N Mari
email: n.mari.1@research.gla.ac.uk.

A J V Riches

L J Hallis

Y Marrocchi

J Villeneuve

P Gleissner

H Becker

M R Lee

Syneruptive incorporation of martian surface sulphur in the nakhlite lava flows

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Abstract

Martian lava flows likely acquired S-rich material from the regolith during their emplacement on the planet's surface. We investigated five of the twenty known nakhlites (Nakhla, Lafayette, Miller Range (MIL) 090032, Yamato 000593, and Yamato 000749) to determine whether these lavas show evidence of regolith assimilation, and to constrain the potential implications that this process has on chemical tracing of martian mantle source(s). To establish the proportionate influence of atmospheric, hydrothermal, and volcanic processes on nakhlite isotopic systematics we obtained in situ sulphur isotope data (Δ 33 S and δ 34 S) for sulphide grains (pyrrhotite and pyrite) in all five nakhlite samples. For Nakhla, Lafayette, and MIL 090032, these data are integrated with highly siderophile element (HSE) abundances and Os-isotope compositions, as well as textural information constrained prior to isotopic analysis. This work thereby provides the first Re-Os isotope systematics for two different nakhlites, and also the first Re-Os isotope data for martian sample for which detailed petrographic information was constrained prior to digestion.

We report the largest variation in δ 34 S yet found in martian meteorites (-13.20 ‰ to +15.16 ‰). The relatively positive Δ 33 S and δ 34 S values of MIL 090032 (δ 34 S = +10.54 ± 0.09 ‰; Δ 33 S = -0.67 ± 0.10 ‰) indicate this meteorite assimilated sulphur affected by UV-photochemistry. In contrast, the strongly negative values of Lafayette (δ 34 S = -10.76 ± 0.14 ‰; Δ 33 S = -0.09 ± 0.12 ‰) are indicative of hydrothermal processes on Mars. Nakhla, Yamato 000593, and Yamato 000749 sulphides have a narrower range of sulphur isotope compositions (Δ 33 S and δ 34 S ~ 0) that is consistent with no assimilation of martian surface materials during lava flow emplacement. Consequently we used this second group of Δ 33 S values to approximate the Δ 33 S of the nakhlite source, yielding a Δ 33 S value of -0.1 ‰.

Nakhlite HSE patterns result from a sulphide-saturated melt where Ru-Os-Ir alloys/sulphide were likely crystallized during earlier phases of magmatic processing in Mars to result in the fractionated HSE patterns of the nakhlites. Our data, alongside a synthesis of previously published data, suggest assimilation of an enriched component to the primary nakhlite melt, potentially a late-stage crystallization cumulate from the martian magma ocean stage. In the context of this model, and within large uncertainties, our data hint at perturbation and potential decoupling of nakhlite Re-Os isotope systematics from other isotopic systems as a result of small degrees of assimilation of a regolith component with highly radiogenic 187 Os/ 188 Os.

-Introduction

Magmas represent windows to comprehend the interior evolution and geochemical diversity of terrestrial planets. Magmatic activity and degassing are key processes for transferring sulphur, along with other elements, from the interior to the surface during the evolution of a planetary body. In the case of Mars, low water activity, low temperatures, and the lack of plate tectonics has favoured the preservation of a sulphur-rich regolith during the last ~2 billion years [START_REF] King | Sulfur on Mars[END_REF]. In fact, the martian regolith contains concentrations of SO 2 up to 8 wt.% [START_REF] Clark | Inorganic analyses of Martian surface samples at the Viking landing sites[END_REF][START_REF] Foley | Final chemical results from the Mars Pathfinder Alpha Proton X-ray Spectrometer[END_REF].

The terrestrial and martian mantles have been reported to contain similar and chondrite-relative highly siderophile elements (HSE; Os, Ir, Ru, Rh, Pt, Pd, Au, and Re) abundances [START_REF] Birck | Contrasting Re/Os magmatic fractionation in planetary basalts[END_REF][START_REF] Warren | Siderophile trace elements in ALHA84001, other SNC meteorites and eucrites: evidence of heterogeneity, possibly time-linked, in the mantle of Mars[END_REF][START_REF] Brandon | Re-Os isotopic evidence for early differentiation of the Martian mantle[END_REF][START_REF] Brandon | Evolution of the martian mantle inferred from the 187Re-187Os isotope and highly siderophile element abundance systematics of shergottite meteorites[END_REF][START_REF] Dale | Late accretion on the earliest planetesimals revealed by the highly siderophile elements[END_REF][START_REF] Tait | Chondritic late accretion to Mars and the nature of shergottite reservoirs[END_REF], which has important implications for accretion theory and astrophysical modelling of Solar System evolution (e.g., [START_REF] Bottke | Stochastic late accretion to Earth, the Moon, and Mars[END_REF]. However, sulphur abundance estimates for the martian mantle range between 400 and 2200 ppm [START_REF] Wang | Chalcophile elements in the martian meteorites indicate a low sulfur content in the martian interior[END_REF] and references therein) -much higher than the Earth's mantle (around 250 ppm;[START_REF] Mcdonough | The composition of the Earth[END_REF]. The aim of this study was to use rhenium-osmium (Re-Os) isotope systematics and HSE abundances, alongside S-isotope systematics, to test whether the nakhlite group of martian meteorites preserve robust isotopic information from the martian interior (Morgan, 1986;Shirey & Walker, 1998;Righter et al., 2000;McSween & Huss, 2010;[START_REF] Day | Highly siderophile elements in Earth, Mars, the Moon, and Asteroids[END_REF].

Martian meteorites are the only available rocks from the surface of Mars. These meteorites can be divided into shergottites (basalts), nakhlites (clinopyroxene-rich rocks), and chassignites (olivine cumulates), with a few other exceptional meteorites. [START_REF] Berkley | Comparative petrology and origin of Governador Valadares and other nakhlites[END_REF], [START_REF] Treiman | The parental magma of the Nakhla achondrite: Ultrabasic volcanism on the shergottite parent body[END_REF][START_REF] Treiman | The nakhlite meteorites: Augite-rich igneous rocks from Mars[END_REF], and [START_REF] Bridges | Evaporite mineral assemblages in the nakhlite (martian) meteorites[END_REF] argued that nakhlite petrographic features are consistent with this suite of meteorites sampling a single cumulate pile. However, recent 40 Ar- 39 Ar geochronology suggests that their crystallization ages differ by ~93 Ma, consistent with the nakhlites being derived from a series of lava flows or sills that were emplaced between ~1416 and 1322 Ma, probably from the same source [START_REF] Cohen | Taking the pulse of Mars via dating of a plume-fed volcano[END_REF][START_REF] Udry | 1.34 billion-year-old magmatism on Mars evaluated from the cogenetic nakhlite and chassignite meteorites[END_REF]. In this manuscript, we refer to the nakhlites as a series of lava flows. [START_REF] Franz | Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars[END_REF] used a combination of bulk rock sulphur analyses (δ 34 S, Δ 33 S, Δ 36 S) and in situ pyrrhotite mineral analyses (δ 34 S, Δ 33 S) to determine sulphur isotope anomalies in martian meteorites. These authors determined the Δ 33 S of the shergottite mantle source to be 0.009 ‰, based on the mean value of 28 meteorites. This value closely corresponds to the value measured for the shergottite Yamato (Y)-980459, which reportedly retains the most reliable signatures of the martian mantle (e.g., [START_REF] Usui | Origin of water and mantlecrust interactions on Mars inferred from hydrogen isotopes and volatile element abundances of olivine-hosted melt inclusions of primitive shergottites[END_REF]. However, [START_REF] Franz | Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars[END_REF] were unable to calculate a robust value for the nakhlite mantle source region, as in situ secondary ion mass spectrometry (SIMS) analyses of sulphide grains were acquired from only two of the nakhlites (Nakhla and Miller Range (MIL) 03346) and their Δ 33 S values varied widely (0.06 ± 0.21 ‰ and -0.72 ± 0.13 ‰, respectively). This variation was reported to have been caused by sulphate assimilation during melt eruption, affecting subsequent pyrrhotite crystallization. [START_REF] Franz | Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars[END_REF] argued that sulphides and sulphates in the martian meteorites can thus be affected by assimilation of sulphur derived from atmospheric UV photochemical reactions, which was deposited at the surface as oxidized sulphur and incorporated in the martian regolith. This data is in agreement with other previously published sulphur isotope data for the nakhlites, including evidence for mass independent fractionation (MIF), which suggests assimilation of sulphur occurred at some point during nakhlite formation (e.g., [START_REF] Farquhar | Evidence of atmospheric sulphur in the martian regolith from sulphur isotopes in meteorites[END_REF][START_REF] Farquhar | Implications from sulfur isotopes of the Nakhla meteorite for the origin of sulfate on Mars[END_REF]Greenwood et al., 2000a,b;[START_REF] Dottin | Evidence for oxidation at the base of the nakhlite pile by reduction of sulfate salts at the time of lava emplacement[END_REF].

These sulphur isotope systematics can be used to discern if the HSE abundances in nakhlite magmas are affected by crustal assimilation, or if they represent Mars mantle reservoirs. The HSE systematics of martian meteorites have been used to infer chondritic relative abundances of these elements in the martian mantle, and to thereby trace late-accretion of broadly chondritic materials to Mars after the last major magma ocean phase at ~4.5 Ga (e.g., [START_REF] Brandon | Re-Os isotopic evidence for early differentiation of the Martian mantle[END_REF][START_REF] Brandon | Evolution of the martian mantle inferred from the 187Re-187Os isotope and highly siderophile element abundance systematics of shergottite meteorites[END_REF][START_REF] Riches | Petrology and geochemistry of Yamato 984028: A cumulate lherzolitic shergottite with affinities to Y 000027, Y 000047, and Y[END_REF][START_REF] Tait | Chondritic late accretion to Mars and the nature of shergottite reservoirs[END_REF]. Crucially, the HSEs exhibit chalcophile element behaviour when metal is absent from the mineralogical assemblage, preferring to partition into sulphides [START_REF] Day | Highly siderophile elements in Earth, Mars, the Moon, and Asteroids[END_REF] references therein), which is important in terms of HSE partitioning.

Rhenium-Os isotope data are available for many shergottites and one chassignite, but with respect to the nakhlite meteorites there are only two analyses of Nakhla [START_REF] Brandon | Re-Os isotopic evidence for early differentiation of the Martian mantle[END_REF][START_REF] Dale | Late accretion on the earliest planetesimals revealed by the highly siderophile elements[END_REF]. This lack of published data is, in part, due to the low abundance of HSE (0.1-2 ppb or less) in the nakhlites [START_REF] Treiman | The parental magma of the Nakhla achondrite: Ultrabasic volcanism on the shergottite parent body[END_REF][START_REF] Jones | Signatures of the highly siderophile elements in the SNC meteorites and Mars: a review and petrologic synthesis[END_REF]. In addition, a large age correction needs to be applied (1.3 Ga since nakhlite crystallization), and the effects of crustal assimilation within Nakhla are not clear (McCubbin et al., 2003;[START_REF] Franz | Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars[END_REF][START_REF] Udry | 1.34 billion-year-old magmatism on Mars evaluated from the cogenetic nakhlite and chassignite meteorites[END_REF]. Therefore, Nakhla may not be a reliable indicator of the nakhlite's true Os-isotopic mantle source composition. To address these challenges, we have expanded the nakhlite Re-Os isotope and HSE dataset to include Lafayette and one of the paired Miller Range nakhlites (MIL 090032). These two meteorites are potentially highly informative as they plot at the two extremes of S-isotope composition for the nakhlites [START_REF] Farquhar | Evidence of atmospheric sulphur in the martian regolith from sulphur isotopes in meteorites[END_REF]Greenwood et al., 2000;[START_REF] Franz | Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars[END_REF]. We also analysed a fraction of Nakhla. This nakhlite is known to have S-isotope composition of aggregated sulphides intermediate to the Miller Range and Lafayette meteorites. Sulphur isotope (Δ 33 S and δ 34 S) data were acquired from sulphide grains in Nakhla, Lafayette, MIL 090032, Y-000749, and Y-000593 to determine the amount of crustal assimilation that has occurred in each meteorite during eruption, and to define the possible Δ 33 S range for the nakhlite mantle source.

