Lionel G Vacher
email: lvacher@crpg.cnrs-nancy.fr

Yves Marrocchi

Johan Villeneuve

Maximilien J Verdier-Paoletti

Matthieu Gounelle

Collisional and alteration history of the CM parent body

Keywords: Clasts, calcite, aragonite, oxygen and carbon isotopes, impacts, X-ray tomography

ABSTRACT

Boriskino is a little studied CM2 chondrite composed of millimeter-sized clasts of different lithologies and degrees of alteration. Boriskino thus offers a good opportunity to better understand the preaccretionary alteration history and collisional evolution that took place on the CM parent body. The least altered lithology displays 16 O-poor Type 1a calcite and aragonite grains ( 18 O ≈ 30-37‰,  17 O ≈ 15-18‰ and  17 O ≈ -2 to 0‰, SMOW) that precipitated early, before the establishment of the petrofabric, from a fluid whose isotopic composition was established by isotopic exchange between a 16 O-poor water and 16 O-rich anhydrous silicates. In contrast, the more altered lithologies exhibit 16 O-rich Type 2a and veins of calcite ( 18 O ≈ 17-23‰,  17 O ≈ 6-9‰ and  17 O ≈ -4 to -1‰, SMOW) that precipitated after establishment of the deformation, from transported 16 O-rich fluid in preexisting fractures. From our petrographic and X-ray tomographic results, we propose that the more altered lithologies of Boriskino were subjected to high intensity impact(s) (10-30 GPa) that produced a petrofabric, fractures and chondrule flattening. Taking all our results together, we propose a scenario for the deformation and alteration history of Boriskino, in which the petrographic and isotopic differences between the lithologies are explained by their separate locations into a single CM parent body. Based on the  13 C- 18 O values of the Boriskino Type 2a calcite ( 13 C ≈ 30-71‰, PDB), we propose an alternative  13 C- 18 O model where the precipitation of Type 2a calcite can occurred in an open system environment with the escape of 13 C-depleted CH 4 produced from the reduction of C-bearing species by H 2 released during serpentinization or kamacite corrosion. Assuming a mean precipitation temperature of 110°C, the observed δ 13 C variability in T2a calcite can be reproduced by the escape of ≈ 15-50% of dissolved carbon into CH 4 by Rayleigh distillation.

INTRODUCTION

The CM carbonaceous chondrites are samples of dark primitive C-type asteroids [START_REF] Clark | Spectroscopy of B-type asteroids: Subgroups and meteorite analogs[END_REF][START_REF] Cloutis | Spectral reflectance properties of carbonaceous chondrites: 1. CI chondrites[END_REF] accreted closed to the snowline [START_REF] Morbidelli | Fossilized condensation lines in the Solar System protoplanetary disk[END_REF] and that contain a high proportion of water (i.e. water/rock ratio = 0.4; [START_REF] Marrocchi | Origin and abundance of water in carbonaceous asteroids[END_REF], mainly in hydroxyl form in the matrix [START_REF] Rubin | Progressive aqueous alteration of CM carbonaceous chondrites[END_REF]. Their mineralogy and petrography suggest they have undergone brecciation and low temperature hydrothermal alteration, which could have been induced by low velocity impacts and/or by heat released by the decay of the 26 Al, respectively [START_REF] Dufresne | On the chemical evolution of the carbonaceous chondrites[END_REF][START_REF] Metzler | Accretionary dust mantles in CM chondrites: Evidence for solar nebula processes[END_REF][START_REF] Zolensky | CM chondrites exhibit the complete petrologic range from type 2 to 1[END_REF][START_REF] Nakamura | Post-hydration thermal metamorphism of carbonaceous chondrites[END_REF][START_REF] Rubin | Progressive aqueous alteration of CM carbonaceous chondrites[END_REF][START_REF] Nakato | Evaluation of dehydration mechanism during heating of hydrous asteroids based on mineralogical and chemical analysis of naturally and experimentally heated CM chondrites[END_REF]. CM chondrites experienced different degrees of aqueous alteration, from moderate (CM2) to high (CM1), as reflected by their varying proportion of secondary phases, including Fe-, Mg-and S-rich phyllosilicates (e.g., sulfide-hydroxide/cronstedtite association, hereafter referred as TCI), Fe-Ni sulfides, and carbonates [START_REF] Mcsween | Are carbonaceous chondrites primitive or processed? A review[END_REF][START_REF] Bunch | Carbonaceous chondrites-II. Carbonaceous chondrite phyllosilicates and light element geochemistry as indicators of parent body processes and surface conditions[END_REF][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] Zolensky | CM chondrites exhibit the complete petrologic range from type 2 to 1[END_REF][START_REF] Brearley | The action of water[END_REF][START_REF] Rubin | Progressive aqueous alteration of CM carbonaceous chondrites[END_REF][START_REF] Howard | Modal mineralogy of CM2 chondrites by X-ray diffraction (PSD-XRD). Part 1: Total phyllosilicate abundance and the degree of aqueous alteration[END_REF][START_REF] Howard | Classification of hydrous meteorites (CR, {CM} and {C2} ungrouped) by phyllosilicate fraction: PSD-XRD modal mineralogy and planetesimal environments[END_REF][START_REF] Hewins | The Paris meteorite, the least altered CM chondrite so far[END_REF][START_REF] Lee | Aragonite, breunnerite, calcite and dolomite in the CM carbonaceous chondrites: High fidelity recorders of progressive parent body aqueous alteration[END_REF][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][START_REF] Rubin | Meteoritic minerals and their origins[END_REF].

Carbonates are ubiquitous in CMs and represent a minor proportion of secondary mineral assemblages (i.e., up to 2-3 vol.%; [START_REF] Marrocchi | The Paris CM chondrite: Secondary minerals and asteroidal processing[END_REF][START_REF] Lee | Aragonite, breunnerite, calcite and dolomite in the CM carbonaceous chondrites: High fidelity recorders of progressive parent body aqueous alteration[END_REF]. Their mineralogy provides information about the chemical evolution of the fluid during aqueous alteration. For example, Ca-carbonates occur as aragonite and calcite in most CM2 chondrites, whereas dolomites are only found in the more altered CM chondrites [START_REF] Johnson | Carbonate compositions in CM and CI chondrites and implications for aqueous alteration[END_REF][START_REF] Riciputi | Minor and trace element concentrations in carbonates of carbonaceous chondrites, and implications for the compositions of coexisting fluids[END_REF][START_REF] Browning | On the Origin of Rim Textures Surrounding Carbonate Grains in CM Matrices[END_REF][START_REF] Benedix | Carbonates in CM2 chondrites: constraints on alteration conditions from oxygen isotopic compositions and petrographic observations[END_REF][START_REF] Leuw | Carbonates in CM chondrites: Complex formational histories and comparison to carbonates in CI chondrites: Carbonates in CM chondrites[END_REF][START_REF] Lee | Extended chronologies of aqueous alteration in the CM2 carbonaceous chondrites: Evidence from carbonates in Queen Alexandra Range 93005[END_REF][START_REF] Lee | Aragonite, breunnerite, calcite and dolomite in the CM carbonaceous chondrites: High fidelity recorders of progressive parent body aqueous alteration[END_REF][START_REF] Tyra | Episodic carbonate precipitation in the CM chondrite ALH 84049: An ion microprobe analysis of O and C isotopes[END_REF][START_REF] Vacher | Petrographic and C & O isotopic characteristics of the earliest stages of aqueous alteration of CM chondrites[END_REF]. Furthermore, their oxygen isotopic compositions (i.e.,  17,18 O) can be used to decipher their precipitation temperature and the origin and evolution of the fluid. Based on the O-isotopic compositions of Ca-carbonates, it has been proposed (i) that they precipitated at varying temperatures, in the range 0-300°C [START_REF] Clayton | The oxygen isotope record in Murchison and other carbonaceous chondrites[END_REF][START_REF] Benedix | Carbonates in CM2 chondrites: constraints on alteration conditions from oxygen isotopic compositions and petrographic observations[END_REF][START_REF] Guo | Temperatures of aqueous alteration and evidence for methane generation on the parent bodies of the CM chondrites[END_REF][START_REF] Alexander | Carbonate abundances and isotopic compositions in chondrites[END_REF]Verdier-Paoletti et al., 2017a), (ii) that aqueous alteration processes occurred essentially in a closed system with a static fluid interacting with anhydrous silicates [START_REF] Dufresne | On the chemical evolution of the carbonaceous chondrites[END_REF][START_REF] Clayton | Oxygen isotope studies of carbonaceous chondrites[END_REF][START_REF] Benedix | Carbonates in CM2 chondrites: constraints on alteration conditions from oxygen isotopic compositions and petrographic observations[END_REF] and (iii) that the least altered CMs (i.e., Paris and Maribo) accreted a significant proportion of 17,18 O-rich water inherited from the outer Solar System [START_REF] Horstmann | Tracking aqueous alteration of CM chondrites-Insight from in-situ oxygen isotope measurements of calcite[END_REF][START_REF] Vacher | Inward radial mixing of interstellar water ices in the solar protoplanetary disk[END_REF]. Carbon isotopic composition of carbonates ( 13 C) also reflects aqueous alteration and can constrain the origin of dissolved carbon into the fluid. From bulk and in situ C-isotopic compositions of CM carbonates, it has been postulated that carbonates precipitated from C-bearing inorganic molecules (i.e., CO or CO 2 ; [START_REF] Alexander | Carbonate abundances and isotopic compositions in chondrites[END_REF] or soluble organic matter (SOM) [START_REF] Vacher | Petrographic and C & O isotopic characteristics of the earliest stages of aqueous alteration of CM chondrites[END_REF]. C-isotopes can also be affected by different fractionation mechanisms, such as escape of C-bearing gas (e.g., CH 4 , [START_REF] Guo | Temperatures of aqueous alteration and evidence for methane generation on the parent bodies of the CM chondrites[END_REF] during, for example, venting event [START_REF] Telus | In situ analyses of carbonate and magnetite in CM1 chondrites[END_REF].

