# Multistage aqueous alteration in CeC 022 and other nakhlites

L. Krämer Ruggiu, Bertrand Devouard, J. Gattacceca, L. Bonal, L. Piani, H.

Leroux, O. Grauby

► To cite this version:

L. Krämer Ruggiu, Bertrand Devouard, J. Gattacceca, L. Bonal, L. Piani, et al. Multistage aqueous alteration in CeC 022 and other nakhlites. Meteoritics and Planetary Science, 2024, 689, pp.A183. 10.1111/maps.14295. hal-04918990

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1 Multi-stage aqueous alteration in CeC 022 and other nakhlites

2 L. Krämer Ruggiu¹·², B. Devouard², J. Gattacceca², L. Bonal³, L. Piani⁴, H. Leroux⁵, O.

3 Grauby⁶.

4 ¹Archaeology, Environmental changes and Geo-Chemistry, Vrije Universiteit Brussel,
5 Brussels, Belgium (lisa.kramer.ruggiu@vub.be)

6 ²Aix Marseille Univ, CNRS, IRD, INRA, CEREGE, Aix-en-Provence, France

7 ³Univ. Grenoble Alpes, CNRS, IPAG, Grenoble, France 11

8 ⁴CRPG, CNRS, Université de Lorraine, UMR 7358, Vandoeuvre-les-Nancy, France

9 ⁵Univ. Lille, CNRS, INRAE, Centrale Lille, UMR 8207 - UMET, F-59000, Lille, France

10 ⁶CNRS, CINaM, Aix-Marseille Université, 13009 Marseille, France
11 Abstract

We studied Caleta el Cobre 022, a nakhlite showing a high abundance of aqueous alteration products, commonly called "iddingsite" and compared it to 8 other nakhlites, in order to constrain the composition and the history of the aqueous alteration of nakhlites. Olivine grains in nakhlites display planes of secondary fluid inclusions, composed of pyroxene, magnetite and a void potentially filled by a fluid. They were formed by a first fluid alteration event, previous to the iddingsite alteration event, probably from a late magmatic fluid circulation. We observed magnetite-pyroxene symplectites in olivine grains in most nakhlites, related to the same fluid assisted tardi-magmatic event as the crystallization of the secondary inclusion planes. Those secondary inclusions and symplectites can be observed at the center of iddingsite veins, inside the most altered nakhlites, and are thus interpreted as being weakness planes, easing the circulation of the fluid forming the iddingsite inside the olivine grains. In every nakhlite, the alteration veins show at least two types of iddingsite: a coarse iddingsite with crystals around 50 nm, up to 200 nm, and a fine iddingsite with a nanocrystalline to amorphous texture with crystalline domains <10 nm. Both iddingsite types are composed mainly of Si, Mg and Fe, with anticorrelated Si and Fe contents. The coarse iddingsite is composed of a mixture of phyllosilicates, with Fe-oxyhydroxides and minor siderite, and the fine iddingsite has a composition close to saponite. Organic matter located in coarse iddingsite is detected by Raman spectroscopy in the iddingsite of many nakhlites, and was confirmed by the TEM study of NWA 10153. In addition, the TEM study of NWA 10153 display complex chemical zoning in the fine iddingsite of Mg, Ca, Mn, S, P and Al, suggesting at least two stages of circulations. Both the compositions and textures of the two types of iddingsite are suggestive of a progressive evolution of the alteration fluid, enriched in elements from basaltic mineral
34 dissolution, with crystallization mainly by filling of existing fractures, and selective dissolution
35 of host olivine. We also observe pyrrhotite-magnetite veinlets at the center of iddingsite veins
36 and crosscutting iddingsite veins and silicates, which are interpreted as the result of another
37 later fluid circulation.

38

39

# 1 Introduction

40 Nakhlites are a group of basaltic meteorites originating from the mid-Amazonian igneous crust
41 of Mars (McSween, 1985; Treiman et al., 2000; Bogard and Johnson, 1983; McSween Jr, 1994;
42 Nyquist et al., 2001). To date, the nakhlite group comprises 32 meteorites: 18 from Northwest
43 Africa (NWA), 7 from Antarctica, 6 from other provenances, 1 fall (Nakhla), and Caleta el
44 Cobre 022 from Chile (Krämer Ruggiu et al., 2020). After pairing, this number is reduced to
45 17 nakhlites. Nakhlites share broadly similar texture, whole-rock composition and mineralogy.
46 In addition, they all present similar crystallization ages around 1.3-1.4 Ga (Nyquist et al., 2001;
47 Korochantseva et al., 2011; Herzog et al., 2015; Wieler et al., 2016; Cohen et al., 2017)
48 suggesting they originate from a single volcanic edifice. They show similar ejection ages,
49 within error, with cosmic exposure ages around 10-11 Ma, indicating a single ejection event
50 (Nyquist et al., 2001; Herzog et al., 2015; Cohen et al., 2017).

51 Nakhlites are clinopyroxene-rich cumulates, composed of euhedral clinopyroxene and olivine,
52 and a fine-grained intercumulus mesostasis. This mesostasis contains dendritic fayalite,
53 apatite, titanomagnetite, with low-Ca pyroxene, sulfide, and silica, surrounded by feldspar-
54 composition glass and/or feldspar laths (e.g. Treiman, 2005). Nakhlites originate from a low-
55 degree partial melting of the martian mantle (McCubbin et al., 2013), with a cumulus
56 crystallization in a shallow magma chamber (Day et al., 2006). They erupted over a short
period of time ~93 Myr with magma ascending at the martian surface as thick lava flows or at
the sub-surface as shallow sills (Mikouchi et al., 2003; Day et al., 2006; Cohen et al., 2017;
Udry and Day, 2018), and their final cooling took place at depth of 1 to 30 m (Lentz et al.,
1999; Mikouchi et al., 2012, 2017), over a short period of time from 5 to 184 days (Day et al.,
2006; Udry and Day, 2018). The nakhlite stratigraphy has been long discussed (Treiman, 1987,
2005; Mikouchi et al., 2003; Bridges and Warren, 2006; Day et al., 2006; McCubbin et al.,
2013; Balta et al., 2016; Jambon et al., 2016; Cohen et al., 2017). Recently, Udry and Day,
2018 proposed in a comprehensive study that nakhlites originated from at least six different
lava flows or sills, distributed around one or several volcano vents. All nakhlites except NWA
5790 (Jambon et al., 2016), show post-eruption aqueous alteration phases. The alteration of
nakhlites is mainly observed in cracks in olivine and, to lesser extent, in the mesostasis.
Truncation by the fusion crust observed in Nakhla and Lafayette (Gooding et al., 1991;
Treiman et al., 1993) confirms the martian origin of the aqueous alteration. The abundance and
mineralogy of alteration phases vary among nakhlites. The major alteration phase has been
commonly termed as such as “iddingsite”, a relatively loose name describing intergrowths of
hydrated silicates (smectite, serpentines, or other phyllosilicates, amorphous gel, and minor
opal-A), laihunite, Fe-oxides and oxyhydroxides, siderite, gypsum and halite (Gooding et al.,
1991; Reid and Bunch, 1975; Gooding et al., 1991; Treiman et al., 1993; Bridges, 2000; Irving
et al., 2002; Gillet et al., 2002; Noguchi et al., 2009; Changela and Bridges, 2010; Hicks et
al., 2014; Kuebler, 2013; Lee et al., 2013; Tomkinson et al., 2013; Chatzitheodoridis et al.,
2014; Lee et al., 2018; Piercy et al., 2022). These secondary minerals could have been formed
from a brine percolating through the nakhlites at low temperature, estimated <150 °C, based
on the Ca content in siderite in Lafayette (Bridges, 2000; Bridges et al., 2001; Bridges &
Schwenzer, 2012). The precipitation of the iddingsite could result from a CO2-rich fluid crystallizing the Ca-rich siderite at 150-200 °C, with a pH of 6-8 and a water/rock ratio <300, and as the fluid cooled to 50 °C, pH 9 and water/rock ratio of 6, Fe-rich phyllosilicate precipitated, followed in turn by rapid precipitation of an amorphous gel. It was enriched in the most soluble species (e.g. K, Na), of alkaline pH, and similar to terrestrial, i.e. not seawater-influenced, dilute brines in basaltic terrains on Earth. (Bridges and Schwenzer, 2012). One hypothesis is that the hydrothermal assemblage of the nakhlite resulted from an impact adjacent to the nakhlites location (Changela and Bridges, 2010), based on the geometry of the toothed brittle fractured veins. Several methods have been used to estimate the age of the iddingsite assemblage such as Rb-Sr, Sm-Nd, Ar-Ar and K-Ar isotopic measurements, indicating an approximate age of alteration between 650 and 700 Myr (Shih et al., 1998; Swindle et al., 2000; Misawa et al., 2003; Tremblay, 2020). Studying aqueous phases in nakhlites can reveal the water-crust interactions, and the physico-chemical conditions that prevailed at the martian subsurface, with implications for the past habitability of Mars, and in particular for microbial life during the Amazonian period.

In this paper, we study the alteration phases in the following nakhlites: Nakhla, Governador Valadares, Lafayette, Miller Range (MIL) 003346, Yamato 000953, North West Africa (NWA) 11053, NWA 817, NWA 998, and Caleta el Cobre (CeC) 022. This latter nakhlite has a high abundance of iddingsite with an unusual complexity of phases that makes it a key sample to study the aqueous alteration in nakhlites. We studied the iddingsite assemblages in detail in order to better constrain its mineralogy and to discuss the sequence of aqueous alteration events in nakhlites.

