctahedral 1:1 phyllosilicates[END_REF]. Two non-MDO polytypes of cronstedtite are also known: 9R polytype found at Cournocopia Mines (Nevada, USA) (Frodel, 1962), and 6T 2 polytype recently identified in Pohled (Czech Republic) samples [START_REF] Hybler | Polytypism of cronstedtite from Pohled, Czech Republic[END_REF][START_REF] Hybler | Crystal structure of cronstedtite-6T 2 , a non-MDO polytype[END_REF].

Cronstedtite can exhibit intergrowths of two polytypes of the same group, for example 3T + 1M, 2H 1 + 2H 2 , and the possible intergrowth of 2M 1 and 6T 2 [START_REF] Ďurovič | Cronstedtite-1M and co-existence of 1M and 3T polytypes[END_REF][START_REF] Kogure | A HRTEM study of cronstedtite: determination of polytypes and layer polarity in trioctahedral 1:1 phyllosilicates[END_REF][START_REF] Hybler | Crystal structure of cronstedtite-6T 2 , a non-MDO polytype[END_REF][START_REF] Hybler | Polytypism of cronstedtite from Nižná Slaná, Slovakia[END_REF], as well as the intergrowths of polytypes of groups A and C [START_REF] Kogure | A HRTEM study of cronstedtite: determination of polytypes and layer polarity in trioctahedral 1:1 phyllosilicates[END_REF][START_REF] Kogure | Coexistence of two polytypic groups in cronstedtite from Lostwithiel England[END_REF]. Recently, the existence of twinning in cronstedtite has been also proved: twins by reticular merohedry of the 3T and 6T 2 polytypes have been described in samples from Nižná Slaná and Pohled, [START_REF] Hybler | Polytypism of cronstedtite from Pohled, Czech Republic[END_REF][START_REF] Hybler | Polytypism of cronstedtite from Nižná Slaná, Slovakia[END_REF].

Cronstedtite occurs in both terrestrial and extraterrestrial environments. On the Earth, cronstedtite is found in: i) low-temperature hydrothermal veins of sulfides [START_REF] Frondel | Polytypism in cronstedtite[END_REF]; ii) metamorphosed massive sulphide deposits (López- [START_REF] García | Primera aparición en España de cronstedtita. Caracterización estructural[END_REF]; iii) hydrothermal quartz veins intersecting metasomatic siderite deposits [START_REF] Hybler | Polytypism of cronstedtite from Nižná Slaná, Slovakia[END_REF]; iv) hydrothermal veins containing pyrite developed in migmatized rocks [START_REF] Hybler | Polytypism of cronstedtite from Pohled, Czech Republic[END_REF]. An iron-rich phyllosilicate identified as possibly cronstedtite is formed with low-temperature retrograde minerals of banded-iron formations in Australian metabasites (Gole, 1980a,b).

Spectroscopic data let suppose that cronstedtite formed also in extraterrestrial environments, such as in some dark regions of Mars [START_REF] Calvin | Could Mars be dark and altered?[END_REF] and on the dwarf planet Ceres (Zolotov, 2014 and references therein). Moreover, cronstedtite is reported in CM meteorites (e.g. [START_REF] Tomeoka | Indicators of aqueous alteration in CM carbonaceous chondrites: microtextures of a layered mineral containing Fe, S, O and Ni[END_REF][START_REF] Mcsween | Alteration in CM carbonaceous chondrites inferred from modal and chemical variations in matrix[END_REF][START_REF] Pignatelli | Multiple precursors of secondary mineralogical assemblages in CM chondrites[END_REF], although its identification is questionable. In fact, what is described as "cronstedtite" in meteoritic studies is often a solid solution of T-O phyllosilicates, e.g.

chysotile and greenalite or chrysotile and cronstedtite [START_REF] Velbel | Stoichiometric reactions describing serpentinization of anhydrous primary silicates: a critical appraisal, with application to aqueous alteration of chondrule silicates in CM carbonaceous chondrites[END_REF], leading to confusion and misunderstanding. Few data are known about the polytypism of meteoritic cronstedtite: 1T polytype is found in Cold Bokkeveld and Cochamba meteorites, but the latter also contains the 1M polytype and an unidentified polytype with the cell parameter c ≈ 14 Å [START_REF] Zega | Fine-grained-rim mineralogy of the Cold Bokkeveld CM chondrite[END_REF][START_REF] Müller | Chemical and crystallographic study of cronstedtite in the matrix of the Cochabamba (CM2) carbonaceous chondrite. Tschermaks Mineral[END_REF].

Thus, the aim of this work is to improve the current knowledge about the polytypism of meteoritic cronstedtite, describing the polytypes recently found in Paris meteorite and identified by 3D electron diffraction data.

Material and methods

Paris meteorite is the least altered carbonaceous chondrite belonging to the CM group [START_REF] Hewins | The Paris meteorite, the least altered CM chondrite so far[END_REF]. It is characterized by 47% of matrix, 45 % of chondrules and 8% of fine-grained rims; and it contains both fresh and more altered domains [START_REF] Hewins | The Paris meteorite, the least altered CM chondrite so far[END_REF][START_REF] Leroux | GEMS-like material in the matrix of the Paris meteorite and the early stages of alteration of CM chondrites[END_REF][START_REF] Verdier-Paoletti | Oxygen isotope constraints on the alteration temperatures of CM chondrites[END_REF][START_REF] Vacher | Petrographic and C & O isotopic characteristics of the earliest stages of aqueous alteration of CM chondrites[END_REF]. Pseudomorphised silicates are dispersed throughout the matrix regardless of the alteration degree of domains. They are characterized by a complex compositional zoning made of three different Fe-bearing secondary minerals: tochilinite, cronstedtite and hydroxides [START_REF] Pignatelli | Multiple precursors of secondary mineralogical assemblages in CM chondrites[END_REF][START_REF] Pignatelli | Mineralogical, crystallographic and redox features of the earliest stages of fluid alteration in CM chondrites[END_REF].

Cronstedtite crystals found in pseudomorphised olivine and pyroxene of Paris meteorite were analysed in this study. For this purpose, two thin foils were extracted from the #2010-1section of Paris with a FEI strata DualBeam 235 at the Institute d' Electronique, de Microélectronique et de Nanotechnologie (Lille, France), using a lift-out procedure described by [START_REF] Heaney | Focused ion beam milling: a method of site-specific sample extraction for microanalysis of earth and planetary materials[END_REF]. The FIB foils were analysed at Università degli Studi di Siena (Italy) with a JEOL 2010 microscope operated at 200 kV and equipped with LaB 6 gun and UHR pole pieces able to achieve a point-to-point resolution of 0.19 nm. The chemical composition of cronstedtite crystals was determined by energy dispersive X-ray (EDX) spectroscopy using an Oxford ISIS spectrometer with a probe diameter of ~100 nm, a counting time of 60 s, a dead time lower than 15 %, and K AB factors calibrated on standards. The structural formulae were calculated on the basis of seven oxygens and of the Fe 3+ /ΣFe ratio measured by X-ray adsorption near-edge structure spectroscopy (XANES). The details on Fe 3+ /ΣFe measurements and results are given in [START_REF] Pignatelli | Mineralogical, crystallographic and redox features of the earliest stages of fluid alteration in CM chondrites[END_REF].

3D electron diffraction data were collected by combining electron diffraction tomography (EDT) (Kolb et al., 2007;Kolb et al., 2008;Mugnaioli, 2015) and precession electron diffraction (PED) (Vincent & Midgley, 1994;Mugnaioli et al., 2009) Diffraction patterns of two orthogonal reciprocal lattice sections are usually sufficient to identify an MDO polytype: the diffraction pattern of (h0l) * (hhl in hexagonal indexing) containing the subfamily reflections and the diffraction pattern of (0kl) *  (hhl in hexagonal indexing), containing both subfamily and non-family reflections (Ďurovič, 1997). However, the diffraction pattern of the (0kl) * plane is different from that of (h0l) * in non-trigonal and non-hexagonal poytypes, because they are not symmetrically equivalent [START_REF] Hybler | Refinement of cronstedtite-1M[END_REF]. This means that for the identification of such polytypes both planes have to be recorded and analyzed.

Results and discussion

Crystallo-chemistry

TEM-EDX data indicate that cronstedtite crystals have low amounts of Mg and Al, i.e. ≤ 8.09 and 2.25 at. % (Table 1 and2), substituting iron in both octahedral and tetrahedral sites. The averaged Fe 3+ /ΣFe ratio for cronstedtite crystals formed from a pyroxene and olivine precursors is respectively of 36.5 % and 48% [START_REF] Pignatelli | Mineralogical, crystallographic and redox features of the earliest stages of fluid alteration in CM chondrites[END_REF]. According to these data, the mean formulae are:

( The formulae indicate that: (i) cronstedtite in Paris meteorite shows a composition similar to those reported for terrestrial one (e.g., [START_REF] Smrčok | Refinement of the crystal structure of cronstedtite-3T[END_REF]Hybler et al., 2000); and (ii) there is no significant compositional variation among cronstedtite crystals with different precursors, i.e. olivine and pyroxene, suggesting that they formed under the same conditions.

