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Mars early crust is more complex than homogenously basaltic with evolved magmatism evidenced by intermediate and felsic igneous rocks found in various locations in the southern hemisphere and martian meteorites. Geophysical constraints argue against a dense thick basaltic crust in the southern hemisphere, rather consistent with a buried light crust (<3,100 kg m−3), possibly evolved, underneath a basaltic surface. One of the oldest crustal components accessible at the surface of Mars, Terra Cimmeria/Sirenum (TSC), presents geochemical anomalies potentially suggesting an evolved crustal component at depth. Using visible/near infrared spectroscopy, we identify nine excavated feldspar‐rich locations in this region, and thermal infrared data suggest a silica concentration corresponding to intermediate compositions. The low density of such terrains compared to basalts supports that TSC crustal component is evolved. Early crusts of planetary bodies in the solar system were thus not restricted to basaltic compositions, and evolved crusts might have been widespread. Plain Language Summary: Despite basaltic terrains widely observed at the surface of Mars, recent missions and a martian meteorite evidenced evolved magmatism (SiO2 > 53 wt.%), highlighting a heterogeneous crust on Mars. Geophysical and seismic constraints suggest the presence of buried evolved crustal components with low density compared to basalts, below subsequent basaltic lava flows. We investigate one of the most ancient region accessible at the surface of Mars using visible/near infrared and thermal infrared spectroscopy to verify that hypothesis. Nine feldspar‐rich terrains excavated by impact, fractures, and erosion are detected with evolved compositions. One of the oldest crustal component on Mars thus presents an evolved crust underneath the surface, in agreement with geophysical/seismic data. Hence, planetary bodies early crusts are not systematically basaltic as generally thought, but could be evolved too as inferred from several rare evolved meteorites (e.g., Erg Chech 002). Key Points: Nine feldspar‐rich regions of intermediate silica compositions were identified in Terra Sirenum/Cimmeria (TSC)The feldspar‐rich terrains are excavated crustal materials supporting a pre‐Noachian evolved crust at TSCAn early evolved crust on Mars suggests that early crusts in the solar system were not restricted to basaltic [ABSTRACT FROM AUTHOR]

Geochemical results are presented from Curiosity's exploration of Vera Rubin ridge (VRR), in addition to the full chemostratigraphy of the predominantly lacustrine mudstone Murray formation up to and including VRR. VRR is a prominent ridge flanking Aeolis Mons (informally Mt. Sharp), the central mound in Gale crater, Mars, and was a key area of interest for the Mars Science Laboratory mission. ChemCam data show that VRR is overall geochemically similar to lower‐lying members of the Murray formation, even though the top of VRR shows a strong hematite spectral signature as observed from orbit. Although overall geochemically similar, VRR is characterized by a prominent decrease in Li abundance and Chemical Index of Alteration across the ridge. This decrease follows the morphology of the ridge rather than elevation and is inferred to reflect a nondepositionally controlled decrease in clay mineral abundance in VRR rocks. Additionally, a notable enrichment in Mn above baseline levels is observed on VRR. While not supporting a single model, the results suggest that VRR rocks were likely affected by multiple episodes of postdepositional groundwater interactions that made them more erosionally resistant than surrounding Murray rocks, thus resulting in the modern‐day ridge after subsequent erosion. Plain Language Summary: Results from the ChemCam instrument on Vera Rubin ridge (VRR) in Gale crater, Mars, are presented and compared with observations from similar rocks leading up to the ridge. VRR is a prominent ridge, flanking the central mound, Aeolis Mons, in Gale crater, Mars. The ridge attracted early attention because it displays strong iron‐oxide spectral signatures. Surprisingly, ChemCam data show that VRR rocks do not show an overall increase in iron abundance relative to the comparable bedrock analyzed for almost 300 m in elevation leading up to the ridge. While similar overall, some notable variations were observed on VRR relative to lower‐lying rocks. In particular, geochemical variations suggest a strong decrease in clay content on the ridge, above which, a notable enrichment in Mn is observed. No single geological process confidently explains all observations on the ridge. Rather, we think that VRR rocks underwent a series of interactions with groundwater that caused the rocks of VRR to become more resistant to erosion than their surroundings, thus emerging as a ridge as the rocks around them eroded. This likely implies that groundwater persisted in Gale crater even long after the disappearance of the ancient lake. Key Points: A decrease in Li and Chemical Index of Alteration, reflecting clay mineral content, is observed across Vera Rubin ridge (VRR)A Mn‐rich interval is observed stratigraphically above the decrease in clay mineral content on VRRVRR likely resulted from increased induration from late‐stage fluid interactions long after the lake environment in Gale crater ceased [ABSTRACT FROM AUTHOR]