102

## 2 Methods
The nine nakhlites have been studied in polished sections: CeC 022, Governador Valadares, Lafayette, MIL 003346, Nakhla, NWA 817, NWA 998, NWA 11053 and Y 000953.

## 2.1 Scanning electron microscopy

Backscattered electron (BSE) images, microanalyses by Energy-dispersive X-ray spectroscopy (EDS), and chemical maps were acquired with a Hitachi S3000-N scanning electron microscopy (SEM), operated at 15 kV, and equipped with a Bruker X-ray X-Flash detector and a Spirit analyzer at CEREGE, France. Additional field emission gun (FEG) SEM images were obtained on both (1) a ZEISS Gemini 500 SEM at Centre Pluridisciplinaire de Microscopie Electronique et de Microanalyse (CP2M), Marseille; and (2) a Jeol JSM 7900F equipped with an XFlash 6/60 Bruker EDS detector at CINAM laboratory. Elemental maps were acquired using a probe current of 10 nA, and an acceleration voltage of 5 to 15 kV and 20-45 min counting time. Composite elemental maps obtained by SEM-EDS were used to measure modal abundances of iddingsite inside olivine for all nakhlites using pixel counting with ImageJ software.

## 2.2 Electron microprobe

Quantitative major elements analyses of minerals were obtained using an electron microprobe Cameca SX100 at UPMC CAMPARIS facility. The operating conditions were 15 kV accelerating voltage with a current of 10 nA and a counting time of 30 s, with a focused beam (1 µm) for pyroxene, olivine, plagioclase, and apatite, and a defocused beam (5 µm) for fine-grained mesostasis and alteration phases. Both natural and synthetic standards were used for calibration: albite for Na; anorthite for Al; apatite for P; diopside for Mg, Si, Ca; orthoclase for K; pyrite for S; $MnTiO_3$ for Mn and Ti; $Cr_2O_3$ for Cr; $Fe_2O_3$ for Fe; and NiO for Ni. The
detection limits are (ppm): 445 for Na, 466 for Al, 714 for Mg, 669 for Si, 605 for Ca, 602 for K, 392 for S, 1044 for Mn, 419 for Ti, 496 for Cr, 1271 for Fe, and 1331 for Ni.

## 2.3 Transmission Electron Microscopy

Ultra-thin sections were extracted from CeC 022, Lafayette and NWA 10153 by focused ion beam (FIB) at CP2M Marseille on a Dual beam FIB (FEI Helios 600 Nano Lab). TEM observations of the FIB sections were made on a Thermo-Fisher Titan Themis S/TEM operating at 300 kV, at the microscopy facility of the University of Lille for HAADF imaging and the EDX mapping of FIB sections. Elemental mappings were recorded with a probe current of 60 pA, a probe of ~9 nm and a counting time of ~20 min. High-resolution TEM images and diffraction patterns were recorded on a STEM Jeol JEM-2010 operated at 200 kV at CINaM laboratory, Marseille.

## 2.4 Raman spectroscopy

Raman spectra were obtained at Laboratoire de Géologie de Lyon (ENS Lyon—France) using a Labram HR800 spectrometer equipped with an Nd ion laser providing 532 nm excitation. The laser spot was <2 µm with the x50 microscope objective. Individual spectra were acquired at various locations in veins of iddingsite, optically localized throughout the sections of the different nakhlites.

## 2.5 Secondary ion mass spectrometry

Hydrogen isotopic measurements were performed on the SIMS IMS1280 HR2 at CRPG (France) using a 20 keV Cs⁺ primary beam following the methodology developed by (Métrich and Deloule, 2014). Prior to analysis, 180s of presputtering was applied over 15 µm × 15 µm to remove the gold coating and reach the sputtering steady state. The samples were then measured with the 500 pA primary current rastered over 10 µm × 10 µm. A small field aperture
(1000 µm) was used to eliminate hydrogen contamination from outer part of the beam. The
¹⁷O⁻, ¹⁶OH⁻, ¹⁸O⁻, ¹⁷OH⁻ and ¹⁶OD⁻ ions were collected sequentially by changing the magnetic
field and counted with the monocollection electron multiplier for ¹⁷O⁻, ¹⁸O⁻, ¹⁷OH⁻ and ¹⁶OD⁻
and the monocollection faraday cup equipped with a 10¹²-ohm resistor for ¹⁶OH⁻. The mass
resolution (M/ΔM) was set to 11,500 to avoid interferences of ¹⁷OH⁻ on ¹⁶OD⁻. An electron
gun was used for charge compensation. Four amphiboles and one serpentine were used as
reference materials to correct for the instrumental mass fractionation. The water content was
corrected from the instrumental mass fractionation using the whole series of standards having
water content ranging from 1.5 to 12.2 wt.% H₂O. The D/H ratios where corrected from
instrumental mass fractionation using the four amphiboles as a function of the #Mg following
the method proposed in Deloule & Robert (1995). The highest source of uncertainty is the
reproducibility obtained for the amphibole standards, which are comprised between 5 and 2 %
for the H₂O contents and 9 and 44 ‰ for the D/H ratios (2SD).

# 3 Results

## 3.1 Petrography

Aqueous alteration can be observed already in hand sample, as it appears as reddish material
in olivine (Fig. 1). The martian origin of alteration veins is asserted on the basis of the similarity
between nakhlites, especially with Nakhla and Layette, where iddingsite veins are truncated
by the fusion crust, proving their extraterrestrial origin, as also previously observed in the
literature by e.g. Gooding et al. (1991) and Treiman et al. (1993). Martian aqueous alteration
in nakhlites is found mainly as veins crosscutting olivine crystals. No iddingsite veins were
observed cutting pyroxenes, agreeing with Gillet et al. (2002). Iddingsite veins do not follow
a preferential orientation, and seem unrelated to the olivine crystal structure using BSE images.
This should be verified as BSE imaging is 2D and preferential orientation could be observed
only in 3D (using EBDS for further mineral orientation analyses). The veins often display saw-
tooth edges (Fig. 2). The mesostasis displays nano to micron size patches of iddingsite (Fig.
2), although here we chose to focus on the most represented type of iddingsite, being iddingsite
veins inside olivine. Aqueous alteration products were found in all nakhlite samples, except
for NWA 5790 (Fig. 3). Modal abundances were measured using 3 olivine grains in each
nakhlite (except for MIL 03346 only 1 olivine grain), giving between 5 to 20 iddingsite veins
studied per nakhlite (Fig. 3). Caleta el Cobre 022 and NWA 10153 have the highest content of
iddingsite in olivine, with respectively 45 and 45 vol% of olivine transformed into iddingsite.
MIL 03346, Lafayette, NWA 817 and NWA 998 also show abundant iddingsite with 8-18
vol%. Finally, Y 000593, Nakhla and Governador Valadares have less abundant iddingsite,
representing 2 to 3 vol% of the olivine fraction (Fig. 3).

184 **3.2** Textural observation

185 **3.2.1** Iddingsite types

All nine nakhlite samples show at least two types of iddingsite: “coarse” and “fine” based on
their aspect on the BSE-SEM images (Fig. 2). The “coarse” iddingsite is found in contact with
the olivine, showing a crystallized coarse texture (Fig. 2). Some grains show preferred
orientations, in rosette clusters (in Lafayette) or perpendicular to the contact with olivine (Fig.
2D). The “fine” iddingsite is found at the center of the vein, showing a smooth homogenous
texture with a darker contrast on BSE images (Fig. 2). The iddingsite veins contain more fine
iddingsite than coarse iddingsite, except for Lafayette (Fig. 2D).

193 **3.2.2** Simple center of veins
The veins display a thin central veinlet inside the fine iddingsite (Fig. 2C). Most commonly, the center of the veins is observed as a darker thin line on BSE-SEM images, with texture and composition close to the fine iddingsite. The nakhlites that display more abundant iddingsite show iddingsite veins with a center of more complex mineralogies (Fig. 2A, Fig. 2B).

### 3.2.3 Secondary inclusions

In CeC 022 secondary inclusion planes can be observed in olivine grains, with inclusions size ranging from 1 to 10 µm (Fig. 4). Those inclusions show euhedral shapes and are distributed in singular planes crosscutting olivine grains, with no preferential direction (Fig. 4C). They are usually triphasic, composed of pyroxene, magnetite, and a void that possibly contained or still contains a fluid (gas or liquid) (Fig. 4B). In CeC 022, the secondary alteration inclusions can be found at the center of some iddingsite veins, with rare nanoscale apatite and sulfide (Fig. 4A). Relict secondary fluid alteration inclusions can also be observed in pyroxenes surrounding the olivine in nakhlites (Bridges et al., 2020), but they were not studied in this paper as they did not show any traces of other aqueous alteration as iddingsite.

### 3.2.4 Magnetite-pyroxene symplectites

We observe symplectite inclusions composed of pyroxene, magnetite and rare apatite in olivine grains of CeC 022 (Fig. 4), as previously described in Nakhla by Mikouchi et al. (2000). They show fine lamellar elongated shape of sized commonly around 10 µm long and 1 µm large, and are distributed throughout the olivine crystals in thin linear planes with parallel preferential direction following crystallographic orientation of the host olivine. They show dendritic magnetite and pyroxene, shaped as “herring-bone” within the symplectite. In some cases, they are observed in contact with the previously described secondary inclusions and are sometimes hardly distinguishable from one another (Fig. 4). CeC 022 and MIL 03346 show iddingsite
217 veins with magnetite-pyroxene symplectites at the center of the veins (Fig. 2A).