-Methodology

-Sample preparation and chemical mapping

Chips were used for Re-Os isotope and HSE analysis, while thin sections were used for S-isotope analyses. The chips (~0.5 g) were from Nakhla (BM.1913,25), Lafayette (BM.1979,755), and MIL 090032 (100); thin sections were from Nakhla (BM.1913,26#2), Lafayette (BM.1979,755), MIL 090032 (28), Y-000593 (37), and Y-000749 (59). Samples were obtained from the Natural History Museum of London (Nakhla, Lafayette), NASA Johnson Space Center (MIL 090032), and JAXA (Y-000593, Y-000749). All samples were from the interior portions of the meteorite, lacking any fusion crust.

We used a novel methodology in which petrographic information was constrained, for the first time, prior to destruction of that same sample volume via acid digestion. This approach provides mineralogical context to inform our interpretations of HSE-abundance and Re-Os isotopic data. To achieve this, we polished the sample chips of Nakhla (0.4 g) and Lafayette (0.6 g) using disks of SiC and 0.3 µm of Al 2 O 3 , then rinsed with MQ H 2 O. The procedure was undertaken to remove any potential contamination to the chips' surface from earlier cutting and processing by the meteorite curators. As the final step of this treatment involved repeated rinsing in MQ H 2 O and visual inspection, we believe that any potential contamination of the sample by Al 2 O 3 residue was removed. However, it remains possible that microscopic traces of Al 2 O 3 could introduce Re, very small amounts of radiogenic Os, and potentially perturb the HSE and Os-isotopic systematics, in which case we would anticipate variable chondrite-relative HSE patterns for the analysed nakhlites.

The MIL 090032 chip (0.5 g) had a flat surface and did not require polishing. These chips were not subject to carbon coating during the acquisition of high spatial resolution images and compositional mapping. Corresponding thin sections for each of the nakhlites used in this work were carbon coated to a thickness of 20-25 nm for compositional mapping by secondary electron microscopy prior to ion microprobe work.

A Zeiss field-emission Scanning Electron Microscope (SEM), housed in the Imaging Spectroscopy and Analysis Centre of the University of Glasgow, was used to characterise thin-sections and the flat side of the prepared chips. Operating conditions were: 8.5 mm working distance, 2.15 nA beam current, and 20 kV accelerating voltage. Acquired X-ray spectra were calibrated using mineral standards.

Backscattered electron (BSE) images and energy dispersive spectroscopy (EDS) X-ray element maps (for Si, Mg, Fe, Ca) were obtained for the chips lacking carbon coating with the SEM operated in low vacuum. Backscattered electron images and EDS X-ray spectra were generated for carbon coated thin sections of Nakhla, Lafayette, MIL 090032, Y-000749, and Y-000593 with the SEM operated at high vacuum. Of particular interest were the sulphides (pyrrhotite/pyrite). Every recognized sulphide on the exposed surface was imaged and quantitatively chemically analysed to determine its mineralogy (see Supplementary Materials for further details).

-Sulphur isotope systematics

To obtain the desired spatial resolution during in situ analysis of pyrrhotite and pyrite for δ 34 S, δ 33 S, and Δ 33 S, five polished thin-sections (one each of Nakhla, Lafayette, MIL 090032, Y-000749, and Y-000593) were analysed via SIMS. Samples were cleaned with ethanol and coated with gold to a thickness of ~20 µm, to permit conductivity, before loading into the sample chamber of the ion probe.

Sulphur isotope compositions were measured on the CAMECA IMS 1280 ion microprobe (SIMS) at the Centre de Recherches Pétrographiques et Géochimiques (CRPG) in Nancy (France) by simultaneous measurements of 32 S-, 33 S-, and 34 S-in multicollection mode with three off-axis Faraday cups (FCs) in slit 2 mode that allows for a mass resolution M/ΔM = 5000. The FCs were intercalibrated before the analytical session to determine their relative yields. Samples were sputtered with a Cs + primary beam of 3-nA intensity, accelerated at 13 kV and focused on a spot of ~15 µm diameter. Pyrite, pyrrhotite and galena standards were used to determine the instrumental mass fractionation (IMF) and the reference mass instrumental law (allowing Δ 33 S to be calculated).

Typical 32 S count rates were between ~1.2 × 10 9 and 1.5 × 10 9 cps, depending on the sulphide standard analysed. A typical analysis consisted of 2 min of pre-sputtering with a 20 µm raster, followed by data acquisition for 40 cycles of 5 s each. Faraday cup backgrounds were measured during the pre-sputtering before each analysis and then used for correcting the data. Automatic mass and transfer deflector centerings were implemented in the analysis routine to ensure reproducible analytical conditions during the session. Each measurement takes around 7 minutes per spot. Typical ±2σ standard errors achieved under these conditions were ~0.1-0.3 ‰ for δ 34 S, ~0.1-0.2 ‰ for δ 33 S, and ~0.1-0.25 ‰ for Δ 33 S.

-Analytical procedure for Os-isotope systematics and HSE

Nakhla, Lafayette, and MIL 090032 were analysed for HSE abundances and Re-Os isotope compositions. Textural characterisation of each sample fragment was retained prior to destruction of the same material fraction. All samples were weighed before and after crushing so that any loss of sample during this process could be quantified. The HSE chemical separation for Nakhla and Lafayette was conducted in ultra-clean laboratories at the Durham Geochemistry Centre (class 100), Durham University (see Supplementary Materials for further details). We used a mixed 190 Os-191 Ir-99 Ru-194 Pt-106 Pd-185 Re basalt spike for Nakhla and Lafayette. This spike was selected because we anticipated fractionated HSE in the nakhlites relative to chondrite or peridotite-like HSE abundances; the basalt spike has high Re/Os thereby ensuring accurate spiking. The Total Procedural Blank (TPB) and sample digestions were processed in a high pressure asher and run at 270° C for 18 hours to liberate the HSE from sample powders and to achieve sample-spike equilibration. Following this digestion step, extraction of Os from the solution was performed using a chloroform solvent extraction approach (after [START_REF] Cohen | Separation of osmium from geological materials by solvent extraction for analysis by thermal ionisation mass spectrometry[END_REF]. Osmium was then back-extracted into HBr, and was purified via microdistillation [START_REF] Birck | Re-Os isotopic measurements at the femtomole level in natural samples[END_REF] prior to filament loading. All the other analysed HSE were separated and purified using anion exchange and LN-spec chromatography (cf., [START_REF] Pearson | Solvent extraction/anion exchange separation and determination of PGEs (Os, Ir, Pt, Pd, Ru) and Re-Os isotopes in geological samples by isotope dilution ICP-MS[END_REF][START_REF] Puchtel | Highly Siderophile Element Abundances in SNC Meteorites: An Update[END_REF][START_REF] Chu | A Comprehensive Method for Precise Determination of Re, Os, Ir, Ru, Pt, Pd Concentrations and Os Isotopic Compositions in Geological Samples[END_REF]; Supplementary Materials).

MIL 090032 was analysed in the laboratories at the Freie Universität Berlin following similar laboratory processing protocols to those of Durham University. The polished surface of the sample chip was cleaned with some ethanol but not further abraded because the surface appeared porous and the chip fragile. Afterwards the chip was powdered in an agate mill. Sample digestion and chemical separation was conducted following the protocol of [START_REF] Fischer-Gödde | Rhodium, gold and other highly siderophile element abundances in chondritic meteorites[END_REF], 2011). To remove Zr an additional clean-up step was applied for Pd following the protocol of [START_REF] Chu | A Comprehensive Method for Precise Determination of Re, Os, Ir, Ru, Pt, Pd Concentrations and Os Isotopic Compositions in Geological Samples[END_REF].

Acquisition of 187 Os/ 188 Os for this one sample fragment was unsuccessful.

The HSE were measured using an Element XR instrument (Berlin) and Element 2 (Durham). The sample was introduced via a conventional Scott-type glass spray chamber. An Aridus I membrane desolvation system was used for HSE at Berlin. Highly siderophile element signals were detected in low resolution mode with a secondary electron multiplier. Rubidium, Sr, Y, Zr, Mo, Cd, Tm, Yb, Lu, Hf, Ta, Os, and Hg were analyzed to monitor isobaric interferences and potentially interfering oxide species. Oxide formation rates were <4.5 % and <0.8 % for the Scott-type spray chamber at Berlin and Durham, respectively, and <0.15 % using the Aridus at Berlin. The internal precision of measured isotope ratios ranges from 0.2 to 0.8 % (2σ). Background-corrected element ratios were corrected for mass discrimination using IUPAC values by comparison with ratios in a HSE standard solution measured in the same sequence. Isotopic ratios of 99 8.4 % Re; 24 % Ir; 3.8 % Ru; 1.1 % Pt; 2.9 % Rh; 17.5 % Pd; 24 % Au at Berlin; while blank contributions at Durham are Re, 0.42-0.49 %; Os, 0.70-4.20 %, 187 Os/ 188 Os = 0.132; Ir, 0.10-0.26 %; Ru, 0.04 %; Pt, 0.25-0.4 %; Pd, 0.87-1.0 %. The elemental abundances of the samples were corrected using the blank values reported in the Supplementary Materials.

-Results

-Textural characterization of the chips

The Nakhla chip (Fig. 1a) was characterized by a high proportion of mostly euhedral augite (~80%; 1-1.5 mm), and a lesser volume of euhedral to subhedral olivine (~8%; 0.3-1 mm in maximum dimension) -extensive areas of the chip had no olivine crystals. Plagioclase made up ~5 vol.% of the sample, while mesostasis represented ~7 vol.%. Texturally, a low degree (< 10%) of fracturing was observed among the minerals. A single 0.3 mm long sulphate grain was present in a Si-rich area of the chip (Fig. 1a). Other smaller (< 0.1 mm) sulphates and sulphides were present throughout the chip.

The Lafayette chip (Fig. 1b) was characterized by a higher proportion of euhedral to subhedral olivine (~15%; 200-800 µm crystal size) and a lower volumetric percentage of pyroxene (~75%; 500-1800 µm in maximum dimension) relative to the Nakhla chip; mesostasis was ~10 vol.%. Pyroxene was mostly subhedral and in some cases contained olivine inclusions of <50 µm. The chip was characterized by a low degree (< 10%) of mineral fracturing and several small (< 0.1 mm) sulphates and sulphides.

The MIL 090032 chip (Fig. 1c) was characterized by a high proportion of mostly euhedral pyroxene (~80%; 1000-1300 µm crystal sizes), with a minor amount of olivine (~10%; generally 500-700 µm in maximum dimension) and a magnetite/olivine-rich mesostasis (~10%) that contains-numerous microcrystals (<5 µm) of olivine. The chip shows a low degree (< 15%) of fracturing. In some areas, both olivine and pyroxene contained glassy inclusions of 30 µm in maximum dimension. Olivine was distributed heterogeneously and it occurred only in one area.