Polytypes found

In order to identify the polytypes, we compared the distribution of reflections on electron diffraction 2D patterns with the identification diagrams for MDO cronstedtite polytypes available in literature [START_REF] Ďurovič | Cronstedtite-1M and co-existence of 1M and 3T polytypes[END_REF][START_REF] Hybler | Polytypism in cronstedtite[END_REF] and with the diffraction patterns calculated theoretically by using the DIFK91 program (Smrčok and Weiss, 1993).

The results underline that the most common polytype occurring in the analyzed FIB foils is 1T (Fig. 1).

This polytype belongs to the subfamily C as shown by the reflections' distribution along the [11l] * row on the (hhl hex ) * plane (Fig. 2a). Moreover, the reflections' distribution on (0kl hex ) * plane corresponds to MDO group I (Ďurovič, 1997) and indicates that this is 1-layer polytype (Fig. 2b).

1T is the most abundant polytype both in terrestrial samples [START_REF] Hybler | Polytypism in cronstedtite[END_REF] and in few analyzed extraterrestrial ones [START_REF] Zega | Fine-grained-rim mineralogy of the Cold Bokkeveld CM chondrite[END_REF][START_REF] Müller | Chemical and crystallographic study of cronstedtite in the matrix of the Cochabamba (CM2) carbonaceous chondrite. Tschermaks Mineral[END_REF]. The first structural refinement of this polytype was carried out less than two decades ago by Hybler and co-workers (Hybler et al., 2000).

Many cronstedtite crystals are characterized by stacking disorder, resulting in streaking along c* direction. However, a number of these disordered crystals preserve sharp maxima in the (hhl hex ) * plane, allowing to attribute them to the subfamily C. Also in these cases, streaks still affect the non-family reflections as visible on (0kl hex ) * plane of Fig. 3, hampering the polytype identification.

Only one cronstedtite crystal, found close to the remnant of a pseudomorphised olivine (Fig. 4), must necessarily be attributed to a different polytype subfamily. Although reflections are severely streaked, due to a high degree of disorder of this polytype, one can see that: (i) the distribution of reflections along [11l] * row is consistent with that of polytypes belonging to the subfamily A, and (ii) there are three reflections in the 1/7 Å -1 period along [10l] * row, indicating that it is a 3-layer polytype. It is, thus, a 3T polytype. However, the presence of other reflections not attributable to 3T implies its coexistence with other polytypes, probably ordered at the scale of few atomic layers. Reflections belonging to three 1M polytype cannot be excluded, as these would overlap with those of 3T.

Moreover, in some [10l] * rows the maxima corresponding to 2M 1 polytype can be recognized. This would be the first time that the contemporary occurrence of 3T + 2M 1 polytypes is recognized, as the 3T polytype is commonly described in association with 1M [START_REF] Ďurovič | Cronstedtite-1M and co-existence of 1M and 3T polytypes[END_REF][START_REF] Hybler | Polytypism of cronstedtite from Pohled, Czech Republic[END_REF][START_REF] Hybler | Polytypism of cronstedtite from Nižná Slaná, Slovakia[END_REF].

Conclusions

This work is the first reliable characterization of cronstedtite in meteorite. Firstly, the crystallochemical and redox data clearly indicate that the analyzed phyllosilicates are cronstedtite sensu stricto whereas in meteoritic studies the word "cronstedtite" is generally used to describe a solid-solution between T-O phyllosilicates with different compositions. Secondly, the polytypic sequences of this mineral were reported in literature only twice due to the small size of the crystals leading to analytical problems. Our results show that the electron diffraction tomography (EDT) combined to the precession electron diffraction (PED) is well adapted to investigate sub-micrometric crystal even those that are beam sensitive. The acquired 3D electron diffraction data allowed for the identification of disordered polytypes, 1T polytypes as well as a possible coexistence between 3T and 2M 1 . All polytypes have similar chemical composition, regardless of their polytypic sequence. The results presented here can be useful to better reconstruct the formation conditions of cronstedtite in meteorite, taking into account the stability field of different polytypes.

Tables

  at the Università degli Studi di Siena (Italy). Sequential selected area electron diffraction (SAED) patterns were collected with an Olympus Tengra CCD camera in a tilt range of up to -40/+40° with a step of 1°, using an area selector of 10 μm, equivalent to a beam size on the sample of about 100 nm. ADT3D software and in-house Matlab routines were used for the data processing, including three-dimensional reciprocal space reconstruction, cell parameter determination and intensity integration. The advantages of electron diffraction tomography for characterizing nanometric crystals, such as those in meteorites, are detailed in[START_REF] Kolb | Automated electron diffraction tomographya new tool for nano crystal structure analysis[END_REF] and[START_REF] Pignatelli | A multitechnique, micrometer-to atomic-scale description of a synthetic analogue of chukanovite, Fe 2 (CO 3 )(OH) 2[END_REF].2.1 Features of diffraction pattern of T-O phyllosilicatesOn the basis of Order-Disorder theory, it is possible to distinguish two kinds of reflections in the diffraction patterns of T-O phyllosilicates: family, and non-family reflections. The family reflections 00l are common to all polytypes of the same family (i.e. T-O phyllosilicates in this case). Family reflections having k = 3n (in orthohexagonal indexing, or h -k = 3n in hexagonal indexing) are common to all polytypes belonging to the same subfamily, thus they are generally referred as "subfamily reflections". They enable for identification of subfamilies or Bailey's groups A, B, C and D in function of the shift and/or rotation between adjacent layers. The non-family reflections with k = 3n (in orthohexagonal indexing, or h -k = 3n in hexagonal indexing) are typical of each polytype and are, thus, used to identify the stacking sequence. These reflections are affected by diffuse streaking and appear broadened when the polytype is disordered.

FiguresFigure 1 .

 1 Figures

Figure 2 .

 2 Figure 2. Sections of the 3D reconstructed diffraction volume of a sub-micrometric crystal of ordered 1T

Figure 3 .

 3 Figure 3. Projection of the 3D reconstructed diffraction volume of a sub-micrometric crystal of disordered

Figure 4 .

 4 Figure 4. (a) TEM image of a cronstedtite crystal formed close to the remnant of a pseudomorphised

Table 1 .

 1 TEM-EDX data of cronstedtite crystals (at %) formed from an olivine precursor.

		O	Mg	Al	Si	Fe	Total
		62.75 8.09 0.42 7.37 21.38 100.01
		62.95 4.29 0.75 7.85 24.15 99.99
		63.92 4.19 2.25 10.08 19.56 100.00
		65.50 2.02 0.49 8.99 23.00 100.00
		65.92 3.90 0.89 8.52 20.75 99.98
		66.36 3.57 1.24 8.46 20.37 100.00
		66.07 4.41 1.30 9.36 18.86 100.00
		64.39 4.43 2.04 10.28 18.86 100.00
		65.22 2.43 0.95 9.53 21.87 100.00
		66.15 1.67 0.75 8.90 22.53 100.00
		67.40 2.98 1.08 7.95 20.59 100.00
		68.67 2.64 0.96 8.89 18.84 100.00
		66.78 2.99 0.81 9.49 19.93 100.00
		66.68 3.01 0.96 9.43 19.92 100.00
		64.47 3.50 1.21 10.59 20.23 100.00
		64.24 3.00 1.08 7.91 23.77 100.00
		68.78 2.48 0.97 7.16 20.61 100.00
	average	65.66 3.51 1.07 8.87 20.90
	σ	1.75 1.45 0.47 1.00 1.66

Table 2 .

 2 TEM-EDX data of cronstedtite crystals (at %) formed from a pyroxene precursor.

Acknowledgements

This work was supported by l'Agence Nationale de la Recherche through grant ANR-14-CE33-0002-01 SAPINS and by the Italian national project FIR2013-Exploring the Nanoworld.


Yves Marrocchi
email: yvesm@crpg.cnrs-nancy.fr

David V Bekaert

Laurette Piani Crpg

Origin and abundance of water in carbonaceous asteroids

Keywords: carbonaceous asteroids, water, oxygen isotopes, protoplanetary disk, Jupiter

The origin and abundance of water accreted by carbonaceous asteroids remains underconstrained, but would provide important information on the dynamic of the protoplanetary disk. Here we report the in situ oxygen isotopic compositions of aqueously formed fayalite grains in the Kaba and Mokoia CV chondrites. CV chondrite bulk, matrix and fayalite O-isotopic compositions define the mass-independent continuous trend ( 17 O = 0.84 ± 0.03 ×  18 O -4.25 ± 0.1), which shows that the main process controlling the O-isotopic composition of the CV chondrite parent body is related to isotopic exchange between 16 O-rich anhydrous silicates and 17 O-and 18 O-rich fluid. Similar isotopic behaviors observed in CM, CR and CO chondrites demonstrate the ubiquitous nature of O-isotopic exchange as the main physical process in establishing the O-isotopic features of carbonaceous chondrites, regardless of their alteration degree. Based on these results, we developed a new approach to estimate the abundance of water accreted by carbonaceous chondrites (quantified by the water/rock ratio) with CM (0.3-0.4) ≥ CR (0.1-0.4) ≥ CV (0.1-0.2) > CO (0.01-0.10). The low water/rock ratios and the O-isotopic characteristics of secondary minerals in carbonaceous chondrites indicate they (i) formed in the main asteroid belt and (ii) accreted a locally derived (inner Solar System) water formed near the snowline by condensation from the gas phase.