218 **3.2.5 Sulfide-magnetite veinlets**

219 In CeC 022 and NWA 10153, veinlets of width from <1 to 10 µm, composed of sulfide
220 (pyrrhotite) and magnetite were observed crosscutting olivine, pyroxene and mesostasis (Fig.
221 4E-F). Those sulfide veinlets can be found either at the center of some iddingsite veins in CeC
222 022 and NWA 10153 (Fig. 2B). In addition, they were observed crosscutting iddingsite veins
223 (Fig. 4E-F), but they were never observed being cross-cut by iddingsite veins and/or
224 symplectites.

225 **3.3** <u><b>Mineralogy of iddingsite</b></u>

226 **3.3.1 Coarse iddingsite**

227 The coarse iddingsite is made of an assemblage of phases, resulting in a variety of Raman
228 spectra, depending on the location of the spot analyses rather than a difference between
229 nakhlites (Fig. 5). The Raman spectra of the coarse iddingsite shows mainly a phyllosilicate
230 signature as observed in the 200-600 cm⁻¹ regions (Hallis and Taylor, 2011), Fe-oxides
231 (magnetite) (major peak around 675 cm⁻¹) and/or Fe-oxyhydroxides, forming broad peaks
232 around 290-400-680 and 1150 cm⁻¹. The large peaks formed by low crystallinity did not allow
233 precise identification. Some spectra show weak H₂O peak around 3600 cm⁻¹ (e.g., Lafayette,
234 MIL 03346 and CeC 022 in Fig. 5). Rare siderite detection (major peak around 1095 cm⁻¹), as
235 well as organic matter (in the 1500 cm⁻¹ region) were identified.

236 On high-resolution TEM images (CeC 022, Lafayette, NWA 10153), the coarse iddingsite
237 shows 50-200 nm crystals (Fig. 6), with a crystallinity varying amongst nakhlites. Selected
238 area electron diffraction (SAED) patterns show Debye-Scherrer-type spotted rings, indicating
239 nanocrystals with multiple grain orientations (Fig. 6). Diffraction patterns show rings
corresponding to d-spacing of about 4.7 Å, 3.1 Å and 2.6 Å, which can be attributed to 020, 022 and 200 reflections of phyllosilicates (Fig. 6). We also observe six other rings with d-spacings smaller than 2.5 Å, including one at 1.5-1.6 Å which could be indicative of mixing with oxides or ferrihydrite. High-resolution TEM images show lattice d-spacings of ~0.7 nm (Fig. 6), typical of 1:1 phyllosilicates (Changela and Bridges, 2010; Hicks et al., 2014). The contact between olivine and coarse iddingsite is sharp, with selective dissolution of olivine along etch pits, forming triangular cavities inside the olivine (Fig. 7B and 11).

### 3.3.2 Fine iddingsite

The Raman spectra of fine iddingsite are similar for all nakhlites, showing a poorly crystalline material signature with broad peaks (Fig. 5). The 100-600 cm⁻¹ signature correspond to clay mineral translation (Changela and Bridges, 2010), but the broad feature of the peaks does not allow to distinguish any specific phase. All nakhlites show marked hydration bands around 3600 cm⁻¹. The fine and coarse iddingsite spectra in Lafayette are very similar. This is explained by a Raman spot size (~2 µm) larger than the thin layer of fine iddingsite in Lafayette, resulting in coarse iddingsite being analyzed together with the fine iddingsite (Fig. 2D). The SAED patterns (Fig. 6D) show diffuse rings indicating poorly organized material, but the rings are nevertheless sharper than expected for an amorphous phase, indicating nanocrystalline rather than strictly amorphous textures. Diffraction patterns show rings corresponding to d-spacings of about 4.6 Å and 2.6 Å, which can be attributed to 020 and 200 reflections of phyllosilicates. On HR-TEM images, the fine iddingsite appears to be extremely fine-grained, with <10 nm domains of coherence, not allowing lattice-spacing measurements (Fig. 6). The contact between the fine and coarse iddingsite is gradual around 100 nm thick (Fig. 7).
263

**3.4** <u>**Chemical characterization**</u>

264

**3.4.1** <u>**Major element analyses**</u>

265

The major element composition of iddingsite, as determined by EPMA analyses, is reported Table 1. The composition of both iddingsite types is dominated by Si, Fe and Mg. The low analytical totals (average 89.9-95.2 wt%) suggest the presence of hydrated phases, but could also be lowered by the presence of organic matter as observed on Raman spectra (Fig. 5). The fine iddingsite in the nakhlites with the lowest fraction of iddingsite, is the most hydrated with analytical totals of 79.5-86.5 wt% (Governador Valadares, Nakhla, Y 00593). Nakhlites with the highest fraction of iddingsite (CeC 022, NWA 10153 and MIL 03346) and Y 00593 show Fe-enriched coarse iddingsite. In addition, those nakhlites and NWA 817 show Ca enriched fine iddingsite. In contrast, the nakhlites showing the smallest abundance of iddingsite in this study (Governador Valadares and Nakhla) show Mg enriched iddingsites. Finally, CeC 022, Y 00593 and NWA 817 show Al enrichment in their iddingsite (coarse and fine). Lafayette has unusual Al and Mg content compared to other nakhlites (Table 1).

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277

On a tertiary diagram (SiO₂+Al₂O₃) vs MgO vs Fe₂O₃ (Fig. 8), the coarse and fine iddingsite are relatively well separated. The fine iddingsite has a chemical composition closer to stoichiometric (Mg, Fe) solid solutions of saponite, while the coarse iddingsite has a composition closer to stoichiometric (Mg, Fe) solid solutions serpentine, potentially mixed with nano-sized oxide/oxyhydroxides crystals. Lafayette has both iddingsite types close to the saponite solution line. The tertiary diagram represents stoichiometric (Mg, Fe) solid solutions lines of saponite, serpentine and nontronite, and has to be used in combination with structural data (e.g. HRTEM) in order to distinguish smectite to serpentine like phyllosilicate structures. On a Fe₂O₃ vs SiO₂, coarse iddingsite and fine iddingsite plot in distinct zones, with a clear

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284

285
anticorrelation between the two types of iddingsite (Fig. 9). The coarse iddingsite is Si-depleted, with high Fe content compared to fine iddingsite, and fine iddingsite is Fe-depleted with high Si content compared to coarse iddingsite (Table 1, Fig. 9). Microprobe profiles through the different iddingsite veins in olivine reveal that the coarse iddingsite has Fe content similar or higher than olivine, and lower Mg, Ca and Si (Fig. 9). Fine iddingsite is Si-, Ca-rich and Fe-poor compared to olivine. Compositional transition between coarse and fine iddingsite is gradual (Fig. 8 and Fig. 9), reflecting the transitional contact observed in TEM analyses (Fig. 7). Most veins show symmetrical composition patterns, except for NWA 10153 and Governador Valadares (Fig. 9). The asymmetry in these two meteorites may be found in other nakhlites, and additional EPMA transects in multiple veins are needed in order to conclude if this asymmetry is restricted to some nakhlites. The simple veins centers have composition similar to fine iddingsite, with slight composition differences (higher SiO₂ and MgO, lower Fe₂O₃) (NWA 817) (Fig. 2C). The centers of the veins with symplectite assemblages of pyroxene, magnetite and rare apatite (CeC 022) show complex EMPA profiles (Fig. 2A).

## 3.4.2 Chemical mappings of complex iddingsite veins

### Caleta el Cobre 022

We studied one FIB section for NWA 10153 and CeC 022 each, selected in iddingsite veins with widths similar to the extracted FIB section in order to observe the complete width of the veins. We chose to extract the FIB sections from the most representative iddingsite veins of the two nakhlites. On STEM-EDS maps, NWA 10153 and CeC 022 iddingsite have different chemical complexities. CeC 022 iddingsite vein show three sub-types of iddingsite, and a complex center of vein (Fig. 10). The fine “iddingsite 1” is homogeneous, with Si enrichment and lower Fe and Ca content compared to olivine and coarse iddingsite (Fig. 10). The coarse
iddingsite chemical compositions reflect the nanoscale textural observations (TEM and Raman), with two chemical sub-types 2a and 2b (Fig. 10). The coarse iddingsite 2a is chemically close to the fine iddingsite, with lower Si content, probably transitional between crystallized coarse iddingsite 2b and fine iddingsite. The more crystallized coarse iddingsite 2b is Fe and Ca enriched. The center of the vein is composed of Ca-rich magnetite and Ca-pyroxene, with nanoscale sulfides (pyrrhotite) and apatite, surrounded by coarse iddingsite 2b (Fig. 10, Table 2). This center is made of the previously described secondary inclusions mixed with sulfide-magnetite exsolutions.

## NWA 10153

NWA 10153 iddingsite veins are more complex than the veins in CeC 022, showing three chemical subtypes of coarse iddingsite and at least three chemical subtypes of fine iddingsite (Fig. 11). The fine iddingsites show similar texture, but chemical zoning of Si, Ca, S, Mg and Fe. The fine iddingsite 1a is found at the center of the vein, and is Ca- and Mg-rich, the fine iddingsite 1b is Ca-rich, and fine iddingsite 1c is S enriched, and Ca-depleted.

The coarse iddingsite in NWA 10153 is composed of three different chemical types (Fig. 12). The coarse iddingsite 2a is a transitional iddingsite from coarse to fine in texture and in composition. The coarse iddingsite 2b is Fe, Al, Ca, S and P enriched, with lower Mg and Si, compared to the fine iddingsite. The coarse iddingsite 2a and 2b are similar CeC 022 2a and 2b. A fine center of vein is composed of iddingsite with a composition similar to the coarse iddingsite 2b. The coarse iddingsite 2c is similar to the coarse iddingsite 2b, but it comprises carbon-rich pockets of around 200 nm (Fig. 12). Those pockets contain only C and low N and O (Fig. S1). The carbon signature observed on Raman spectra in multiple nakhlites (Fig. 5)
demonstrate that organic matter could be present in many nakhlites, and will be the focus of a
further study.

