Nakhlite and chassignite meteorites are important samples for understanding the evolution of Mars as they all derive from the same ∼1.34 Ga magmatic system. More than half of the nakhlite-chassignite meteorites have been found in hot deserts and leaching experiments reveal terrestrial weathering strongly affects bulk rock 87Rb-87Sr systematics. Excluding these meteorites, nakhlites and chassignites have bulk rock measured 87Sr/86Sr from 0.704184 to 0.706155. Correcting for in-situ 87Sr ingrowth from 87Rb decay over 1.34 Ga, nakhlites and chassignites possess significant variability in their initial 87Sr/86Sr ratios. Radiogenic initial 87Sr/86Sr for more fractionated nakhlites correspond with more radiogenic initial 187Os/188Os and mass-independently fractionated S isotopes. These signatures of crustal assimilation can be modelled by adding <10% of ancient (at least 2.4 Ga) martian surface basalt. Uncontaminated chassignites and nakhlites define a long-lived (∼4.5 Ga) mantle reservoir with low 87Rb/86Sr (0.069), making it at least 50 to 60% more depleted in 87Rb than bulk silicate Mars estimates. The low Rb/Sr of the nakhlite-chassignite mantle source, combined with published 142Nd-143Nd and Hf-W isotope systematics, indicates formation coincident with early martian differentiation, requiring crust extraction processes similar to those that produce Earth’s depleted mid-ocean ridge basalt mantle. The similarity in highly siderophile element contents estimated for the nakhlite-chassignite source and for bulk silicate Mars based on shergottites indicates that post-core formation late accretion must have occurred prior to the formation of these reservoirs, less than 100 million years after the accretion of Mars. Trace element signatures, including low Rb/Sr in nakhlites are consistent with 0.1–0.5% carbonate metasomatism of their depleted lithospheric source <30 million years prior to magmatism. Metasomatism of the nakhlite-chassignite source was probably engendered by plume magmatism that preceded rejuvenated magmatism, because of volcanic loading of the martian lithosphere.

The nakhlite and chassignite meteorites are the only confirmed group of rocks derived from a single volcanic system on Mars, offering a unique opportunity to investigate the composition of the martian mantle and magmatic differentiation mechanisms. Nakhlites and chassignites are thought to result from low-degree partial melting of a hydrated and metasomatized depleted mantle lithosphere, unlike shergottites that predominantly sample deeper mantle reservoirs. This study presents the first comprehensive dataset on highly siderophile element (HSE: Au, Re, Pd, Rh, Pt, Ru, Ir, Os) abundances in sulfide assemblages from twelve nakhlites and two chassignites, together with siderophile (Ni, Co, W) and chalcophile (Cu, Se, Zn, Pb) element abundance data. Sulfides in chassignites exhibit relatively high total HSE abundances at - 5 x carbonaceous (CI) chondrite abundances, with patterns that are generally flat, apart from notable enrichments in Pt and/or Ru. Conversely, nakhlite sulfides display more fractionated HSE patterns with total HSE abundances - 1.6 x CI, characterized by lower overall abundances and enrichment in Re, Pt and Pd relative to Ru, Ir and Os. These results confirm that sulfides are the principal reservoirs of the HSE in chassignites and nakhlites. Fractionation modeling suggests that the nakhlite compositions can be reproduced following up to 15 % fractional crystallization through the removal of an olivine (+Cr-spinel)-dominated cumulate, while chassignites experienced between 20 to 30 % of fractionation. The preservation of magmatic signatures in sulfide HSE compositions allows for an in-depth reconstruction of the evolution of the nakhlite-chassignite parental melt composition.