Such results imply low influx of D-and 17 O-and 18 O-rich water ice grains from the outer part of the Solar System. The latter is likely due to the presence of a Jupiter-induced gap in the protoplanetary disk that limited the inward drift of outer Solar System material at the exception of particles with size lower than 150 m such as presolar grains. Among carbonaceous chondrites, CV chondrites show O-isotopic features suggesting potential contribution of 17-18 O-rich water that may be related to their older accretion relative to other hydrated carbonaceous chondrites. Highlights Bulk, matrix and fayalite grains of CV chondrites define a continuous trend. O-isotopic compositions of C-rich asteroids are established by isotopic exchange. We estimated the abundance of water accreted by carbonaceous chondrites. Carbonaceous asteroids formed in the asteroid belt and accreted local water. Our results support low influx of 17 O-and 18 O-rich water ice from the outer Solar System.

1-Introduction

Water played a key role in shaping the Solar System as it account for about 50% by mass of all condensable species in a gas of cosmic composition [START_REF] Lodders | Solar system abundances and condensation temperatures of the elements[END_REF]. Water vapor controls oxygen fugacity, affecting the chemistry of sub-millimeter materials formed during the evolution of the solar protoplanetary disk. As bouncing and fragmentation limit the coagulation of dust particles, the growth processes from dust to planetesimals are not fully understood [START_REF] Güttler | The outcome of protoplanetary dust growth: pebbles, boulders, or planetesimals?[END_REF]. Water-ice mantling grain surfaces is believed to enhance their adhesion and promote particle coagulation processes [START_REF] Gundlach | The stickiness of micrometer-sied water-ce particles[END_REF]. Thus, condensed water ices can locally increase the abundance of solids, favoring conditions that trigger streaming instabilities, and allowing the growth of decimeter-sized pebbles that can accrete to form planetesimals [START_REF] Ros | Ice condensation as a planet formation mechanism[END_REF]. Water ice is thus fundamental to the evolution of the Solar System, and, alongside oxides, silicates and metal, likely represented a significant fraction of the building blocks of planets. Ice-free chondrite accretion likely took place during the evolution of the protoplanetary disk as attested by enstatite chondrites, which

show really limited traces of water [START_REF] Brearley | The action of water. Meteorites and the early solar system II[END_REF][START_REF] Piani | Structure, composition, and location of organic matter in the enstatite chondrite Sahara 97096 (EH3)[END_REF].

Within the solar protoplanetary disk, the formation of water ice is mainly controlled by the snowline, i.e., the distance from the Sun at which temperature is low enough for water to condense (about 150-170 K). The location of the snowline in the protoplanetary disk is a direct function of the stellar accretion rate and is expected to move inward as the accretion rate decreases with time [START_REF] Bitsch | The structure of protoplanetary discs around evolving young stars[END_REF]. Based on astronomical observations, stellar accretion rates are estimated to have decreased on average from 10 -8 M  /y at 1 My to 1-5 10 -9

M  /y at 3 My (M  = the solar mass ~ 2 10 30 kg) [START_REF] Hartmann | Accretion and the Evolution of T-Tauri Disks[END_REF], inducing the snowline to drift from 3 AU to 1 AU (astronomical unit AU = 150 × 10 6 km, the distance from Earth to the Sun) [START_REF] Bitsch | The structure of protoplanetary discs around evolving young stars[END_REF]. Such a snowline drift implies that water ice grains were ubiquitous in the inner Solar System, and formed abundant ice-rich planetesimals. This point is not insignificant as geochemical constraints and numerical simulations suggest that inner planetesimals should have grown "dry" with only a small contribution of ice-rich planetesimals originating from larger heliocentric distances [START_REF] Albarède | Volatile accretion history of the terrestrial planets and dynamic implications[END_REF][START_REF] Marty | The origins and concentrations of water, carbon, nitrogen and noble gases on Earth[END_REF].

Yet, the accretion of chondrites occurred ~2-4 My after the formation of Calcium-Aluminum-rich Inclusions (CAIs; [START_REF] Sugiura | Correlated accretion ages and ε 54Cr of meteorite parent bodies and the evolution of the solar nebula[END_REF], when the snowline should have been closer to the Sun than the inner edge of the asteroid belt [START_REF] Morbidelli | Fossilized condensation lines in the Solar System protoplanetary disk[END_REF]. Such a conundrum, referred as the snowline problem [START_REF] Oka | Evolution of snowline in optically thick protoplanetary disks: Effects of water ice opacity and dust grain size[END_REF], could be linked to inhibited water ice condensation due to the slower drift of the snowline than that of gas in the protoplanetary disk [START_REF] Morbidelli | Fossilized condensation lines in the Solar System protoplanetary disk[END_REF]. This would bring "dry" gas (from which water had already condensed farther out in the disk) in the vicinity of the snowline [START_REF] Morbidelli | Fossilized condensation lines in the Solar System protoplanetary disk[END_REF]. However, chondrites have been affected by variable but widespread water alteration processes, suggesting they accreted a significant amount of water ice [START_REF] Doyle | Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by fayalite[END_REF][START_REF] Garenne | The abundance and stability of "water" in type 1 and 2 carbonaceous chondrites (CI, CM and CR)[END_REF][START_REF] Vacher | Petrographic and C & O isotopic characteristics of the earliest stages of aqueous alteration of CM chondrites[END_REF]. Thus, the origin and the abundance of water accreted by different group of chondrites are not yet fully understood [START_REF] Alexander | The origin of inner Solar System water[END_REF][START_REF] Vacher | Inward radial mixing of interstellar water ices in the Solar protoplanetary disk[END_REF]. Additionally, the oxygen isotopic evolution of water during secondary alteration processes has not been fully investigated, and could provide invaluable information on the physico-chemical processes occurring during the geological evolution of carbonaceous asteroids [START_REF] Clayton | Oxygen isotope studies of carbonaceous chondrites[END_REF][START_REF] Clayton | The oxygen isotope record in Murchison and other carbonaceous chondrites[END_REF].

Oxygen isotopic compositions are expressed in delta units (‰) relative to Standard Mean Ocean Water (SMOM) as

 x O = [( x O/ 16 O) sample /( x O/ 16 O) SMOW -1] × 1000) with x being
17 O or 18 O; mass-independent oxygen isotope fractionation are described by the parameter

 17 O =  17 O -0.52 ×  18 O.
Among meteorites, carbonaceous chondrites present the most widespread evidences of fluid-rock interactions, in that the contain important diversity of aqueously formed minerals such as phyllosilicates, carbonates and magnetite [START_REF] Brearley | The action of water. Meteorites and the early solar system II[END_REF]. Oxygen isotopic compositions of these secondary minerals can be used to decipher the origin of water in the chondrite-forming region as outer water ices are expected to exhibit significant 17 O and 18 O enrichment ( 17 O >> 0) relative to inner Solar System values ( 17 O ≈ 0) due to the self-shielding of 16 O-rich nebular CO gas by UV light [START_REF] Yurimoto | Molecular cloud origin for the oxygen isotope heterogeneity in the solar system[END_REF]. In addition, oxygen isotopic compositions at both the bulk and mineral scales can be used to quantify (i) the abundance of water accreted by carbonaceous parent bodies [START_REF] Clayton | The oxygen isotope record in Murchison and other carbonaceous chondrites[END_REF][START_REF] Young | Fluid Flow in Chondritic Parent Bodies: Deciphering the Compositions of Planetesimals[END_REF] and (ii) the prevailing conditions during subsequent fluid-rock [START_REF] Verdier-Paoletti | Oxygen isotope constraints on the alteration temperatures of CM chondrites[END_REF]. Among secondary minerals, fayalite (Fe 2 SiO 4 ) is of primary importance as it represents a proxy of the fluid from which it formed due to its low fractionation factor  Fa-water [START_REF] Zheng | Calculation of oxygen isotope fractionation in anhydrous silicate minerals[END_REF] at the temperature range estimated for fayalite formation (i.e., 100-300°C) [START_REF] Doyle | Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by fayalite[END_REF][START_REF] Zolotov | Thermodynamic constraints on fayalite formation on parent bodies of chondrites[END_REF]. In this contribution, we report the oxygen isotopic compositions of fayalite in the CV chondrites Kaba and Mokoia.

We compute the amount of water ice accreted by combining these results with the bulk Oisotopic compositions of CV chondrites [START_REF] Clayton | Oxygen isotope studies of carbonaceous chondrites[END_REF]. We also compare the O-isotopic composition at both the bulk and (secondary) mineral scales for CO, CM and CR chondrites to propose a quantitative view of the origin, abundance and O-isotopic evolution of water in the carbonaceous asteroids.

2-Materials and methods

We surveyed a thin section each of Kaba (Kaba N4075) and Mokoia (Mokoia N1185;

both from the National Museum History, Vienna, Austria). Sections were examined microscopically in transmitted and reflected light. Scanning electron microscope (SEM) and Energy Dispersive X-ray (EDX) spectral analyses were performed at Centre de Recherches

Pétrographiques et Géochimiques (CRPG-CNRS, Nancy, France) using a JEOL JSM-6510 equipped with an EDX Genesis X-ray detector, using a 3 nA primary beam at 15 kV.