The host olivine of CeC 022 and NWA 10153 iddingsite veins do not display chemical zoning
in contact with the iddingsite (Fig. 10 and Fig. 11). Likewise, the center of the veins (as
observed in CeC 022) does influence the coarse iddingsite composition covering the center
minerals (Ca-pyroxene, apatite, pyrrhotite).

## 3.5 Hydrogen isotopes

Hydrogen isotope measurements have been acquired *in situ* in iddingsite veins in olivine
crystals in CeC 022, NWA 817 and NWA 10153 (Fig. 13, Table 3). The measured δD of the
iddingsite show slight differences among nakhlites. As observed in Gillet et al. (2002), NWA
817 shows the lowest δD, ranging from -156 to -169 ‰ (average -165.7 ‰) (Fig. 13). CeC 022
show δD from -96 to -52 ‰ (average -75.4 ‰), and NWA 10153 has slightly higher values
from -55 to -2 ‰ (average -31.7 ‰). The water content estimated from SIMS data range from
7.21 wt% for CeC 022, 8.3 wt% for NWA 10153 and 9.87 wt% for NWA 817 (Table 3). Those
data are close to the one deducted from EMPA total analyses, closest to the fine iddingsite,
which is consistent with the fact that the SIMS analyses were acquired from the center of the
iddingsite veins (Table 1).

## 4 Discussion

### 4.1 Extraterrestrial origin

The martian origin of alteration veins observed in the nakhlites in this study is asserted on the
basis of the similarity between nakhlites, and previous extraterrestrial criteria established in
previous studied on nakhlites. Indeed, in Nakhla and Layette, iddingsite veins are truncated
by the fusion crust, proving their extraterrestrial origin, as also previously observed in the
literature by e.g. Gooding et al. (1991) and Treiman et al. (1993). In addition, Nakhla is a
martian meteorite fall, therefore the terrestrial weathering is negligible, and all secondary
phases have a high probability of being pre-terrestrial. Also, most nakhlites show limited
terrestrial alteration, and a fresh fusion crust (e.g., Fig. 1), supporting the extraterrestrial origin
of the veins found inside the olivines. In some nakhlites, such as NWA 998 and NWA 817,
we observed very little terrestrial alteration in the form of calcite and jarosite, typical of
terrestrial desert weathering in martian meteorites (e.g., Changela and Bridges, 2010). As the
terrestrial alteration veins were physically separated, as well as chemically different from
iddingsite veins studied in this paper, they were easily recognized and differentiated from the
extraterrestrial iddingsite veins studied in this paper. Those terrestrial phases and veins were
therefore not considered in this study. Previous studies observed relict of carbonates within
phyllosilicates in alteration veins in Lafayette, interpreted as relicts of original siderite-
ankerite precipitated from a previous martian event of fluid alteration (Percy et al., 2022).
Those extraterrestrial carbonates mixed with iddingsite were not observed in this study,
especially in CeC 022.

## 4.2 Iddingsite abundances

Nakhlites used to be interpreted as coming from a single cumulate pile (Treiman, 1987, 2005; Mikouchi et al., 2003, 2012; Bridges and Warren, 2006; Day et al., 2006; McCubbin et al., 2013), but recent studies describe an emplacement in at least seven different lava flows or sills, distributed around a common volcanic edifice (Udry and Day, 2018; Krämer Ruggiu et al., 2020). Thus, the proximity to the alteration fluid source cannot be simply summed up to a simple bottom to surface scenario. The Na+K contents of the iddingsite may reflect the nakhlites position relative to the fluid source, as the most soluble elements precipitate far from
the source. Thus, a higher Na+K content would mean a greater distance from the fluid source (Hicks et al., 2014). MIL 03346 has the lowest Na+K content, placing it closest from the fluid source, followed by Y 00593 and NWA 817. CeC 0022, NWA 10153 and Governador Valadares have similar intermediate Na+K contents, suggesting a similar transitional distance from the fluid source. Finally, Nakhla is the furthest from the fluid source with the highest Na+K. This order does not correspond directly to the abundance of iddingsite in olivine grains of the nakhlites (Fig. 2). Thus, if the Na+K represents distance from the fluid source, the distance from the fluid source, on its own, does not influence the abundance of iddingsite in the nakhlites.

Textural observations showed that iddingsite is found mainly in veins in olivine crystals, reflecting the susceptibility of olivine to low temperature aqueous alteration. It is known that ferroan olivine are most susceptible to aqueous alteration than magnesian olivine (Leshin and Vicenzi, 2006). Here, the volume fraction of iddingsite does not show a direct correlation to the olivine composition. In addition, except for MIL 03346, the volume fraction of olivine seems to be anticorrelated to the abundance of iddingsite in the olivine grains. In conclusion, the volume fraction of iddingsite cannot be readily correlated with a single parameter, but could be influenced by the combination of several factors: distance from the fluid source, Fa content of olivine, and other factors such as temperature, permeability of the rocks and other constituent compositions.

## 4.3 The nature of iddingsite

In the literature, iddingsite in nakhlites is referred as a mixture of multiple phases: mixture of phyllosilicates, Fe-oxides and hydroxides, and minor intergrown siderite, gypsum and halite (Gooding et al., 1991; Reid and Bunch, 1975; Gooding et al., 1991; Treiman et al., 1993; Bridges
and Grady 2000; Gillet et al., 2002; Noguchi et al., 2009; Lee et al., 2013, 2015; Changela and Bridges, 2010). In our study we did not detect any gypsum or halite, which we attribute more to terrestrial weathering. Both iddingsite types show hydration evidence, with the fine iddingsite having a higher water content, both on Raman spectroscopy and EPMA data (Table 1, Fig. 5).

Hicks et al. (2014) identified the iddingsite to be ferric-saponite in the olivine veins, and ferric-serpentine in the mesostasis alteration patches, based on chemical compositions, HRTEM and XANES analyses (in Lafayette and NWA 817). Later, Lee et al. (2018) described three types of iddingsite in NWA 817, by their atomic number Z: high-Z, mid-Z, low-Z. The mid-Z is the equivalent to our fine iddingsite, the high-Z is equivalent to our coarse iddingsite and the low-Z in the thin fine center of vein we described as being a variation of fine iddingsite composition (Fig. 2).

Lee et al. (2018) described the high-Z iddingsite (equivalent to coarse iddingsite) in the olivine as being an assemblage of nanocrystalline smectite (saponite) and Fe-oxyhydroxide based on composition and HRTEM. In this study, we describe the coarse iddingsite as an assemblage of nanocrystallized phyllosilicates and Fe-oxyhydroxides, with rare siderite. The chemical compositions (EPMA) of the coarse iddingsite show phyllosilicates compositions close to serpentine with a high Fe-content, in agreement with HRTEM observations, with an average structural formula calculated from the average of all nakhlites of (Fe²⁺ ²,³₄ Fe³⁺ ⁰,¹³ Mg⁰,⁵⁴) (Si₁,⁸⁴ Al₀,⁰³ Fe³⁺₀,¹³) O₅ OH) (Fig. 8). This composition is close to greenalite end member with some Mg²⁺ in the octahedral layer and Fe³⁺ in the tetrahedral layer (cronstedite). Although, the coarse iddingsite is observed as an assemblage of mainly phyllosilicates with minor other phases as observed on TEM images and Raman spectra, the EPMA composition thus represents an average of the coarse iddingsite assemblage. Siderite grains are observed in Lafayette (Fig. 2D) (Changela
and Bridges 2010; Lee et al., 2015; Piercy et al., 2022), but we did not observe clear siderite grains on TEM observations, probably due to a lower abundance of siderite grains in the coarse iddingsite compared to Lafayette, unsampled in the FIB sections. Lafayette shows more crystallized coarse iddingsite compared to the other nakhlites, with phyllosilicates up to 200 nm, and higher relative abundance compared to fine iddingsite (Fig. 2D), and higher Mg and Al content (Table 1). The different mineralogy of Lafayette maybe due to an alteration by slightly different fluid composition and/or conditions (Changela and Bridges, 2010; Hicks et al., 2014; Lee et al., 2015; Lee et al., 2018). Indeed, Lafayette shows phyllosilicates in rosette (Fig. 2D) and high Mg and Al composition (Fig. 8, Table 1), probably from phyllosilicate replacing Fe-rich carbonate (Percy et al., 2022), with small siderite detection on the Raman spectra (Fig. 5), also relict of the original siderite-ankerite precipitates from a previous event of fluid alteration. Lafayette also shows a presence of saponite mostly in the iddingsite veins observed inside olivine, and serpentine found mostly in the mesostasis (Hick et al., 2014). Those characteristics were not observed in the other nakhlites. In addition, Lafayette shows larger crystallization in the coarse iddingsite, and lesser abundance of fine iddingsite compared to other nakhlites, showing altogether a different iddingsite crystallization compared to other nakhlites. This could be explained by the existence of previous carbonate veins in Lafayette from a previous alteration event (Piercy et al., 2022), creating a different environment for iddingsite crystallization during the iddingsite formation aqueous alteration event in Lafayette, compare to the other nakhlites, without any previous carbonate veins.

