Geologic interpretation of the aeromagnetic survey in the Agourai area (Central Morocco)

Abstract The aim of this work is to interpret the geologic structures of the Agourai area (Paleozoic and Mesozoic structures) from processed magnetic maps. The detected magnetic anomalies from different standard methods used in aeromagnetism (Residual map, RTP map, horizontal gradient map) were compared to geologic structures and permit enhancing the mapping quality of some areas, and thus defining many geologic features. Existing geologic maps and geologic field studies allow interpreting some detected anomalies. It was thus possible to define the limits between the Paleozoic basement and the Mesozoic cover, to determine magnetic anomalies according to NE-SW trends compatible with the regional geologic structures and finally to detect a NE to SW-oriented fault system in the Mesozoic cover of the Agourai Plateau. Despite the reliability of this approach, some folded basaltic sills occurring in this region were not well detected, probably because of their reduced thickness

A swarm of small shield volcanoes on Syria Planum, Mars

International audienceThis study focuses on the volcanism in Syria Planum, located at the center of the Tharsis bulge at an altitude of 6 to 8 km above Mars datum. Syria Planum was previously recognized as a center for the tectonic activity of Tharsis, but not as a major locus for volcanic activity, despite its centrality over the bulge. Using high-resolution images from the high resolution stereo camera on Mars Express combined with Mars Observer Laser Altimeter data, we have characterized a volcanic system that reveals a number of very interesting aspects of Mars volcanism. We identified a swarm of tens of coalesced shallow volcanic edifices, typically 10–30 km diameter, 0.1–0.2 km high, and with slopes around 0.5°. These characteristics are similar to those of small shield volcanoes found in Iceland. In addition, an intermediate-sized volcano, which is the source of lava flows that extend over >200 km, is observed west of this shield swarm. Our study characterizes a previously unrecognized volcanic assemblage on Mars which appears to be much more developed than was documented before, in terms of morphology, inferred origin, and periodicity of eruption. The estimated lava flux of the Syria Planum volcanoes is of the same order as the lava flux of Tharsis Montes. These characteristics suggest that Syria Planum experienced a very specific style of volcanism, which we dated to the Hesperian period

New insight on genetic links between outflows and chasmata on Valles Marineris plateau, Mars

Within the Valles Marineris region on Mars, a huge system of interconnected valleys interpreted as flood channels reveals the presence of braided channels and strong incisions into the bedrock. We focus our study on Ganges Chasma, where two examples of outflow channels lie on the Valles Marineris plateau and take source in depressions. These channels may represent good examples for studying the relationship between the formation of Chasmata and outflow channels. No mass deposition is observed at the mouth of both channels, indicating that outflows were active before the opening of Ganges Chasma. In addition, possible sapping valleys were formed at the mouth in both cases. Residual aquifer could have been responsible for a late hydrogeological activity in this region after the opening and the widening of Ganges Chasma. From these observations and our flux calculations, we conclude that overpressure due to dyke ascent could have initiated outflows on Valles Marineris plateau, which is consistent with previous studies. Our results suggest that these mechanisms played a role in the opening and the widening of the Chasmata around 3 Gy to 3.5 Gy.Dans la région de Valles Marineris sur Mars, de nombreuses vallées interconnectées interprétées comme d’anciennes vallées issues de débâcle sont profondément incisées dans le substratum. Notre étude se concentre sur Ganges Chasma, une région où deux de ces vallées présentes sur le plateau prennent source dans des dépressions fermées. Ces deux vallées pourraient être de bons exemples pour la compréhension des relations entre la formation généralement découplée des Chasmata d’une part et celle des vallées issues de débâcle d’autre part. L’absence d’accumulation à l’embouchure suggère que la mise en place de ces vallées est antérieure à l’ouverture de Ganges Chasma. Par ailleurs, des vallées probablement formées par du sapement, sont observables au niveau des embouchures des deux vallées issues de débâcle. La présence d’une aquifère résiduelle pourrait alors expliquer l’activité hydrogéologique tardive dans cette région. À partir de ces observations, de nos calculs de débits, et en accord avec des travaux antérieurs, nous concluons que la surpression causée par la remontée de dykes sur le plateau de Valles Marineris a pu déclencher l’écoulement et ainsi jouer un rôle important dans l’ouverture des Chasmata il y a environ 3 Ga à 3,5 Ga

Oxford Research Encyclopedia of Planetary Science

International audienc

Estimate of aeolian dust thickness in Arabia Terra, Mars: implications of a thick mantle (> 20 m) for hydrogen detection