3-Results

Fayalite grains in Kaba and Mokoia occur in peripheral portions of type I chondrules, in fine-grained chondrule rims, and in matrix (Fig. 1). Fayalite are large, subhedral-toanhedral grains, and sometimes associated with magnetite and sulfide grains (Fig. 1A), although sulfide-and magnetite-free fayalite grains are commonly observed in the matrix (Fig. 1B). Fayalite are chemically homogeneous (Fa 97 to Fa 100 ; Table 1) with compositions similar to those previously reported fayalite-bearing assemblages [START_REF] Choi | Oxygen isotopes in magnetite and fayalite in CV chondrites Kaba and Mokoia[END_REF][START_REF] Hua | Fayalite in the Kaba and Mokoia carbonaceous chondrites[END_REF][START_REF] Jogo | Fayalite in the Vigarano CV3 carbonaceous chondrite: Occurrences, formation age and conditions[END_REF] [START_REF] Clayton | A Component of Primitive Nuclear Composition in Carbonaceous Meteorites[END_REF]. In detail, it rather appears that bulk and matrix O-isotopic compositions of CV chondrites define the trend  17 O = 0.84 ×  18 O -4.25 (r 2 = 0.99; Fig. 2A; [START_REF] Clayton | Oxygen isotope studies of carbonaceous chondrites[END_REF][START_REF] Greenwood | The relationship between CK and CV chondrites[END_REF], which likely corresponds to secondary alteration processes. The O-isotopic compositions of fayalite grains reported here do not fall on the TFL but show  17 O > 0‰ (Fig. 2B). When plotted with the bulk, matrix and dark inclusions O-isotopic compositions of CV chondrites, the Kaba and Mokoia fayalite grains define the continuous trend  17 O = (0.83 ± 0.02) ×  18 O -(4.18 ± 0.13) (2σ, r 2 = 0.99, and Mean Squared Weight Deviation, MSWD = 3.9; Fig. 2A). Fayalite grains reported in the CV3 chondrite A-881317 also fall on this trend (Fig. 2A) [START_REF] Doyle | Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by fayalite[END_REF]. Comparison with other studies is difficult due to the large uncertainties associated with O-isotope measurements (e.g., 4.4 and 2.5‰ on  18 O and  17 O (2σ), respectively) [START_REF] Choi | Oxygen isotopes in magnetite and fayalite in CV chondrites Kaba and Mokoia[END_REF].

However, recent measurements in the Kaba chondrite aligns perfectly along the line of slope 0.83 (Fig. 2A; [START_REF] Krot | Evidence for oxygen-isotope exchange in chondrules and refractory inclusions during fluid-rock interaction on the CV chondrite parent body[END_REF]. The continuous trend defined by bulk, matrix and fayalite compositions does not follow a mass-dependent fractionation relationship (Fig. 2A), implying that fayalite O-isotopic compositions did not result from fluid circulation along a temperature gradient, which would produce a trend with slope 0.52. Instead, this implies that the main process controlling the O-isotopic composition of the CV chondrite parent body is related to isotopic equilibrium between 16 O-rich anhydrous silicates and 17 O-and 18 O-rich fluid as recently reported in CM chondrites [START_REF] Verdier-Paoletti | Oxygen isotope constraints on the alteration temperatures of CM chondrites[END_REF]. In such a scheme, Thermodynamic calculations suggest that nearly pure fayalite grains (Fa > 90) as observed in CV3 OxB chondrites are stable at temperatures below 350°C [START_REF] Zolotov | Thermodynamic constraints on fayalite formation on parent bodies of chondrites[END_REF], and likely down to 100-200°C [START_REF] Doyle | Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by fayalite[END_REF]. Considering the low  Fa-water at this temperature range (i.e., at 100°C and -1.1 ‰ at 200°C, [START_REF] Zheng | Calculation of oxygen isotope fractionation in anhydrous silicate minerals[END_REF], fayalite O-isotopic compositions represent a direct record of the oxygen isotopic compositions of the fluid from which they precipitated. Additionally, fayalite and magnetite from chondrite A-881317 lie on a mass-dependent fractionation line with  17 O = -0.3‰, consistent with equilibrium crystallization from the same fluid reservoir (Fig. 3B) [START_REF] Doyle | Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by fayalite[END_REF]. The -8.4 ‰ difference between  18 O values of fayalite and magnetite [START_REF] Doyle | Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by fayalite[END_REF] corresponds to fayalite crystallization at ≈ 150°C [START_REF] Zheng | Calculation of oxygen isotope fractionation in anhydrous silicate minerals[END_REF], at which temperature the fractionation factor is minimal with 1000 ln Fa-water

Considering then that fayalite formation likely occurred in a very narrow range of temperatures (i.e., 150-200°C), their parent fluids are characterized by near terrestrial values with  17 O from -1 to +3.5‰ (Fig. 2A). However, these values do not necessarily correspond to the initial O-isotopic composition of water accreted by CV chondrites as protracted fluidrock interactions likely occurred before the precipitation of the rare, nearly pure, fayalite grains.

There is a lively debate on the conditions of secondary alteration processes that have affected chondrites, which is basically divided into open-system [START_REF] Young | Fluid Flow in Chondritic Parent Bodies: Deciphering the Compositions of Planetesimals[END_REF]) versus closed-system models [START_REF] Clayton | Oxygen isotope studies of carbonaceous chondrites[END_REF]. Although the O-isotopic compositions of secondary minerals have been used to argue for both models, petrographic observations appear more consistent with closed-system alteration. For instance, there is little evidence for the redistribution of soluble elements within chondrites at scale greater than 100 m [START_REF] Brearley | The action of water. Meteorites and the early solar system II[END_REF], thus suggesting that aqueous alteration processes are mostly isochemical. This is consistent with the estimated low permeability of chondrites [START_REF] Bland | Why aqueous alteration in asteroids was isochemical: High porosity≠high permeability[END_REF] and the lack of variations in bulk chemical compositions between meteorites with different degrees of aqueous alteration [START_REF] Brearley | The action of water. Meteorites and the early solar system II[END_REF]. Based on these observations, we thus considered a closed-system model to discuss the alteration conditions of carbonaceous asteroids.

In a closed system, the difference between the final (f) oxygen isotopic composition of rock r and water w can be described as:

(

The amount of water accreted by CV chondrites can be estimated by the water/rock ratio [START_REF] Young | Fluid Flow in Chondritic Parent Bodies: Deciphering the Compositions of Planetesimals[END_REF] (2)

where N corresponds to the number of oxygen atoms in the reacting water (w) or rock (r),  0 their initial isotopic compositions,  f their final isotopic compositions and  represent the difference between rock and water at equilibrium. Such a formalism does not include the final isotopic composition of the water, which is generally not known. However, in the case where this parameter can be calculated, Eqn. 2 simplifies to:

(3)

Considering the bulk O-isotopic composition of Kaba ( 18 O = 2.18‰, [START_REF] Clayton | Oxygen isotope studies of carbonaceous chondrites[END_REF]) and a more 16 O-rich bulk CV chondrite as a plausible CV protolith ( 18 O = -4.22‰; [START_REF] Clayton | Oxygen isotope studies of carbonaceous chondrites[END_REF], we calculate the water/rock ratio by assuming that the lowest  18 O value of fayalite represent the final O-isotopic composition of CV water, after weighting by the fractionation factor at 150°C (i.e., 17.4 -0.6 = 16.8‰; Table 2). Although the initial composition of water accreted by CV chondrite is unknown, it must be (i) located on the trend defined by both bulk CV and fayalite (Fig. 2A) and (ii) characterized by  18 O value higher than the highest fayalie  18 O value. Assuming an initial water with  18 O = 30‰ (as estimated for CM chondrites; [START_REF] Clayton | The oxygen isotope record in Murchison and other carbonaceous chondrites[END_REF] leads to an estimated water/rock ratio of 0.48 for Kaba; the same calculation giving a result of 0.74 for Mokoia. These values are slightly lower than those estimated on the basis of mineral assemblages and thermodynamic modeling (i.e., 0.8-1.1; [START_REF] Zolensky | Mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites[END_REF] However, it is noted that our estimations represent maximum water/rock ratios, as increasing the  18 O of the initial water or decreasing  18 O of final water lowers the water/rock ratio. For instance, an initial water with  18 O = 45‰ gives estimated water/rock ratios for Kaba and Mokoia of 0.30 and 0.22, respectively. Considering the range of water/rock ratios modeled for the formation of near pure fayalite (i.e., 0.1-0.2; [START_REF] Zolotov | Thermodynamic constraints on fayalite formation on parent bodies of chondrites[END_REF] provides  18 O ≥ + 60 ‰ (i.e.,  17 O > 15 ‰) for the initial CV water, suggesting a potential contribution of water ice from the outer Solar System [START_REF] Sakamoto | Remnants of the Early Solar System Water Enriched in Heavy Oxygen Isotopes[END_REF][START_REF] Seto | Mineralogical characterization of a unique material having heavy oxygen isotope anomaly in matrix of the primitive carbonaceous chondrite Acfer 094[END_REF].