The martian soil is of particular interest as it can help us understand the different processes that have occurred on Mars by studying the chemistry and mineralogy of its constituents as a function of grain size. The finegrained martian soil is thought to be homogeneous across the planet and thus to represent a global component. In this study we report on the soil targets analysed by the SuperCam instrument aboard the Perseverance rover, which is currently exploring Jezero crater. A total of 343 targets were analysed. Their grain size distribution confirms the sparsity of 250-900 Acirc;mu m particles in the martian soil, although both smaller and larger grains are present. We found that the local components, due to erosion of the local bedrock, are present not only in the very coarse grains or larger gravels of the soil, but also in the very fine ones (<250 Acirc;mu m). We detected some very coarse grains enriched in olivine, pyroxene and carbonate in both the crater floor and the delta front locations, whereas phyllosilicate-rich grains have been encountered only in the delta front. We have compared the Jezero fine-grained soil targets with those of Gale crater using ChemCam data. We found that those at Jezero show no evidence of Mg sulfates, in contrast to the observation at Gale. In addition, the fine-grained soil at Jezero is more hydrated than that at Gale, probably due to its higher specific surface area.

Mars Sample Return (MSR) missions have been a priority for the planetary community for decades. The NASA Perseverance rover mission is collecting diverse samples from Mars for potential return to Earth, whereas the JAXA Martian Moons eXploration (MMX) mission will bring back samples from Phobos, the largest of Mars' two moons. High-resolution analyses of these samples in Earth-based laboratories will enable us to answer key questions that current martian data (meteorites, rovers, and orbiters) are unable to fully address. MSR results will better inform our understanding of the geological and planetary evolution of the red planet, the possibility of habitability and life on Mars, the potential for human exploration, and the formation of its moons and the martian system.

Nakhlites, clinopyroxene‐rich rocks, are the largest single‐origin suite of samples from Mars. Despite extensive study to discern their petrogenetic histories, nakhlite emplacement mechanisms and environments are not well‐constrained, and it is unknown whether they represent intrusive or extrusive igneous rocks, or a combination. Here, we use X‐ray computed microtomography (XCT) and three‐dimensional (3D) quantitative textural analyses (e.g., 2D–3D modal abundances, crystal size distributions [CSDs], and petrofabrics) to place additional constraints on nakhlite formation and emplacement. Modal abundances between and within the nakhlites are variable on both a 2D and 3D basis, highlighting the significance of XCT and 3D analyses when studying these samples. All nakhlites in our study have similar crystallization conditions and histories based on 3D CSDs. Cumulus phases (=olivine and pyroxene) crystallized from magma(s) with high nucleation densities, likely related to effective undercooling, and subsequently underwent a period of magma storage. The CSD profiles record evidence for magma recharge events. Pyroxene long‐axis orientations in the nakhlites studied here exhibit a magmatic foliation, which likely developed during crystal settling and accumulation in low‐to‐no flow settings, such as magma chambers, shallow intrusions (e.g., sills and dikes), lava lake or pond infills, or thick lava flows. We also show that the pyroxenitic layer of Theo's Flow (Canada) may not be an appropriate terrestrial analog for the nakhlites due to differences in emplacement mechanisms and conditions. Our findings suggest that lava flows may be less prevalent in the martian meteorite collection, while intrusive bodies and rocks may be more common than initially thought.

The Mars 2020 rover, Perseverance , encountered a range of basaltic igneous rocks on the floor of Jezero crater, two of which are olivine cumulates, formed by accumulation of olivine crystals from basaltic magma. These olivine cumulates lie in a geomorphically distinct region, named Séítah, on the Jezero crater floor. To understand the origin of the olivine cumulates and their relationship with the adjacent basalts of the Máaz formation, we calculated the composition of the parent magma of one of the olivine cumulates, named Brac, based on chemical analyses and mineralogic interpretations from the Planetary Instrument for X‐ray Lithochemistry (PIXL) instrument. Acceptable Brac/Dourbes parent magmas are olivine tholeiite basalts with SiO 2 ∼ 45%, MgO ∼ 8%, FeO Tot ∼ 27%, Al 2 O 3 ∼ 6%, and total alkali oxides of ∼2.8% weight. These compositions are similar to one of the Máaz basalts, the rock Rimplas, which is stratigraphically close to Séítah, but chemically distinct from other Máaz basalts. Rimplas could (within uncertainty) be a sample of the Brac parent magma, but it is more likely that Rimplas and Brac had a common (or similar) parent magma. Geochemical similarities between Rimplas and the other Máaz basalts thus suggest that Brac (and other olivine‐rich rocks of Séítah) and the Máaz basalts could be geochemically related; they could have been cogenetic and possibly contemporaneous, or could have been derived (at different times) from similar or related mantle source(s).