Understanding magmatic processes is critical to understanding Mars as a system, but Curiosity's investigation of dominantly sedimentary rocks has made it difficult to constrain igneous processes. Igneous classification of float rocks is challenging because of the following: (1) the possibility that they have been affected by sedimentary processes or weathering, and (2) grain size heterogeneity in the observed rock textures makes the small‐scale compositions measured by rover instruments unreliable for bulk classification. We avoid these ambiguities by using detrital igneous mineral chemistry to constrain models of magmatic processes in the source region for the fluvio‐deltaic Bradbury group. Mineral chemistry is obtained from X‐ray diffraction of three collected samples and a new stoichiometric and visual filtering of ~5,000 laser induced breakdown spectroscopy (LIBS) spots to identify compositions of individual igneous minerals. Observed mineral chemistries are compared to those produced by MELTS thermodynamic modeling to constrain possible magmatic conditions. Fractionation of two starting primary melts derived from different extent of adiabatic decompression melting of a primitive mantle composition could result in the crystallization of all minerals observed. Crystal fractionation of a subalkaline and an alkaline magma is required to form the observed minerals. These results are consistent with the collection of alkaline and subalkaline rocks from Gale as well as clasts from the Martian meteorite Northwest Africa 7034 and paired stones. This new method for constraining magmatic processes will be of significant interest for the Mars 2020 mission, which will also investigate an ancient volcaniclastic‐sedimentary environment and will include a LIBS instrument. Plain Language Summary: Using instruments on Mars rovers, classification of rocks as igneous or sedimentary can be ambiguous, as many of the sedimentary rocks are made of barely altered igneous minerals. We avoid this issue by using the chemistry of individual igneous minerals found in both sedimentary and igneous rocks to assess possible magmatic processes. We focus on rocks in the Bradbury group observed by the Curiosity rover, which includes river and lake deposits coming from a source area to the north of Gale crater. We report the chemistry of pure igneous minerals hit by the ChemCam laser. Then, using modeling, we assess several scenarios for magmatic processes to identify conditions that could have reproduced the mineral chemistries observed. This new method shows that fractional crystallization of two compositionally distinct parental melts formed during the ascent of a mantle composition can explain the igneous mineral chemistry observed. These results are consistent with previous works in Gale, and are interesting because (1) both alkaline and subalkaline magmas were likely produced very early in Mars history, and (2) this provides a new way to constrain magmatic processes from observations of sedimentary rocks, which will be important for the Mars 2020 mission. Key Points: Detrital feldspar and pyroxene mineral compositions were estimated for the first time from stoichiometric analyses of ChemCam compositionsMELTS modeling was used to constrain possible ancient magmatic contributions to the Martian surface mineral chemistry without igneous outcropsOur method is important for future missions like Mars 2020 where igneous outcrops may be rare but detrital minerals are preserved [ABSTRACT FROM AUTHOR]

At Gale crater, Mars, ChemCam acquired its first laser-induced breakdown spectroscopy (LIBS) target on Sol 13 of the landed portion of the mission (a Sol is a Mars day). Up to Sol 800, more than 188 000 LIBS spectra were acquired on more than 5800 points distributed over about 650 individual targets. We present a comprehensive review of ChemCam scientific accomplishments during that period, together with a focus on the lessons learned from the first use of LIBS in space. For data processing, we describe new tools that had to be developed to account for the uniqueness of Mars data. With regard to chemistry, we present a summary of the composition range measured on Mars for major-element oxides (SiO2, TiO2, Al2O3, FeOT, MgO, CaO, Na2O, K2O) based on various multivariate models, with associated precisions. ChemCam also observed H, and the non-metallic elements C, O, P, and S, which are usually difficult to quantify with LIBS. F and Cl are observed through their molecular lines. We discuss the most relevant LIBS lines for detection of minor and trace elements (Li, Rb, Sr, Ba, Cr, Mn, Ni, and Zn). These results were obtained thanks to comprehensive ground reference datasets, which are set to mimic the expected mineralogy and chemistry on Mars. With regard to the first use of LIBS in space, we analyze and quantify, often for the first time, each of the advantages of using stand-off LIBS in space: no sample preparation, analysis within its petrological context, dust removal, sub-millimeter scale investigation, multi-point analysis, the ability to carry out statistical surveys and whole-rock analyses, and rapid data acquisition. We conclude with a discussion of ChemCam performance to survey the geochemistry of Mars, and its valuable support of decisions about selecting where and whether to make observations with more time and resource-intensive tools in the rover's instrument suite. In the end, we present a bird's-eye view of the many scientific results: discovery of felsic Noachian crust, first observation of hydrated soil, discovery of manganese-rich coatings and fracture fills indicating strong oxidation potential in Mars' early atmosphere, characterization of soils by grain size, and wide scale mapping of sedimentary strata, conglomerates, and diagenetic materials. [ABSTRACT FROM AUTHOR]