Kaba is considered the least altered oxidized CV chondrite with a petrographic grade of 3.1-3.4 [START_REF] Bonal | Determination of the petrologic type of CV3 chondrites by Raman spectroscopy of included organic matter[END_REF]. Interestingly, Kaba fayalite grains are not in isotopic equilibrium with sulfide-associated magnetite (SAMs) poikilitically enclosed in low-Ca pyroxenes of chondrules (Fig. 3; [START_REF] Marrocchi | Early scattering of the solar protoplanetary disk recorded in meteoritic chondrules[END_REF]. Based on petrographic and isotopic characteristics, SAMs have been interpreted as magmatic minerals, resulting from the crystallization of FeS melts containing variable amounts of dissolved oxygen (Marrocchi et al., 2016;[START_REF] Marrocchi | Sulfur and sulfides in chondrules[END_REF]. The fact that the  17 O of SAMs and fayalite grains from Kaba do not overlap (Fig. 3B) confirms that chondrule SAMs could be primary mineral formed during the high-temperature chondrule-forming event [START_REF] Marrocchi | Early scattering of the solar protoplanetary disk recorded in meteoritic chondrules[END_REF]. This does not exclude the potential occurrence of low-temperature aqueously formed magnetite in CV chondrites, but rather suggests that both processes occurred at different settings and under different physico-chemical conditions.

Comparison of CV to CM, CR and CO chondrites

CM chondrites

In a oxygen three-isotope plot, the continuous trend observed between whole rocks and secondary minerals is not unique to CV chondrites. In CM chondrites, Ca-carbonates replace fayalite as aqueously formed minerals defining the trend  17 O = (0.66 ± 0.05) ×  18 O - show water/rock ratios of 0.32 and 0.36, respectively, in good agreement with previous estimates for CM2 chondrites (i.e., 0.3-0.6; [START_REF] Clayton | The oxygen isotope record in Murchison and other carbonaceous chondrites[END_REF][START_REF] Zolensky | CM chondrites exhibit the complete petrologic range from type 2 to 1[END_REF].

With the exception of few Ca-carbonates enriched in 17 O-and 18 O relative to the main carbonate trend [START_REF] Vacher | Inward radial mixing of interstellar water ices in the Solar protoplanetary disk[END_REF], the O-isotopic characteristics of secondary mineral in CM chondrites indicate a dominant local origin of water during accretion [START_REF] Alexander | The Provenances of Asteroids, and Their Contributions to the Volatile Inventories of the Terrestrial Planets[END_REF]. Near terrestrial  17 O values of the CM water line (-1 to + 4 ‰; Fig. 4B) confirm a local water origin. Consequently, the contribution in CM chondrites of water coming from large heliocentric distances is probably limited to few %. Such contributions could have been overprinted by water inherited from the inner Solar System, as indicated by the hydrogen isotopic composition of CM chondrites [START_REF] Piani | A Dual Origin for Water in the CM Carbonaceous Chondrites. 48 th Lunar and Planetary Science Conference[END_REF].

CR chondrites

Of the carbonaceous chondrites, CR chondrites are of primary importance because they exhibit low degree of aqueous alteration and thermal metamorphism (Le [START_REF] Guillou | Relationships between organics, water and early stages of aqueous alteration in the pristine CR3.0 chondrite MET 00426[END_REF]. Nonetheless, they experienced significant alteration as attested by the corrosion of Fe-Ni metal beads [START_REF] Morlok | Aqueous alteration in CR chondrites: Meteorite parent body processes as analogue for long-term corrosion processes relevant for nuclear waste disposal[END_REF] and the presence of Cacarbonates [START_REF] Brearley | The action of water. Meteorites and the early solar system II[END_REF]. Interestingly, CR chondrites show similar O-isotopic characteristics as CV and CM chondrites, with bulk and Ca-carbonates O-isotopic compositions defining the trend with  17 O = (0.63 ± 0.02) ×  18 O -(2.22 ± 0.26) (Fig. 5A; [START_REF] Clayton | The oxygen isotope record in Murchison and other carbonaceous chondrites[END_REF][START_REF] Jilly | Timescales and conditions for the aqueous alteration of chondrites[END_REF][START_REF] Schrader | The formation and alteration of the Renazzo-like carbonaceous chondrites I: Implications of bulk-oxygen isotopic composition[END_REF]. This similarity attests the ubiquitous nature of O-isotopic exchange as the main physical process controlling the Oisotopic compositions of carbonaceous chondrites, whatever the extent of alteration.

Magnetite in CR chondrites is sometimes in close association with Ca-carbonates [START_REF] Brearley | The action of water. Meteorites and the early solar system II[END_REF][START_REF] Jilly | Timescales and conditions for the aqueous alteration of chondrites[END_REF]. Within a given CR chondrite, the two fall on a mass-dependent line (e.g., GRO 95577; Fig. 5B) with  17 O ~ 0 ‰ [START_REF] Jilly | Timescales and conditions for the aqueous alteration of chondrites[END_REF][START_REF] Jilly | Oxygen isotope fractionation among secondary calcite and magnetite in CR chondrites[END_REF], indicating that they probably formed at isotopic equilibrium from the same fluid reservoir. Assuming such equilibrium, the fractionation factor between carbonates (cc) and magnetite (mt)  18 O mt- cc (i.e.,  18 O mt - 18 O cc ) is a function of their formation temperature [START_REF] Chacko | Equilibrium Oxygen, Hydrogen and Carbon Isotope Fractionation Factors Applicable to Geologic Systems[END_REF]:

 18 O mt-CC = (-2.10 × 10 -4 T -2 ) + (0.12 T) -34.46 (4)
Based on data from different CR chondrites [START_REF] Jilly | Timescales and conditions for the aqueous alteration of chondrites[END_REF], this calculation provides a formation temperature estimate of 15-110°C, in good agreement with previous estimations of 50-150°C [START_REF] Zolensky | Mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites[END_REF]. At those temperature, we compute the O-isotopic compositions of water from which carbonates and magnetite formed in the different CR chondrites [START_REF] Jilly | Timescales and conditions for the aqueous alteration of chondrites[END_REF][START_REF] Jilly | Oxygen isotope fractionation among secondary calcite and magnetite in CR chondrites[END_REF]. CR water thus (i) defines a trend with  17 O = (0.61 ± 0.03) ×  18 O + (0.42 ± 0.15) (Fig. 6A) and (ii) is characterized by  17 O ~ 0 ‰, consistent with water originating from the inner Solar System. Interestingly, the CR water trend estimated from the O-isotopic compositions of Ca-carbonates and magnetite perfectly aligns with the estimation of the O-isotopic composition of water accreted by CM chondrites [START_REF] Clayton | Oxygen isotope studies of carbonaceous chondrites[END_REF][START_REF] Clayton | The oxygen isotope record in Murchison and other carbonaceous chondrites[END_REF] (Fig. 5A). This suggests that both types of chondrites could have accreted similar water, implying that the  17 O and  18 O values of initial CM water could be used to estimate the CR chondrite W/R ratios.

Definition of the CR water line allows calculation of the O-isotopic composition of the specific fluid from which a given CR carbonate precipitated, as their respective O-isotopic could originate from distinct parent bodies [START_REF] Schrader | CM and CO chondrites: A common parent body or asteroidal neighbors? Insights from chondrule silicates[END_REF], they probably formed in a common region within the accretion disk; the anhydrous precursors of CM2 were CO3-like, but CM accreted more water [START_REF] Hewins | The Paris meteorite, the least altered CM chondrite so far[END_REF]. (iii) Taken together, the CM and CO falls define a trend with  17 O = (0.69 ± 0.04) ×  18 O -(4.05 ± 0.18) (Fig. 6A; r 2 = 0.98, MSWD = 15). Although the bulk O-isotopic compositions of CO chondrites are more restricted than those of CM chondrites (Fig. 6a), they might have recorded fluid alteration processes. (iv) The absence of secondary phases that could be targeted by ion probe measurements precludes the possibility of combining bulk and mineral data (as reported for CV, CM and CR chondrites). However, MacAlpine Hills (MAC) 88107, a CO-like chondrite,

shows abundant near-pure fayalite and magnetite [START_REF] Krot | Evidence for low-temperature growth of fayalite and hedenbergite in MacAlpine Hills 88107, an ungrouped carbonaceous chondrite related to the CM-CO clan[END_REF] that can be used to interpreted as formation at isotopic equilibrium with the same fluid reservoir [START_REF] Doyle | Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by fayalite[END_REF]. Based on O-isotopic compositions and mineralogical, petrographic and thermodynamic constraints, it has been proposed that fayalite and magnetite formed at low water/rock ratios (0.1-0.2) and relatively elevated temperature (100-200°C; [START_REF] Doyle | Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by fayalite[END_REF]. However, considering the average  18 O values of magnetite and fayalite (i.e., 10.2 ± 1.3‰ and 14.1 ± 0.6‰, respectively), the observed  18 O mt-Fa (=  18 O mt - 18 O Fa ) rather suggests a formation temperature of 480 ± 20°C [START_REF] Chacko | Equilibrium Oxygen, Hydrogen and Carbon Isotope Fractionation Factors Applicable to Geologic Systems[END_REF]. Considering even the larger  18 O mt-Fa [START_REF] Doyle | Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by fayalite[END_REF] leads to an estimate temperature of ~250°C, significantly higher than that previously estimated for CO chondrites (i.e., 0-50°C) [START_REF] Zolensky | Mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites[END_REF].