Our observations of these nakhlite chips are in agreement with previous petrographic observations of thin sections and chips of Nakhla (Treiman, 1990;Lentz et al., 1999;[START_REF] Corrigan | Modal abundances of pyroxene, olivine, and mesostasis in nakhlites: Heterogeneity, variation, and implications for nakhlite emplacement[END_REF]Udry andDay, 2018), Lafayette (Bunch andReid, 1975;Boctor et al., 1976;Treiman et al., 1993;[START_REF] Corrigan | Modal abundances of pyroxene, olivine, and mesostasis in nakhlites: Heterogeneity, variation, and implications for nakhlite emplacement[END_REF][START_REF] Udry | 1.34 billion-year-old magmatism on Mars evaluated from the cogenetic nakhlite and chassignite meteorites[END_REF], and MIL 090032 (Day et al., 2005[START_REF] Day | Petrology and chemistry of MIL 03346 and its significance in understanding the petrogenesis of nakhlites on Mars[END_REF]Stopar et al., 2005;[START_REF] Udry | Paired nakhlites MIL 090030, 090032, 090136, and 03346: Insights into the Miller Range parent meteorite[END_REF][START_REF] Corrigan | Modal abundances of pyroxene, olivine, and mesostasis in nakhlites: Heterogeneity, variation, and implications for nakhlite emplacement[END_REF][START_REF] Udry | 1.34 billion-year-old magmatism on Mars evaluated from the cogenetic nakhlite and chassignite meteorites[END_REF]. However, the Nakhla chip studied here differs from previous observations in hosting a large sulphate grain, supporting heterogeneously distributed HSE-carrying trace phases in nakhlites.

-Sulphur isotopes

Pyrrhotite and pyrite grains were identified adjacent to mesostasis (glass) in each thin section, and also occur as inclusions within augite (Fig. 2). These sulphides differ in size between meteorites: Nakhla 20-40 µm; Lafayette 20-60 µm; MIL 090032 10-60 µm; Y-000593 50-250 µm; and Y-000749 15-40 µm. The sulphide grains are relatively pure, containing few inclusions, or exsolved blebs/lamellae, of other phases. Sulphides in the five nakhlites analysed here show significant variation in sulphur isotopic composition, with Δ 33 S from -0.76 to 0.04 ‰ and δ 34 S from -13.2 to 15.1 ‰ (Table 1). Sulphur isotopes analysed from five pyrrhotite grains in Nakhla give a range of Δ 33 S from -0.12 to 0.02 ‰, with an average of -0.05 ± 0.08 ‰ and an average δ 34 S of -1.59 ± 0.10 ‰.

These values are in agreement with Δ 33 S = -0.09 ‰ analysed via acid extraction and with δ 34 S of -1.6 ‰ analysed via chrome reducible sulphur extraction in sulphides from Nakhla by [START_REF] Farquhar | Implications from sulfur isotopes of the Nakhla meteorite for the origin of sulfate on Mars[END_REF]. However, our data show a slightly more negative result relative to the data of Franz et al.

(2014) (mean Δ 33 S = 0.08 ‰ with some grains as low as -0.33 ‰, and mean δ 34 S = -0.51 ‰. The SIMS measurements of Greenwood et al. (2000b) for pyrrhotite grains in Nakhla agree well with our values, having a range in Δ 33 S = -0.4 ± 0.5 to -0.07 ± 0.5 ‰ and a δ 34 S = -4.5 ± 0.4 to 1.4 ± 0.4 ‰.

Similar to Nakhla, two pyrrhotite grains in Y-000749 gave an average Δ 33 S = -0.10 ± 0.15 ‰ and δ 34 S = -1.1 ± 0.11, while only one pyrrhotite was analysed for Y-000593 (Δ 33 S = -0.18 ± 0.07 ‰; δ 34 S = -1.3 ± 0.08). Lafayette pyrite analysis (five grains) yielded a range of values in Δ 33 S = -0.26 to 0.04 ‰ and a δ 34 S = -13.2 to -8.53 ‰, with an average Δ 33 S = -0.09 ± 0.12 ‰, which approaches the Δ 33 S = 0.07 ‰ in Lafayette pyrite analysed by [START_REF] Farquhar | Evidence of atmospheric sulphur in the martian regolith from sulphur isotopes in meteorites[END_REF]. Sulphur isotope data obtained for five grains of MIL 090032 show a Δ 33 S = -0.76 to -0.62 ‰ and a δ 34 S = 7.60 to 15.1 ‰, with an average Δ 33 S = -0.67 ± 0.10 ‰ and δ 34 S = 10.5 ‰. Previous measurements via chemical extractions from the four paired Miller Range nakhlites gave a range of Δ 33 S from -0.43 to -0.53 ‰, in particular an earlier study of the MIL 090136 material gave values that are in the range of our own analysis, with an average Δ 33 S = -0.4 ‰ and δ 34 S = 7.66 ‰ [START_REF] Franz | Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars[END_REF][START_REF] Dottin | Evidence for oxidation at the base of the nakhlite pile by reduction of sulfate salts at the time of lava emplacement[END_REF].

-Rhenium-Os isotope systematics and HSE

Lafayette and Nakhla have broadly similar CI-normalized HSE patterns (Fig. 3a), with a general depletion of Os, Ir, and Ru relative to Pd and Re (Table 2). However, osmium normalised to CIchondrite/10,000 (Os N ) is slightly more abundant (1.69) in Lafayette than in Nakhla (0.25). Osmium, Ir, Ru, and Pt are in agreement with earlier HSE-abundance studies of Nakhla (as reviewed by [START_REF] Jones | Signatures of the highly siderophile elements in the SNC meteorites and Mars: a review and petrologic synthesis[END_REF], with the exception of Pd and Re that show higher abundances in our new data (2.24 and 0.117 ppb, respectively). In general, Os, Ir, Ru, and Pt in Nakhla fall in the range between previous HSE analyses of Nakhla by [START_REF] Dale | Late accretion on the earliest planetesimals revealed by the highly siderophile elements[END_REF] and [START_REF] Jones | Signatures of the highly siderophile elements in the SNC meteorites and Mars: a review and petrologic synthesis[END_REF]. Platinum, Pd, and Re of Nakhla and Lafayette show similarities with measured Pt and Pd in Chassigny [START_REF] Jones | Signatures of the highly siderophile elements in the SNC meteorites and Mars: a review and petrologic synthesis[END_REF].

Nakhla has the highest (Re/Ir) N = 148 and (Pt/Ir) N = 96 among the studied set of samples, while Lafayette has the highest value in (Os/Ir) N = 3.44 for these nakhlites (Fig. 5). The MIL 090032 CInormalised HSE pattern is slightly different from the patterns of Nakhla and Lafayette, with higher absolute Os, Ir, and Ru, and Pt (4.54 ppb) having the highest CI-chondrite normalised value.

Nakhla and Lafayette display different Re and Os abundances and Re-Os isotope systematics (Table 2; Fig. 3b). Lafayette has a 187 Re/ 188 Os and 187 Os/ 188 Os of 6 ± 6 and 0.1849 ± 0.0003 (uncertainties are expressed as 2σ internal precision), respectively. Nakhla is characterized by the highest 187 Re/ 188 Os value of 49 ± 49 and an 187 Os/ 188 Os of 0.4542 ± 0.0018. Despite large uncertainties on 187 Re/ 188 Os and crystallisation ages >1 Gyr, we tried to calculate the initial 187 Os/ 188 Os composition of the sample with its percent deviation from the chondritic reference (Shirey & Walker, 1998) using the ϒOs i notation. The assumed crystallization ages of the most recent 39 Ar-40 Ar dating [START_REF] Cohen | Taking the pulse of Mars via dating of a plume-fed volcano[END_REF] were used for our calculations. The calculated ϒOs i is strongly negative. Data on initial 187 Os/ 188 Os and ϒOs i are reported in Table 2.

-Discussion

-Potential for terrestrial alteration and weathering

Some of the nakhlites analysed here could have been affected by alteration during their residence on Earth. In samples recovered from hot deserts the formation of terrestrial clay and carbonate (e.g., [START_REF] Crozaz | Chemical alteration and REE mobilization in meteorites from hot and cold deserts[END_REF] can modify lithophile isotope systematics (e.g., [START_REF] Symes | The age of the martian meteorite Northwest Africa 1195 and the differentiation history of the shergottites[END_REF] and potentially perturb the Re-Os isotope system. Nakhla was seen to fall, and was recovered shortly thereafter. The provenance of Lafayette is less clear, but its fresh fusion crust suggests it was collected soon after it fell (e.g., [START_REF] Graham | Catalogue of Meteorites. Fourth Edition. British Museum (Natural History)[END_REF]. However, even weathering events lasting a few hours have been shown to cause Re and minor Os redistribution in chondrites from fresh falls [START_REF] Walker | Rapid effects of terrestrial alteration on highly siderophile elements in the Sutter's Mill meteorite[END_REF]. Terrestrial clays or carbonates are not found within either of these nakhlites, hence the Re-Os isotope system and their sulphides (as supported by our petrographic observations)

should not be significantly affected by terrestrial alteration. In addition, initial 87 Sr/ 86 Sr ratios of Nakhla and Lafayette (0.70254 and 0.70260, respectively) also show little variation (Gale et al., 1975;[START_REF] Shih | The Chronology of the Nakhlite, Lafayette: Rb-Sr and Sm-Nd Isotopic Ages[END_REF], suggesting minor or no modification of Sr isotope due to clay and carbonate mineralization.

In contrast, the Miller Range and Yamato nakhlites are Antarctic finds, hence have had greater exposure to the terrestrial environment. The light rare earth element, cerium (Ce) can act as an alteration tracer via the conversion of Ce 3+ to Ce 4+ due to oxidation, with pigeonite being the most susceptible mineral [START_REF] Crozaz | Chemical alteration and REE mobilization in meteorites from hot and cold deserts[END_REF]. Cerium anomalies can be found in silicates of the Antarctic Yamato nakhlites [START_REF] Crozaz | Chemical alteration and REE mobilization in meteorites from hot and cold deserts[END_REF], and terrestrially derived jarosite sulphate has been reported towards the exterior of Yamato 000749 [START_REF] Changela | Alteration assemblages in the nakhlites: Variation with depth on Mars[END_REF]. However, Pb isotope systematics within these nakhlites reflect minimal terrestrial contamination [START_REF] Yamashita | Pb isotopic signature of Martian meteorite Yamato 000593 (a preliminary report)[END_REF], and the Rb-Sr and Sm-Nd isotope systematics provide little evidence for terrestrial weathering.

Olivine and sulphide within the Miller Range nakhlites has suffered aqueous corrosion during residence in Antarctica (Dyar et al., 2005;[START_REF] Hallis | Comparisons of the four Miller Range nakhlites, MIL 03346, 090030, 090032 and 090136: Textural and compositional observations of primary and secondary mineral assemblages[END_REF][START_REF] Hallis | Alteration assemblages in the Miller Range and Elephant Moraine regions of Antarctica: Comparisons between terrestrial igneous rocks and Martian meteorites[END_REF][START_REF] Velbel | Aqueous corrosion of olivine in the Mars meteorite Miller Range (MIL) 03346 during Antarctic weathering: Implications for water on Mars[END_REF]. Long exposure to water/snow may have resulted in an addition of anthropogenic radiogenic osmium [START_REF] Chen | Anthropogenic osmium in rain and snow reveals global-scale atmospheric contamination[END_REF]. However, terrestrial alteration in the Miller Range nakhlites was considered in previous studies to have no significant impact on the Δ 33 S and δ 34 S of its unweathered sulphides, which thereby robustly trace processes on Mars [START_REF] Dottin | Evidence for oxidation at the base of the nakhlite pile by reduction of sulfate salts at the time of lava emplacement[END_REF]. Hafnium-W isotope values for Nakhla, Lafayette, and MIL 03346 are 0.7-2.25 [START_REF] Lodders | A survey of Shergottite, Nakhlite and Chassigny meteorites whole-rock compositions[END_REF][START_REF] Barrat | Bulk chemistry of the Nakhlite Miller Range 03346 (MIL 03346)[END_REF], with a calculated ԑ 182 W of 3.13 ± 0.30 for Nakhla [START_REF] Lee | Core formation on Mars and differentiated asteroids[END_REF]) and of -2.95 ± 0.08 for MIL 03346 [START_REF] Wadhwa | Trace element and 142Nd systematics in the nakhlite MIL03346 and the orthopyroxenite ALH84001: Implications for the Martian mantle[END_REF], thus demonstrating minor variation and minimal Hf-W isotope disturbance between these nakhlites.