This study describes a method for estimating dust thickness on the surface of Mars using the distribution of small impact craters (3 Ga). Results also suggest that hydrogen, detected by the Neutron Spectrometer within this region in the top meter, is present in the dust and not in the underlying bedrock.Notre étude présente une méthode d’estimation de l’épaisseur de poussière à la surface de Mars en utilisant les petits cratères d’impact (< 1 km de diamètre) observés à haute résolution avec l’imagerie de l’instrument Mars Observer Camera de la sonde Mars Global Surveyor. La distribution des petits cratères est différente de celle prédite par le flux météoritique car les cratères sont progressivement recouverts de dépôts éoliens. La hauteur des remparts des plus gros cratères non enfouis permet d’obtenir une estimation approximative de l’épaisseur de ces dépôts éoliens. Cette méthode est appliquée à la région d’Arabia Terra. Les résultats montrent une couverture de poussière d’environ 20 m au minimum. Ceci indique que cette région est une zone de dépôt durant la période Amazonienne (< 3 Ga). Notre étude suggère également que l’hydrogène, qui est détecté par le spectromètre Neutron de Mars Odyssey dans cette région, se localise dans les dépôts éoliens et non pas dans le socle sous-jacent

Sinuous gullies on Mars: frequency, distribution, and implications for flow properties

International audienceRecent gullies on Mars are suspected to be the result of liquid‐water‐bearing flows. A formation from wet flows has been challenged by studies invoking granular (dry) flows. Our study focuses on the sinuous shapes observed for some of the recent Martian gullies. Sinuous gullies are found in locations and slopes (of 10°-15°) similar to straight gullies, and they are therefore related to the same formation processes. Numerical simulations of granular flows are performed here by introducing topographic variations such as obstacles, roughness, or slope changes that could possibly generate flow sinuosity. None of these simulations was able to reproduce sinuous shapes on a slope lower than 18° with friction angles typical of dry granular material. The only way to simulate sinuous shapes is to create small‐amplitude periodic variations of the topography of the deposit, an origin not supported by current Martian imagery. Given the presence of sinuosity in natural terrestrial debris flows, we have concluded that sinuous Martian gullies are better reproduced by liquid‐water‐bearing debris flows. Sinuous shapes in leveed flows are used to derive mechanical parameters from several Martian gullies using photoclinometry. Values in yield strength of 100-2200 Pa, velocities of 1.1-3.3 m s−1, and viscosities from 40 to 1040 Pa s are found, which are all within the range of values for terrestrial debris flows with various proportions of liquid water (20%-40%)

Estimated Minimum Lifespan of the Jezero Fluvial Delta (Mars)

International audienceThe paleo-lake floor at the edge of the Jezero delta has been selected as the NASA 2020 rover landing site. In this paper we demonstrate the sequences of lake filling and delta formation, and constrain the minimum lifespan of the Jezero paleo-lake from sedimentological and hydrological analyses. Utilizing imagery provided by the High Resolution Imaging Science Experiment (NASA Mars Reconnaissance Orbiter) and High Resolution Stereo Camera (ESA Mars Express), two main phases of delta evolution can be recognized. 1) Basin infilling before the breaching of the Jezero rim; and 2) the delta formation itself. Our results suggest delta formation occurred over a 90-550 year period of hydrological activity. Breaching of the Jezero rim occurred in at least three distinct episodes, which spanned a far longer time-period than overall delta formation. This evolutionary history implies the Jezero-lake floor would have been a haven for fine-grained sediment accumulation, and hosted an active environment of significant astrobiological importance

Fluvial Regimes, Morphometry and Age of Jezero Crater Paleolake Inlet Valleys and their Exobiological Significance for the 2020 Rover Mission Landing Site

International audienceJezero crater has been selected as the landing site for the Mars 2020 Perseverance rover, because it contains apaleolake with two fan-deltas, inlet and outlet valleys. Using the data from the High Resolution Stereo Camera(HRSC) and the High Resolution Imaging Science Experiment (HiRISE), we conducted a quantitative geomorphological study of the inlet valleys of the Jezero paleolake. Results show that the strongest erosion is related to a network of deep valleys that cut into the highland bedrock well upstream of the Jezero crater and likely formed before the formation of the regional olivine-rich unit. In contrast, the lower sections of valleys display poorbedrock erosion and a lack of tributaries but are characterized by the presence of pristine landforms interpreted asfluvial bars from preserved channels, the discharge rates of which have been estimated at 10^3–10^4 m^3s^-1. The valleys’ lower sections postdate the olivine-rich unit, are linked directly to the fan-deltas, and are thus formed inan energetic, late stage of activity. Although a Late Noachian age for the fan-deltas’ formation is not excludedbased on crosscutting relationships and crater counts, this indicates evidence of a Hesperian age with significantimplications for exobiology

Structure of the Martian Crust Below InSight From Surface Waves and Body Waves Generated by Nearby Meteoroid Impacts

International audienceWe measure group velocity dispersion of surface waves generated by two meteoroid impacts on Mars close to the lander of the InSight mission. This allows us to probe the crustal structure in the first few kilometers beneath the InSight lander. In combination with body wave arrival times from five impact events, we obtain direct seismic constraints on the seismic velocity of the crust in the vicinity of the InSight landing site. We confirm the existence of a uppermost low-velocity layer with a mean thickness of ∼1.2 km, interpreted as layered volcanic materials, possibly interstratified with sedimentary and altered materials. Our joint inversion of surface and body waves shows a four-layer model for the Martian crust, compatible with high- and low-frequency P-to-S receiver functions estimated in previous studies.<br/