Carbonate precipitation in response to stress events, such as impacts or accretional/gravitational compaction [START_REF] Cain | Structural deformation of the Leoville chondrite[END_REF]Fujimara et al., 1983) has previously been reported based on the presence of different petrographic features: e-twinned calcite, calcite veins and replacement of chondrules by calcite grains [START_REF] Bunch | Carbonaceous chondrites-II. Carbonaceous chondrite phyllosilicates and light element geochemistry as indicators of parent body processes and surface conditions[END_REF][START_REF] Benedix | Carbonates in CM2 chondrites: constraints on alteration conditions from oxygen isotopic compositions and petrographic observations[END_REF][START_REF] Lee | Aragonite in the Murray (CM2) carbonaceous chondrite: implications for parent body compaction and aqueous alteration[END_REF][START_REF] Lindgren | Microstructure of calcite in the CM2 carbonaceous chondrite LON 94101: Implications for deformation history during and/or after aqueous alteration[END_REF][START_REF] Tyra | An oxygen isotope dichotomy in CM2 chondritic carbonates-A SIMS approach[END_REF][START_REF] Lee | Aragonite, breunnerite, calcite and dolomite in the CM carbonaceous chondrites: High fidelity recorders of progressive parent body aqueous alteration[END_REF]. Calcite veins show 16 O-rich isotopic compositions that suggest late precipitation from evolved solutions [START_REF] Lindgren | Fluid evolution in CM carbonaceous chondrites tracked through the oxygen isotopic compositions of carbonates[END_REF]. This assumption is consistent with a late carbonate precipitation event, during which the evolved fluid would have been mobilized from different region of the parent body or by dehydration of existing phyllosilicates [START_REF] Rubin | Collisional facilitation of aqueous alteration of CM and CV carbonaceous chondrites[END_REF]Lee et al., 2013). In addition, it has been proposed that impacts could create open fracture networks and microcracks in CM chondrites that would facilitate the circulation of fluids [START_REF] Decarli | Shock-induced compaction and porosity in meteorites[END_REF][START_REF] Rubin | Collisional facilitation of aqueous alteration of CM and CV carbonaceous chondrites[END_REF]. Impact-induced formation of fractures and/or cracks has been reported in shock experiments involving carbonaceous chondrites [START_REF] Nakamura | Impact-induced chondrule flattening in the Allende CV3 carbonaceous chondrite: Shock experiments[END_REF][START_REF] Tomeoka | Experimental shock metamorphism of the Murchison CM carbonaceous chondrite[END_REF][START_REF] Nakamura | Impact-Induced Textural Changes of CV Carbonaceous Chondrites: Experimental Reproduction[END_REF]. These experiments also highlighted the formation of foliation petrofabrics of the chondritic particles (i.e., chondrules, calcium-aluminum-rich refractory inclusions, clumps of tochilinite-cronstedtite intergrowths, olivine grains and flattened aggregates) and the flattening of chondrules with the increase in impact intensity [START_REF] Nakamura | Impact-induced chondrule flattening in the Allende CV3 carbonaceous chondrite: Shock experiments[END_REF][START_REF] Tomeoka | Experimental shock metamorphism of the Murchison CM carbonaceous chondrite[END_REF][START_REF] Nakamura | Impact-Induced Textural Changes of CV Carbonaceous Chondrites: Experimental Reproduction[END_REF]. Preferential orientations have been observed in CM and CV chondrites with different degrees of foliation intensity [START_REF] Rubin | Collisional facilitation of aqueous alteration of CM and CV carbonaceous chondrites[END_REF][START_REF] Lindgren | The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity impacts[END_REF][START_REF] Hanna | Impact-induced brittle deformation, porosity loss, and aqueous alteration in the Murchison CM chondrite[END_REF]. However, impact events are not the only processes able to create preferential orientation of particles; lithostatic compaction may also produce flattened chondrules and CAIs and crystallographic orientation of phyllosilicates and carbonates [START_REF] Fujimura | Preferred orientation of phyllosilicate [001] in matrix of Murchison meteorite and possible mechanisms of generating the oriented texture in chondrites[END_REF][START_REF] Cain | Structural deformation of the Leoville chondrite[END_REF][START_REF] Zolensky | CM chondrites exhibit the complete petrologic range from type 2 to 1[END_REF][START_REF] Lee | Aragonite in the Murray (CM2) carbonaceous chondrite: implications for parent body compaction and aqueous alteration[END_REF][START_REF] Lindgren | The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity impacts[END_REF]. This latter process was likely involved in the establishment of the CM and CV petrofabrics as attested by (i) the occurrence of preferential orientation in poorly altered CM chondrites without fractures and carbonate veins [START_REF] Lindgren | The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity impacts[END_REF][START_REF] Hanna | Impact-induced brittle deformation, porosity loss, and aqueous alteration in the Murchison CM chondrite[END_REF] and (ii) the lack of evidence for strong shock characteristics in some meteorites [START_REF] Scott | Shock metamorphism of carbonaceous chondrites[END_REF]. In addition, CM chondrites were probably highly porous prior to their deformation (i.e., 30-50%, [START_REF] Hanna | Impact-induced brittle deformation, porosity loss, and aqueous alteration in the Murchison CM chondrite[END_REF], allowing the impact energy to be dissipated from the collapse of the pore spaces [START_REF] Suttle | Shock fabrics in fine-grained micrometeorites[END_REF]. This inconsistency between a low shock-stage and evidence of compaction in CM chondrites [START_REF] Lindgren | The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity impacts[END_REF] highlights that the relationship between aqueous alteration and stress deformation remains poorly understood.

Most of the CM chondrites are breccias and exhibit clats with various degrees of aqueous alteration [START_REF] Rubin | Chondrules in the Murray CM2 meteorites and compositional differences between CM-CO and ordinary chondrite chondrules[END_REF][START_REF] Metzler | Accretionary dust mantles in CM chondrites: Evidence for solar nebula processes[END_REF][START_REF] Lindgren | Clasts in the CM2 carbonaceous chondrite Lonewolf Nunataks 94101: Evidence for aqueous alteration prior to complex mixing[END_REF][START_REF] Bischoff | Breccia classification of CM chondrites[END_REF]. These clasts provide important constraints on the post-accretionary alteration history and collisional activity of the CM chondrites [START_REF] Lindgren | Clasts in the CM2 carbonaceous chondrite Lonewolf Nunataks 94101: Evidence for aqueous alteration prior to complex mixing[END_REF]. A recent report of the carbonaceous chondrite Boriskino, a CM2 chondrite that fell in Russia in 1930, describes the presence of centimetric clasts with contains clasts with a variety of lithologies (Verdier-Paoletti et al., 2017b), suggesting that this chondrite may provide a good opportunity to better understand the link between aqueous alteration and the deformation history of the CM chondrites that is not well investigated yet. The present study therefore aims to (i) understand the preaccretional alteration history of CM chondrites by characterizing clasts in CM2 Boriskino that exhibit different degrees of alteration, (ii) retrace the isotopic evolution of the fluid from the O & C-isotopic composition of Ca-carbonates, and

(iii) identify the mechanisms that induced preferential orientation and aqueous alteration in CM chondrites. From a survey of two Boriskino polished sections, we adopt a multi-pronged approach composed of petrographic observations, preferential orientation measurements on chondritic particles, mineralogical identifications, and O and C-isotopic measurements on Cacarbonates. We focus our attention on bulk Boriskino samples by performing X-ray computed tomography to map flattening chondrules and measure their preferential orientation.

MATERIALS AND METHODS

2-1 SEM imaging, characterizations and petrofabric analyses

Petrographic observations of two polished sections of the Boriskino CM chondrites (#3788-3 and #3788-4) from the Muséum National d'Histoire Naturelle of Paris (MNHN) were made at the Centre de Recherches Pétrographique et Géochimiques (CRPG) using a scanning electron microscope (SEM) JEOL JSM-6510 equipped with an energy dispersive Xray detector (Bruker-AXS XFlash, silicon drift detector: SDD). The SEM observations were performed with a beam current of 3 nA at 15 kV. The entire two polished sections were mapped to produce the Back-Scattered Electron (BSE) mosaics. The modal abundance of phases for each lithology was determined from the BSE mosaics using JMicroVision software.

Using the BSE mosaics of the two polished sections, the petrofabric characteristics of each clast were determined following the method of [START_REF] Rubin | Collisional facilitation of aqueous alteration of CM and CV carbonaceous chondrites[END_REF]. In order to compare the median orientation of the petrofabrics within each polished section (i.e., #3788-4), we measured the tilt angle between an arbitrary reference (i.e., the horizontal = 0°) and the primary axis length of each particle (i.e., chondrule, TCI clump and olivine grain). The tilt angles were measured using Adobe Illustrator. We then estimated the standard deviation (c) of the petrofabric(s), the high maximum frequency (a) and the mean value of the Gaussian curve (b) for each clast using a Gaussian fit on the data set (

).

2-2 Raman spectroscopy

Raman spectra were collected using a LabRAM HR spectrometer (Horiba Johin Yvon) equipped with a 600 g.mm -1 grating and an Edge filter. The confocal hole aperture and slit aperture were 500 µm and 100 µm, respectively. The excitation beam was produced by a 457.94 nm blue laser at a power of ~20mW, focused on the sample using a ×100 LWD IR objective (Olympus). The number of accumulations and the acquisition time were 2x5s. The signal-to-noise ratio (S/N) was less than 1% of the signal. Calcite and aragonite were identified on the basis of their minor Raman bands; calcite has specific bands at 282 and 713 cm -1 while aragonite has bands at 207 and 704 cm -1 [START_REF] White | Laser Raman spectroscopy as a technique for identification of seafloor hydrothermal and cold seep minerals[END_REF].