The potential effects of terrestrial alteration on HSE abundances and Re-Os isotopic compositions are addressed in Section 4.3.1.

-Origin of sulphur isotopic anomalies in sulphides of nakhlites

The variation of Δ 33 S and  34 S in the nakhlites, in reference to our dataset, could be due to differences in the chemistry of the atmosphere and surface or alteration by subsurface martian fluids [START_REF] Farquhar | Evidence of atmospheric sulphur in the martian regolith from sulphur isotopes in meteorites[END_REF][START_REF] Franz | Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars[END_REF]. To have confidence in which of our nakhlite HSE and Re-Os isotope data are the most representative of the martian magma source(s) for nakhlite meteorites, it is useful to know the extent to which each nakhlite might have been affected by regolith assimilation; where with 'regolith' we refer to heterogeneous, unconsolidated, and relatively superficial martian surface deposits.

-Isotopic fractionation of Δ 33 S in sulphides of nakhlites

Our analyses of Nakhla, Lafayette, MIL 090032, Y-000749, and Y-000593 sulphide grains gave mean Δ 33 S values of -0.05 ± 0.08 ‰, -0.09 ± 0.12 ‰, -0.67 ± 0.10 ‰, -0.10 ± 0.15 ‰, and -0.18 ± 0.07 ‰, respectively (Fig. 4a). Assuming that some of these sulphide grains may be more isotopically fractionated than others, it is important to determine whether the sulphur isotopic signatures are representative of the sample as a whole, and if they are magmatic or non-magmatic in origin.

Appraisal of the petrographic characteristics of our studied samples prior to SIMS analyses showed that we sampled a representative set of pyrite and pyrrhotite grains in terms of textural associations, but that we observed a bias toward grains > 10 μm in size. Virtually, the magma involved in the generation of the nakhlites can be considered as affected by a degree of crustal assimilation coincident with eruption onto the martian surface (e.g., [START_REF] Franz | Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars[END_REF]. The challenge is to disentangle the degree to which the chemistries of the analysed nakhlites were affected by assimilation during the transit of magmas through Mars' crust and during eruptive processes.

Anomalous sulphur is constrained by its mass-independent fractionation (MIF) signature. Large variations in  34 S can modify the Δ 33 S of a sulphide by chemical mixing. However, it has been demonstrated that the values of  34 S in martian meteorites do not vary enough to be able to explain the observed variation in Δ 33 S [START_REF] Farquhar | Evidence of atmospheric sulphur in the martian regolith from sulphur isotopes in meteorites[END_REF][START_REF] Farquhar | Implications from sulfur isotopes of the Nakhla meteorite for the origin of sulfate on Mars[END_REF][START_REF] Franz | Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars[END_REF].

Detection of MIF or non-MIF signatures for sulphur could be constrained by the displacement of non-zero values of Δ 33 S for each meteorite analysed here, where a magmatic only Δ 33 S is characterized by near zero values (i.e., Δ 33 S = 0). Lafayette has zero (0.03 ± 0.08‰) to slightly negative (-0.26 ± 0.08‰) Δ 33 S in its sulphide grains. This inter-grain variation in Lafayette is the largest heterogeneity in Δ 33 S of the meteorite dataset that we analysed, implying the presence of both non-MIF (i.e., magmatic) and MIF signatures (assimilation) in Lafayette sulphur. In the case of MIF signatures, these were likely induced by assimilation of regolith-derived sulphur (including regolith affected by brines) during emplacement of Lafayette lava flow on the martian surface.

Though relevant for the present-day Mars, data from NASA's Curiosity rover shows a δ 34 S with a range far in excess of that observed among nakhlites (-47 to 28‰; [START_REF] Franz | Large sulfur isotope fractionations in Martian sediments at Gale crater[END_REF], it is reasonable to conclude that these observations imply that the assimilation of even a small percentage of Mars' regolith at the time of nakhlite formation could significantly shift the sulphur isotopic composition of these nakhlites (by several ‰).

For Nakhla we obtained a Δ 33 S equal to zero (-0.05 ± 0.08‰, n = 5), suggesting a magmatic origin (non-MIF signature) for all sulphur in Nakhla. This value is in accordance with a previously reported mean Δ 33 S of 0.06‰ for Nakhla sulphides [START_REF] Franz | Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars[END_REF]. However, Nakhla is internally variable and some of the studied sulphides show more negative Δ 33 S, with Δ 33 S as low as -0.33‰ and -0.4‰ (Greenwood et al., 2000a,b;[START_REF] Franz | Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars[END_REF]. We report similar near zero values of Δ 33 S from the three sulphide grains in Y-000749 (average Δ 33 S = -0.10 ± 0.15 ‰; with one sulphide having a magmatic Δ 33 S = 0.00 ± 0.13 ‰) and from the sulphide grain in Y-000593 (Δ 33 S = -0.18 ± 0.07 ‰). However, we were not able to analyse sulphide grains smaller than 10 μm in these nakhlites and Δ 33 S values may be somewhat internally variable. Based on the analysed sulphide grains, we suggest a non-primordial mantle sulphur signal but still a dominantly magmatic origin for the sulphur isotopic systematics of Nakhla, Y-000749, and Y-000593, without large extents of regolith assimilation during their magmatic emplacement. Miller Range 090032 represents the meteorite with the most marked MIF signatures in sulphide grains, with a negative mean Δ 33 S of -0.67 ± 0.10‰, with wide variability between grains (Fig. 4). Large variability in Δ 33 S in sulphides of the Miller Range paired nakhlites is also in agreement with [START_REF] Franz | Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars[END_REF] and [START_REF] Dottin | Evidence for oxidation at the base of the nakhlite pile by reduction of sulfate salts at the time of lava emplacement[END_REF]. These values suggest that sulphides in MIL 090032 are affected by MIF signatures, probably caused by secondary processes that occurred on Mars [START_REF] Mikouchi | Mineralogy and petrology of Yamato 000593: Comparison with other martian nakhlite meteorites[END_REF], as suggested by [START_REF] Franz | Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars[END_REF] for the paired stone MIL 03346. Secondary processing possibilities are explored below.

-Isotopic fractionation of  34 S in sulphides of nakhlites

The absence of crustal recycling on Mars may have been effective in leaving heterogeneous sulphur signatures on the surface. Sulphur isotope ratios can be fractionated by three main processes: hydrothermal (e.g., [START_REF] Ohmoto | Sulfur and carbon isotopes[END_REF], photochemical (e.g., [START_REF] Zmolek | Large mass independent sulfur isotope fractionations during the photopolymerization of l2CS2 and 13CS2[END_REF][START_REF] Farquhar | Observation of wavelength-sensitive mass-independent sulfur isotope effects during SO2 photolysis: Implications for the early atmosphere[END_REF], and biological (e.g., [START_REF] Parnell | Sulfur isotope signatures for rapid colonization of an impact crater by thermophilic microbes[END_REF]. In addition to these processes, we discuss also possible magmatic processes that can fractionate  34 S. Large isotopic fractionations of  34 S have been investigated recently by the NASA's Curiosity rover from a 13 km long transect in Gale Crater [START_REF] Franz | Large sulfur isotope fractionations in Martian sediments at Gale crater[END_REF]. The measured  34 S ranged from -47 ± 14 ‰ to 28 ± 7 ‰ (Fig. 4b); whether the negative values occurred in sulphides and the positive values occurred in sulphates or sulphites (mudstone and sandstone) is yet to be resolved. The reason Curiosity reported a greater range in  34 S than that observed in martian meteorites is probably due to the accumulation of fine crustal materials in Gale crater following long periods of fluvial and/or aeolian transport.

Nakhlite sulphur isotopic signatures have been interpreted as reflecting both equilibrium fractionation in a warmed martian groundwater environment (low  34 S) or atmospheric photochemical processes (high  34 S) [START_REF] Franz | Large sulfur isotope fractionations in Martian sediments at Gale crater[END_REF]. In particular, the  34 S enrichment is reported to derive from atmospheric processing of SO 2 and H 2 S via martian volcanic activity (processes capable of producing positive  34 S signatures) with subsequent incorporation of these products into the martian surface/subsurface [START_REF] Franz | Large sulfur isotope fractionations in Martian sediments at Gale crater[END_REF], see Fig. 2). This was also deduced experimentally [START_REF] Franz | Mass-independent fractionation of sulfur isotopes during broadband SO2 photolysis: comparison between 16O-and 18O-rich SO2[END_REF] and from oxidation of SO 2 in volcanic ashes [START_REF] Savarino | UV induced mass-independent sulfur isotope fractionation in stratospheric volcanic sulfate[END_REF].

Fractionation of  34 S differs for all the five nakhlites analysed here (Fig. 4b). However, it is important to notice that the δ 34 S variation could not be a full signature of the contaminant. It is possible that S loss processes can fractionate δ 34 S, and such processes would not be expected to significantly shift the Δ 33 S. Thus, the δ 34 S of the samples with the most anomalous Δ 33 S might reflect a different combination of processes, related to addition of sulphur, that would exert the first order control on Δ 33 S, and then loss of sulphur that would exert a first order control on δ 34 S due to kinetic stable isotopic fractionation. Sulphides in Nakhla, Y-000749, and Y-000593 have the most convincing magmatic signatures, being characterized by a near zero mean δ 34 S (mean -1.59 ± 0.10‰, -1.18 ± 0.11‰, and -1.36 ± 0.08‰, respectively), supported also from their magmatic Δ 33 S values described above. Conversely, MIL 090032 has an enriched  34 S (mean +10.54 ± 0.09‰), that is the largest intra-meteorite variation in sulphur isotopic fractionation and the largest positive  34 S value obtained in a martian material (+15.2 ± 0.1‰). These values suggest enrichment of  34 S due to martian atmospheric processes characterised by oxidation of H 2 SO 4 or photolysis of sulphur compounds (gases) introduced by volcanic eruptions and outgassing [START_REF] Savarino | UV induced mass-independent sulfur isotope fractionation in stratospheric volcanic sulfate[END_REF][START_REF] Franz | Large sulfur isotope fractionations in Martian sediments at Gale crater[END_REF]. This finding is similar to reported measurements of  34 S fractionation close to the vents of terrestrial volcanoes (+7.7 ± 0.8‰; [START_REF] Mather | Oxygen and sulfur isotopic composition of volcanic sulfate aerosol at the point of emission[END_REF].