The fine iddingsite is often described as an amorphous phase, or a gel-like material (e.g. Changela and Bridges 2010; Hicks et al., 2014; Lee et al., 2015, 2018). In this study, the texture of the fine iddingsite is nano-crystallized, with crystalline domains of <10 nm, as SAED patterns show rings that are definitely sharper than amorphous material (Fig. 5, Fig. 6). The chemical composition of
the fine iddingsite is close to Fe-rich saponite end member (smectite), with higher Si and lower Fe
content compared to the coarse iddingsite, with an average formula calculated from an average of
all nakhlites of Ca<sub>0.1</sub> Na<sub>0.03</sub> K<sub>0.04</sub> (Fe<sup>2+</sup><sub>2.42</sub> Mn<sub>0.05</sub> Mg<sub>0.53</sub>) (Si<sub>3.81</sub> Al<sub>0.06</sub> Fe<sup>3+</sup><sub>0.13</sub>) O<sub>10</sub> OH<sub>2</sub> (Table 1,
Fig. 8). As for the coarse iddingsite, this structural formula assumes that iddingsite consists in
phyllosilicates, an assumption that may not be completely correct since other evidence such as
Raman suggests a mixture with other phases such as iron oxides or hydroxides. The textural
transition from the coarse to the fine iddingsite are progressive (Fig. 7, 11, 13), with a transition
layer ~100 nm observed by TEM (Fig. 12). This switch of atomic layers organization, going from
a 1:1 (TO) clay organization for the coarse iddingsite (greenalite), to a 2:1 (TOT) for the fine
iddingsite (saponite) while maintaining similar compositions of the tetrahedral and octahedral
layers, could be produced by a switch in the alteration conditions of the system, but suggests that
both iddingsite crystallized from a single fluid, and reflect a temporal evolution of the alteration
conditions and/or fluid composition.

4.4 Chronology of iddingsite veins formation

460 **4.4.1 Secondary inclusions and magnetite-pyroxene symplectites**

461 CeC 022 shows euhedral secondary inclusions of size from 1 to 10 µm in olivine grains, distributed
462 in planes crosscutting olivine grains, with no preferential orientation, and composed of pyroxene,
463 magnetite, and voids (Fig. 4). The voids probably contained or still contain fluids (gas or liquid)
464 from which the nature is still to be identified, in a potential further study focused on those
465 inclusions, although quantitative fluid inclusions studies in martian meteorites have not been
466 successful to date, probably due to issues of shock-induced splitting, or sample contamination
467 during polishing (Bridges and Schwenzer, 2012). Their alignment, their euhedral shape, with their
468 triphasic texture and the presence of a void are characteristics of secondary fluid inclusions as
469 observed in terrestrial basalts. Those secondary inclusions form potentially from an oxidizing
470 tardi-magmatic fluid assisted event, predating and distinct from the the iddingsite forming event
471 (Fig. 14). In CeC 022, those secondary alteration can be observed at the center of some iddingsite
472 veins, with the addition of low abundance of nanoscale apatite and pyrrhotite (Fig. 4A, Table 2).
473 They represent weakness planes, similar to stamp perforations, easing the circulation of the fluid
474 inside the olivine.

475 In most nakhlites, symplectites of pyroxene and magnetite shaped as “herring-bone” were
476 observed (Fig. 4) individually or in contact with the secondary inclusions. Similar symplectites
477 were already observed in olivine grains of Nakhla (Fig. 4D) and Governador Valadares, and
478 described as symplectite exsolutions (Mikouchi et al., 2000). Our study shows that they are found
479 intermixed with the secondary inclusions and/or in fractures, showing similar composition to the
480 secondary inclusions (Fig. 4). Furthermore, no chemical zonation of the olivine can be observed
481 (Fig 6), and the composition with high-Ca content cannot be explained by the host low-Ca olivine
482 (Table 2). The non isochemical composition compared to olivine, together with the textural and
483 chemical links with the secondary inclusions, do not support the formation mechanism of the
484 symplectites by exsolution of the olivine. Their morphology shows a reaction texture, formed in
485 contact with the host crystal. Their crystallization is related to the formation of the secondary
486 inclusions and occurred during the same oxidizing tardi-magmatic fluid-assisted alteration event
487 (Fig. 14). Furthermore, CeC 022 and MIL 03346 show those magnetite-pyroxene symplectite as a
488 center of the veins, representing weakness planes for the alteration fluid to pass through the olivine
489 together with the secondary inclusions.

490

**4.4.2 Iddingsite formation**
Changela and Bridges (2010) described the conditions of alteration of the nakhlites in an impact-induced hydrothermal fluid alteration model, where the iddingsite crystallize in shock-induced fractures suggesting dominant *in situ* dissolution of olivine around preexisting fracture. However, our study shows that the contact between olivine and coarse iddingsite are created mainly by fracture filling from a fluid enriched in elements before contact with the host olivine, and only selective dissolution of the host olivine along etch pits (Fig. 7). In addition, a scenario in which iddingsite is formed primarily by *in situ* dissolution cannot explain the layering of coarse and fine iddingsite, and the chemical zoning observed in the fine iddingsite (Fig. 10, Fig. 11). All nakhlites show a thin center of vein up to 1 µm, made of material with a lower average atomic number that is a chemical variation of the fine iddingsite (Fig. 2C). Lee et al. (2018) proposed that the thin center of vein with lower average atomic number, together with the different chemistry of the two types of iddingsite, indicate a crystallization by centripetal replacement starting from a hairline fracture, being the crystallization from the vein axis outwards, as proposed for the serpentinization of terrestrial olivine (Delvigne et al., 1979; Velbel, 2012). Thus, the formation of the iddingsite veins as observed in the nakhlites would start with initial crystallization of fine iddingsite and subsequent formation of coarse iddingsite.

The major composition in Fe, Mg and Si of the iddingsite is explained by a fluid composition mainly composed by dissolution of magmatic minerals such as olivine and pyroxene from basaltic rocks (Table 1). The olivine hosting the iddingsite veins does not display chemical zoning at contact with the iddingsite, and the magnetite-pyroxene symplectite do not display composition change when in contact the iddingsite (Fig. 10, Fig. 11). In addition, the carbon-rich organic matter pockets in the coarse iddingsite (Fig. 5, Fig. 12, Fig. S1), and the siderite and the Ca-rich zones in the fine iddingsite (Fig. 11), and the presence of Fe-rich carbonates in Lafayette, cannot be created
by an isochemical alteration of low-Ca olivine in the nakhlites. Al and Ca enrichment in the 514 515 iddingsite cannot be explained by dissolution of the host olivine alone, but by clinopyroxene 516 dissolution (Table 1). We conclude that the iddingsite alteration event originates from an impact- 517 induced heating resulting in the melting of the permafrost, inducing a circulation of fluid, with 518 crystallization of iddingsite inside olivine grains are formed dominantly by fractures filling, with 519 small selective dissolution of olivine along etch pits, in an open system by the circulation of 520 aqueous fluids rich in Si, Mg, Fe, Ca, Al, as well as organic matter from external dissolution of 521 basaltic minerals. 522

Organic matter inside the coarse iddingsite is detected by Raman spectroscopy (Fig. 6), and NWA 522 523 10153 displays carbon-rich pockets of around 200 nm on TEM (Fig. 5, Fig. 12). Organic matter 524 has already been studied in martian meteorites, in ALH84001 using isotopic measurement (McKay 525 et al., 1996; Becker et al., 1999), or pyrolysis (Sephton et al., 2002); in Tissint by isotopic analyses 526 (Lin et al., 2014), or in Nakhla by isotopic analyses (Jull et al., 2000). Here we provide the first 527 precise location of potential organic matter in nakhlites, and clear genetic link with aqueous 528 activity and iddingsite formation on Mars. Further isotopic studies of this organic matter, by nano- 529 SIMS, could provide insights into the composition and the origin of organic matter on Mars, such 530 as done on Y 000593 by McLoughlin et al. (2019). 531

### 4.4.3 Sulfide-magnetite veinlets

Veinlets of magnetite and sulfide are observed at the center of some iddingsite veins, as well as in 532 pyroxene and mesostasis (without iddingsite), and sometimes crosscutting iddingsite veins (Fig. 533 4). By rules of relative chronology, they have to be related to an alteration event postdating the 534 iddingsite formation event. Although, we cannot rule out that they could also represent a late stage 535 of the same alteration event as the iddingsite, with the evolution of the composition of the alteration 536
fluid becoming more oxidizing, allowing the crystallization of late magnetite and sulfide veins
(Changela and Bridges, 2010; Chevrier et al., 2011) (Fig. 14).

## 4.5 Iddingsite formation conditions

The petrographic and mineralogic similarities of the iddingsite observed in all nakhlites suggest that they were altered under similar physicochemical conditions. Iddingsite is composed mainly of an assemblage of phyllosilicates (Fig. 8), crystallized from a fluid at low temperature (< 100 °C), and with low water/rock ratios (Treiman et al., 1993; Treiman and Lindstrom, 1997; Mustard et al., 2008; Changela and Bridges, 2010). Detailed iddingsite aqueous alteration conditions, such as Eh-pH condition and temperature, were calculated for Nakhla siderite and saponite/serpentine-like phyllosilicate replacement around 75-100 °C and pH = 4, with water/rock ratio (W/R) = 100 (Bridges and Schwenzer, 2012). The anoxic conditions existing at the martian surface can result in the observed dominance of Fe-rich phyllosilicates observed in the iddingsite. Also, the mobilization of Al occurs in fluid with low pH (Stumm and Morgan, 1996). In summary, the formation of iddingsite probably occurs by hydrothermal acidic fluid dissolution of basaltic rocks, originating from melted permafrost heated by nearby volcanic activity or impact events (Borg and Drake, 2005; Changela and Bridges, 2010).