2-3 Carbon and Oxygen isotopes

The two polished sections were initially coated with carbon to measure oxygen isotopes. Oxygen isotopic compositions of Ca-carbonates were measured using a CAMECA ims 1280 HR2 at CRPG (Nancy, France). 16 O -, 17 O -, and 18 O -ions produced by a Cs + primary ion beam (≈15 m spot size, 5 nA) were collected in multi-collection mode using three Faraday cups. A normal-incidence electron gun was used for charge compensation. In order to remove 16 OH -interference on the 17 O -peak and achieve maximum flatness on the top of the In order to avoid carbon contamination inherited from previous carbon coatings (i.e., after the SEM and O-isotopes), sample surfaces were polished with liquid cerium oxide and ultrasonically cleaned in ethanol for 5 min [START_REF] Hanon | High carbon concentrations in meteoritic chondrules: A record of metal-silicate differentiation[END_REF]. The samples were then coated with gold (≈ 50 nm) in preparation for carbon isotope analysis using a CAMECA ims 1280

HR2 ion microprobe at CRPG-CNRS (Nancy, France). A Cs + primary Gaussian beam of 5 nA was focused to produce a spot size of ≈ 20 m. A normal-incidence electron gun was used for charge compensation. The microprobe was specifically tuned to obtain a MRP of ≈ 5000 so that the 12 CH -contribution to 13 C could be eliminated. Typical measurement errors (2), which took into account the errors in each measurement as well as the external reproducibility of the standard, were estimated to be ≈ 0.8 ‰ for  13 C.

2-4 X-ray computed tomography (XCT)

A bulk sample of Boriskino with a mass of 328 mg was subjected to X-ray computed tomography (XCT) imaging to provide a full 3D dataset of the sample (Fig. 1a). The CT imaging was made on the AST-RX platform of the Muséum National d'Histoire Naturelle of Paris (MNHN) using a GE Sensing and Inspection Technologies Phoenix|x-ray v|tome|x L240-180 CT scanner. We used the microfocus RX source at 240 kV/320 W, detector 400 × 400 mm, with a matrix of 2024 pixels (pixel size: 200 × 200 microns). The settings parameters were as follows: voltage = 80 kV; current = 230 µA; exposure: 500 ms; and isotropic voxel size = 8 µm. Data were reconstructed using datos|x reconstruction software (Phoenix|x-ray, release 2.0), then exported into a 16-bit TIFF image stack of 1740 virtual slices in transverse view.

In the full 3D data set of the sample, the grey level of each slice corresponds to the Xray attenuation, which is related to density and the atomic number of the material. The darkest pixels represent the least attenuating material or the lowest density (e.g., matrix and chondrules) while the brightest pixels represent the most attenuating material or the highest density (e.g., metal and sulphide grains). Thus, based on the grey level of each image, we observed 61 elliptic dark-toned objects that we interpret as type I chondrules (Fig. 1b). We painted all voxels into these chondrules on each step of 5 slices for the biggest objects and on each slice for the smallest object with the Avizo TM software. Each chondrule was then modeled in 3D volume by interpolation of the painted voxels. Next, an ellipsoid was fitted to each chondrule by merit function using Blob3D software package (Ketcham, 2005a, Ketcham, 2005b). The orientation, axial length, aspect ratio and location of each ellipsoid were measured (Table 2). Plunges, trends and eigenvectors (v 1 , v 2 and v 3 ) of the raw data were calculated and plotted on a stereogram with Stereonet software from the direction cosines given by the Blob3D results. The eigenvalues (λ 1 , λ 2 and λ 3 ) were also determined in order to estimate whether the orientation of the ellipsoids were non-random and defined a petrofabric, according to the method of [START_REF] Woodcock | Randomness testing in three-dimensional orientation data[END_REF]. In this method, two parameters must be determined: (i) the shape parameter (K), which ranges from K = 0 (girdle distribution) to K >1 (cluster distribution); and (ii) the strength parameter (C), which ranges from C ≈ 0 (weak petrofabric) to C > 4 (strong petrofabric).

RESULTS

Petrography of Boriskino

The two polished sections of Boriskino are composed of millimeter-sized clasts in direct contact with each other, which can be distinguished by their petrography (Fig. 2). Among these clasts, we defined three lithologies (labeled 1 to 3) characterized by varying contents of (i) phyllosilicate, (ii) metallic iron, (iii) sulfide, and

(iv) different petrographic types of Ca-carbonates (Fig. 3, Table 1).

Lithology 1 is present in both sections of Boriskino and represents 88% and 24% of the sample's surface of section #3 and #4, respectively (Fig. 2a). This lithology is characterized by a moderate proportion of matrix and chondrules (≈ 60.15 vol.% and ≈ 30 vol.%, respectively), a high proportion of Fe-Ni sulphide grains (≈ 8.6 vol.%) and a low abundance of Ca-carbonates (≈ 1.2 vol.%) and metallic Fe-Ni (≈ 0.05 vol.%) (Table 1; Fig. 3a).

Lithology 2 is only present in section #4 and corresponds to 26% of the sample's surface, where it is found in two separated clasts. This lithology shows comparable proportions of matrix, chondrules and Ca-carbonate relative to lithology 1 (≈ 62.3 vol.%, ≈ 34.7 vol.% and ≈ 1.4 vol.%, respectively) but a lower proportion of Fe-Ni sulphide (1.6 vol.%) and a lack of Fe-Ni metal (Table 1; Fig. 3b). Lithology 3 is present in section #4 and represents 22% of the sample's surface, and possibly in section #3 although it is difficult to assess properly due to its low surface area (i.e., 5%, Fig. 2). This lithology differs from the others in that it is characterized by a high abundance of matrix and Ca-carbonate (≈ 68.5 vol.% and ≈ 2.4 vol.%, respectively). It has a similar proportion of chondrules to lithology 1 (≈ 23.9 vol.%), a moderate proportion of Fe-Ni sulphide (5.2 vol.%) and a high proportion of Fe-Ni metal (≈ 0.5 vol.%) (Table 1; Fig. 3c).

Ca-carbonate grains

Twenty Ca-carbonate grains were observed in the three different lithologies of Boriskino (Fig. 2). They mainly occur as calcite in all three lithologies (n = 17, Table 3), but a few grains of aragonite were also identified in lithology 3 (n = 4, Table 3) (Fig. 2 &4). Based on the mineralogical classification of CM carbonates [START_REF] Tyra | Terrestrial alteration of carbonate in a suite of Antarctic CM chondrites: Evidence from oxygen and carbon isotopes[END_REF][START_REF] Tyra | An oxygen isotope dichotomy in CM2 chondritic carbonates-A SIMS approach[END_REF][START_REF] Lee | Aragonite, breunnerite, calcite and dolomite in the CM carbonaceous chondrites: High fidelity recorders of progressive parent body aqueous alteration[END_REF][START_REF] Vacher | Petrographic and C & O isotopic characteristics of the earliest stages of aqueous alteration of CM chondrites[END_REF], they can be classified into two types:

(i) Type 1a grains, which are surrounded by a serpentine/tochilinite rim, and (ii) Type 2a grains, which have replaced primary minerals with inclusions of Fe-Ni sulphide inclusions.

Type 1a Ca-carbonates (represented in figures as green circles for calcite and diamonds for aragonite)

Type 1a Ca-carbonates (hereafter T1a) are scattered throughout the matrix of lithology 3 (Fig. 2a &2b). They mostly occur in the form of subhedral or anhedral single or polycrystalline grains with typical sizes in the range from a few tens to hundreds of micrometers (Fig. 4b). They are systematically partially or totally surrounded by a serpentine/tochilinite rim with an average thickness of a few micrometers (Fig. 4a &4b).

These rims show irregular boundaries at the contacts with the host-grains. The proportions of T1a calcite and aragonite grains are similar, with a fraction of ≈ 66% of calcite (n = 5) and ≈ 44% of aragonite (n = 4). T1a Ca-carbonates have  18 O values ranging from 29.8 to 36.8‰

(mean of 33.9‰,  = 2.4‰),  17 O values from 15.2 to 18.3‰ (mean of 16.7‰,  = 1‰) and variable  17 O values, ranging from -1.8 to -0.4‰ (mean of -1‰,  = 0.4‰) (Fig. 5, Table 3).

Significant variation in C isotopes is also observed, with  13 C values between 18.3 and 91.8‰

(mean of 55.8‰,  = 25.7‰).

Type 2a calcites (red circles in figures)

The Type 2a calcites (hereafter T2a) were all found in lithologies 1 and 2, with the exception of grain CC16, which was in lithology 3 (Fig. 2, Table 3). They occur as polycrystalline grains of hundreds of micrometers in size containing Fe-Ni sulphide inclusions of a few tens of micrometers in size (Fig. 4c). According to their location and morphology, T2a calcites can be divided into two groups: (i) polycrystalline aggregates located in the matrix, exhibiting phyllosilicate and a high proportion of Fe-Ni sulphide (Fig. 3). T2a calcites have variable C-isotopic compositions with  13 C values ranging from 30 to 70.7‰ (mean of 50.1‰,  = 12.4‰) (Fig. 6, Table 3).

Veins of calcite (blue triangles in figures)

Calcite veins were only identified in lithology 1 (in the #3, Fig. 2a) where they occur as polycrystalline grains of hundreds of micrometers in length and tens of micrometers in width (Fig. 4d). These veins are in direct contact with the matrix, are free of phyllosilicate, and can contain micrometer-sized Fe-Ni sulphide inclusions. Due to their irregular form and their low thickness, only one successful O-isotopic measurement was carried out, revealing a  18 O value of 16.9‰ (2 = 0.6‰), a  17 O value of 6.7‰ (2 = 0.5‰) and a  17 O value of -2‰ (2 = 0.7‰). Unfortunately, no C-isotopic composition was successfully measured due to the narrow width of the veins.