Lafayette has the greatest  34 S depletion yet described for a martian meteorite (average of -10.7 ± 0.2‰), with values of  34 S reaching -13.2 ± 0.1‰ -and lower than the Allan Hills (ALH) 84001,  34 S values (~-9‰) previously reported for pyrite grains (Greenwood et al., 2000a). These values are suggestive of late-stage equilibrium fractionation with martian groundwater, consistent with the Lafayette Δ 33 S results. Previous analysis of Lafayette reported values of  34 S of -3.2 ± 2.1‰ (Greenwood et al., 2000b;[START_REF] Farquhar | Evidence of atmospheric sulphur in the martian regolith from sulphur isotopes in meteorites[END_REF]. The greater depletion in our  34 S values may reflect heterogeneous assimilation of sulphur from the martian regolith. Alternatively (or in addition), Lafayette sulphides have 'spongy' textures (Fig. 2c), which could be the product of alteration by shock melting with subsequent volatilisation effects (e.g., [START_REF] Gattacceca | Opaque minerals, magnetic properties, and paleomagnetism of the Tissint Martian meteorite[END_REF]. Both Greenwood et al. (2000b) and [START_REF] Farquhar | Evidence of atmospheric sulphur in the martian regolith from sulphur isotopes in meteorites[END_REF] proposed mixing of fluids with heavy ( 34 S > 0) and light sulphur ( 34 S < 0) as a hydrothermal process that can produce negative  34 S. Some of the nakhlite lava flows may have been in contact with, or in close proximity, to a heavy sulphur source, while, in general, all may have been affected by mixing with fluids characterized by contrasting  34 S values.

At temperatures <1200°C the magmatic degassing of SO 2 can modify the sulphur isotope ratios of magmas [START_REF] Sakai | Chemistry and isotope ratios of sulfur in basalts and volcanic gases at Kilauea volcano, Hawaii[END_REF], depending on the fO 2 [START_REF] Carroll | Solubilities of sulfur, noble gases, nitrogen, chlorine, and fluorine in magmas[END_REF]. Two cases are possible: 1) if fO 2 >> quartz-fayalite-magnetite (QFM) buffer, sulphate is the dominant sulphur phase in the magma. The consequent equilibrium isotopic fractionation factor will be positive (ΔSO 4 2 -SO 2 > 0; [START_REF] Sakai | Chemistry and isotope ratios of sulfur in basalts and volcanic gases at Kilauea volcano, Hawaii[END_REF], hence the residual melt is enriched in  34 S due to SO 2 degassing, producing sulphides enriched in  34 S. 2) If fO 2 = QFM or fO 2 < QFM sulphide is the dominant sulphur phase in the magma, with consequent negative equilibrium isotopic fractionation factor (ΔS 2 -SO 2 < 0; [START_REF] Sakai | Chemistry and isotope ratios of sulfur in basalts and volcanic gases at Kilauea volcano, Hawaii[END_REF]. In this way, the melt may become depleted in  34 S. This mechanism leads to crystallization of sulphides that are depleted in  34 S. Magmatic degassing could have been the cause of the positive  34 S signature in MIL 090032, by shifting the SO 4 in the silicate melt structure sulphates can be reduced to yield more positive  34 S values (see [START_REF] Labidi | Multiple sulphur isotope composition of oxidized Samoan melts and the implications of a sulfur isotope ''mantle array" in chemical geodynamics[END_REF][START_REF] Mandeville | Stable isotope and petrologic evidence for open-system degassing during the climactic and pre-climactic eruptions of Mt. Mazama, Crater Lake. Oregon[END_REF][START_REF] Dottin | Evidence for oxidation at the base of the nakhlite pile by reduction of sulfate salts at the time of lava emplacement[END_REF], that was subsequently reduced to form the sulphides.

-Assimilation versus acquisition of Martian regolith during lava emplacement

The Δ 33 S and  34 S values presented here (Fig. 4), along with the fact that nakhlite sulphides are associated with the mesostasis (hence are some of the last phases to crystallise) [START_REF] Chevrier | Sulfide petrology of four nakhlites: Northwest Africa 817, Northwest Africa 998, Nakhla, and Governador Valadares[END_REF]; Fig. 2), indicate assimilation of an S-rich martian regolith occurred within at least some of the nakhlite lava flows (Lafayette and MIL 090032). The range in Δ 33 S among the nakhlites may be broadly related to the total sulphur content of each lava flow, where nakhlites with larger Δ 33 S anomalies were in proximity of a "sulphur source", contrary to nakhlites with smaller Δ 33 S anomalies [START_REF] Dottin | Evidence for oxidation at the base of the nakhlite pile by reduction of sulfate salts at the time of lava emplacement[END_REF]. This sulphur source could be represented by the S-rich martian regolith [START_REF] Foley | Final chemical results from the Mars Pathfinder Alpha Proton X-ray Spectrometer[END_REF]. Sulphides also occur in several different sizes and modal abundances in all nakhlite meteorites. In the meteorite samples studied sulphide grain sizes range from 10 µm to 250 µm (Fig. 2). The recently recovered nakhlite Caleta el Cobre 022 has unusually abundant and coarse grained pyrrhotite (up to 200 µm) [START_REF] Gattacceca | Nakhlite Caleta el Cobre 022: Initial Description and Comparison with other Nakhlites[END_REF]. These inter-meteorite differences in sulphide grain sizes are therefore further evidence to support the suggestion that sulphur-rich material was acquired at different points of lava extrusion on the martian surface.

Nakhla and the two Yamato nakhlites contain dominantly magmatic sulphur isotope signatures (near zero Δ 33 S and  34 S), indicating a lack of regolith incorporation. A 17 O excess of sulphate in Nakhla reportedly suggests it spent a significant period of time in contact with the Martian atmosphere [START_REF] Farquhar | Evidence of atmospheric sulphur in the martian regolith from sulphur isotopes in meteorites[END_REF]. The simplest way of reconciling this atmospheric exposure with minimal regolith uptake is to place Nakhla at the top of a lava flow. Alternatively, it could have been present

inside the carapace of a lava tube, where the main flow is in contact with the surface and easily acquires sulphide/sulphate material from the Martian regolith while the carapace of the lava tube is never in contact with the regolith but can be in contact with the atmosphere. This hypothesis could also explain the regolith uptake of MIL 090032, if it was part of the main lava tube. These two nakhlites have the same age (within uncertainty; [START_REF] Cohen | Taking the pulse of Mars via dating of a plume-fed volcano[END_REF], but they have different  34 S (Nakhla = -1.59 ± 0.10 ‰, MIL 090032 = +10.54 ± 0.09 ‰). This lava emplacement scenario is supported by the quench-textured mesostasis of MIL 090032 and the other paired MIL nakhlites, indicating surface exposure [START_REF] Hallis | Comparisons of the four Miller Range nakhlites, MIL 03346, 090030, 090032 and 090136: Textural and compositional observations of primary and secondary mineral assemblages[END_REF], possibly as a break-out event at the front or side of the lava flow [START_REF] Hammer | Application of a textural geospeedometer to the late-stage magmatic history of MIL 03346[END_REF]. Further, skeletal mineral phases, glass, and thin hedenbergite pyroxene rims in the MIL nakhlites has been taken as evidence of the fastest cooling rate among all the nakhlites (6 °C/h) [START_REF] Hammer | Experimental crystallization of Fe-rich basalt: Application to cooling rate and oxygen fugacity of nakhlite MIL 03346[END_REF][START_REF] Day | Petrology and chemistry of MIL 03346 and its significance in understanding the petrogenesis of nakhlites on Mars[END_REF]. Alternatively, if the MIL nakhlites and Nakhla are not from the same lava flow, mineralogical evidence suggests that after quenching the MIL nakhlite lava flow may have been blanketed with another flow that slowed down the cooling rate [START_REF] Domeneghetti | Thermal history of nakhlites: A comparison between MIL 03346 and its terrestrial analogue Theo's flow[END_REF] -this flow may have been that containing Nakhla.

-Δ 33 S of the nakhlite mantle source

Nakhla and the two Yamato meteorites have  34 S close to zero, and the smallest fractionation of Δ 33 S. This signature is interpreted to have a magmatic origin, hence these meteorites represent the least isotopically disturbed of the nakhlites analysed here (from a sulphur isotope perspective), and by inference the most appropriate to constrain a possible Δ 33 S for the nakhlite mantle source region.

The average Δ 33 S value obtained for Nakhla, Yamato 000749, and Yamato 000593 sulphide grains is -0.1 ± 0.09‰. This is slightly more negative than the shergottite mantle source value (Δ 33 S of 0.009 ‰) calculated by [START_REF] Franz | Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars[END_REF], possibly due to the fact that different mantle reservoirs were involved in the genesis of the shergottites and the nakhlites (e.g., [START_REF] Harper | Rapid accretion and early differentiation of Mars indicated by 142Nd/144Nd in SNC meteorites[END_REF][START_REF] Lee | Core formation on Mars and differentiated asteroids[END_REF][START_REF] Wadhwa | Redox state of Mars' upper mantle and crust from Eu anomalies in shergottite pyroxene[END_REF][START_REF] Jones | Signatures of the highly siderophile elements in the SNC meteorites and Mars: a review and petrologic synthesis[END_REF][START_REF] Foley | The early differentiation history of Mars from 182W-142Nd isotope systematics in the SNC meteorites[END_REF].

It is unlikely that a Δ 33 S of a mantle reservoir shifted by 0.1 ‰ from an initial value of zero. Instead, we attribute this Δ 33 S value to contamination by mass-independent sulphur that would have originated in the martian atmosphere [START_REF] Farquhar | Evidence of atmospheric sulphur in the martian regolith from sulphur isotopes in meteorites[END_REF]. It is conceivable that such atmospheric sulphur (SO 2 , H 2 S), after its deposition as oxidized sulphur on the martian surface, could have affected the source of the nakhlite magmas by mobilization beneath the martian crust due to geochemical cycling, therefore suggesting the presence of a shallow magma chamber for the generation of the nakhlites.

-Constraining the magmatic and chemical-physical processes in controlling Re-Os isotope systematics and HSE

Several different chemical-physical processes may have influenced the HSE-abundance Re-Os isotope systematics of the nakhlites. These processes can be distinguished essentially as: lowtemperature disturbance(s), post-crystallization impact disturbance, and HSE partitioning under magmatic conditions. To discriminate which of these processes may have affected each of our samples, and to what degree, we discuss each sequentially and begin by appraising those processes that could modify the HSE and Re-Os isotope chemistry of a magmatic sample after its crystallisation.

-Low-temperature and post-crystallization impact disturbance

Late-stage open-system effects on nakhlite HSE due to alteration on Mars' or Earth's surface have the potential to disturb nakhlite Re-Os isotope systematics and to mobilise and/or add HSE present in potentially susceptible phases. For example, the possibility of low-temperature alteration in deserts could result in the addition of Re (Peucker-Ehrenbrink and Jahn, 2001) (Fig. 3). However, there is limited variation of inter-element HSE ratios and we conclude that nakhlite HSE-abundance has not been significantly affected by low-temperature alteration on Earth or Mars after their magmatic crystallisation.

Impact disturbance as considered here refers to the process(es) through which materials of chondritic composition are transferred to martian magmatic materials due to impacts/shock events after their crystallisation. Such processes are capable of enriching the sample toward chondriterelative HSE abundances following magmatic crystallisation (e.g. as was observed by [START_REF] Riches | Rhenium-osmium isotope and highly-siderophile-element abundance systematics of angrite meteorites[END_REF]. All studied nakhlites are characterised by highly fractionated HSE patterns relative to CIchondrite (e.g., Pd/Os = 19.6 to 131.3), have relatively low total osmium abundances (< 0.08 ppb), and suprachondritic 187 Os/ 188 Os (0.18 to 0.45 ± 0.0010). These nakhlite HSE characteristics do not tend toward a potential chondritic contaminant and thereby preclude significant late-stage modification of the studied samples by chondritic materials on the martian surface or during their impact liberation.