Whatever the alteration temperature of MAC 88107, the fractionation factor  Fa-water is relatively small (i.e., 3.4‰ at 100°C and -3.6‰ at 500°C) [START_REF] Zheng | Calculation of oxygen isotope fractionation in anhydrous silicate minerals[END_REF], allowing the final O-isotopic composition of CO water to be computed at  18 O of 15 ± 3.5‰. Although the bulk O-isotopic composition of MAC 88107 has not been determined, it is possible to estimate the water/rock ratio of CO chondrites by following some reasonable assumptions. Considering that MAC 88107 likely has a bulk O-isotopic composition falling in the lower range observed for CO chondrites (i.e., -4 to -2‰) and assuming that COs have similar initial water and anhydrous protolith as CMs (+30.3 and -4.2 ‰, respectively; [START_REF] Clayton | The oxygen isotope record in Murchison and other carbonaceous chondrites[END_REF], the water/rock estimated for MAC 88107 range from 0.01 to 0.10. These values are consistent with previous estimates [START_REF] Zolensky | Mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites[END_REF] and the limited alteration of CO chondrites relative to CV and CM. However, it should be kept in mind that the lack of secondary phases in CO chondrites makes this estimation less robust than those reported for CM, CR and CV chondrites.

Implications for the structure and evolution of the accretion disk

All carbonaceous chondrites show varying degrees of fluid alteration suggesting that water ice grains were significant components of their parent bodies. By combining bulk and mineral O-isotope data, we estimate the water/rock ratios of carbonaceous chondrites to be: CM (0.3-0.4) ≥ CR (0.1-0.4) ≥ CV (0.1-0.2) > CO (0.01-0.10) (Fig. 7). Our results suggest that water was heterogeneously distributed across the chondrite accretion regions. Current debate considers carbonaceous chondrites formation either in the main asteroid belt [START_REF] Alexander | The Provenances of Asteroids, and Their Contributions to the Volatile Inventories of the Terrestrial Planets[END_REF] or in the outer Solar System (i.e., 5-15 UA) before subsequent implantation into the main belt during the dynamic evolution of the Solar System (the Grand Tack model; [START_REF] Walsh | A low mass for Mars from Jupiter's early gas-driven migration[END_REF]. The low water/rock ratios estimated in this study support carbonaceous chondrite accretion close to the snowline as accretion at greater heliocentric distances would have induced a solar water/rock ratio of 1.2 [START_REF] Lodders | Solar system abundances and condensation temperatures of the elements[END_REF]. The low carbonaceous chondrite water/rock ratios suggest that the snowline did not drift closer to the Sun than the inner edge of the asteroid belt [START_REF] Morbidelli | Fossilized condensation lines in the Solar System protoplanetary disk[END_REF] and was probably located at 2-3 AU during the accretion of the carbonaceous asteroid, ~2-4 My after the formation of CAIs [START_REF] Krot | Sources of Water and Aqueous Activity on the Chondrite Parent Asteroids[END_REF].

The majority of secondary minerals in carbonaceous chondrites show O-isotopic signatures that are consistent with accretion of locally derived water from the inner Solar System. Such water presents minimal mass-independent O-isotopic variations (i.e.,  17 O ~ 0‰), contrary to outer water ices enriched in 17 O-and 18 O ( 17 O >> 0%), implying that water ice originating from the outer Solar System was not the main source for water in carbonaceous chondrites [START_REF] Yurimoto | Molecular cloud origin for the oxygen isotope heterogeneity in the solar system[END_REF]. This conclusion is consistent with D-poor compositions of carbonaceous chondrite waters [START_REF] Alexander | The Provenances of Asteroids, and Their Contributions to the Volatile Inventories of the Terrestrial Planets[END_REF][START_REF] Piani | A Dual Origin for Water in the CM Carbonaceous Chondrites. 48 th Lunar and Planetary Science Conference[END_REF]. Based on the expected heliocentric D/H gradient ratio in the accretion disk [START_REF] Jacquet | Water transport in protoplanetary disks and the hydrogen isotopic composition of chondrites[END_REF], both H and O isotopes suggest an inner Solar System origin of water accreted into carbonaceous chondrite, probably where carbonaceous asteroids are located today [START_REF] Alexander | The origin of inner Solar System water[END_REF].

The low influx of 17 O-and 18 O-rich and D-rich water ice from the outer part of the Solar System may be due to the early growth of Jupiter (≈ 1My after the start of the Solar System), which would have prevented inward radial drift in the protoplanetary disk [START_REF] Walsh | A low mass for Mars from Jupiter's early gas-driven migration[END_REF]). An inner Solar System origin of carbonaceous chondrites is consistent wit their type I chondrules containing olivines with Mg#>90, suggesting formation at relatively low oxygen fugacity, whereas formation beyond the orbit of Jupiter should have occurred under more oxidizing conditions. Contrary to these conclusions, [START_REF] Kruijer | Age of Jupiter inferred from the distinct genetics and formation times of meteorites[END_REF] attribute the molybdenum and tungsten isotopic compositions of iron meteorites derived from a carbonaceous meteorite reservoir to a late addition of W-and Mo-bearing presolar material to the outer Solar System. However, presolar grains (generally < 20 μm in size), being tightly coupled to gas motions (i.e., particles < 150 μm in size; Fig. 8C) might have crossed Jupiter's orbit and reached the inner Solar System [START_REF] Zhu | Dust filtration by planetinduced gap edges: Implications for transitional disks[END_REF]. As the carrier phases of Mo and W isotope anomalies [START_REF] Kruijer | Age of Jupiter inferred from the distinct genetics and formation times of meteorites[END_REF], presolar grains could have thus been preferentially incorporated into asteroids accreting near the snow line, i.e. carbonaceous chondrites (Fig. 8D). Chondrites forming at smaller heliocentric distances and/or earlier in the history of the protoplanetary disk would have incorporated a different population of presolar grains.

Ordinary chondrites are consistent with such an origin, as their potential earlier onset of aqueous activity [START_REF] Krot | Sources of Water and Aqueous Activity on the Chondrite Parent Asteroids[END_REF][START_REF] Sugiura | Correlated accretion ages and ε 54Cr of meteorite parent bodies and the evolution of the solar nebula[END_REF] as well as D-rich water and organic matter relative to carbonaceous chondrites [START_REF] Piani | Micron-scale D/H heterogeneity in chondrite matrices: A signature of the pristine solar system water? Earth Planet[END_REF] could have resulted from accretion before the Jupiter-induced gap in the protoplanetary disk. Additionally, ordinary chondrites contain more type II chondrules characterized by low Mg# olivines (i.e., Mg# < 90) than carbonaceous chondrites, indicating their formation in more oxidizing environments.

Carbonaceous chondrites and their water are thus by-products of the evolution of the inner Solar System. The O-isotopic composition of water produced via self-shielding photodissociation decreases with time and increasing heliocentric distance in the accretion disk, becoming similar to that observed in carbonaceous chondrites after 1 My [START_REF] Yang | Oxygen isotope anomalies in the solar nebula inherited from the proto-solar cloud[END_REF]. Consequently, the O-isotopic of water upon the accretion of hydrated carbonaceous parent bodies (i.e., 2-4 Ma; [START_REF] Sugiura | Correlated accretion ages and ε 54Cr of meteorite parent bodies and the evolution of the solar nebula[END_REF] should have been smoothed toward Earth-like values, potentially via re-equilibration with silicates in the disk [START_REF] Alexander | The origin of inner Solar System water[END_REF][START_REF] Yurimoto | Molecular cloud origin for the oxygen isotope heterogeneity in the solar system[END_REF]. Inner solar water accreted by hydrated carbonaceous asteroids may be ice condensed at the snow line and/or liquid water adsorbed at the grain surfaces. The increasing water/rock ratios of CO, CV, CR, and CM reflects that these classes of carbonaceous asteroids accreted near to the snow line, but at increasing heliocentric distances. We note that some Ca-carbonates of the least altered CM chondrite Paris have peculiar O-isotopic compositions suggesting accretion of few percent water ice grains originating from the outer part of the Solar System [START_REF] Vacher | Inward radial mixing of interstellar water ices in the Solar protoplanetary disk[END_REF]. This is supported by the distinct C/H vs. D/H correlation reported for the Paris' matrix compared to the other CM chondrites [START_REF] Piani | A Dual Origin for Water in the CM Carbonaceous Chondrites. 48 th Lunar and Planetary Science Conference[END_REF]. These results suggest limited but significant contribution of outer Solar System materials to the chondrite-forming regions. Interestingly, CV chondrites may have accreted 17 O-and 18 O-rich water (i.e.,  17 O > 15‰) during their formation ≈ 1My before the more hydrated carbonaceous chondrites [START_REF] Sugiura | Correlated accretion ages and ε 54Cr of meteorite parent bodies and the evolution of the solar nebula[END_REF]. It is possible that inward radial mixing was more efficient at the time of CV chondrite accretion but significantly decreased upon the formation of Jupiter, which limited later contribution of outer water ices in favor of locally derived water in the accretion zones of carbonaceous asteroids.