Similar alteration phases are found in Antarctic basalts, with fluid alteration conditions being a good analogue of martian alteration conditions (Allen and Conca, 1991; Hallis and Taylor, 2011). Those alteration phases are created from the complete evaporation of a low amount of water, while the basalts retain residual heat. This creates a rapid and low-temperature precipitation of crystalline salts, with a Si, Al, K and Mg-rich gel formation. On Earth, the gel is later converted into a mixture of quartz and phyllosilicates (illite) aided by solar illumination. A similar formation for martian iddingsite may have happened on Mars, with slightly different fluid and basalt compositions. In
addition, the solar illumination on Mars being weaker, or the nakhlites being at the subsurface, the
recrystallization could also be only partial, explaining the low crystallinity of the fine iddingsite.

The debate about the δD of iddingsite material reflecting the hydrogen isotopic compositions of
the martian fluid or contamination by terrestrial water has already been discussed in the literature
(Gillet et al., 2002; Hallis et al., 2012; Lee et al., 2018). The martian atmosphere δD value is
measured around 4200 ‰ (Bjoraker et al., 1989). With a fractionation factor of 0.94 from the
martian atmosphere, the martian iddingsite would have δD values of 3880-3950 ‰, depending on
the composition of the iddingsite (Hallis et al., 2012). Nakhla is the only nakhlite observed fall,
and is thus likely the least contaminated by terrestrial water. It shows the highest δD value, with
1165 ± 116 ‰, being the closest value to the theoretical value (Hallis et al., 2012). Other Nakhlites
all show lower values, with our three nakhlites show values ranging from -169 to -2 ‰ (Fig. 13).

Nakhlites all have been exposed either to terrestrial water, and/or to terrestrial atmosphere either
since their fall, or during sample preparation and/or sample storage. While it remains possible that
the negative δD values of the nakhlites reflect the composition of a fluid derived from the martian
mantle, the highest δD of iddingsite in Nakhla indicates that the δD of iddingsite preserved from
terrestrial isotopic contamination is closer to martian atmospheric values. In addition, a thin section
of Nakhla, which has been exposed to atmosphere since its preparation in 1998, shows negative
δD, proving that the isotope exchange in the iddingsite happens rapidly (Hallis et al., 2012). The
variation in δD between our three studied nakhlites (CeC 022, NWA 817, NWA 10153) could
reflect variable initial signatures, as isotopic resetting on Earth of interlayer water in serpentine is
less efficient than for smectite (Fig. 13). Although, it could also reflect heterogenous terrestrial
contamination amongst the Nakhlites, making the δD values measured in our three nakhlites reflect
different alteration by terrestrial atmosphere and water exposure, rather than a fluid composition
variation (Fig. 13).

## 4.6 Single or multiple fluid circulation ?

The inclusions of pyroxene, magnetite and void probably containing fluid, found in the olivine
grains, are interpreted as secondary fluid inclusions from a first alteration event (Fig. 4). Those
secondary inclusions are created by an initial potentially a tardi-magmatic fluid circulation (Fig.
14), probably happening just after the crystallization of the Nakhlites around 1.3-1.4 Ga, previous
and distinct from the iddingsite alteration event (Nyquist et al., 2001; Korochantseva et al., 2011;
Herzog et al., 2015; Wieler et al., 2016; Cohen et al., 2017).

The physical aspect of the fine iddingsite in NWA 10153, with chemical zoning and a sub-vein,
suggest at least two fluid circulation, with remobilization of element such as Fe and S (Fig. 11).
Only one of two samples observed by TEM-EDS mapping (CeC 022 and NWA 10153) shows this
complex chemical zoning in the fine iddingsite. At this stage, we cannot conclude whether NWA
10153 is an exception, or if others nakhlites may bear evidence for multiple fluid circulation. Thus,
the global iddingsite formation event, dated ~650-700 Myr (Shih et al., 1998; Swindle et al., 2000;
Misawa et al., 2003; Tremblay 2020) could be the result of a series of fluid circulations (Fig. 14).
Finally, veinlets of magnetite and sulfides are observed at the center of some iddingsite veins (e.g.,
CeC 022, Fig. 2). They are probably related to a new alteration event, postdating the iddingsite
formation and represent a separate final fluid circulation (Fig. 14), between 650-700 Myr and the
ejection age of ~10 Myr (Nyquist et al., 2001; Herzog et al., 2015; Cohen et al., 2017). Multistage
alteration has already been described in martian meteorites, such as in ALH84001 which shows a
multistage formation of carbonate nodules with two generation of carbonates evidenced by a very
sharp change in composition (Moyano-Cambero et al., 2017). The change of composition
supporting a multistage aqueous alteration is similarly observed in the iddingsite veins of the nakhlites, especially CeC 022.

## 4.7 Martian iddingsite compared to terrestrial iddingsite

Iddingsite material is found in terrestrial rocks as the alteration product of olivine that is the first mineral to be altered in the earlier stages of volcanic rock alteration. The terrestrial iddingsite is formed in hydrothermal condition and the interaction of Mg-rich fluids with glass and primary minerals, resulting in smectite formation (Środoń et al., 2019; Vingiani et al., 2010; García-Romero and Suarez, 2021). The phyllosilicates formed are mainly Fe-smectite, Fe-saponite and Fe-rich dioctahedral type phyllosilicates (García-Romero et al., 2005; Christidis, 2006; Giorgetti et al., 2009; Rasmussen et al., 2010). Kendrick and Jamieson (2016) showed that terrestrial metagabbro with iron-oxides contain iddingsite alteration with similar compositions as the martian iddingsite, although with slightly smaller amount of ferric oxides (Lee et al., 2015). Additionally to oxidizing fluid conditions on Mars (Hick et al., 2014), octahedral site substitutions of Fe²⁺ and Fe³⁺ in smectite solid solutions have been experimentally confirmed (Grauby et al., 1994) and could create the higher Fe content in the smectite found in the Fe-rich terrestrial and martian iddingsite. Another difference between terrestrial and martian assemblages is that the secondary alteration fluid was described to be dominated by Fe-rich carbonate composition, at least in the early stages of alteration, in some studied martian meteorites such as Lafayette and ALH84001 (Moyano-Cambero et al., 2017; Piercy et al. 2022).

Terrestrial basaltic rocks alteration can also form palagonite from the alteration of the glass mesostasis (García-Romera and Suarez, 2021), which could represent an analogue to martian iddingsite, in terms of texture, chemistry and formation. Palagonite is a complex material consisting of poorly crystallized phyllosilicates (smectite and/or serpentine intergrowths), similar
628 to what we observe in our nakhlites. Palagonite formation is two-staged : (1) dissolution of glass
629 and precipitation of amorphous material; (2) reaction with the surrounding fluid and crystallization
630 of smectite. Palagonite shows chemical variation with enrichment in Mg and Fe and
631 impoverishment in Al, Na, and K. This can be compared to the compositional variations
632 between fine and coarse iddingsites in nakhlites, mainly observed in Si, Fe, Mg, Ca, and Al,
633 although with different elements due to martian alteration conditions (Table 1). Finally, palagonite
634 was already reported as being a good analog to the soil of Mars, for the Viking and Earth-based
635 spectral measurements, in bulk composition, particle size, reflectance spectra, and magnetic
636 properties (Allen et al., 1981).

637 5 Martian iddingsite from orbital observations

638 The infrared mapping spectrometer CRISM on Mars Reconnaissance Orbiter and OMEGA on the
639 Mars Express have been used to identify phyllosilicates and carbonates at the surface of Mars.
640 Phyllosilicates (smectite and serpentine) and carbonates (siderite), similar to the ones identified in
641 the iddingsite, have been observed in complex craters in the Noachian or Hesperian terrains on
642 Mars (Bibring et al., 2005; Poulet et al., 2005; Ehlmann et al., 2008; Mustard et al., 2008).
643 Phyllosilicates have been observed in walls, ejecta and more especially in central peaks of the
644 ancient highlands of Mars. The conditions for the formation of smectite in complex craters have
645 been suggested to involve impact-induced hydrothermal activity, with water and warm
646 temperatures, at the surface or subsurface of Mars (Poulet et al., 2005; Mustard et al., 2008;
647 Schwenzer and Kring, 2009), compatible with the conditions suggested for the formation of
648 iddingsite in the nakhlites. On the other hand, Fe-Mg-phyllosilicates (clays group, including
649 smectite), have been reported as not being exclusively attributed to aqueous alteration processes,
650 but may also indicate changes in volcanic eruption styles (Meunier et al., 2012). Further data such
as higher rare earth elements and isotopic signature similar to martian magma could support this scenario (Meunier et al., 2012). More recently, Mars2020 Perseverance mission in the Jezero crater has detected clay formation inside the Nili Fossae olivine-clay-carbonate lithology, called the Séitah unit. They detected smectite clay minerals, talc, using in situ SuperCam multitechnique instrument suite, as well as new orbital CRISM maps (e.g. Brown et al., 2023 and references therein).