Petrofabric analyses and aspect ratio of type I chondrules

Polished sections

Lithology 1 in section #3 contains several sets of ~200-300 µm fractures and ~100-200 µm veins of calcite orientated in planes near the petrofabric plane (i.e., within 30° of the median azimuth), but also randomly oriented (Fig. 8a). Lithologies 1 and 3 in section #3 define a strong petrofabric with 46% and 41%, respectively, of the particle long-axes within 10° of the median azimuth (Fig. 8a &8d). In contrast, lithologies 1 and 2 in section #4 express a weak petrofabric with 26% and 21%, respectively, of the particle long-axes within 10° of the median azimuth (Fig. 8b &8c).

Bulk Boriskino

The orientation of the primary (R1) and tertiary (R3) axis lengths of 61 elliptic type I chondrules were plotted on stereonets in order to determine their degree of preferred alignment (Fig. 9a &9b). According to the method of [START_REF] Woodcock | Randomness testing in three-dimensional orientation data[END_REF], the primary ellipsoid axis orientations of type I chondrules have a girdle distribution, with a shape parameter (K) of 0.6 and a moderately weak foliation fabric strength, with a strength parameter (C) of 1.3 (Fig. 9a). The R3 ellipsoid axis orientations of type I chondrules have a cluster distribution, with a shape parameter (K) of 1.9 and a moderately weak foliation fabric strength, with a strength parameter (C) of 1.3 (Fig. 9b). Both sample distributions are nonrandom at the 99% confidence level (S 1 /S 3 = 3.77 and S 1 /S 3 = 3.61 for R1 and R3, respectively; [START_REF] Woodcock | Randomness testing in three-dimensional orientation data[END_REF]. The diameters and volumes of best-fit chondrule ellipsoids are variable and range from ~82 to 531 µm (primary axis length) and from 2 to 213 µm 2 , respectively (Table 2). Their aspect ratios are also heterogeneous, ranging from 1.11 to 3.34 (mean value of 1.87,  = 0.46, with a mean and occur as small subhedral grains dispersed throughout the matrix of lithology 3 (Fig. 5, Table 2). In contrast, the T2a grains and calcite veins in lithologies 1 and 2 exhibit 16 O-rich compositions compared to T1a grains (mean  18 O and  17 O values of 19‰ and 7.4‰ respectively, Fig. 5, Table 2). Some of the T2a calcites were observed in association with olivine grains and phyllosilicates located within chondrules that are surrounded by FGRs (Fig. 7a [START_REF] Clayton | Oxygen isotope studies of carbonaceous chondrites[END_REF]. In addition, the trend defined by the Boriskino Ca-Carbonates is, within error, parallel to the CM Water line (i.e., 0.69, Verdier-Paoletti et al., 2017a), and thus supports a mean carbonate precipitation temperature of ≈110°C. However, this isotopic exchange model does not exclude the possibility that small temperature variations could have occurred during the course of alteration, generating a shift in carbonate O-isotopic compositions along a slope of 0.52 for a given degree of isotopic exchange (Fig. 10). In such a scenario, the 16 O-poor population of Ca-carbonates would have precipitated early in Boriskino's alteration history, while the 16 Orich population would have formed later from more evolved fluids [START_REF] Fujiya | Oxygen and carbon isotopic ratios of carbonates in the Nogoya CM chondrite[END_REF]. These two stages of precipitation are also supported by (i) the identification of several aragonite grains in population 1 (Fig. 4a)aragonite is expected to have predated calcite in some other least altered CM chondrites [START_REF] Sofe | The oldest carbonate minerals on Earth: Insights into the early history of the Solar System[END_REF][START_REF] Lee | The oxygen isotope evolution of parent body aqueous solutions as recorded by multiple carbonate generations in the Lonewolf Nunataks 94101 CM2 carbonaceous chondrite[END_REF][START_REF] Lee | Aragonite, breunnerite, calcite and dolomite in the CM carbonaceous chondrites: High fidelity recorders of progressive parent body aqueous alteration[END_REF][START_REF] Lindgren | Fluid evolution in CM carbonaceous chondrites tracked through the oxygen isotopic compositions of carbonates[END_REF][START_REF] Vacher | Petrographic and C & O isotopic characteristics of the earliest stages of aqueous alteration of CM chondrites[END_REF], and (ii) the occurrence of chondrule-hosted calcite in population 2calcites which are frequently found in other highly altered CM chondrites and are inferred to have formed under extensive episodes of aqueous alteration [START_REF] Tyra | An oxygen isotope dichotomy in CM2 chondritic carbonates-A SIMS approach[END_REF][START_REF] Lee | The oxygen isotope evolution of parent body aqueous solutions as recorded by multiple carbonate generations in the Lonewolf Nunataks 94101 CM2 carbonaceous chondrite[END_REF][START_REF] Lee | Aragonite, breunnerite, calcite and dolomite in the CM carbonaceous chondrites: High fidelity recorders of progressive parent body aqueous alteration[END_REF][START_REF] Fujiya | Oxygen and carbon isotopic ratios of carbonates in the Nogoya CM chondrite[END_REF]. Determining the sequence of precipitation of Boriskino's Cacarbonates within each population is difficult to assess however. T1a calcites and aragonites are commonly surrounded by Fe-, S-and Si-rich phyllosilicates (Fig. 4a &4b), suggesting that the precipitation of T1a Ca-carbonates predates the formation of phyllosilicates, as already observed in other CM chondrites [START_REF] Browning | On the Origin of Rim Textures Surrounding Carbonate Grains in CM Matrices[END_REF][START_REF] Lee | The oxygen isotope evolution of parent body aqueous solutions as recorded by multiple carbonate generations in the Lonewolf Nunataks 94101 CM2 carbonaceous chondrite[END_REF][START_REF] Fujiya | Oxygen and carbon isotopic ratios of carbonates in the Nogoya CM chondrite[END_REF][START_REF] Pignatelli | Mineralogical, crystallographic and redox features of the earliest stages of fluid alteration in CM chondrites[END_REF][START_REF] Pignatelli | Cronstedtite polytypes in the Paris meteorite[END_REF][START_REF] Vacher | Petrographic and C & O isotopic characteristics of the earliest stages of aqueous alteration of CM chondrites[END_REF]. Nevertheless, our isotopic and petrographic results do not allow us to discriminate the formation sequence of T1a calcite and aragonite (Fig. 5 & 6; Table 3). In population 2, the T2a calcites were identified in lithologies 1 and 2. These lithologies exhibit high proportions of phyllosilicates compared to lithology 3 (Table 1) and show systematic evidence of mafic silicate replacement by serpentine (Fig. 3a, 3b and7). To the contrary, T2a calcites and calcite veins have not been affected by phyllosilicate replacement, as demonstrated by the absence of serpentine rims around these grains (Fig. 4c, 4d and7). Taken together, these results indicate that T2a and veins of calcite precipitated after the formation of phyllosilicates. However, based on our results, no order of precipitation for T2a grains and calcite veins can be inferred. 4.2 A complex deformation history arising from high pressure impact(s) Our 2D measurements of aligned particles in the three lithologies of Boriskino confirmed that lithologies 1 (section #3) and 3 define a strong petrofabric whereas lithologies 1 (section #4) and 2 exhibit a weak petrofabric (Fig. 8). Conceptually, it might appear surprising that, from one section to another, the level of aligned particles can show dramatically different values within a given lithology. However, similar results have already been reported from SEM-BSE images of several faces of a 3D block of Murchison [START_REF] Lindgren | The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity impacts[END_REF].

Significant differences in the level of chondrule alignment were reported, based on the orientation of the sides of the block (20%, 40% and 50% of chondrule long axes within 10° of the median azimuth for +z, -y and +x sides, respectively; [START_REF] Lindgren | The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity impacts[END_REF]. Because the Boriskino lithology 1 occurs in two different sections, clasts from lithology 1 could show different spatial orientations, depending on their location on the sample or the orientation of the section cutting and thus, display varying petrographic intensities. Nevertheless, the strongest fabric value measured in lithology 1 (i.e., 46%, Fig. 8a) is probably the one with the closest value to the actual maximum. Consequently, we assume that lithology 1 defines a strong petrofarbic despite variations of its particle orientations.

