We surveyed the Martian surface in order to identify possible source craters of the nakhlite Martian meteorites. We investigated rayed craters that are assumed to be younger than 11 Ma, on lava surfaces with a solidification age around 1.2 Ga. An area of 17.3 million km Amazonian lava plains was surveyed and 53 rayed craters were identified. Although most of them are smaller than the threshold limit that is estimated as minimum of launching fragments to possible Earth crossing trajectories, their observed size frequency distribution agrees with the expected areal density from cratering models characteristic for craters that are less than few tens of Ma old. We identified 6 craters larger than 3 km diameter constituting the potentially best source craters for nakhlites. These larger candidates are located mostly on a smooth lava surface, and in some cases, on the earlier fluvial-like channels. In three cases they are associated with fluidized ejecta lobes and rays - although the rays are faint in these craters, thus might be older than the other craters with more obvious rays. More work is therefore required to accurately estimate ages based on ray system for this purpose. A more detailed search should further link remote sensing Martian data with the in-situ laboratory analyses of Martian meteorites, especially in case of high altitude, steep terrains, where the crater rays seems to rarely survive several Ma.

International audienceThe Chalkidiki block is a major domain in the North Aegean that, contrary to other domains in the region, largely escaped thermal perturbations during Tertiary extension. As a result, the Chalkidiki block is an ideal candidate to glean information related to the timing of Mesozoic thermal events using appropriate geochronological techniques. We have undertaken a laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) study (U-Th-Pb on monazites and U-Pb on zircons) coupled with 40Ar/39Ar dating on nine samples from various structural levels within the thrust system of the Chalkidiki block. The eastern, and structurally lower part of the system revealed a complete isotopic reset of Carboniferous – Early Triassic monazites coeval with partial monazite destruction, REE-mobilisation and formation of apatite-allanite-epidote coronas at ~ 132 Ma, a reaction that is commonly observed in amphibolite-facies rocks. These coronas formed after crystallisation of garnet (i.e., at T > 580 °C) and, in all probability, either close to the peak-temperature conditions (~ 620 °C) on a prograde path or during retrogression between the peak-temperature and the low-temperature boundary of the amphibolite facies. Cooling of these rocks and arrival at mid-crustal levels occurred at 95–100 Ma. By contrast, the western, and structurally uppermost part of the system went through the same event by 120–125 Ma. Further structural considerations with respect to medium-temperature geochronology data imply that syn-metamorphic thrusting must have ceased by early Late Cretaceous. We emphasize that, with the sole exception of the Chalkidiki block, no pre-45 Ma medium-temperature geochronology data are preserved in other North Aegean domains, a feature that is clearly related to the extension-induced thermal perturbation of the region during the Tertiary

A conspicuous biomorphic ovoid structure has been discovered in the Nakhla martian meteorite, made of nanocrystalline iron-rich saponitic clay and amorphous material. The ovoid is indigenous to Nakhla and occurs within a late-formed amorphous mesostasis region of rhyolitic composition that is interstitial to two clinopyroxene grains with Al-rich rims, and contains acicular apatite crystals, olivine, sulfides, Ti-rich magnetite, and a new mineral of the rhoenite group. To infer the origin of the ovoid, a large set of analytical tools was employed, including scanning electron microscopy and backscattered electron imaging, wavelength-dispersive X-ray analysis, X-ray mapping, Raman spectroscopy, time-of-flight secondary ion mass spectrometry analysis, high-resolution transmission electron microscope imaging, and atomic force microscope topographic mapping. The concentric wall of the ovoid surrounds an originally hollow volume and exhibits internal layering of contrasting nanotextures but uniform chemical composition, and likely inherited its overall shape from a preexisting vesicle in the mesostasis glass. A final fibrous layer of Fe-rich phases blankets the interior surfaces of the ovoid wall structure. There is evidence that the parent rock of Nakhla has undergone a shock event from a nearby bolide impact that melted the rims of pyroxene and the interstitial matter and initiated an igneous hydrothermal system of rapidly cooling fluids, which were progressively mixed with fluids from the melted permafrost. Sharp temperature gradients were responsible for the crystallization of Al-rich clinopyroxene rims, rhoenite, acicular apatites, and the quenching of the mesostasis glass and the vesicle. During the formation of the ovoid structure, episodic fluid infiltration events resulted in the precipitation of saponite rinds around the vesicle walls, altered pyrrhotite to marcasite, and then isolated the ovoid wall structure from the rest of the system by depositing a layer of iron oxides/hydroxides. Carbonates, halite, and sulfates were deposited last within interstitial spaces and along fractures. Among three plausible competing hypotheses here, this particular abiotic scenario is considered to be the most reasonable explanation for the formation of the ovoid structure in Nakhla, and although compelling evidence for a biotic origin is lacking, it is evident that the martian subsurface contains niche environments where life could develop.