## 6 Conclusion

In all nine studied nakhlites, we observed complex alteration veins reflecting an alteration history made of multiple alteration events. Secondary fluid inclusion planes and symplectite exsolutions, suggest a first fluid alteration event, previous to iddingsite formation, probably from the circulation of a late magmatic fluid. Those secondary inclusions and symplectites can be observed at the center of iddingsite veins, inside the most altered nakhlites, and represent weakness planes easing the circulation of the fluid inside the olivine grains forming the iddingsite. In all nakhlites, we observed two types of iddingsite: the first to form is a fine iddingsite showing a nanocrystalline to amorphous texture with crystalline domains <10 nm, then a coarse iddingsite showing a crystallized texture with crystals around 50 nm, up to 200 nm. The two different iddingsites show progressive evolution of the alteration fluid as observed both texturally and chemically, that could be explained by a switch in the alteration conditions of the system and the temporal evolution of the alteration condition and/or fluid composition. Finally, sulfide-magnetite veinlets at the center of iddingsite veins of CeC 022 and NWA 10153 could represent a later and distinct alteration event with the circulation of a different fluid. With the complex different centers of veins and the complex chemical zoning in the fine iddingsite, we suggest that the history of the fluid alteration in the nakhlites is made of multistage fluid circulations of a fluid rich in Si, Mg, Fe, Ca, Al, S and C
provided by the dissolution of basaltic minerals. The variation in iddingsite composition and
abundance among nakhlites must be related to the combination of multiple factors such as distance
from the fluid and heat source. The composition of the iddingsite veins (poorly crystallized
smectite and serpentine) suggest physiochemical conditions at temperature of 50 °C and alkaline
pH and low water/rock ratio. The presence of aqueous alteration products in martian meteorites
proves that water activity triggered by volcanism or impact was still present of Mars even for
recent periods (650-700 Ma), and that Mars water activity is only dormant at the subsurface, only
waiting to be awakened by geologic activity.

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910

<figure><img src="image_1.png" /></figure>

Figure 1: Photo of CeC 022 nakhlite after cutting out the type specimen. Note the reddish spots (arrows) being the iddingsite-bearing olivine phenocrysts.

911
<figure><img src="image_2.png" /><figcaption>Figure 2: BSE images of iddingsite veins in olivine: A: CeC 022, with magnetite-pyroxene symplectite as center of vein. B: CeC 022 with magnetite and sulfide veinlet as center of vein. C: NWA 817. D: Lafayette. E, F: Patches of iddingsite observed in the mesostasis of CeC 022. Iddingsite is showed by the red arrows. Idd c: coarse iddingsite; Idd f: fine iddingsite; Mt: magnetite; Sul: sulfide; Ilm: ilmenite; Ol: olivine; Px: pyroxene.</figcaption></figure>
<figure><img src="image_3.png" /><figcaption>Figure 3: Total volume fraction of secondary minerals in olivine (i.e. veining volume). GV: Governador Valadares.</figcaption></figure>
<figure><img src="image_4.png" /></figure>

Figure. 4: BSE images. A: iddingsite starting the crystallize around secondary inclusions (red arrow) composed of magnetite, pyroxene and a void and symplectites (blue arrow) of magnetite and pyroxene inside an olivine grain of CeC 022. B: symplectites and secondary inclusions. We observe that the symplectites seem to grow in contact with the plane of secondary inclusions. C: large view of secondary inclusion planes showing no preferential direction in olivine grains. D: symplectite observed in an olivine grain in Nakhla in a fracture for comparison. E: veinlets of sulfide (pyrrhotite) and magnetite. The vertical veinlet has no iddingsite envelope, in contrary to the diagonal veinlet. F: sulfide (pyrrhotite) veinlets crossing an iddingsite vein. Idd: iddingsite; Px: pyroxene; Mt: magnetite; Ol: olivine; Sulf: sulfide; Symp: symplectite; Incl : secondary inclusion.
<figure><img src="image_5.png" /><figcaption>Figure 5: Raman spectra of coarse and fine iddingsite in the 9 studied nakhlites. Dashed blue lines: major peaks; orange vertical band: organic matter signature zone. Spectra are normalized by maximum intensities and shifted for comparison.</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>Figure 6: a) High resolution TEM (HRTEM) image of coarse iddingsite in Lafayette Lafayette from iddingsite veins inside olivine. b) Diffraction pattern of coarse iddingsite in Lafayette from iddingsite veins inside olivine. c) High-resolution TEM (HRTEM) image of fine iddingsite Lafayette from iddingsite veins inside olivine in Lafayette. d) Diffraction pattern of fine iddingsite Lafayette from iddingsite veins inside olivine in Lafayette. Numbers correspond to d-spacing measurements.</figcaption></figure>
920

<figure><img src="image_7.png" /></figure>

Figure 7: Bright Field (BF) TEM images of the contact between coarse iddingsite and olivine, and between coarse and fine iddingsite in two nakhlites. A: Lafayette; B: NWA 10153. Ol: olivine; Idd: iddingsite.

921
<figure><img src="image_8.png" /><figcaption>Figure 8: MgO vs Fe₂O₃ vs (SiO₂ + Al₂O₃) (wt%) ratios of fine and coarse iddingsite in nakhlites alteration veins in olivine. The horizontal lines are stoichiometric (Mg, Fe) solid solutions compositions of nontronite, saponite, and serpentine.</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>Figure 9: Transect microprobe major elements analyses in iddingsite veins in olivine. Background colors represent the iddingsite types or olivine. Lafayette and NWA 998 have not been measured.</figcaption></figure>
<figure><img src="image_10.png" /><figcaption>Figure 10: A: STEM image of an iddingsite vein in CeC 022. B: EDS map of the iddingsite vein. C: Zoom of the coarse iddingsite of the vein. D: schematic representation of the different major element variation in the iddingsite vein in CeC 022. Sulf: sulfide; Ap: apatite; Mag: magnetite; Ca-px: Ca-pyroxene; Idd: iddingsite; Ol: olivine.</figcaption></figure>
<figure><img src="image_11.png" /><figcaption>Figure 11: Left: STEM-EDS map of an iddingsite vein in NWA 10153. Idd: iddingsite; Ol: olivine. Right: schematic representation of different major element variation in the different iddingsite subtypes.</figcaption></figure>
<figure><img src="image_12.png" /><figcaption>Figure 12: Top and middle rows : Zoom of zone A of Fig. 11. Inhomogeneous coarse iddingsite. Idd: iddingsite; Ol: olivine. Bottom row : Zoom of zone B of Fig. 11 of: coarse iddingsite type 2c with potential OM pockets. Idd: iddingsite; Ol: olivine; OM: organic matter.</figcaption></figure>
<figure><img src="image_13.png" /></figure>

Figure 13: Hydrogen isotope data obtained by SIMS on iddingsite materials in three nakhlites. Colored rectangles for comparisons: NWA 817 (Gillet al., 2002); MIL 003346, Y 000593 and Nakhla (data up to 1165 ± 116 ‰ not shown in the figure) (Hallis et al., 2012).
<figure><img src="image_14.png" /></figure>

Zoom

<figure><img src="image_15.png" /></figure>

Crystallization of the nakhlites

<figure><img src="image_16.png" /></figure>

Injection of tardi-magmatic fluid
Formation of planes of secondary inclusions
and symplectites

<figure><img src="image_17.png" /></figure>

First aqueous fluid injection
Alteration of the olivine into fine
iddingsite

<figure><img src="image_18.png" /></figure>

Small dissolution of olivine
Crystallisation of coarse iddingsite
Second (?) fluid injection

<figure><img src="image_19.png" /></figure>

Third (?) fluid injection
Formation of magnetite-sulfides veinlets
<caption>Fig. 14 : Summarized schematic illustration of the fluid alteration of nakhlites.</caption>