-Magmatic processes

All [START_REF] Brandon | Re-Os isotopic evidence for early differentiation of the Martian mantle[END_REF] supports perturbation of the Re-Os isotope systematics in these martian magmas, but with little consequent effect to the abundances of Os, Ru, Ir, Pt, Pd, ± Au. Such a process requires interaction with a martian regolith of variable Re content and low Os abundance, but with highly radiogenic 187 Os/ 188 Os (> 0.7 at total HSE abundances much less than 2 ppb and with 0.005 ppb Os in the ancient martian regolith) such that a small proportion of assimilated material has perturbed the Os-isotopic signature of the nakhlite lava flows.

Fractionation of HSE during partial melting of the mantle and during possible late-sulphide saturation in evolved magmas will change HSE inventories in different ways [START_REF] Jones | Signatures of the highly siderophile elements in the SNC meteorites and Mars: a review and petrologic synthesis[END_REF][START_REF] Sun | Enhanced mantle-tocrust rhenium transfer in undegassed arc magmas[END_REF][START_REF] Fonseca | How chalcophile is rhenium? An experimental study of the solubility of Re in sulfide mattes[END_REF]Mallmann & O'Neill, 2007). In the following sub-paragraphs we explore these possible processes.

-Magmatic fractionation of HSE from the nakhlite and shergottite mantle source

Regression approaches using MgO content have been used to infer Mars mantle composition and give similar abundances of Re, Os, Ir, and Ru for the mantle of Earth and Mars (e.g., [START_REF] Warren | Origin of planetary cores: evidence from highly siderophile elements in martian meteorites[END_REF][START_REF] Tait | Chondritic late accretion to Mars and the nature of shergottite reservoirs[END_REF]. In addition, martian meteorites are characterised by Re abundances that are high, somewhat close to the terrestrial basalts, and define a broad anti-correlation of HSE abundances with the degree of magmatic evolution (e.g., [START_REF] Jones | Signatures of the highly siderophile elements in the SNC meteorites and Mars: a review and petrologic synthesis[END_REF]. Several prior studies have appraised martian magmatic process through the HSE abundances of martian meteorites (e.g. [START_REF] Warren | Origin of planetary cores: evidence from highly siderophile elements in martian meteorites[END_REF][START_REF] Jones | Signatures of the highly siderophile elements in the SNC meteorites and Mars: a review and petrologic synthesis[END_REF][START_REF] Riches | Petrology and geochemistry of Yamato 984028: A cumulate lherzolitic shergottite with affinities to Y 000027, Y 000047, and Y[END_REF][START_REF] Brandon | Evolution of the martian mantle inferred from the 187Re-187Os isotope and highly siderophile element abundance systematics of shergottite meteorites[END_REF][START_REF] Dale | Late accretion on the earliest planetesimals revealed by the highly siderophile elements[END_REF][START_REF] Chin | Geochemistry of intermediate olivine-phyric shergottite northwest Africa 6234, with similarities to basaltic shergottite northwest Africa 480 and olivinephyric shergottite northwest Africa 2990[END_REF][START_REF] Tait | Update on highly-siderophile element abundances and Re-Os isotopic systematics of martian meteorites[END_REF][START_REF] Tait | Chondritic late accretion to Mars and the nature of shergottite reservoirs[END_REF]. In general, what the HSE datasets of these previous studies show are CI-normalised HSE patterns that vary from absolutely flat to increasingly fractionated (elevated Pd/Os) with decreasing total HSE abundance.

Nakhla, Lafayette, and MIL 090032 all show broadly similar HSE patterns (Fig. 3a). Though previous data showed that Nakhla and Chassigny are similar in their HSE patterns [START_REF] Jones | Signatures of the highly siderophile elements in the SNC meteorites and Mars: a review and petrologic synthesis[END_REF], here isotope dilution approaches show that Nakhla has more Pd and Re relative to Chassigny and that Lafayette and MIL 090032 are very similar to this pattern, rather than the HSE pattern of Chassigny.

These substantial differences in the HSE fractionation evident among different classes of martian meteorite and thus their magmas, extended also to shergottite groups. Primitive shergottites (Mg/Mg+Fe > 0.7) have high Os/Pt, Ir/Pd and Ru/Pt [START_REF] Brandon | Evolution of the martian mantle inferred from the 187Re-187Os isotope and highly siderophile element abundance systematics of shergottite meteorites[END_REF][START_REF] Tait | Chondritic late accretion to Mars and the nature of shergottite reservoirs[END_REF]. A broadly similar pattern was observed for the high MgO shergottites (Mg/Mg+Fe = 0.5-0.7), but with higher Re/Pt and Re/Pd than the primitive shergottites. Nakhlites analysed here diverge from the patterns of the primitive and high MgO shergottites in terms of relative abundances, but they approach the HSE patterns of the intermediate/low MgO shergottites having high Re/Ir, Pt/Ir, and Pd/Ru (Fig. 5). These differences could reflect different initial magmatic conditions between the nakhlite and shergottite parental melt(s), as for example, melting temperature, fO 2 , and parental melt composition (including sulphur concentration and its relation to the point of sulphide saturation). We address the possible late-stage sulphide saturation as well as potential involvement of residual alloys during the production of magmas parental to nakhlite lavas below.

-HSE fractionation due to late-stage sulphide saturation and residual alloys formation

Sulphides, silicate phases, and spinel can control the geochemical behaviour of the HSE during partial melting [START_REF] Fonseca | How chalcophile is rhenium? An experimental study of the solubility of Re in sulfide mattes[END_REF]Mallmann & O'Neill, 2007), with Os inclined to be partitioned into sulphide melts [START_REF] Brenan | Re-Os fractionation by sulfide melt silicate melt partitioning: a new spin[END_REF]. The solubility of Os and Ir has been constrained experimentally in sulphide melts, over a range of fO 2 (-1.5 < QFM < +1.5) and fS 2 (Iron-Wüstite (IW) ~-1) at T = 1300°C [START_REF] Fonseca | Solubility of Os and Ir in sulphide melt: implications for Re/Os fractionation in the upper mantle[END_REF]. It is important to take into account that these experimental approaches can generally only replicate batch melting, and that a fractional melting scenario (± aggregation of those fractional melts) may be applicable to both ancient and recent martian magmatic systems. Nevertheless, experimental approaches provide a useful framework through which we can infer key aspects of nakhlite petrogenesis. The outcome of these experiments has shown that Os and Ir have low solubilities in silicate melts and that high fO 2 conditions can inhibit the solubility of Os and Ir in sulphide melts [START_REF] Fonseca | Solubility of Os and Ir in sulphide melt: implications for Re/Os fractionation in the upper mantle[END_REF]. Oxygen fugacity for nakhlites is higher than shergottites. For Nakhla, fO 2 is equal to the quartz-fayalite-magnetite (QFM) oxygen buffer (at an equilibration temperature of 810° C) while for Lafayette the fO 2 is equal to QFM +0.1

(at an equilibration temperature of 780° C; [START_REF] Szymanski | High oxidation state during formation of Martian nakhlites[END_REF]. For MIL 03346 (paired with MIL 090032) the proportion of Fe 3+ in augite was found to be in agreement with high-temperature equilibration near the QFM buffer (Dyar et al., 2005). Conversely, estimated fO 2 for the shergottites are low and varies from -1 to -4 QFM (e.g., [START_REF] Herd | The oxygen fugacity of olivine-phyric Martian basalts and the components within the mantle and crust of Mars[END_REF]. These differences in fO 2 would limit the solubility of Os and Ir in nakhlite sulphide melts, due to their higher fO 2 than shergottites.

Residual alloys crystallised from parental melts and the formation of platinum group minerals throughout a magmatic column are able to control fractionation of Os, Ir, Ru, Rh, Pt, and Pd during magma genesis [START_REF] Mungall | Partitioning of platinum-group elements and Au between sulfide liquid and basalt and the origins of mantle-crust fractionation of the chalcophile elements[END_REF]. In particular, [START_REF] Mungall | Partitioning of platinum-group elements and Au between sulfide liquid and basalt and the origins of mantle-crust fractionation of the chalcophile elements[END_REF] reported how, at low pressure, partial melting of Earth's mantle retains HSE in chondritic relative abundances (if correct as the starting proportions of these elements) until complete sulphide saturation, then evolving to very high Pt/Pd and low Pd/Ir -due to Pt and Ir alloy formation in the restite phase.

Ruthenium, Os, and Ir are thought to be initially present in parts per million abundances in mantle sulphide melts, then, a decrease in fS 2 during partial melting leads to the exolution of Ru-Os-Ir alloys from a refractory residue in the mantle [START_REF] Fonseca | New constraints on the genesis and long-term stability of Os-rich alloys in the Earth's mantle[END_REF]. In particular, a sulphide melt appears to be required for Os-rich alloy formation since Os is likely the element that triggers the exolution of the Ru-Os-Ir alloys [START_REF] Fonseca | New constraints on the genesis and long-term stability of Os-rich alloys in the Earth's mantle[END_REF].

As described above, the higher fO 2 in Nakhla, Lafayette, and MIL 090032 likely prevented the solubility of Os and Ir in possible late-stage sulphide melts, inducing formation of Pt-and Ir-alloys in the restite phase. Accordingly to [START_REF] Fonseca | Solubility of Os and Ir in sulphide melt: implications for Re/Os fractionation in the upper mantle[END_REF], the higher solubility of Os and Ir at high fO 2 would imply the existence of a melt saturated in sulphides (sulphide melt) for the generation of the nakhlite parent magmas. In contrast to nakhlite magmas, for which present data sets and constraints are relatively limited, it is well established that the parent magmas of the relatively well-studied shergottites were sulphide-undersaturated in their mantle sources [START_REF] Wang | Chalcophile elements in the martian meteorites indicate a low sulfur content in the martian interior[END_REF]. In particular, Pd/Pt in shergottites tend to reflect chondritic abundances, but this is not the case for Os-Ir-Ru, as indicated by suprachondritic Pd/Ir or Pt/Ir [START_REF] Wang | Chalcophile elements in the martian meteorites indicate a low sulfur content in the martian interior[END_REF]. The reason of this difference could be attributed to the formation of residual alloys of Os-Ir-Ru in the martian mantle (similar to the Earth's mantle; e.g., Fonseca et al., 2012 and references therein).

-Implications for nakhlite mantle source and early Mars differentiation

Mantle heterogeneities have been proposed for Mars based on the trace element and 182 Hf-182 W, 146 Sm-142 Nd, 87 Rb-87 Sr, and 187 Re-187 Os isotope systematics of magmatic products represented by martian meteorites (e.g., [START_REF] Harper | Rapid accretion and early differentiation of Mars indicated by 142Nd/144Nd in SNC meteorites[END_REF]Lee andHalliday, 1997, 1995;[START_REF] Brandon | Re-Os isotopic evidence for early differentiation of the Martian mantle[END_REF][START_REF] Brandon | Evolution of the martian mantle inferred from the 187Re-187Os isotope and highly siderophile element abundance systematics of shergottite meteorites[END_REF][START_REF] Wadhwa | Redox state of Mars' upper mantle and crust from Eu anomalies in shergottite pyroxene[END_REF][START_REF] Herd | The oxygen fugacity of olivine-phyric Martian basalts and the components within the mantle and crust of Mars[END_REF][START_REF] Jones | Signatures of the highly siderophile elements in the SNC meteorites and Mars: a review and petrologic synthesis[END_REF][START_REF] Foley | The early differentiation history of Mars from 182W-142Nd isotope systematics in the SNC meteorites[END_REF][START_REF] Debaille | Martian mantle mineralogy investigated by the 176Lu-176Hf and 147Sm-143Nd systematics of shergottites[END_REF][START_REF] Debaille | Early martian mantle overturn inferred from isotopic composition of nakhlite meteorites[END_REF][START_REF] Herd | The Northwest Africa 8159 martian meteorite: Expanding the martian sample suite to the early Amazonian[END_REF][START_REF] Lapen | Two billion years of magmatism recorded from a single Mars meteorite ejection site[END_REF][START_REF] Tait | Chondritic late accretion to Mars and the nature of shergottite reservoirs[END_REF][START_REF] Day | Martian magmatism from plume metasomatized mantle[END_REF]. In general, at least four mantle reservoirs have been previously argued to exist on Mars: two for the shergottites, one for the nakhlites/chassignites, and one for NWA 8159. These different mantle domains can be tapped by magmas and these magmas can mix producing different compositions as noticeable from the different groups of martian meteorites.