The findings of the present study could imply that both materials are indicated for use in an acidic environment.

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Methane, perchlorates, chlorates, and methyl chlorides have all been detected on Mars. The origin of these species has never been adequately explained. In this paper, we irradiated mixtures of CO2, HCl, and a mineral catalystanatase, rutile, montmorillonite, and the Nakhla meteoritewith soft UV radiation for up to 3500 h and observed the formation of perchlorates, chlorates, methyl chlorides, and methane in a single experiment. Additionally, the methanogenesis for anatase was observed at −196 °C. Further, we propose that while methane is decomposed relatively quickly and therefore attains a steady-state concentration (0.41 ± 0.16 ppbv), the chlorinated compounds are much more stable and therefore would have accumulated throughout the Martian history. We estimate that this mechanism would be sufficient in the course of Martian history to accumulate perchlorate in the soil in 0.5 wt % in 5–50 cm depth, which is in accordance with the observed perchlorate content on Mars. This predicted perchlorate gradient may be observed with the Insight rover. Further, if microbes are present on Mars, they will likely inhabit depths below the perchlorate (i.e., 5–50 cm). This chemistry likely still continues on Mars to a certain extent, and any future exploration by rovers or planetary models should account for this process during their analyses.

International audienceThe Chalkidiki block in Northern Greece represents the southwesternmost piece of theultrahigh-pressure Rhodope and has played an important role in the evolution of the NorthAegean. The eastern part of the Chalkidiki block is a basement complex (Vertiskos Unit) thatis made largely of Palaeozoic granitoids and clastic sediments metamorphosed during theMesozoic. This basement is traditionally considered as part of the Rhodopean hanging-wall,an assignment mainly supported by the absence of high-pressure mineral indicators and thepresence of a regional medium-pressure/medium-temperature amphibolite-facies Barrovianmetamorphic imprint. Toward the west, the basement is juxtaposed with meta-sedimentary(Circum-Rhodope belt) and arc units (Chortiatis Magmatic Suite) that carry evidence of aMesozoic high-pressure/low-temperature event. In this study, garnet-staurolite-mica schistsfrom the eastern part of the basement were examined by means of micro-textures, mineralchemistry and isochemical phase-diagram sections in the system NCKFMASHMn(Ti)[Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-MnO-(TiO2)]. The schists represent formerMesozoic sedimentary sequences deposited on the Palaeozoic basement. We document thepresence of a relict eclogite-facies mineral assemblage (garnet + chloritoid + phengite +rutile) in an amphibolite-facies matrix composed of garnet + staurolite + phengite ± kyanite.Model results suggest the existence of a high-pressure/medium-temperature metamorphicevent (1.9GPa / 520°C) that preceded regional re-equilibration at medium-pressure/mediumtemperatureconditions (1.2GPa / 620°C). Clearly, the eastern part of the Chalkidiki block(basement complex) retains memory of an as yet unidentified Mesozoic eclogiticmetamorphic event that was largely erased by the later Barrovian overprint. In the light of ourfindings, the basement complex of the Chalkidiki block shares a common tectonometamorphicevolution with both the high-pressure units to the west, and the high-gradeRhodopean gneisses further to the northeast. Our results are consequential for the geodynamic reconstruction of the Rhodope since they require participation of the Chalkidikiblock to the well-established Mesozoic subduction system

The objectives of this 14 days experiment were to investigate the effect of spaceflight on the growth of Ulocladium chartarum, to study the viability of the aerial and submerged mycelium and to put in evidence changes at the cellular level. U. chartarum was chosen for the spaceflight experiment because it is well known to be involved in biodeterioration of organic and inorganic substrates covered with organic deposits and expected to be a possible contaminant in Spaceships. Colonies grown on the International Space Station (ISS) and on Earth were analysed post-flight. This study clearly indicates that U. chartarum is able to grow under spaceflight conditions developing, as a response, a complex colony morphotype never mentioned previously. We observed that spaceflight reduced the rate of growth of aerial mycelium, but stimulated the growth of submerged mycelium and of new microcolonies. In Spaceships and Space Stations U. chartarum and other fungal species could find a favourable environment to grow invasively unnoticed in the depth of surfaces containing very small amount of substrate, posing a risk factor for biodegradation of structural components, as well as a direct threat for crew health. The colony growth cycle of U. chartarum provides a useful eukaryotic system for the study of fungal growth under spaceflight conditions.