<table><caption>Table 1. Major element compositions of the coarse and fine iddingsite in different nakhlite (in wt%)</caption><thead><tr><th></th><th></th><th>SiO<sub>2</sub></th><th>TiO<sub>2</sub></th><th>Al<sub>2</sub>O<sub>3</sub></th><th>Cr<sub>2</sub>O<sub>3</sub></th><th>Fe<sub>2</sub>O<sub>3</sub>*</th><th>MnO</th><th>MgO</th><th>CaO</th><th>Na<sub>2</sub>O</th><th>K<sub>2</sub>O</th><th>SO<sub>2</sub></th><th>NiO</th><th>P<sub>2</sub>O<sub>5</sub></th><th>Cl</th><th>Total</th><th>FeO<br>/SiO<sub>2</sub></th></tr></thead><tbody><tr><td colspan="2"><strong>Coarse iddingsite n</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>CeC 022</td><td>19</td><td>28.0</td><td>0.02</td><td>0.18</td><td>bdl</td><td>59.3</td><td>1.52</td><td>2.47</td><td>1.47</td><td>0.16</td><td>0.04</td><td>0.09</td><td>0.03</td><td>0.32</td><td>0.07</td><td>93.7</td><td>1.91</td></tr><tr><td>Gov. Val.</td><td>2</td><td>31.3</td><td>0.03</td><td>0.03</td><td>0.01</td><td>50.6</td><td>1.01</td><td>9.35</td><td>0.41</td><td>0.28</td><td>0.14</td><td>0.06</td><td>0.04</td><td>bdl</td><td>0.17</td><td>93.4</td><td>1.45</td></tr><tr><td>MIL 03346</td><td>15</td><td>32.1</td><td>0.05</td><td>0.29</td><td>bdl</td><td>58.1</td><td>0.95</td><td>7.49</td><td>0.28</td><td>0.02</td><td>0.01</td><td>0.72</td><td>bdl</td><td>0.15</td><td>0.03</td><td>100</td><td>1.63</td></tr><tr><td>Nakhla</td><td>3</td><td>29.3</td><td>0.04</td><td>0.03</td><td>bdl</td><td>53.2</td><td>0.89</td><td>9.01</td><td>0.58</td><td>0.32</td><td>0.20</td><td>0.01</td><td>0.01</td><td>bdl</td><td>0.36</td><td>94.0</td><td>1.63</td></tr><tr><td>NWA 10153</td><td>5</td><td>32.4</td><td>0.06</td><td>0.23</td><td>0.01</td><td>59.7</td><td>0.88</td><td>4.53</td><td>1.08</td><td>0.05</td><td>0.09</td><td>0.24</td><td>bdl</td><td>0.27</td><td>0.04</td><td>99.6</td><td>1.66</td></tr><tr><td>NWA 817</td><td>4</td><td>33.3</td><td>0.03</td><td>1.78</td><td>0.02</td><td>51.8</td><td>0.75</td><td>6.78</td><td>1.76</td><td>0.10</td><td>0.39</td><td>0.08</td><td>0.01</td><td>0.21</td><td>0.02</td><td>97.0</td><td>1.40</td></tr><tr><td>Y 000593</td><td>6</td><td>23.1</td><td>0.01</td><td>0.68</td><td>0.05</td><td>59.7</td><td>1.66</td><td>1.91</td><td>0.49</td><td>0.03</td><td>0.06</td><td>0.76</td><td>0.03</td><td>0.02</td><td>bdl</td><td>88.5</td><td>2.33</td></tr><tr><td>Lafayette<sup>a</sup></td><td>30</td><td>49.5</td><td>0.01</td><td>4.48</td><td>0.00</td><td>32.3</td><td>0.49</td><td>13.6</td><td>0.72</td><td>0.33</td><td>0.35</td><td>0.81</td><td>0.01</td><td>0.09</td><td>0.45</td><td>103</td><td>0.59</td></tr><tr><td>Average<br>without Lafayette</td><td></td><td>29.9</td><td>0.03</td><td>0.46</td><td>0.02</td><td>56.1</td><td>1.09</td><td>5.94</td><td>0.87</td><td>0.14</td><td>0.13</td><td>0.28</td><td>0.02</td><td>0.19</td><td>0.10</td><td>95.2</td><td>1.72</td></tr><tr><td>max</td><td></td><td>33.3</td><td>0.06</td><td>1.78</td><td>0.05</td><td>59.7</td><td>1.66</td><td>9.35</td><td>1.76</td><td>0.32</td><td>0.39</td><td>0.76</td><td>0.04</td><td>0.32</td><td>0.36</td><td>100</td><td>2.33</td></tr><tr><td>min</td><td></td><td>23.1</td><td>0.01</td><td>0.03</td><td>bdl</td><td>50.6</td><td>0.75</td><td>1.91</td><td>0.28</td><td>0.02</td><td>0.01</td><td>0.01</td><td>bdl</td><td>0.02</td><td>bdl</td><td>88.5</td><td>1.40</td></tr><tr><td colspan="2"><strong>Fine iddingsite n</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>CeC 022</td><td>27</td><td>49.2</td><td>0.12</td><td>1.59</td><td>0.01</td><td>34.5</td><td>0.90</td><td>3.44</td><td>1.22</td><td>0.57</td><td>0.18</td><td>0.03</td><td>0.01</td><td>0.12</td><td>0.03</td><td>91.9</td><td>0.63</td></tr><tr><td>Gov. Val.</td><td>3</td><td>44.3</td><td>0.03</td><td>0.06</td><td>0.01</td><td>33.8</td><td>0.54</td><td>7.77</td><td>0.31</td><td>0.32</td><td>0.31</td><td>0.12</td><td>bdl</td><td>bdl</td><td>0.41</td><td>88.0</td><td>0.69</td></tr><tr><td>MIL 03346</td><td>18</td><td>44.9</td><td>0.09</td><td>0.27</td><td>0.01</td><td>38.3</td><td>0.54</td><td>2.88</td><td>1.76</td><td>0.04</td><td>0.08</td><td>0.60</td><td>bdl</td><td>1.04</td><td>0.32</td><td>90.9</td><td>0.77</td></tr><tr><td>Nakhla</td><td>6</td><td>41.9</td><td>0.03</td><td>0.14</td><td>0.01</td><td>39.8</td><td>0.51</td><td>6.56</td><td>0.34</td><td>0.19</td><td>0.64</td><td>0.02</td><td>0.03</td><td>0.02</td><td>0.42</td><td>90.6</td><td>0.85</td></tr><tr><td>NWA 10153</td><td>17</td><td>41.2</td><td>0.10</td><td>0.21</td><td>0.01</td><td>46.0</td><td>0.25</td><td>2.50</td><td>2.15</td><td>0.08</td><td>0.32</td><td>0.30</td><td>0.01</td><td>0.19</td><td>0.04</td><td>93.4</td><td>1.01</td></tr><tr><td>NWA 817</td><td>21</td><td>38.4</td><td>0.04</td><td>1.38</td><td>0.01</td><td>43.3</td><td>0.47</td><td>4.56</td><td>1.51</td><td>0.17</td><td>0.56</td><td>0.21</td><td>0.01</td><td>0.17</td><td>0.02</td><td>90.9</td><td>1.01</td></tr><tr><td>Y 000593</td><td>1</td><td>44.0</td><td>0.10</td><td>0.70</td><td>0.05</td><td>34.3</td><td>1.45</td><td>0.90</td><td>0.47</td><td>0.05</td><td>0.12</td><td>0.69</td><td>bdl</td><td>bdl</td><td>0.02</td><td>82.9</td><td>0.70</td></tr><tr><td>Lafayette<sup>a</sup></td><td>23</td><td>50.3</td><td>0.01</td><td>4.16</td><td>0.00</td><td>30.9</td><td>0.49</td><td>14.5</td><td>0.75</td><td>0.30</td><td>0.38</td><td>0.83</td><td>0.09</td><td>0.09</td><td>0.39</td><td>103</td><td>0.55</td></tr><tr><td>Average<br>without Lafayette</td><td></td><td>43.4</td><td>0.07</td><td>0.62</td><td>0.01</td><td>38.6</td><td>0.66</td><td>4.09</td><td>1.11</td><td>0.20</td><td>0.32</td><td>0.28</td><td>0.01</td><td>0.31</td><td>0.18</td><td>89.8</td><td>0.81</td></tr><tr><td>max</td><td></td><td>49.1</td><td>0.12</td><td>1.59</td><td>0.05</td><td>46.0</td><td>1.45</td><td>7.77</td><td>2.15</td><td>0.57</td><td>0.64</td><td>0.69</td><td>0.03</td><td>1.04</td><td>0.42</td><td>93.4</td><td>1.01</td></tr><tr><td>min</td><td></td><td>38.4</td><td>0.03</td><td>0.06</td><td>0.01</td><td>33.8</td><td>0.25</td><td>0.90</td><td>0.31</td><td>0.04</td><td>0.08</td><td>0.02</td><td>bdl</td><td>0.02</td><td>0.02</td><td>82.9</td><td>0.63</td></tr></tbody></table>

Bdl: below detection limit

a: Lee et al., 2015; *: total Fe content
<table><caption>Table 2. EDS compositions of secondary inclusions-symplectite in the center of iddingsite vein in CeC 022</caption><thead><tr><th>at%</th><th>Magnetite</th><th>Augite</th><th>Sulfide</th><th>Apatite</th></tr></thead><tbody><tr><td>Al</td><td>0.41</td><td>0.29</td><td>na</td><td>0.07</td></tr><tr><td>Ca</td><td>bdl</td><td>9.47</td><td>na</td><td>24.0</td></tr><tr><td>Cr</td><td>0.2</td><td>0.02</td><td>na</td><td>na</td></tr><tr><td>Fe</td><td>42.9</td><td>4.05</td><td>46.8</td><td>0.27</td></tr><tr><td>Mg</td><td>0.04</td><td>6.16</td><td>na</td><td>na</td></tr><tr><td>Mn</td><td>0.35</td><td>0.13</td><td>na</td><td>na</td></tr><tr><td>Ni</td><td>0.06</td><td>0.02</td><td>0.56</td><td>na</td></tr><tr><td>O</td><td>53.5</td><td>58.6</td><td>na</td><td>61.3</td></tr><tr><td>P</td><td>bdl</td><td>0.04</td><td>na</td><td>14.1</td></tr><tr><td>K</td><td>bdl</td><td>bdl</td><td>na</td><td>na</td></tr><tr><td>Si</td><td>0.22</td><td>20.9</td><td>na</td><td>0.19</td></tr><tr><td>Na</td><td>bdl</td><td>0.36</td><td>na</td><td>na</td></tr><tr><td>S</td><td>0.08</td><td>bdl</td><td>52.6</td><td>na</td></tr><tr><td>Ti</td><td>2.13</td><td>bdl</td><td>na</td><td>na</td></tr><tr><td>Tot</td><td>100</td><td>100</td><td>100</td><td>100</td></tr></tbody></table>

Bdl: below detection limit. na: not analyzed

<table><caption>Table 3. D/H ratios and H₂O content estimated from SIMS measurements of iddingsite veins in 3 nakhlites</caption><thead><tr><th>Names</th><th>N</th><th>D/H x 10<sup>-4</sup></th><th>Error x 10<sup>-6</sup></th><th>δD (‰)</th><th>Error (‰)</th><th>H<sub>2</sub>O (wt%)</th></tr></thead><tbody><tr><td>CeC 022</td><td>9</td><td>1.44</td><td>6.37</td><td>-75.4</td><td>40.9</td><td>7.21</td></tr><tr><td>NWA 10153</td><td>5</td><td>1.51</td><td>6.84</td><td>-31.7</td><td>43.9</td><td>8.36</td></tr><tr><td>NWA 817</td><td>6</td><td>1.30</td><td>6.95</td><td>-165.7</td><td>47.9</td><td>9.87</td></tr></tbody></table>