Magma mixing phenomena have been argued to be responsible of the generation of the depleted and enriched shergottites [START_REF] Borg | Constraints on Martian differentiation processes from Rb-Sr and Sm-Nd isotopic analyses of the basaltic shergottite QUE94201[END_REF][START_REF] Wadhwa | Redox state of Mars' upper mantle and crust from Eu anomalies in shergottite pyroxene[END_REF][START_REF] Herd | The oxygen fugacity of olivine-phyric Martian basalts and the components within the mantle and crust of Mars[END_REF][START_REF] Borg | A petrogenetic model for the origin and compositional variation of the Martian basaltic meteorites[END_REF][START_REF] Shearer | Petrogenetic linkages among Martian basalts: Implications based on trace element chemistry of olivine[END_REF]. However, the clear isotopic gaps that are present for their lithophile elements [START_REF] Ferdous | Evaluating crustal contributions to enriched shergottites from the petrology, trace elements, and Rb-Sr and Sm-Nd isotope systematics of Northwest Africa 856[END_REF] are difficult to reconcile with magma mixing, since this process would not result in large isotopic gaps. This is especially noticeable for the nakhlites since they do not present clear signs of disequilibrium textures in their mineral assemblages. Instead, we propose a single magma composition for the generation of the nakhlites (as also suggested by their trace element compositions; [START_REF] Udry | 1.34 billion-year-old magmatism on Mars evaluated from the cogenetic nakhlite and chassignite meteorites[END_REF], whether after the Nakhla eruption assimilation with an unknown enriched component affected the nakhlite source during 61 Myr, producing subsequently the Lafayette parent melt at 1321 ± 9 Ma (ages accordingly to [START_REF] Cohen | Taking the pulse of Mars via dating of a plume-fed volcano[END_REF].

Assimilation of crustal materials with markedly elevated 187 Re/ 188 Os could be a cause of the higher 187 Re/ 188 Os of Nakhla in respect to Lafayette. This enriched component possibly included ancient (primordial?) crustal materials, with consequent highly radiogenic Os isotopic compositions for which a very small fraction would significantly shift a magmatic Os isotopic signature but with potentially negligible effects on HSE abundances. On the other hand, this characteristic could also reflect phenomena of mantle metasomatism as recently argued for Mars magmatism [START_REF] Day | Martian magmatism from plume metasomatized mantle[END_REF], or even inheritance from an interior reservoir that experienced variable earlier magmatic fractionation resulting in reservoirs with long-term high 187 Re/ 188 Os and/or complementary low [START_REF] Brandon | Re-Os isotopic evidence for early differentiation of the Martian mantle[END_REF] and [START_REF] Norman | The composition and thickness of the crust of Mars estimated from rare earth elements and neodymium-isotopic compositions of Martian meteorites[END_REF] were used (Fig. 6).

The distribution of the nakhlites in respect to the primitive and evolved martian crust is inconsistent with their magma sources being affected by assimilation of modern martian crust. The ϒOs vs. ԑ 143 Nd appear instead decoupled suggesting preferential/selective mixing of the nakhlite reservoir with an unknown enriched component that must have occurred early during Mars differentiation, possibly represented by assimilated ancient MMO cumulates. However, drawing conclusions from the initial ϒOs for Nakhla and Lafayette are currently thwarted by large uncertainties for these relatively ancient magmas with low Os abundances. Similarly, the correlation between ԑ 143 Nd and ϒOs in shergottites suggested that the endmember sources were generated by mixing between residual melts and cumulates during the crystallization stages of a MMO [START_REF] Debaille | Martian mantle mineralogy investigated by the 176Lu-176Hf and 147Sm-143Nd systematics of shergottites[END_REF][START_REF] Brandon | Evolution of the martian mantle inferred from the 187Re-187Os isotope and highly siderophile element abundance systematics of shergottite meteorites[END_REF].

Mixing within MMO cumulates and evolved liquids may explain our observed Re-Os isotope systematics as seen in Nakhla and Lafayette, as well as previously reported Rb and Sr isotope systematics. In fact, sulphides crystallisation from the last stage of MMO's melts could result in locally fractionated 187 Re/ 188 Os within the martian mantle thereby presenting the possibility to trace different mantle reservoirs and to discern this from assimilation of primordial crust characterized by long-term elevated 187 Re/ 188 Os. In addition, the first MMO cumulates that crystallize would be extremely depleted in REE, Rb and Sr, with the last more evolved liquids characterised by a ԑ 142 Nd of +0.64 [START_REF] Debaille | Early martian mantle overturn inferred from isotopic composition of nakhlite meteorites[END_REF].

Magma ocean overturn could explain the early formation and isolation of these different local heterogeneities in the martian mantle [START_REF] Debaille | Early martian mantle overturn inferred from isotopic composition of nakhlite meteorites[END_REF][START_REF] Bouvier | Evidence for extremely rapid magma ocean crystallization and crust formation on Mars[END_REF]. This process likely happens as a result of instabilities due to the density stratification that occurs during the crystallisation of magma oceans on terrestrial planets [START_REF] Elkins-Tanton | Magma ocean fractional crystallization and cumulate overturn in terrestrial planets: Implications for Mars[END_REF].

-Conclusions

Sulphur isotopic compositions were determined for sulphides in five nakhlites to ascertain the degree to which they have been affected by assimilation of the martian regolith. Nakhla, Yamato 000749, and Yamato 000593 are the meteorites that have most faithfully retained a magmatic signature, and which are therefore the most reliable for using osmium isotopes and HSEs to reveal the nature of nakhlite petrogenesis. For the first time, Re-Os isotope systematics and HSE abundances have been investigated for two different nakhlites, to constrain the degree to which they have been affected by crustal assimilation and the ability of martian meteorite HSE to testify to Mars' interior composition. The following results have been obtained:

(1) The Lafayette and MIL 090032 lava flows acquired S-rich martian regolith material that carry information about martian atmospheric and hydrological processes. Results show that UVphotochemistry and hydrothermal processes are the main cause of Δ 33 S and δ 34 S fractionation. This result may have implications for the nature of the martian atmosphere and hydrothermal activity prior to nakhlite eruption.

(2) Nakhla, Yamato 000593, and Yamato 000749 retained a magmatic signature in their sulphides, and were unaffected by assimilation of martian regolith. Using these meteorites we estimate the Δ 33 S of the nakhlite source to be -0.1 ‰.

(3) Nakhlite HSE patterns are in agreement with the presence of a sulphide melt involved in nakhlite petrogenesis. Ruthenium-Os-Ir alloys likely formed in this sulphide-saturated melt and controlled the abundances of Ru, Os, Ir in the final lava products.

(4) Our Re-Os isotope data for nakhlites hint at perturbation and potential decoupling of nakhlite 187 Os/ 188 Os isotope systematics from other isotopic systems as a result of small degrees of assimilation of an S-rich regolith with low total HSE contents but highly radiogenic 187 Os/ 188 Os (> 0.7 at total HSE abundances much less than 2 ppb and with 0.005 ppb Os in the ancient martian regolith).

(5) Nakhlites formed from a primary magma that we consider to have been generated from a wellmixed martian mantle that subsequently (at some point after the Nakhla emplacement) assimilated an enriched component during ascent toward the surface, and where this enriched mantle material was potentially represented by a late-stage crystallization cumulate from a martian magma ocean.

enthusiastically introducing her to planetary science studies for which she has developed an addiction.

Figure caption

Figure previously published data in grey (from [START_REF] Jones | Signatures of the highly siderophile elements in the SNC meteorites and Mars: a review and petrologic synthesis[END_REF][START_REF] Dale | Late accretion on the earliest planetesimals revealed by the highly siderophile elements[END_REF]; (b) 187 Re/ 188 Os vs.

187 Os/ 188 Os data for Nakhla and Lafayette are shown, along with previous literature data (from [START_REF] Brandon | Re-Os isotopic evidence for early differentiation of the Martian mantle[END_REF][START_REF] Dale | Late accretion on the earliest planetesimals revealed by the highly siderophile elements[END_REF]. The 1.3 Ga reference line is shown for comparison and represents single-stage Re-Os isotope evolution from a chondritic 187 Os/ 188 Os reservoir, assuming a Solar System initial 187 Os/ 188 Os = 0.9524 [START_REF] Smoliar | Re-Os ages of Group IIA, IIIA, IVA, and IVB Meteorites[END_REF]. Uncertainty = 2σ, vertical error bars are less than symbol size. Comparison of δ 34 S value between the present study (yellow symbols) and literature data from martian meteorites [START_REF] Farquhar | Evidence of atmospheric sulphur in the martian regolith from sulphur isotopes in meteorites[END_REF]Greenwood et al., 2000a;[START_REF] Franz | Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars[END_REF][START_REF] Franz | Large sulfur isotope fractionations in Martian sediments at Gale crater[END_REF] and the Curiosity rover [START_REF] Franz | Large sulfur isotope fractionations in Martian sediments at Gale crater[END_REF]. The δ 34 S value of the martian mantle (from Franz et al., 2014) is shown by the dashed line. The red box identifies the nakhlites that have a δ 34 S very close to the martian mantle δ 34 S value and so have been least affected by regolith assimilation (Nakhla,. Some of the data used in the graphs are from previous studies [START_REF] Farquhar | Evidence of atmospheric sulphur in the martian regolith from sulphur isotopes in meteorites[END_REF]Greenwood et al., 2000a;[START_REF] Franz | Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars[END_REF][START_REF] Franz | Large sulfur isotope fractionations in Martian sediments at Gale crater[END_REF]. from [START_REF] Jones | Signatures of the highly siderophile elements in the SNC meteorites and Mars: a review and petrologic synthesis[END_REF], [START_REF] Riches | Petrology and geochemistry of Yamato 984028: A cumulate lherzolitic shergottite with affinities to Y 000027, Y 000047, and Y[END_REF], [START_REF] Brandon | Evolution of the martian mantle inferred from the 187Re-187Os isotope and highly siderophile element abundance systematics of shergottite meteorites[END_REF], [START_REF] Dale | Late accretion on the earliest planetesimals revealed by the highly siderophile elements[END_REF], and [START_REF] Tait | Chondritic late accretion to Mars and the nature of shergottite reservoirs[END_REF]. [START_REF] Brandon | Re-Os isotopic evidence for early differentiation of the Martian mantle[END_REF] and [START_REF] Norman | The composition and thickness of the crust of Mars estimated from rare earth elements and neodymium-isotopic compositions of Martian meteorites[END_REF]. The plotted samples follow a direction that diverge from the martian crust evolution (here represented by the dashed line), thus implying that the mixing end-member is likely represented by a different enriched component (dashed box) rather than the evolved martian crust. Alternatively, decoupling of the data could suggest that the ϒOs is a sensitive tracer of strictly different process to that which ԑ 143 Nd provides evidencepotentially recording involvement of early martian crust whereas ԑ 143 Nd may be more effective in probing the nature of nakhlite mantle reservoirs. Error bars are less than symbol size. As the calculated ϒOs in Lafayette and Nakhla is negative and below the Solar System initial of [START_REF] Smoliar | Re-Os ages of Group IIA, IIIA, IVA, and IVB Meteorites[END_REF] disturbance of the Re-Os isotope system in these samples has taken place (linked to crustal contamination). For these reasons, the strongly negative calculated ϒOs should be considered as an extreme minimum at ~1.4 Ga. Unperturbed samples, not impacted by crustal assimilation, would likely have been derived from internal reservoirs characterized by higher ϒOs at that time (blue arrow).