The 3D bulk analyses of type 1 chondrules revealed that Boriskino exhibits a moderately weak foliation fabric (C = 1.3) and a high degree of chondrule flattening (1.87 ± 0.46). This result is consistent with the two XCT studies of Murchison that showed moderately weak petrofabric (R1) and high aspect ratio (C = 1.46, aspect ratio = 1.75 ± 0.39, [START_REF] Lindgren | The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity impacts[END_REF]; C = 1.02, aspect ratio = 1.54 ± 0.22, [START_REF] Hanna | Impact-induced brittle deformation, porosity loss, and aqueous alteration in the Murchison CM chondrite[END_REF]. A large number of studies have reported chondrule flattening and/or occurrence of petrofabrics in (i) ordinary chondrites (hereafter OCs) [START_REF] Cain | Structural deformation of the Leoville chondrite[END_REF][START_REF] Stöffler | Shock metamorphism of ordinary chondrites[END_REF][START_REF] Scott | Shock metamorphism of carbonaceous chondrites[END_REF][START_REF] Gattacceca | An impact origin for the foliation of chondrites[END_REF][START_REF] Rubin | Flattened chondrules in the LAP 04581 LL5 chondrite: Evidence for an oblique impact into LL3 material and subsequent collisional heating[END_REF], (ii) CV chondrites [START_REF] Nakamura | Impact-Induced Textural Changes of CV Carbonaceous Chondrites: Experimental Reproduction[END_REF][START_REF] Watt | Fabric analysis of Allende matrix using EBSD[END_REF][START_REF] Rubin | Collisional facilitation of aqueous alteration of CM and CV carbonaceous chondrites[END_REF] (iii) fined-grained micrometeorites (hereafter FgMMs) [START_REF] Suttle | Shock fabrics in fine-grained micrometeorites[END_REF] and (iv) CM chondrites [START_REF] Tomeoka | Experimental shock metamorphism of the Murchison CM carbonaceous chondrite[END_REF][START_REF] Rubin | Collisional facilitation of aqueous alteration of CM and CV carbonaceous chondrites[END_REF][START_REF] Lindgren | The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity impacts[END_REF][START_REF] Hanna | Impact-induced brittle deformation, porosity loss, and aqueous alteration in the Murchison CM chondrite[END_REF]. Chondrule flattening or petrofabrics are generally interpreted to be the result of impact-induced preferential orientations [START_REF] Sneyd | Origin of Petrofabrics and Magnetic Anisotropy in Ordinary Chondrites[END_REF][START_REF] Stöffler | Shock metamorphism of ordinary chondrites[END_REF][START_REF] Scott | Shock metamorphism of carbonaceous chondrites[END_REF][START_REF] Tomeoka | Experimental shock metamorphism of the Murchison CM carbonaceous chondrite[END_REF][START_REF] Nakamura | Impact-Induced Textural Changes of CV Carbonaceous Chondrites: Experimental Reproduction[END_REF][START_REF] Gattacceca | An impact origin for the foliation of chondrites[END_REF]Rubin and Swindel, 2011;[START_REF] Rubin | Collisional facilitation of aqueous alteration of CM and CV carbonaceous chondrites[END_REF][START_REF] Lindgren | The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity impacts[END_REF][START_REF] Hanna | Impact-induced brittle deformation, porosity loss, and aqueous alteration in the Murchison CM chondrite[END_REF][START_REF] Forman | Hidden secrets of deformation: Impact-induced compaction within a CV chondrite[END_REF][START_REF] Suttle | Shock fabrics in fine-grained micrometeorites[END_REF] rather than a consequence of lithostatic compaction [START_REF] Martin | Preferred chondrule orientations in meteorites[END_REF]Fujimara et al., 1983;[START_REF] Cain | Structural deformation of the Leoville chondrite[END_REF][START_REF] Zolensky | CM chondrites exhibit the complete petrologic range from type 2 to 1[END_REF][START_REF] Lee | Aragonite in the Murray (CM2) carbonaceous chondrite: implications for parent body compaction and aqueous alteration[END_REF]. Shock metamorphism evidence in OCs was used to propose a comprehensive petrographic classification of their degree of shock (S1 to S6, [START_REF] Stöffler | Shock metamorphism of ordinary chondrites[END_REF]. Based on shock classification, [START_REF] Gattacceca | An impact origin for the foliation of chondrites[END_REF] demonstrated a relationship between the anisotropy of magnetic susceptibility (AMS) and the silicates's shock features in OCs. Collisional evidence was also reported in CV chondrites with (i) the occurrence of S3-S4 petrofabrics [START_REF] Rubin | Collisional facilitation of aqueous alteration of CM and CV carbonaceous chondrites[END_REF] and shock features in olivine and pyroxene grains [START_REF] Nakamura | Shock effects of the Leoville CV carbonaceous chondrite: a transmission electron microscope study[END_REF] and (ii) a strong anticorrelation between their porosity content and their level of shock stage [START_REF] Gattacceca | An impact origin for the foliation of chondrites[END_REF]. More recently, the study of a large number of micrometeorites showed that around 40-80% of FgMMs display petrofabrics, biaxial fabrics and brittle deformation features, indicating that at least some fabrics are impacted at shock pressures > 0.08 GPa. [START_REF] Suttle | Shock fabrics in fine-grained micrometeorites[END_REF]. Based on oxygen isotopic compositions as well as textural and geochemistry features, it appears that micrometeorites are related to CM chondrites [START_REF] Kurat | Petrology and geochemistry of Antarctic micrometeorites[END_REF][START_REF] Brownlee | The elemental composition of stony cosmic spherules[END_REF][START_REF] Genge | The textures and compositions of finegrained Antarctic micrometeorites: Implications for comparisons with meteorites[END_REF][START_REF] Suavet | Identification of the parent bodies of micrometeorites with high-precision oxygen isotope ratios[END_REF][START_REF] Gounelle | Small Antarctic micrometeorites: A mineralogical and in situ oxygen isotope study[END_REF]. Although CM chondrites contain shock compaction features similar to FgMMs, [START_REF] Lindgren | Microstructure of calcite in the CM2 carbonaceous chondrite LON 94101: Implications for deformation history during and/or after aqueous alteration[END_REF][START_REF] Rubin | An American on Paris: extent of aqueous alteration of a CM chondrite and the petrography of its refractory and amoeboid olivine inclusions[END_REF][START_REF] Rubin | Collisional facilitation of aqueous alteration of CM and CV carbonaceous chondrites[END_REF][START_REF] Hanna | Impact-induced brittle deformation, porosity loss, and aqueous alteration in the Murchison CM chondrite[END_REF], they do not contain high grade shock features (i.e., > S1-S2; [START_REF] Scott | Shock metamorphism of carbonaceous chondrites[END_REF]. This contradiction might be related to the capability of porous CMs to absorb and dissipate impact energy due to collapse of the pore space [START_REF] Suttle | Shock fabrics in fine-grained micrometeorites[END_REF]. A such process has been demonstrated in Murchison with (i) the observation of squeezed chondrules resulting from a component of noncoaxial shear induced by impact and (ii) the loss of ≈10-31% of chondrule bulk porosity after shock compactions [START_REF] Hanna | Impact-induced brittle deformation, porosity loss, and aqueous alteration in the Murchison CM chondrite[END_REF]. In Boriskino, we also observed squeezed chondrules within lithology 1 (#4, Fig. 7c). Other evidence of impact-induced CM petrofabrics has been highlighted in different studies, including the regolith-brecciated nature of CMs [START_REF] Metzler | Accretionary dust mantles in CM chondrites: Evidence for solar nebula processes[END_REF][START_REF] Rubin | Collisional facilitation of aqueous alteration of CM and CV carbonaceous chondrites[END_REF] and multiple episodes of deformation recorded by a calcite vein in the LON 94101 CM [START_REF] Lindgren | Microstructure of calcite in the CM2 carbonaceous chondrite LON 94101: Implications for deformation history during and/or after aqueous alteration[END_REF]. Shock recovery-experiments were performed on CM2 and CV3 chondrites and successfully reproduced the flattened shapes of chondrules and their petrofabrics [START_REF] Nakamura | Impact-induced chondrule flattening in the Allende CV3 carbonaceous chondrite: Shock experiments[END_REF][START_REF] Nakamura | Impact-Induced Textural Changes of CV Carbonaceous Chondrites: Experimental Reproduction[END_REF][START_REF] Tomeoka | Experimental shock metamorphism of the Murchison CM carbonaceous chondrite[END_REF]. These experiments were carried out at various peak pressure intensities on Murchison (4-49 GPa) and Allende (11-21GPa) and demonstrated a good correspondence between the aspect ratio of CM and CV chondrules and impact pressures (Fig. 11). From these experimental correlations, it is possible to quantitatively estimate the intensity of a single impact that induced the chondrule aspect ratio in Boriskino.

The mean XCT chondrule aspect ratio of 1.87 ± 0.46 (Table 2) corresponds to impacts with intensities ranging from 18 to > 30 GPa and 8-31 GPa, taking into account the experiment results obtained on Murchison and Allende, respectively (Fig. 11; [START_REF] Tomeoka | Experimental shock metamorphism of the Murchison CM carbonaceous chondrite[END_REF][START_REF] Nakamura | Impact-Induced Textural Changes of CV Carbonaceous Chondrites: Experimental Reproduction[END_REF]. They are consistent with those determined in the CMs MET 01072, Murchison and LAP 031166 [START_REF] Lindgren | The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity impacts[END_REF][START_REF] Hanna | Impact-induced brittle deformation, porosity loss, and aqueous alteration in the Murchison CM chondrite[END_REF] (Fig. 11). Taken together, our results suggest that some of the CMs probably underwent high intensity impacts.

Nevertheless, shock pressure estimations should be treated with caution as they represent the effect of only a single impact on the parent body. Because Boriskino represents the final assemblage of several clasts of different lithology and deformation degree, it seems unlikely that each clast experienced the same collisional history. In addition, the pressure estimates determined from shock-recovery experiments on Murchison suggest a high intensity of shock pressure, with pressures that may have exceeded 30 GPa and which should have induced melting of the matrix and chondrules [START_REF] Tomeoka | Experimental shock metamorphism of the Murchison CM carbonaceous chondrite[END_REF]. However, no evidence for melting has been observed in Boriskino.

To summarize, there are several lines of evidence for shock features in Boriskino, including (i) a strong 2D petrofabric in different lithologies, (ii) flattened chondrules, (iii) calcite veins and fractures subparallel to the petrofabric, (iv) squeezed chondrules, and (v) millimeter clasts of various petrographies in direct contact with each other. Based on these observations, we suggest that some of the clasts that make up the Boriskino meteorite (i.e., clasts composed of lithologies 1 and 2) were subjected to high intensity impact(s) (i.e., 10-30 GPa) that produced petrofabrics, chondrule flattening, and fractures.