The unexpected detection of ∼16 wt.% monoclinic tridymite, a high-temperature silica polymorph, within an otherwise lacustrine mudstone in Gale crater, Mars raises significant questions about its formation and the extent of magmatic evolution on that planet. The rock sample, analyzed by the X-ray diffractometer onboard the Curiosity rover, also contained feldspar, cristobalite, and opaline silica (±Si-glass). Monoclinic tridymite is extremely rare on Earth, and has only been discovered in silicic volcanic environments, high-temperature impact settings, and extraterrestrial rocks. We review the most common formation pathways of natural tridymite and run thermodynamical models to investigate possible formation mechanisms. We consider the broader context of the sample to propose a formation and transport mechanism based on: (1) the mineralogical assemblage of the mudstone and rocks in the vicinity, (2) the composition of the mudstone layer, and (3) the overall geological context. Based on the large amount of tridymite, the high SiO 2 and low Al 2 O 3 concentration of the mudstone, and the low temperature context within distal lacustrine mudstone, we propose that an explosive eruption released Si-rich ashes, which were deposited into Gale crater's watershed as a tridymite-rich ashfall along with cristobalite, feldspar, Ti-oxide, and Si-rich glass, when Gale was still a lake (Hesperian). The dissolution of Si-rich glass and mineral sorting during transport would have concentrated tridymite, caused opaline silica precipitation, and relatively lowered the Al 2 O 3 concentration. This scenario implies that explosive volcanism on Mars occurred during the Hesperian and might not be restricted to basaltic eruptions, revealing the complexity of Mars magmatism. • One layer of lacustrine mudstone in Gale contains high temperature silicic minerals. • Tridymite and plagioclase could have co-crystallized from a rhyolitic magma. • The rhyolitic magma is consistent with evolution of observed igneous rock sources. • The Buckskin sample is detrital from tridymite-bearing ash in Gale lake's watershed. • At least one silicic explosive eruption occurred on Mars in the Hesperian. [ABSTRACT FROM AUTHOR]

Introduction: The geological record of the formation and differentiation of our planet has been destroyed by its subsequent evolution, but extremely rare clues may be obtained from other terrestrial planets. Mars provides a unique and accessible example of an early evolutionary path corresponding to that, inaccessible, of our own world. We can investigate it with spacecraft, and samples are available for in-depth analysis on Earth in the form of martian meteorites. So far, the only available martian samples that appear to have recorded the early conditions and the evolution of the planet until the present time are Northwest Africa (NWA) 7034 and its paired stones, nicknamed "Black Beauty". This regolith breccia has been ejected a few million years ago by the formation of a large impact crater, and contains the oldest martian igneous material ever dated: ~4.5 Ga old [1-4]. However, its source and geological context have so far remained unknown. and with it, a region where the earliest geological records of the planet [1-4] are exposed on the surface. Knowing this source region would provide insights into early Mars geological history and crustal extraction [1-4]. This source region may therefore become a high-priority target for detailed orbital analyses and in-situ exploration [5]. Constraints on the meteorite launch site: Following a hypervelocity impact, ejecta materials moving faster than the escape velocity (5 km/s) may get through the martian atmosphere and continue their course into interplanetary space to become martian meteorites [6]. Slower debris fall back on the surface in a radial pattern or ray around the primary crater, forming secondary craters. The presence of 100 meter-size secondaries attests to the freshness of their associated primary craters [7]. Using the size and spatial distribution of more than 90 million impact craters >50 m (both primaries and secondaries) detected using a Crater Detection Algorithm (CDA) [7-8] on the whole surface of Mars from the global Context Camera (CTX) mosaic [9], a previous work [7] identified ray systems of secondary craters <150 m associated with 19 large primary craters, potential source of the ejection of martian meteorites. Here we compare the abundance of K and Th [10-11] as well as the magnetic field intensity and the magnetization of the surface of Mars derived from orbital measurements [12] at the immediate vicinity of each crater candidate with those of the breccia. We also compare the geological context of each of the crater candidates with the chronology and the lithology of the meteorite [e.g. 1-3, 13-14]. The ejection site for Black Beauty: Among the 19 crater candidates investigated, we found that only one match with the characteristics of the meteorite: a 10 km crater located in the north-east of the Terra Cimeria - Sirenum (TCTS) region, between Hesperia Planum and the Tharsis bulge. Our work suggests that clasts contained in the regolith breccia are representative of the TCTS province, making this region a relic of the early crustal processes on Mars [e.g. 15], and thus, a region of high interest for future missions. Details on the identification of the crater source of this unique meteorite, as well a its geological context and broader implications for early crustal processes on Mars will be presented at the conference. [ABSTRACT FROM AUTHOR]