5-Concluding remarks

We report the oxygen isotopic composition of sulfide-and magnetite-free, nearly pure Madre and Andrey Gurenko are thanked for their assistance with isotopic measurements This work was funded by l'Agence Nationale de la Recherche through grant ANR-14-CE33-0002-01 SAPINS (PI Yves Marrocchi). We thanked three anonymous reviewers for constructive comments and Associate Editor Frederic Moynier for careful editing. This is CRPG-CNRS contribution #2517 and SAPINS contribution #10. [START_REF] Clayton | Oxygen isotope studies of carbonaceous chondrites[END_REF][START_REF] Clayton | The oxygen isotope record in Murchison and other carbonaceous chondrites[END_REF]) and fayalite grains from Mokoia, Kaba and A-881317 [START_REF] Doyle | Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by fayalite[END_REF]. The O-isotopic composition of magnetite in Kaba chondrules [START_REF] Marrocchi | Early scattering of the solar protoplanetary disk recorded in meteoritic chondrules[END_REF] and in the matrix of A-881317 [START_REF] Doyle | Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by fayalite[END_REF] and Kaba [START_REF] Krot | Evidence for oxygen-isotope exchange in chondrules and refractory inclusions during fluid-rock interaction on the CV chondrite parent body[END_REF] [START_REF] Clayton | Oxygen isotope studies of carbonaceous chondrites[END_REF][START_REF] Jilly | Timescales and conditions for the aqueous alteration of chondrites[END_REF][START_REF] Jilly | Oxygen isotope fractionation among secondary calcite and magnetite in CR chondrites[END_REF][START_REF] Schrader | The formation and alteration of the Renazzo-like carbonaceous chondrites I: Implications of bulk-oxygen isotopic composition[END_REF]. The O-isotopic compositions of CR alteration water from which Ca-carbonates precipitated are also represented. CR water O-isotopic compositions were calculated based on the isotopic equilibrium between Ca-carbonates and magnetite per CR chondrite (represented in panel (B); data from [START_REF] Jilly | Timescales and conditions for the aqueous alteration of chondrites[END_REF]. Uncertainties shown are 2 Fig. 6: (A) Oxygen three-isotope plot of bulk and matrix in CO chondrites [START_REF] Clayton | Oxygen isotope studies of carbonaceous chondrites[END_REF]. The O-isotopic compositions of fayalite grains in CO-like MacAlpine Hills 88107 are also represented [START_REF] Doyle | Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by fayalite[END_REF]. Together, the data define the continuous trend with  17 O = (0.68 ± 0.08) ×  18 O -(4.08 ± 0.14). CO water corresponds to the O-isotopic composition from which fayalite grains precipitated according to the fractionation factor  between fayalite and water [START_REF] Zheng | Calculation of oxygen isotope fractionation in anhydrous silicate minerals[END_REF]

Figure Caption

  17 O-and 18 O-rich fayalite correspond to early precipitates from primitive fluids that did not suffer significant O-isotopic exchange with 16 O-rich anhydrous silicates[START_REF] Yurimoto | Isotopic compositions of asteroidal liquid water trapped in fluid inclusions of chondrites[END_REF][START_REF] Zolensky | The search for and analysis of direct samples of early Solar System aqueous fluids[END_REF]. Conversely, lighter isotopic compositions indicate that fayalite formed only after significant alteration, as fluid O-isotopic compositions converge toward the typical16 O-rich values of anhydrous silicates. Both bulk and mineral phase data (Fig.2) thus identify O-isotopic exchange between 16 O-rich silicates and 17 O-and 18 O-rich fluid as the key process controlling the O-isotopic composition of the alteration fluids from which fayalite precipitated.

  (4.7 ± 1.5)[START_REF] Verdier-Paoletti | Oxygen isotope constraints on the alteration temperatures of CM chondrites[END_REF]. This implies that isotopic equilibrium between16 Orich anhydrous silicates and 17 O-and 18 O-rich water controls the O-isotopic evolution of bulk CM chondrites and their secondary alteration mineral. To the first order, isotopic equilibrium dominates, with temperature gradients having a lesser effect in establishing the isotopic composition of CV and CM chondrites. Consequently, the isotopic compositions of secondary minerals are mainly controlled by the extent of isotopic exchange between water of initial composition and anhydrous silicates[START_REF] Clayton | The oxygen isotope record in Murchison and other carbonaceous chondrites[END_REF][START_REF] Verdier-Paoletti | Oxygen isotope constraints on the alteration temperatures of CM chondrites[END_REF]. In such a scheme, 17 O-and 18 O-rich secondary minerals correspond to early precipitates from primitive fluids that had not yet suffered significant O-isotopic exchange with anhydrous silicates.In CM chondrites, the O-isotopic compositions of alteration water inferred from direct measurements and mass balance calculations define a continuous trend, parallel within errors to that of bulk CMs and Ca-carbonates, but with a different intercept ( 17 O = (0.69 ± 0.02) ×  18 O -(2.12 ± 0.30);[START_REF] Verdier-Paoletti | Oxygen isotope constraints on the alteration temperatures of CM chondrites[END_REF]. This difference in intercepts is directly related to the isotopic fractionation factorreflecting an average calculated precipitation temperature of 110°C for CM Ca-carbonates[START_REF] Verdier-Paoletti | Oxygen isotope constraints on the alteration temperatures of CM chondrites[END_REF]. Similarly, Cacarbonates of the Murchison and Mighei CM chondrites define a trend parallel to the CM water line, but with an intercept in good agreement, within errors, to that reported for 9 different CM chondrites ( 17 O = (0.70 ± 0.03) ×  18 O -(5.65 ± 1.25) (Fig.4A:[START_REF] Lindgren | Fluid evolution in CM carbonaceous chondrites tracked through the oxygen isotopic compositions of carbonates[END_REF][START_REF] Verdier-Paoletti | Oxygen isotope constraints on the alteration temperatures of CM chondrites[END_REF]. Such results allow calculation of the O-isotopic composition of the fluid from which a given carbonate precipitated by connecting the Cacarbonate trend to the CM water line by a mass-dependent line (see[START_REF] Verdier-Paoletti | Oxygen isotope constraints on the alteration temperatures of CM chondrites[END_REF] for further details). Using the bulk O-isotopic composition ofMurchison and Mighei (i.e., 7.3 and 7.6‰, respectively;[START_REF] Clayton | Oxygen isotope studies of carbonaceous chondrites[END_REF] and the O-isotopic composition of anhydrous CM silicates as plausible CM protolith (i.e.,  18 O = -4.2‰;[START_REF] Clayton | Oxygen isotope studies of carbonaceous chondrites[END_REF], we calculate the water/rock ratio (Eqn. 3) assuming that the lowest Cacarbonate  18 O value in a given CM chondrite represent the final  18 O value of water (weighted by 14.6‰, representing 1000 ln calcite-water at 110°C). Murchison and Mighei thus

  estimate the isotopic characteristics of CO water. The O-isotopic compositions of fayalite from MAC 88107 fall along the trend defined by the bulk CM and CO chondrites,  17 O = (0.69 ± 0.03) ×  18 O -(4.01 ± 0.21) (Fig. 6A; r 2 = 0.98, MSWD = 15). These observations suggest that the O-isotopic characteristics of CO chondrites were established by O-isotopic exchange between anhydrous silicates and significantly less water than the other groups of carbonaceous chondrites. Magnetite and fayalite in MAC 88107 plot along a mass-dependent fractionation line with  17 O = (0.48 ± 0.02) ×  18 O -(1.10 ± 2.05) (Fig. 6B; r 2 = 0.84, MSWD = 0.56),

  fayalite grains in CV chondrites Kaba and Mokoia. When combined with both the bulk and matrix O-isotopic compositions of CV chondrites, their O-isotopic composition define the continuous trend  17 O = (0.84 ± 0.03) ×  18 O -(4.25 ± 0.1). This implies that the process controlling the O-isotopic composition of the CV chondrite parent body was related to isotopic equilibrium between 16 O-rich anhydrous silicates and 17 O-and 18 O-rich fluid. Similar behaviors are observed in CM, CR and CO chondrites, demonstrating the ubiquitous nature of O-isotopic exchange as the main physical process controlling the O-isotopic features of carbonaceous chondrites, regardless of the extent of alteration. Based on these results, we estimate the abundance of water accreted by carbonaceous chondrites (quantified by the water/rock ratio) to be CM (0.4) ≥ CR (0.1-0.4) ≥ CV (0.1-0.2) > CO (0.01-0.10). This suggests a heterogeneous distribution of water in the accretion zone of carbonaceous asteroids. The relatively low water/rock ratios estimated for carbonaceous chondrites indicate their accretion near the snowline, in the inner Solar System, as accretion further out in the disk would have induced solar water/rock ratio of 1.2. Most of aqueously formed minerals in carbonaceous chondrites show O-isotopic characteristics consistent with accretion of local water, likely formed from the condensation of the gas near the snowline and/or liquid water adsorbed at the grain surfaces. These results provide no evidence of carbonaceous chondrite formation beyond the orbit of Jupiter and imply a limited influx of D-and 17 O-and 18 O-rich water ice grains from the outer part of the Solar System. Such a limited influx might result from a gap in the solar protoplanetary disk due to the early and rapid formation of Jupiter, which would limit the inward motion of particles with size higher than 150 µm. This model accounts for the O-and H-isotopic signatures of carbonaceous chondrites, and suggest their accretion in the inner Solar System, closer to Jupiter than non-carbonaceous chondrites.Hence, carbonaceous chondrites would have preferentially accreted W-and Mo-bearing presolar grains crossing the orbit of Jupiter, resulting in significant lower W-and Moanomalies in non-carbonaceous meteorites. Among carbonaceous chondrites, only CV chondrites show O-isotopic features compatible with accretion of17-18 O-rich water, possibly related to their older accretion age relative to other hydrated carbonaceous chondrites.