Relationship between aqueous alteration and impacts

Understanding the relative timing between deformation and aqueous alteration in chondrites is crucial, because it can provide constraints on the conditions of parent-body alteration [START_REF] Brearley | The action of water[END_REF]. It is commonly accepted that aqueous alteration of CM chondrites took place on their parent body(-ies) due to heat released by the decay of 26 Al [START_REF] Dufresne | On the chemical evolution of the carbonaceous chondrites[END_REF][START_REF] Zolensky | CM chondrites exhibit the complete petrologic range from type 2 to 1[END_REF]. Shock compaction has also been advanced as a principal alteration process in CM chondrites [START_REF] Greenwood | Formation and alteration of CAIs in Cold Bokkeveld (CM2)[END_REF][START_REF] Rubin | Collisional facilitation of aqueous alteration of CM and CV carbonaceous chondrites[END_REF][START_REF] Lindgren | The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity impacts[END_REF][START_REF] Hanna | Impact-induced brittle deformation, porosity loss, and aqueous alteration in the Murchison CM chondrite[END_REF]. Based on a strong correlation between the degree of alteration and the intensity of impact compaction (Fig. 12), [START_REF] Rubin | Collisional facilitation of aqueous alteration of CM and CV carbonaceous chondrites[END_REF] proposed that random collisions may induce the formation of fractures and favor the mobilization of liquid water by dehydration of phyllosilicates or the melting of ice. This is also supported by the occurrence of dolomite veins with similar orientation to their respective petrofabrics in the highly altered CM2 QUE 93005 and CM1 SCO 06043 [START_REF] Lindgren | The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity impacts[END_REF]. Other reported petrographic evidence for impact-induced alteration includes (i) serpentine veins parallel to the foliation fabric in Murchison [START_REF] Hanna | Impact-induced brittle deformation, porosity loss, and aqueous alteration in the Murchison CM chondrite[END_REF] and (ii) millimeter lenses rich in phyllosilicates, Nibearing sulfide and Ca-phosphate grains subparallel to fractures and elongated chondrules in the CM1 MET 01070 [START_REF] Rubin | Progressive aqueous alteration of CM carbonaceous chondrites[END_REF][START_REF] Lee | Extended chronologies of aqueous alteration in the CM2 carbonaceous chondrites: Evidence from carbonates in Queen Alexandra Range 93005[END_REF]. The latter suggests the precipitation of secondary minerals from transported fluid in preexisting fractures [START_REF] Rubin | Collisional facilitation of aqueous alteration of CM and CV carbonaceous chondrites[END_REF]. In Boriskino, lithologies 1 and 2 exhibit petrographic features consistent with a high degree of alteration (i.e., petrologic subtype expected to be 2.1) as demonstrated by the (i) partial alteration of mafic silicates into chondrules (Fig. 3a &3b), (ii) low metallic Fe-Ni content (≤ 0.05 vol.%, Table 1) and (iii) occurrence of 16 O-rich T2a grains (Fig. 5a, [START_REF] Rubin | Collisional facilitation of aqueous alteration of CM and CV carbonaceous chondrites[END_REF]. Lithologies 1 and 2 also define strong and weak petrofabrics (i.e., 26 and 46% for lithology 1, respectively, Fig. 8a andb) that probably result from different spatial orientations (also expected for the lithology 2 due to its weak petrofabric) and/or separate section's positions on the cutting plane. However, considering the strongest fabric measured as the closest value to the actual maximum (i.e., 41%, Fig. 8a), the relationship between degree of alteration vs strength of the petrofabric for the lithology 1 is consistent with the correlation defined by [START_REF] Rubin | Collisional facilitation of aqueous alteration of CM and CV carbonaceous chondrites[END_REF] and thus favour models of impact-induced alteration (Fig. 12). In addition, the occurrence of large calcite veins subparallel to the petrofabric (Fig 4a and8a) and the replacement of primary elongated chondrules by T2a calcite (Fig. 7a &b) also support this type of alteration process. For the lithology 2, the lack of calcite vein and the weak intensity of its fabric are more problematic, but according to petrographic observations (i.e., T2a grains and replacement of elongated chondrules), we assumed similar alteration process than for the lithology 1.

In contrast, lithology 3 presents characteristics consistent with a lower degree of alteration (i.e., presumed to be petrologic subtype 2.5-2.6; [START_REF] Rubin | An American on Paris: extent of aqueous alteration of a CM chondrite and the petrography of its refractory and amoeboid olivine inclusions[END_REF], due to: (i) unaltered mafic silicates into chondrules (Fig. 3c), (ii) a significant abundance of Fe-Ni metal beads (i.e., ~0.5 vol.%, Table 1) and (iii) the presence of 16 O-poor T1a calcite and aragonite. Furthermore, lithology 3 does not show any petrographic features characteristics of impact-induced fluid circulation within fractures (e.g., vein of carbonate). Instead, this lithology appears to contain undistorted Ca-carbonates wrapped by phyllosilicates (Fig. 13a), stretched clumps of phyllosilicates, and elongate sulphide grains parallel to the petrofabric (Fig. 13b). These observations suggest that secondary minerals precipitated before the formation of the petrofabric and that aqueous alteration predates the deformation. Furthermore, by reporting the petrofabric intensity (i.e., 41%) as function of the expected CM subtype of the lithology 3 (Fig. 12), it is observed that the percentage of particles with long axes within 10° is to high compared to the predicted value from the correlation of Rubin (2012) (i.e., ≈ 15%, Fig. 12).

The strong petrofabric observed in the lithology 3 probably results on later episodes of deformation that have not affected alteration but only increased the preferential orientation of particles in the lithology 3 (Fig. 12).

Our results demonstrate that Boriskino is a clastic polymict breccia, composed of various lithologies, in direct contact with each other, that display different degrees of alteration and deformation histories. Based on our petrographic and isotopic results, we propose a deformation and alteration history for Boriskino based on a single CM parent body, where the different clasts of the breccia chondrite come from different regions of the asteroid (Fig. 14a) [START_REF] Scott | Chondrules and other components in C, O, and E chondrites: Similarities in their properties and origins[END_REF][START_REF] Lindgren | Clasts in the CM2 carbonaceous chondrite Lonewolf Nunataks 94101: Evidence for aqueous alteration prior to complex mixing[END_REF]. At time t 1 in our scenario, aqueous alteration processes were initiated through the melting of ice induced by 26 Al decay within the parent body (Fig. 14a). Hence, the 16 O-poor primitive fluid interacts with the 16 O-rich anhydrous components of the parent body to precipitate isolated aragonite and calcite grains in the matrix as observed in lithology 3. Then, as alteration progresses, the chemical composition of the fluid changes, stopping the precipitation of T1 carbonate and initiating phyllosilicate formation. We do not exclude the possibility that these events occurred in lithologies 1 and 2 as well, but to date, no evidence for these events has been observed. Next, at time t 2 , one or several high intensity impacts induced the formation of fractures and petrofabrics and the stretching of chondrules, principally in lithologies 1 and 2 due to their location close to the impact zone (Fig. 14b). Subsequently, at time t 3 , the establishment of cracks and fractures favored the circulation of evolved 16 O-rich fluids within the parent body (Fig. 14c). This late fluid flow would have allowed the formation of phyllosilicate and T2 carbonate in chondrules and the precipitation of veins of calcite in fractures (Fig. 14c). Finally, at time t 4 , a new episode of low intensity impact(s) generated the release of all Boriskino's clasts from their initial locations, making possible the mixing of the different altered lithologies together to form the clastic polymict breccia Boriskino (Fig. 14d).

Carbon and oxygen isotopes

The in situ δ 13 C-δ 18 O compositions of Ca-carbonates in Boriskino are consistent with those reported in other CM carbonates (Fig. 15; [START_REF] Fujiya | Comprehensive study of carbon and oxygen isotopic compositions, trace element abundances, and cathodoluminescence intensities of calcite in the Murchison CM chondrite[END_REF][START_REF] Fujiya | Oxygen and carbon isotopic ratios of carbonates in the Nogoya CM chondrite[END_REF][START_REF] Tyra | Episodic carbonate precipitation in the CM chondrite ALH 84049: An ion microprobe analysis of O and C isotopes[END_REF][START_REF] Telus | In situ analyses of carbonate and magnetite in CM1 chondrites[END_REF][START_REF] Vacher | Petrographic and C & O isotopic characteristics of the earliest stages of aqueous alteration of CM chondrites[END_REF]. Our results show that Boriskino's Ca-carbonates exhibit two different populations with distinct  18 O values and significant variations in  13 C values (i.e.,  18 O ≈ 35‰,  13 C ≈ 20-90 ‰ and  18 O ≈ 20‰,  13 C ≈ 30-70‰ for T1a and T2a, respectively). Furthermore, these Ca-carbonates do not show positive or negative δ 13 C-δ 18 O correlations, whether for all the dataset or within each population (Fig. 15). Because the fractionation factor of C isotopes between calcite and HCO 3 -in the fluid is small at 0-300°C (i.e., 1000lnα calcite-HCO3-≈ 1-2 ‰; [START_REF] Deines | Stable carbon isotope ratios and the existence of a gas phase in the evolution of carbonate ground waters[END_REF][START_REF] Luo | Transmission of δ 13C signals and its paleoclimatic implications in Liangfeng Cave system of Guizhou Province, SW China[END_REF], the δ 13 C values of Ca-carbonates are useful for (i) tracking the source of carbon involved in their precipitation [START_REF] Grady | The carbon and oxygen isotopic composition of meteoritic carbonates[END_REF][START_REF] Alexander | Carbonate abundances and isotopic compositions in chondrites[END_REF][START_REF] Fujiya | Comprehensive study of carbon and oxygen isotopic compositions, trace element abundances, and cathodoluminescence intensities of calcite in the Murchison CM chondrite[END_REF][START_REF] Vacher | Petrographic and C & O isotopic characteristics of the earliest stages of aqueous alteration of CM chondrites[END_REF]

identifying fractionation mechanisms, such as equilibrium or kinetic isotope fractionation (e.g., production of CH 4 or loss of C-bearing gas from the fluid during serpentinization or degassing events, respectively; [START_REF] Guo | Temperatures of aqueous alteration and evidence for methane generation on the parent bodies of the CM chondrites[END_REF][START_REF] Fujiya | Oxygen and carbon isotopic ratios of carbonates in the Nogoya CM chondrite[END_REF][START_REF] Telus | In situ analyses of carbonate and magnetite in CM1 chondrites[END_REF].