The Mineral Identification by Stoichiometry (MIST) algorithm can identify mineral species in geochemical data sets. MIST is applied to X-ray fluorescence chemical analyses from the Planetary Instrument for X-ray Lithochemistry (PIXL) on the Mars 2020 Perseverance rover to identify mineral phases in abraded rock targets at Jezero crater. We used a Monte Carlo (MC) error propagation technique to assess confidence in the results. Our study reports 24 high-confidence mineral phases from the first 1100 sols of Perseverance's traverse. Primary mineral groups include plagioclase, pyroxene, and olivine, in agreement with previously published results, and support an (ultra)mafic rock source. Additionally, MIST identified a range of phyllosilicate minerals, including nontronite, saponite, hisingerite, greenalite, minnesotaite, and sepiolite; identification of such alteration phases is essential for constraining the aqueous alteration history of Jezero's rocks. An initial survey of the reported phases suggests multiple, distinct stages of fluid alteration in Jezero's history: high temperature and acidic, moderate temperature and circumneutral, and later stage ambient alkaline conditions. MIST results from PIXL data help determine rocks of interest on Mars' surface for investigation by Perseverance and will also be important for informing analysis of samples when returned to Earth.

The Perseverance rover has sampled mm-size lithic fragments containing olivine likely from at least two source regions from the surface of an inactive megaripple surface, and fine-grained material from the surface and to a depth of similar to 4-6 cm. Some of the mm-size grains lack a coherent diffraction pattern measured by PIXL, consistent with the presence of poorly ordered secondary phases that have been altered. Analysis of these materials on Earth will allow examination of materials that have experienced aqueous, potentially habitable environments that could contain biosignatures. Fluorescence of three different patterns was detected, consistent with inorganic emissions from silica defects or rare earth elements in certain mineral phases, although organic origin cannot be excluded. Analysis of Autofocus Context Imager and Wide Angle Topographic Sensor for Operations and eNgineering images of the subsurface material and MEDA thermal inertia measurements indicate average grain sizes of similar to 125 and similar to 150 mu m, respectively, for the bulk material within the megaripple. The fine-grained material in the sampling location indicates chemical compositions similar to previously proposed global components as well as airfall dust. In situ and associated atmospheric measurements provide evidence of recent processes likely including water vapor in soil crust formation. The sampled material will therefore help elucidate the formation of Martian soils; current surface-atmosphere interactions; the composition, shape, and size distribution of dust grains valuable for studies of past and present Martian climate and for assessing potential health and other risks to human missions; and ancient, aqueously altered environments that could have been habitable, and, if Mars contained life, possibly contain biosignatures.

The Jezero crater floor features a suite of related, iron-rich lavas that were examined and sampled by the Mars 2020 rover Perseverance, and whose textures, minerals, and compositions were characterized by the Planetary Instrument for X-ray Lithochemistry (PIXL). This suite, known as the Máaz formation (fm), includes dark-toned basaltic/trachy-basaltic rocks with intergrown pyroxene, plagioclase feldspar, and altered olivine and overlying trachy-andesitic lava with reversely zoned plagioclase phenocrysts in a K-rich groundmass. Feldspar thermal disequilibrium textures indicate that they were carried from their crustal staging area. Bulk and mafic minerals have very high FeO and low MgO to FeO total ratios, which are partially reproduced by thermodynamic models involving high-degree fractional crystallization of a gabbroic assemblage and possibly also assimilation of iron-rich basement. Together, these in situ constraints on petrogenesis provide a uniquely detailed record of intracrustal processes beneath Jezero crater during a time period not represented by Mars samples to date.