  sources or enriched cumulates may have happened during early differentiation of Mars. By following this logic, the enriched crustal component of our hypothesis likely can be represented by a component generated during the last stages of a martian magma ocean (MMO). This possibility has been investigated for Nakhla and Lafayette by looking at their 187 Os/ 188 Os versus Nd and Sr isotope distributions. The ϒOs versus ԑ 143 Nd constrain a possible end-member for the nakhlite source mixing. The calculated ϒOs and ԑ 143 Nd values of the primitive martian crust and the evolved Martian crust at 180 Ma from

Figure 3 -

 3 Figure 3 -Highly siderophile element (HSE) abundances and Re-Os isotope systematics in nakhlites. (a) CI chondrite normalized HSE data for Nakhla, Lafayette, and MIL 090032 are shown, along with

Figure 4 -

 4 Figure 4 -Sulphur isotope ratios for the nakhlites, compared with previous data from Martian meteorites and Mars rover missions data. (a) δ 34 S vs. Δ 33 S isotope ratios for the nakhlites analysed in this work, compared with the same nakhlites analysed by previous authors. Labels serve to emphasise which processes are inferred to have affected the sulphur isotopic composition of each

Figure 5 -

 5 Figure 5 -CI chondrite normalized HSE abundance comparison between nakhlites, primitive shergottites (Mg/Mg+Fe = > 0.7), high MgO shergottites (Mg/Mg+Fe = 0.5-0.7), shergottites with intermediate MgO (Mg/Mg+Fe = 0.4-0.5), and low MgO shergottites (Mg/Mg+Fe < 0.4). (a) (Pt/Ir) N vs. (Pd/Ir) N ; (b) (Os/Ir) N vs. (Re/Ir) N . The nakhlites plot closest to the low MgO shergottites in (a), and within the scatter of these shergottites in (b). Highly siderophile element data for shergottites are

Figure 6 -

 6 Figure 6 -Initial ϒOs vs. ԑ 143 Nd for nakhlites used to identify a possible end-member for the nakhlite source mixing. The primitive martian crust and the evolved martian crust at 180 Ma are plotted with values taken from[START_REF] Brandon | Re-Os isotopic evidence for early differentiation of the Martian mantle[END_REF] and[START_REF] Norman | The composition and thickness of the crust of Mars estimated from rare earth elements and neodymium-isotopic compositions of Martian meteorites[END_REF]. The plotted samples follow a direction

  Fig. 1

  Fig. 3

Fig. 6

 6 Fig. 6

  Ru/ 101 Ru,105 Pd/ 108 Pd,185 Re/ 187Re, 191 Ir/ 193 Ir and 194 Pt/ 195 Pt were used for isotope dilution calculations. Isotope ratios 105 Pd/ 106 Pd and 194 Pt/ 196 Pt were used to monitor possible interferences. Concentrations of monoisotopic Rh and Au were determined via a combined internal/external standardization technique for the 197 Au/ 191 Ir and 103 Rh/ 101 Ru ratios (Fischer-Gödde et al., 2010). Consistency and possible interferences were checked by comparison to results from 197 Au/ 195 Pt and 103 Rh/ 191 Ir ratios. Four blanks were determined. Blank contributions are:

  three nakhlites analysed in this work display similar HSE patterns. It is unlikely that these similarities in HSE patterns are the product of alteration on Earth or Mars, instead these primarily reflect magmatic fractionation during formation of the nakhlite parent magma(s) and lava crystallisation. These nakhlite HSE characteristics indicate that the incorporation of small amounts of martian regolith (as testified by S-isotope systematics) resulted in a generally negligible modification to the nakhlite HSE inventory, suggesting a low HSE abundance of the martian regolith. Had significant contributions of regolith modified the overall HSE abundances of the studied nakhlites, we would anticipate variable HSE systematics among the nakhlites and a degree of correlation with sulphide S-isotope compositions. Such nakhlite HSE variability and a clear relationship to corresponding sulphide S-isotope systematics is lacking. However, Os-isotope compositions of nakhlites are variable and are decoupled from the overall nakhlite HSE-abundance systematics. The intra-sample variability in Re concentration and Os-isotopic composition testified by two Nakhla fractions (0.117 ppb, this work; 0.052,

Table 1

 1 -S-isotopic compositions for pyrrhotite and pyrite in Nakhla, Lafayette, MIL 090032, Y-000749, and Y-000593.Data on δ 34 S, δ 33 S, and Δ 33 S values are expressed in permil (‰) and associated 2σ standard errors are reported. Uncertainties count statistics. The mean in sulphur isotope abundance for each meteorite is also shown. Sulphur isotope ratios are reported in standard δ notation with respect to Canyon Diablo Troilite (CDT), where δ 34 S = [( 34 S/ 32 S) sample /( 34 S/ 32 S) CDT -1] x 1,000, δ 33 S = [( 33 S/ 32 S) sample /( 33 S/ 32 S) CDT -1] x 1,000, and Δ 33 S = [( 33 S/ 32 S) sample /( 33 S/ 32 S) CDT -[( 34 S/ 32 S) sample /( 34 S/ 32 S) CDT ] 0.515 ] × 1,000.

	Sample	Phase	δ 34 S (‰)	± 2σ	δ 33 S (‰)	± 2σ	Δ 33 S (‰)	± 2σ
	Nakhla	pyrrhotite	-0.4	0.11	-0.33	0.08	-0.12	0.08
	Nakhla	pyrrhotite	-2.2	0.10	-1.15	0.08	0.02	0.07
	Nakhla	pyrrhotite	-1.0	0.09	-0.55	0.09	-0.03	0.09
	Nakhla	pyrrhotite	-2.5	0.11	-1.36	0.08	-0.06	0.08
	Nakhla	pyrrhotite	-1.7	0.08	-0.97	0.08	-0.08	0.07
	mean		-1.5		-0.87		-0.05
	variance		0.62		0.14		0.00
	Lafayette	pyrite	-13.2	0.10	-6.78	0.09	0.03	0.08
	Lafayette	pyrite	-10.1	0.11	-5.51	0.08	-0.26	0.08
	Lafayette	pyrite	-10.7	0.30	-5.65	0.19	-0.12	0.24
	Lafayette	pyrite	-8.5	0.11	-4.56	0.09	-0.16	0.09
	Lafayette	pyrite	-11.1	0.10	-5.72	0.12	0.04	0.11
	mean		-10.7		-5.64		-0.09
	variance		2.28		0.49		0.01
	MIL090032	pyrrhotite	7.6	0.08	3.25	0.08	-0.65	0.07
	MIL090032	pyrrhotite	9.7	0.08	4.34	0.08	-0.65	0.06
	MIL090032	pyrrhotite	9.9	0.10	4.33	0.09	-0.76	0.08
	MIL090032	pyrrhotite	15.2	0.11	7.14	0.18	-0.62	0.18
	MIL090032	pyrrhotite	10.2	0.08	4.58	0.08	-0.69	0.07
	mean		10.5		4.73		-0.67
	variance		6.22		1.66		0.00
	Yamato000749 pyrrhotite	-1.6	0.08	-0.83	0.13	0.00	0.13
	Yamato000749 pyrrhotite	-0.9	0.11	-0.59	0.13	-0.08	0.13
	Yamato000749 pyrrhotite	-0.9	0.14	-0.71	0.20	-0.23	0.20
	mean		-1.1		-0.71		-0.10
	variance		0.09		0.00		0.00
	Yamato000593 pyrrhotite	-0.7	0.07	-0.57	0.07	-0.21	0.05
	Yamato000593 pyrrhotite	-2.0	0.08	-1.19	0.10	-0.16	0.09
	mean		-1.3		-0.88		-0.18
	variance		0.42		0.09		0.00

Table 2 -

 2 Re-Os isotope systematics and HSE abundances (in ppb) for all samples.ϒOs i is given by ϒOs i = 100 x [( 187 Os/ 188 Os sample(t )/ 187 Os/ 188 Os chondrite(t) ) -1]. HSE ratios normalized to Orgueil chondrite are denoted by (N). Initial 143 Nd are from[START_REF] Nakamura | Origin and evolution of the Nakhla meteorite inferred from the Sm-Nd and U-Pb systematics and REE, Ba, Sr, Rb and K abundances[END_REF] and[START_REF] Shih | The Chronology of the Nakhlite, Lafayette: Rb-Sr and Sm-Nd Isotopic Ages[END_REF]. Ages are from[START_REF] Cohen | Taking the pulse of Mars via dating of a plume-fed volcano[END_REF].

			Sample
		Lafayette	Nakhla	MIL 090032
	Mass (g)	0.417	0.405	0.5
	Os (blk %)	0.078 (0.70)	0.012 (4.20)	0.036 (1.3)
	Ir (blk %)	0.022 (0.10)	0.009 (0.26)	0.025 (24)
	Ru (blk %)	_	0.04 (9.89)	0.27 (3.8)
	Pt (blk %)	1.01 (0.40)	1.66 (0.25)	4.54 (1.1)
	Pd (blk %)	1.89 (1)	2.24 (0.87)	1.18 (17.5)
	Re (blk %)	0.098 (0.49)	0.117 (0.42)	0.065 (8.4)
	Rh (blk %)	_	_	0.21 (2.9)
	Au (blk %)	_	_	0.081 (24)
	187 Re/ 188 Os (± 2σ)	6 (6)	49 (49)	_
	187 Os/ 188 Os (± 2σ)	0.1849 (0.0003) 0.4542 (0.0018)	_
	ϒOsi (± 2σ)	-64 (34.3)	-636 (5)	_
	Re/Os	1	10	2
	Pt/Os	12.9	138.3	126.1
	Os/Ir	3.54	1.33	1.44
	(Pt/Pd)N	0.35	0.48	2.51
	(Pd/Os)N	19.6	131.3	26
	ԑ 143 Nd (± 2σ)	16.3 (0.4)	16	_
	Age (Ma) (± 2σ)	1383 (7)	1330 (15)	1392 (10)
	Lab	Durham	Durham	Berlin

Acknowledgement

We are grateful to NASA -ANSMET for providing the Miller Range samples, to the Natural History Museum of London for allocation of the Nakhla and Lafayette samples, and to JAXA for providing the Yamato 000749 and Yamato 000593 samples. We thank P. Chung for its help during SEM-EDS analysis. AJVR was supported on an Independent Fellowship thanks to funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 653066. Analytical work at FUB was funded by CRC TRR 170-B1. This is TRR 170 publication no. 51. We also acknowledge funding from STFC grants ST/N000846/1 and ST/H002960/1. We thank the Editor James M. D. Day for the useful comments and suggestions that improved the quality of the manuscript. We thank James Farquhar and the anonymous reviewers for their review of this manuscript. AJVR thanks Larry Taylor, to whom this Special Issue is dedicated, for