The C and O-isotopic compositions of Boriskino's Ca-carbonates can be explained in numerous ways. Their δ 13 C-δ 18 O values can be reproduced by the equilibration of a CO gas (δ 13 C CO = -33‰) with different mole fraction of CO 2 in a 16 O-rich aqueous fluid (δ 18 O = 5‰) at low temperature (≈ 0-30°C and ≈ 80-120°C for T1a and T2a, respectively; [START_REF] Alexander | Carbonate abundances and isotopic compositions in chondrites[END_REF] (Fig. 16a). They can also be the result from different fluids derived from variable Oisotopic equilibration and contributions of different 12 C-and 13 C-rich water-soluble organic compounds (SOM) which demonstrated similar range of δ 13 C values (i.e., -10 to 60‰, Fig. 16a, [START_REF] Vacher | Petrographic and C & O isotopic characteristics of the earliest stages of aqueous alteration of CM chondrites[END_REF]. However, these two models consider a closed-system alteration without the escape of C-bearing species. As demonstrated by our petrographic results, T2a calcites occur in lithologies that have probably undergone multiple episodes of shock compactions causing the formation of cracks and fractures. Under such conditions, the closedsystem is merely an approximation; highly diffusive gas such as C-bearing molecules (e.g., CO 2 or CH 4 ) likely escaped rapidly from the shocked regions. Such a process has been put forward to explain the occurrence of two distinct isotopic groups of calcite in CM MET 01070, characterized by (i) high δ 18 O and variable δ 13 C compositions, and (ii) low δ 18 O and high δ 13 C values (Fig. 15; [START_REF] Telus | In situ analyses of carbonate and magnetite in CM1 chondrites[END_REF]. The authors interpreted this shift in δ 13 C values as the result of a venting event, in agreement with the petrographic evidence of fluid flow in MET 01070 [START_REF] Rubin | Progressive aqueous alteration of CM carbonaceous chondrites[END_REF]. Based on a negative δ 13 C-δ 18 O correlation observed in CM carbonates, it has been also proposed that carbonate precipitation was accompanied by the production of 13 C-depleted CH 4 and its escape from the CM parent body [START_REF] Guo | Temperatures of aqueous alteration and evidence for methane generation on the parent bodies of the CM chondrites[END_REF]. However, as highlight in terrestrial environment, abiotic methane is not produced directly by serpentinization, but through the reduction of various C-bearing (e.g., CO, CO 2 or

In CM chondrites, H 2 is believed to form during the serpentinization of olivine/pyroxene minerals [START_REF] Pignatelli | Mineralogical, crystallographic and redox features of the earliest stages of fluid alteration in CM chondrites[END_REF] and/or the corrosion of kamacite grains [START_REF] Palmer | Aqueous alteration of kamacite in CM chondrites[END_REF]. Reaction kinetics of FTT or Sabatier processes are theoretically much efficient at high temperature than at lower temperatures (<100ºC). Nevertheless, CH 4 production could be significant at low temperature due to the action of different catalyses, such as chromite, magnetite or Fe-Ni alloys [START_REF] Horita | Abiogenic methane formation and isotopic fractionation under hydrothermal conditions[END_REF][START_REF] Foustoukos | Hydrocarbons in hydrothermal vent fluids: the role of chromium-bearing catalysts[END_REF] which occur in CM chondrites [START_REF] Brearley | The action of water[END_REF][START_REF] Hewins | The Paris meteorite, the least altered CM chondrite so far[END_REF].

Because T2a calcites have precipitated after the formation of fractures and petrofabrics in the lithologies 1 and 2, we propose that the variability in the δ 13 C values can reflects the release of 13 C-depleted CH 4 produced by FFT or Sabatier reactions through cracks induced by high intensity impact(s). We also considered that escape of CH 4 has been limited for T1a carbonates because they probably formed prior serpentine [START_REF] Lee | Aragonite, breunnerite, calcite and dolomite in the CM carbonaceous chondrites: High fidelity recorders of progressive parent body aqueous alteration[END_REF][START_REF] Vacher | Petrographic and C & O isotopic characteristics of the earliest stages of aqueous alteration of CM chondrites[END_REF] and thus, they are no include in the model. Furthermore, escape of CO 2 is not taking account in this model, because carbon dioxide is preferentially release in acid environment (e.g., at pH = 4-6 in terrestrial evaporating Dead Sea brines, [START_REF] Stiller | Extreme carbonisotope enrichments in evaporating brines[END_REF] whereas alteration in CM chondrites appears to occur in alkaline environment [START_REF] Palmer | Aqueous alteration of kamacite in CM chondrites[END_REF][START_REF] Zolotov | Formation of brucite and cronstedtite-bearing mineral assemblages on Ceres[END_REF][START_REF] Pignatelli | Multiple precursors of secondary mineralogical assemblages in CM chondrites[END_REF]2017). Assuming an aqueous fluid with dissolved HCO 3 -, CH 4 and CO 2 at isotopic equilibrium in an open system model, the amount of can be calculated using a Rayleigh-type isotopic equation:

(

where is the isotopic ratio of the HCO 3 -after a certain amount of Rayleigh distillation, is the initial isotopic ratio of HCO 3 -, is the fraction of phase HCO 3 -remaining, and is the equilibrium fractionation factor between HCO 3 -and CH 4 . By incorporating the delta notation (i.e., δ 13 C) instead of the isotopic ratio ( 13 C/ 12 C) in Eqn.

(1), we obtain the following equation:

(

Hence, the estimates of the C-isotopic compositions of the fluid (i.e., the values) for different amounts of HCO 3 -escape are dependent on (i) the initial C-isotopic composition of the fluid (i.e., the value) and (ii) the equilibrium fractionation factor between HCO 3 -and CH 4 , which is a direct function of the temperature. This calculation is also linked to a fundamental assumption, that the oxygen isotopes of the water constitute an infinite reservoir and thus, the O-isotopic composition of the fluid is not affected by the Rayleigh distillation.

Interestingly, the in situ δ 13 C-δ 18 O values of CM2 and CM1 Ca-carbonate define two similar trends (except for the δ 13 C-δ 18 O values of MET 01070) with their C-isotopic compositions converging toward a low range of δ 13 C values for a high degree of O-isotopic equilibration (i.e., δ 13 C calcite ≈ 20-30‰) (Fig. 15). Furthermore, by including the δ 13 C-δ 18 O values of the type 1 and type 2 calcites from the CM2 Nogoya [START_REF] Fujiya | Oxygen and carbon isotopic ratios of carbonates in the Nogoya CM chondrite[END_REF], these two groups exhibit constant δ 13 C values for different O-isotopic compositions (excluding 2 points from the type 2) at δ 13 C calcite ≈ 30‰ (≈ 4‰) (Fig. 16b). As the lowest δ 13 C value of the T2a calcite in Boriskino displays similar C-isotopic composition to the Nogoya calcites and the two CM tendencies (i.e., δ 13 C calcite = 30‰ for the CC9 grain), we assume that this value represents the initial of the fluid. Interestingly, this value is consistent with the range of C-isotopic values of the SOM reported by [START_REF] Sephton | Recognizing life in the Solar System: guidance from meteoritic organic matter[END_REF] in Murchison.

Thus, by combining the carbon equilibrium fractionation factors of HCO 3 -/CO 2 (5-125°C, [START_REF] Mook | Carbon isotope fractionation between dissolved bicarbonate and gaseous carbon dioxide[END_REF] and CO 2 /CH 4 (0-700°C, [START_REF] Bottinga | Calculated fractionation factors for carbon and hydrogen isotope exchange in the system calcite-carbon dioxide-graphite-methane-hydrogen-water vapor[END_REF], we can determine the equilibrium fractionation factor of HCO 3 -/CH 4 for a given temperature. Assuming a mean temperature of precipitation for T2a calcites of 110°C, the equilibrium fractionation factor of HCO 3 -/CH 4 is 0.9535 at 110°C (1000lnα CH4-HCO3-= -47.6‰). Hence, the observed δ 13 C variabilities in T2a calcite in Boriskino (i.e., δ 13 C calcite = 38-65‰, Table 3) can be explained by a loss of ≈ 15-50% of dissolved carbon from the fluid into CH 4 . We note that this estimate is largely temperature dependent, and different results will be found at other temperatures [START_REF] Fujiya | Oxygen and carbon isotopic ratios of carbonates in the Nogoya CM chondrite[END_REF].

CONCLUSIONS

Brecciation is common in CM chondrites and understanding the origin of individual lithologies recorded among clasts in breccia can provide constraints on the preaccretionnary alteration history and collisional activity that took place on their parent body. From a petrographic and isotopic survey of Ca-carbonates in the clastic breccia CM2 Boriskino, we have investigated and traced the relative timings of deformation and aqueous alteration of the CM parent body. The principal results of this paper are:

(1) Boriskino is composed of millimeter clasts, in direct contact with each other, that display various lithologies characterized by different degrees of alteration and deformation histories.

(2) The least altered lithology (lithology 3) contains Type 1a Ca-carbonates that are surrounded by phyllosilicates. Type 1a Ca-carbonates are 16 O-poor and precipitated early in Boriskino's alteration history. This is interpreted as the result of isotopic exchange between a 16 O-poor fluid and 16 O-rich anhydrous silicates in a closed-system model. Petrographic observations suggest that secondary minerals formed before the establishment of the petrofabric, and thus that alteration predated the deformation.

(3) The more altered lithologies (lithologies 1 & 2) are composed of 16 O-rich Type 2a Cacarbonates (calcites) and veins of calcite lying subparallel to the petrofabric. These calcites precipitated after the establishment of the deformation, from transported 16 Orich fluid in preexisting fractures and cracks.

(4) Based on strong evidence of shock features in Boriskino, we propose that some of the clasts that make up the Boriskino meteorite were subjected to high pressure impact(s) (i.e., 10-30 GPa) that generated strong petrofabrics, chondrule flattening and fractures.

(5) Taking all our results together, we propose a reconstruction of the deformation and alteration history of Boriskino in which the different lithologies are explained by their separate positions into the CM parent body. Assuming multiple shock compaction events, the occurrence of a strong petrofabric, calcite veins and elongated chondrules in the more altered lithologies could be explained by their location close to the impact zone, promoting a late circulation of fluid flow into fractures.

