The source and nature of carbon on Mars have been a subject of intense speculation. We report the results of confocal Raman imaging spectroscopy on 11 martian meteorites, spanning about 4.2 billion years of martian history. Ten of the meteorites contain abiotic macromolecular carbon (MMC) phases detected in association with small oxide grains included within high-temperature minerals. Polycyclic aromatic hydrocarbons were detected along with MMC phases in Dar al Gani 476. The association of organic carbon within magmatic minerals indicates that martian magmas favored precipitation of reduced carbon species during crystallization. The ubiquitous distribution of abiotic organic carbon in martian igneous rocks is important for understanding the martian carbon cycle and has implications for future missions to detect possible past martian life.

The Perseverance rover landed in Jezero crater, Mars, to investigate ancient lake and river deposits. We report observations of the crater floor, below the crater’s sedimentary delta, finding the floor consists of igneous rocks altered by water. The lowest exposed unit, informally named Séítah, is a coarsely crystalline olivine-rich rock, which accumulated at the base of a magma body. Fe-Mg carbonates along grain boundaries indicate reactions with CO 2 -rich water, under water-poor conditions. Overlying Séítah is a unit informally named Máaz, which we interpret as lava flows or the chemical complement to Séítah in a layered igneous body. Voids in these rocks contain sulfates and perchlorates, likely introduced by later near-surface brine evaporation. Core samples of these rocks were stored aboard Perseverance for potential return to Earth.

The Mars 2020 Perseverance rover landing site is located within Jezero crater, a ∼ 50 km diameter impact crater interpreted to be a Noachian-aged lake basin inside the western edge of the Isidis impact structure. Jezero hosts remnants of a fluvial delta, inlet and outlet valleys, and infill deposits containing diverse carbonate, mafic, and hydrated minerals. Prior to the launch of the Mars 2020 mission, members of the Science Team collaborated to produce a photogeologic map of the Perseverance landing site in Jezero crater. Mapping was performed at a 1:5000 digital map scale using a 25 cm/pixel High Resolution Imaging Science Experiment (HiRISE) orthoimage mosaic base map and a 1 m/pixel HiRISE stereo digital terrain model. Mapped bedrock and surficial units were distinguished by differences in relative brightness, tone, topography, surface texture, and apparent roughness. Mapped bedrock units are generally consistent with those identified in previously published mapping efforts, but this study's map includes the distribution of surficial deposits and sub-units of the Jezero delta at a higher level of detail than previous studies. This study considers four possible unit correlations to explain the relative age relationships of major units within the map area. Unit correlations include previously published interpretations as well as those that consider more complex interfingering relationships and alternative relative age relationships. The photogeologic map presented here is the foundation for scientific hypothesis development and strategic planning for Perseverance's exploration of Jezero crater.

Here we report Precambrian zircons recovered from basaltic beach sands on Mauritius, 900 km distant from the nearest continental crust (Madagascar). Some twenty zircon grains were recovered from two basaltic sand samples from the northwest (Sample E04-1) and southeast (Sample MBS1) coast of Mauritius. The use of sand samples avoids potential contamination from rock crushing apparatus. The zircons are generally subhedral to anhedral, show diversity in shape and presence of inclusions, and range in size from 50 to 300 µm. The zircons were analysed for U and Pb isotopes by TIMS (Fig. 2, Supplementary Table S1). Sample E04-1 from the Intermediate Series yielded fifteen zircon grains; six were selected for analysis. Sample MBS1 from the Older Series had fewer zircons and two were used for age determination. Most results are somewhat discordant (Fig. 2) Table S1). Their presence in exclusively basaltic detritus suggests that they were brought up by mafic magmas that assimilated underlying sialic crust, likely at relatively shallow levels. There is no clear cut geochemical or isotopic signature of continental crust in the Mauritian basalts, although some of their variability in εNd values (3.9-6.1; refs 8,9) could indicate variable crustal contamination. We suggest that a crustal signature need not be detectable in basaltic lavas that carry xenocrystic zircons.Although small amounts of zircon have been found as crystallization products in young oceanic 2 mafic volcanics and intrusives 11,12 , older xenocrystic zircons have been reliably documented only from oceanic gabbros drilled at the mid-Atlantic ridge 13 . The young Mid-Atlantic ridge gabbros that contain old xenocrystic zircons have lower Zr concentrations 13 (mean ~20 ppm) than Mauritian basalts 8 (mean ~145 ppm), and also lack geochemical indicators of continental crust assimilation.To identify regions in the northwest Indian Ocean that may be underlain by continental crust, we determined crustal thicknesses by gravity anomaly inversion incorporating a lithosphere thermal gravity anomaly correction 14 . The gravity inversion predicts contiguous crust of thickness >25-30 km beneath the Seychelles and northern Mascarenes, which extends southwards towards Mauritius (Fig. 1). Sensitivity tests ( Supplementary Fig. S1) show that predicted crustal thicknesses from gravity inversion under the Seychelles, Mascarenes, Mauritius, Laccadives, Maldives and Chagos are not significantly dependent on breakup and ocean age isochrons used to determine the lithosphere thermal gravity anomaly correction. Crustal thickness determined from gravity inversion for the Seychelles is consistent with wide-angle seismic studies 15 where crustal thicknesses of 32 km and velocity structure are interpreted as continental. On the conjugate Indian margin, the Laccadives, Maldives and Chagos also appear to be underlain by contiguous crust of thickness >25-30 km.Seismic Moho depths (~24 km) beneath the Laccadives 16 and crustal thicknesses from Chagos (up to 27 km) obtained from gravity modell...

Abstract-We report a comprehensive imaging study including confocal microRaman spectroscopy, scanning electron microscopy (SEM), and 3-D extended focal imaging light microscopy of carbonate globules throughout a depth profile of the Martian meteorite Allan Hills (ALH) 84001 and similar objects in mantle peridotite xenoliths from the Bockfjorden volcanic complex (BVC), Svalbard. Carbonate and iron oxide zoning in ALH 84001 is similar to that seen in BVC globules. Hematite appears to be present in all ALH 84001 carbonate-bearing assemblages except within a magnesite outer rim found in some globules. Macromolecular carbon (MMC) was found in intimate association with magnetite in both ALH 84001 and BVC carbonates. The MMC synthesis mechanism appears similar to established reactions within the Fe-C-O system. By inference to a terrestrial analogue of mantle origin (BVC), these results appear to represent the first measurements of the products of an abiotic MMC synthesis mechanism in Martian samples. Furthermore, the ubiquitous but heterogeneous distribution of hematite throughout carbonate globules in ALH 84001 may be partly responsible for some of the wide range in measured oxygen isotopes reported in previous studies. Using BVC carbonates as a suitable analogue, we postulate that a low temperature hydrothermal model of ALH 84001 globule formation is most likely, although alteration (decarbonation) of a subset of globules possibly occurred during a later impact event.