Fig. 1 :

 1 Fig. 1: Back-scattered electron micrographs of fayalite grains in the Kaba CV chondrite.

Fig. 2 :

 2 Fig.2: Oxygen three-isotope plot for bulk and matrix CV chondrites(Clayton and Mayeda,

Fig. 3 :

 3 Fig. 3: (A) Oxygen three-isotope plot for bulk and matrix CV chondrites ((Clayton and

Fig. 4 :

 4 Fig. 4: (A) Oxygen three-isotope plot of Ca-carbonates in CM chondrites Murchison and

Fig. 7 :

 7 Fig. 7: Schematic representation of the water/rock ratio estimated for the CO, CV, CR and

Fig. 8 :

 8 Fig. 8: A) Coexistence and spatial separation of non-carbonaceous chondrite (NCC) and

  Quantitative compositional analyses of fayalite were made with a CAMECA SX-100 electron microprobe at the University of Paris VI. Electron microprobe analyses of silicates were performed with a 40 nA focused beam, 15 kV accelerating potential, and 20 on-peak and background analysis times. Detection limits in silicates were 0.02 wt% for SiO 2 , Al 2 O 3 , CaO and MgO, 0.01 wt% for Na 2 O, K 2 O, and TiO 2 , and 0.04 wt% for Cr 2 O 3 and FeO.Oxygen isotopic compositions were measured with a CAMECA IMS 1280 at CRPG-CNRS.16 O -, 17 O -, and 18 O -ions produced by a 5 nA Cs + primary ion beam were measured in multi-collection mode with three Faraday cup (FC). To avoid interference of 16 OH -and 17 O - signals at mass 17, and to maximize the flatness of the 16 O -and 18 O -peaks, entrance and exit

	slits were adjusted to achieve a Mass Resolving Power of ~7000 for 17 O -on the central FC
	and ~2500 on the off-axis FC. Total measurement time was 240 s (180 s measurement + 60 s
	pre-sputtering). We used four terrestrial standard materials (San Carlos olivine, magnetite,
	diopside, and fayalite) to: (i) define the mass fractionation line (TFL) and (ii) correct the
	matrix effects on instrumental mass fractionation for fayalite. Typical count rates obtained on
	fayalite grains were 3  10 9 cps for 16 O, 1  10 6 cps for 17 O, and 4.5  10 6 cps for 18 O. Typical
	2 errors were ~ 0.7 ‰ for  18 O, ~ 0.8 ‰ for  17 O, and ~ 1 ‰ for  17 O.

1 Origin, abundance and O-isotopic evolution in CV chondrites

	grains were selected for isotopic analyses. Their O-isotopic compositions fall above the TFL,
	with  17 O values ranging from 0.8 to 2.6‰ (Fig. 2, Table 2).
	4-Discussion
	4.It is commonly accepted that bulk O-isotopic compositions of CV chondrites plot
	along the Carbonaceous Chondrite Anhydrous Mineral (CCAM) line [ 17 O = (0.94±0.01) 
	 18 O  4.2], derived from BrF 5 analyses of anhydrous minerals from CAIs in carbonaceous
	chondrites
	. Eight large (> 40 µm) sulfide-and magnetite-free fayalite

  are also represented. Uncertainties shown are 2. (B)  17 O values of bulk, matrix, fayalite and magnetite in the CV chondrites Kaba, Mokoia and A881317. The similar  17 O observed between fayalite and magnetite in A-881317 indicate that they probably formed at isotopic equilibrium from the same fluid reservoir. To the contrary, fayalite and magnetite in Kabashow significantly different  17 O that could be linked to the formation of magnetite during the high-temperature chondrule-forming event[START_REF] Marrocchi | Early scattering of the solar protoplanetary disk recorded in meteoritic chondrules[END_REF]. Uncertainties shown

	are 2.

Table 1 :

 1 Chemical composition and Fa# of fayalite grains observed in the Kaba and Mokoia CV chondrites

	chondrite	point	SiO 2	K 2 O	FeO	Na 2 O	Al 2 O 3	CaO	MnO	MgO	Cr 2 O 3	TiO 2	Total	Fa
	Kaba	Fa-1	29.3	bdl	69.1	bdl	bdl	bdl	0.7	0.8	bdl	bdl	99.9	98.9
		Fa-2	29.4	bdl	69.4	bdl	bdl	bdl	0.4	0.6	bdl	bdl	99.7	99.2
		Fa-3	29.2	bdl	69.2	bdl	bdl	bdl	0.7	0.5	bdl	bdl	99.7	99.2
		Fa-4	29.0	bdl	69.6	bdl	bdl	bdl	0.7	0.0	bdl	bdl	99.4	100.0
		Fa-5	29.8	bdl	67.1	bdl	bdl	bdl	0.8	2.1	bdl	bdl	99.7	97.0
		Fa-6	29.5	bdl	68.2	bdl	bdl	bdl	1.2	0.8	bdl	bdl	99.6	98.9
	Mokoia	Fa-7	29.2	bdl	68.8	bdl	bdl	bdl	0.6	1.2	bdl	bdl	99.8	98.3
		Fa-8	28.9	bdl	68.1	bdl	bdl	bdl	0.9	1.8	bdl	bdl	99.7	97.4

Acknowledgments

All of the data used in the present article are available by contacting Yves Marrocchi (yvesm@crpg.cnrs-nancy.fr). Ludovic Ferrière and the National Museum History of Vienna (Austria) are thanked for the loan of the Kaba and Mokoia sections. Matthieu Gounelle is warmly thanked for helpful scientific discussions. Johan Villeneuve, Nordine Bouden, David

compositions are related by a mass-dependent relationship. This further allows estimation of the water/rock ratio by assuming that (i) the lowest O-isotopic composition of bulk CR chondrites represent the  18 O of the CR protolith (i.e., -2.29‰; Fig. 5A; [START_REF] Schrader | The formation and alteration of the Renazzo-like carbonaceous chondrites I: Implications of bulk-oxygen isotopic composition[END_REF] and (ii) the initial CR water is similar to that accreted by CM chondrites (i.e., 30‰; [START_REF] Clayton | The oxygen isotope record in Murchison and other carbonaceous chondrites[END_REF]. This leads to a maximum estimation of the CR water/rock ratio in the range 0.10 to 0.40, lower than previous values of 0.4-1.1 [START_REF] Zolensky | Mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites[END_REF].

CO chondrites

The case of CO chondrites is more complex than other carbonaceous chondrites. First, CO chondrites have experienced minimal fluid alteration; some show no evidence of alteration, whereas others exhibit alteration features at the sub-micrometer scale [START_REF] Brearley | The action of water. Meteorites and the early solar system II[END_REF]. Rare secondary phases (phyllosilicates, fine-grained serpentine and saponite) are mainly located within the CO matrices [START_REF] Brearley | The action of water. Meteorites and the early solar system II[END_REF]. Secondly, the bulk O-isotopic compositions of CO chondrite finds could have been affected by terrestrial weathering, inducing a shift toward 17 O-and 18 O-rich values [START_REF] Greenwood | Alteration and metamorphism of CO3 chondrites: Evidence from oxygen and carbon isotopes[END_REF]. Finally, a recent report of the bulk O-isotopic composition of CO chondrite falls show they are slightly shifted toward the CCAM line [START_REF] Alexander | A mutli-technique search for the most primitive CO chondrites[END_REF] relative to previous measurements [START_REF] Clayton | Oxygen isotope studies of carbonaceous chondrites[END_REF][START_REF] Greenwood | Alteration and metamorphism of CO3 chondrites: Evidence from oxygen and carbon isotopes[END_REF]) (Fig. S1). The reason for such a shift remains unclear but could be linked to incomplete fluorination in previous measurements [START_REF] Alexander | A mutli-technique search for the most primitive CO chondrites[END_REF]. However, several observations can be used to improve our understanding of CO chondrites. (i) Considering the data reported by [START_REF] Clayton | Oxygen isotope studies of carbonaceous chondrites[END_REF][START_REF] Greenwood | Alteration and metamorphism of CO3 chondrites: Evidence from oxygen and carbon isotopes[END_REF], the bulk O-isotopic compositions of CO chondrite falls show a significant deviation from the primordial slope 1 with  17 O = (0.65 ± 0.12) ×  18 O -(4.19 ± 0.27) (Fig. 6A; r 2 = 0.89, MSWD = 7.6). (ii) This trend is similar to the one defined by CM chondrites (Fig. 6A). Although recent report suggest that CM and CO chondrites