(6) Based on the C-isotopic composition of Boriskino Ca-carbonates, we propose that the formation of T2a calcite probably can took place in an open system environment with a loss of 13 C-depleted CH 4 produced from the reduction of C-bearing species by H 2 released during serpentinization or kamacite corrosion [START_REF] Guo | Temperatures of aqueous alteration and evidence for methane generation on the parent bodies of the CM chondrites[END_REF].

Considering a mean precipitation temperature of Ca-carbonates of 110°C, an escape of ≈ 15-50% of dissolved carbon into CH 4 by Rayleigh distillation is able to reproduce the range of C-isotopic compositions observed in T2a calcites. [START_REF] Nakamura | Impact-Induced Textural Changes of CV Carbonaceous Chondrites: Experimental Reproduction[END_REF]. The mean X-ray computed tomography (XCT) aspect ratio of the Boriskino type I chondrules (yellow square) and Murchison 3 dark-toned XCT objects (purple square; [START_REF] Hanna | Impact-induced brittle deformation, porosity loss, and aqueous alteration in the Murchison CM chondrite[END_REF] is reported on the CV and CM trends. The light grey rectangle that cuts the CM trend represents the end of the correlation and the effects of the CM shock experiments above 30 GPa [START_REF] Tomeoka | Experimental shock metamorphism of the Murchison CM carbonaceous chondrite[END_REF]. Murchison 1 [START_REF] Fujiya | Comprehensive study of carbon and oxygen isotopic compositions, trace element abundances, and cathodoluminescence intensities of calcite in the Murchison CM chondrite[END_REF] and CM2.7 Paris 1 [START_REF] Vacher | Petrographic and C & O isotopic characteristics of the earliest stages of aqueous alteration of CM chondrites[END_REF]. We also show the in

  4c); and (ii) polycrystalline grains that occur in association with phyllosilicates, olivine grains and Fe-Ni sulphide inclusions (Fig. 7a & 7b) inside flattened chondrules surrounded by a fine-grained rim (hereafter FGR) (Fig. 7a & 7b). T2a calcites show  18 O values between 17.2 and 22.5‰ (mean of 19‰,  = 1.4‰),  17 O values between 6.2 and 8.8‰ (mean of 7.4‰,  = 0.8‰) and heterogeneous  17 O values, ranging from -3.5 to -0.6‰ (mean of -2.5‰,  = 0.8‰) (Fig. 5, Table

  & 7b). Based on these petrographic and isotopic features, it thus appears that Boriskino's Ca-carbonates define two distinct populations: a first population, made up of T1a calcite and aragonite, with mean  18 O and  17 O values of 33.9‰ ( = 2.4‰) and -1‰ ( = 0.4‰) respectively; and a second population, composed of T2a calcite and calcite veins, with  18 O and  17 O values of 18.9‰ ( = 1.5‰) and -2.5‰ ( = 0.8‰) respectively (Fig. 5b). Taken together, the O-isotopic compositions of Boriskino's Ca-carbonates define a trend with  17 O = 0.62 (± 0.05 ×  18 O -4.3 (± 1.3 (2R 2 = 0.97; MSWD = 11.6; Fig. 5a) that does not fall on the mass-dependent fractionation line (TFL; Fig. 5a). This trend is closed, within errors, from those reported in previous studies in different CM chondrites with: (i)  17 O = 0.62 (± 0.09 x  18 O -4.1 (± 2.8) (2R 2 = 0.95, MSWD = 0.26, Tyra et al., 2012) (ii)  17 O = 0.62 (± 0.04x  18 O -4.08 (± 1.1 (2R 2 = 0.99, MSWD = 1.7, Benedix et al., 2003) (iii)  17 O = 0.66 (± 0.05) ×  18 O -4.7 (±1.5) (2σ, R 2 = 0.87, MSWD = 3.3, Verdier-Paoletti et al., 2017a) (iv)  17 O = 0.65 (± 0.03) ×  18 O -5.4 (±1.2) (2σ, Horstmann et al., 2014). (v)  17 O = 0.70 (± 0.03) ×  18 O -5.65 (±1.25) (2σ, Lindgren et al., 2017) The trend with a slope of 0.62 ± 0.05 defined by the Boriskino carbonates (and other CMs) cannot result from precipitation of the carbonates from a common fluid (i.e., with identical  17 O values) along a temperature gradient, as this would have produced a slope of 0.52 (Fig. 10). Instead, it implies that the main process controlling the O-isotopic compositions of Ca-carbonates relies on variable degrees of isotopic exchanges between a 16 O-poor fluid (i.e., a CM primordial water with  18 O = 55 ± 13‰ and  17 O = 35 ± 9‰; Fujiya, 2018) and 16 O-rich anhydrous silicates

  2 = CH 4 + H 2 O + OH -(in aqueous phase;[START_REF] Horita | Abiogenic methane formation and isotopic fractionation under hydrothermal conditions[END_REF]

FIGURE CAPTIONS Figure 1 :

 CAPTIONS1 FIGURE CAPTIONS

Figure 2 :

 2 Figure 2: Back-scattered electron (BSE) mosaics of the two polished sections of the CM2

Figure 3 :

 3 Figure 3: BSE mosaics of delimited regions of the three lithologies in section #4. (a) BSE

Figure 4 :

 4 Figure 4: (a) BSE image of Type 1a aragonite (A) surrounded by a fine rim of phyllosilicate

Figure 5 :

 5 Figure 5: (a) Oxygen three-isotope plot for Type 1a aragonite (green diamonds), Type 1a

Figure 6 :

 6 Figure 6: δ 13 C values of Type 1a aragonite (green diamonds), Type 1a calcite (green circles)

Figure 7 :

 7 Figure 7: a) BSE image of Type 2a polycrystalline calcite (C) grains located in a flattened

Figure 8 :

 8 Figure 8: Histograms showing the deviation of particles (i.e., chondrule, TCI clump and

Figure 9 :

 9 Figure 9: Orientation plot of fitted ellipsoid from bulk X-ray computed tomography analyses

Figure 10 :

 10 Figure 10: Schematic diagram representing the main processes controlling the oxygen

Figure 11 :

 11 Figure 11: Relationship between intensity of a single shock pressure and mean chondrule aspect ratio in an experimental shock on the CM Murchison 1 (solid black line and white circle; Tomeoka et al., 1999) and on the CV Allende 2 (black dotted line and black circle;

Figure 12 :

 12 Figure 12: Relationship between degree of alteration vs percentage of particles with long

Figure 13 :

 13 Figure 13: (a) BSE image showing an interpreted pre-deformation Type 1a Ca-carbonate

Figure 14 :

 14 Figure 14: Schematic representation of the thermal and deformation history of the CM parent

Figure 15 :

 15 Figure 15: δ 13 C vs. δ 18 O values for Type 1a aragonite (green diamonds), Type 1a calcite

Figure 16 :

 16 Figure 16: (a) δ 13 C vs. δ 18 O values for Type 1a aragonite (green diamonds), Type 1a calcite

  Figure 2 1193

  Figure 16

Table 2 ). 4. DISCUSSION 4.1 Oxygen isotopes and sequence of Ca-carbonate precipitation

 2

	Boriskino contains two petrographic types of Ca-carbonate depending on the lithology
	considered: T1a Ca-carbonates (calcite and aragonite) and T2a calcites. T1a Ca-
	carbonates are 16 O-poor (mean  18 O and  17 O values of 33.9‰ and 16.7‰, respectively)

Table 1 .

 1 Modal abundance of mixture of phases and components (in vol. %) determined by point counting and petrographic observations of section #4 of Boriskino.

	Lithologies	L1 (n = 510)	L2 (n = 501)	L3 (n = 251)
	Surface counting (mm 2 )	6	4	2
	Matrix (vol. %)	60.15	62.3	68
	Chondrule (vol. %)	30	34.7	23.9
	Sulphide (vol. %)	8.6	1.6	5.2
	Ca-carbonate (vol. %)	1.2	1.4	2.4
	Metallic Fe-Ni (vol. %)	~0.05	Not detected	~0.5
	Chondrule mesostasis	Phyllosilicate	Phyllosilicate	Phyllosilicate
	Mafic silicate into chondrule	Partially altered	Partially altered	Unaltered
	Type of Ca-carbonate	T2a and veins	T2a	T1a

ACKNOWLEDGMENTS

We are very grateful to Nordine Bouden for his helpful assistance with the carbon and oxygen isotope measurements, to Patricia Wils and the AST-RX UMS 2700 MNHN technical facilities for their technical support with the XCT analyses and to Marie-Camille Caumon for her assistance with the Raman analyses. We also thank the Muséum National d'Histoire Naturelle de Paris (MNHN) for the loan of the Boriskino samples. This work was funded by l'Agence Nationale de la Recherche through grant ANR-14-CE33-0002-01 SAPINS (PI Yves Marrocchi). This is a CRPG contribution#2568 And SAPINS contribution #11.

situ δ 13 C-δ 18 O data of the Type 1 (light grey circles) and Type 2 (dark grey circles) calcite from the CM2.2-2.3 Nogoya 1 [START_REF] Fujiya | Oxygen and carbon isotopic ratios of carbonates in the Nogoya CM chondrite[END_REF]. The white triangle lines represent the predicted isotopic compositions of CM carbonates as a function of temperature and the mole fraction of CO 2 in a CO-CO 2 -H 2 O system (δ 13 C CO = -5‰ and δ 18 O H2O = 5‰) (CO-CO 2 gas 1 : [START_REF] Alexander | Carbonate abundances and isotopic compositions in chondrites[END_REF]. The white triangles on the model mark 10°C intervals. The blue rectangle represents the predicted range of δ 13 C-δ 18 O values of Ca-carbonates that precipitated from varying equilibration between 17,18 O-rich water with 12 C-and 13 C-rich soluble organic matter at 110°C [START_REF] Vacher | Petrographic and C & O isotopic characteristics of the earliest stages of aqueous alteration of CM chondrites[END_REF]. The δ 13 C-δ 18 O values of CC6, CC7,