Physical materials from planetary bodies are crucial for understanding fundamental processes that constrain the evolution of the solar system, as samples can be analyzed at high precision and accuracy in Earth-based laboratories. Mars is the only planet outside of Earth from which we possess samples in the form of meteorites. Martian meteorites (n > 350) have enabled constraints to be placed on various aspects of the red planet's formation and evolution, notably: that Mars accreted and differentiated rapidly; that the planet has a complex volatile element evolution; and that it has always been volcanically active with a rich and diverse magmatic history. Meteorites have limitations, however, with lack of field context, restricted lithological diversity compared to the martian surface, and with no sampling of a major portion of Mars' history between 4.1 and 2.4 billion years ago. Returned samples from Mars have the potential to fill these gaps and answer many open questions driven by the study of meteorites, as well as reveal new fundamental research questions. Key questions that Mars Sample Return is likely to answer regard the basic evolution of the martian interior and surface, its potential for habitability and the possibility of past life, and calibration of age dating of the martian surface. Samples of various lithologies and different ages collected at Jezero crater by the Perseverance rover will aid in better understanding our own planet and will answer outstanding questions regarding Mars' future geological evolution and habitability.

Northwest Africa (NWA) 13669 is a recently found nakhlite and here, we use 2-D and 3-D mineralogy and texture, quantitative textural analysis of pyroxene, bulk rock and mineral major and trace element compositions, and melt inclusion analyses to assess its formation and emplacement. Using these combined results, we determine that NWA 13669 is derived from a depleted mantle source common to nakhlites and modeled parental melt compositions from olivine- and pyroxene-hosted melt inclusions record similar major element trends to other nakhlites, including an alkali enrichment. Homogeneous pyroxene and olivine and diffusive reequilibration of trace elements in melt inclusions provide evidence for magma storage in a crystal mush within the nakhlite plumbing system and suggest NWA 13669 has undergone extensive reequilibration. Quantitative textural analysis of NWA 13669, including crystal size distribution (CSD) profiles, CSD slope and intercepts, and residence times, are similar to the Yamato nakhlite group, and indicate that NWA 13669 likely experienced similar emplacement conditions. However, differences in bulk rock and mineral compositions suggest NWA 13669 represents a new flow or sill from a previously unsampled portion of the nakhlite igneous complex, further increasing the diversity of the nakhlite suite.

Nakhlite and chassignite meteorites are cumulate rocks thought to originate from the same location on Mars. Petrogenetic relationships between nakhlites and chassignites are not fully constrained, and the two cumulus phases in nakhlites-olivine and clinopyroxene-possibly formed either together from one magma or separately from different magmas. Primary magma compositions can potentially be determined from studies of melt inclusions (MIs) trapped within early-formed mineral phases. MIs frequently undergo post-entrapment effects, and when such processes occur, there can be significant changes to their compositions. Here, we report major, minor, and trace element abundances for MIs in cumulus phases in nakhlites and chassignites. The melt compositions that they record are variable (MgO = 2.50-13.5 wt%, K2O = 0.03-3.03 wt%, La/Yb = 2.46%-16.4%) and are likely affected by diffusive reequilibration with changing magma composition outside of their host phases. Evidence for diffusive reequilibration suggests that nakhlite and chassignite magmas were generated in an open system, and cumulus phases may have undergone magma storage and mixing. Such processes may be akin to those that occur in terrestrial intrusive magmatic systems by open-system magma recharge. MIs within the nakhlite and chassignite suite therefore provide insights into magmatic processes during magma storage and transit on Mars.

Highly siderophile element abundances and Os isotopes of nakhlite and chassignite meteorites demonstrate that they represent a comagmatic suite from Mars. Nakhlites experienced variable assimilation of >2-billion-year-old altered high Re/Os basaltic crust. This basaltic crust is distinct from the ancient crust represented by meteorites Allan Hills 84001 or impact-contaminated Northwest Africa 7034/7533. Nakhlites and chassignites that did not experience crustal assimilation reveal that they were extracted from a depleted lithospheric mantle distinct from the deep plume source of depleted shergottites. The comagmatic origin for nakhlites and chassignites demonstrates a layered martian interior comprising ancient enriched basaltic crust derived from trace element–rich shallow magma ocean cumulates, a variably metasomatized mantle lithosphere, and a trace element–depleted deep mantle sampled by plume magmatism.