Deep alteration between Hellas and Isidis Basins

Bultel, B.; Quantin‐Nataf, Cathy; Andréani, M.; Clénet, H.; Lozac’h, L.

doi:10.1016/j.icarus.2015.06.037

Cited by 28 publications

(15 citation statements)

References 84 publications

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“…They occur on crater walls and other escarpments at both higher and lower elevations, so phyllosilicates are not limited to ancient basin fill in the study area. The occurrence of phyllosilicates away from impact craters and in deep noncrater exposures suggests that they are not a consequence of the cratering process, however; this interpretation is consistent with that of Bultel et al () in a region ~1,000 km east of our study area. If they are products of Early Noachian surface weathering, then impact gardening would have mixed them into the subsurface over time, and Hellas ejecta would have buried them more deeply.…”

Section: Discussionsupporting

confidence: 93%

Wind‐Eroded Crater Floors and Intercrater Plains, Terra Sabaea, Mars

et al. 2018

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Ancient impact craters with wind‐eroded layering on their floors provide a record of resurfacing materials and processes on early Mars. In a 54 km Noachian crater in Terra Sabaea (20.2°S, 42.6°E), eolian deflation of a friable, dark‐toned layer up to tens of meters thick has exposed more resistant, underlying light‐toned material. These layers differ significantly from strata of similar tone described in other regions of Mars. The light‐toned material has no apparent internal stratification, and visible/near‐infrared spectral analysis suggests that it is rich in feldspar. Its origin is ambiguous, as we cannot confidently reject igneous, pyroclastic, or clastic alternatives. The overlying dark‐toned layer is probably a basaltic siltstone or sandstone that was emplaced mostly by wind, although its weak cementation and inverted fluvial paleochannels indicate some modification by water. Negative‐relief channels are not found on the crater floor, and fluvial erosion is otherwise weakly expressed in the study area. Small impacts onto this crater's floor have exposed deeper friable materials that appear to contain goethite. Bedrock outcrops on the crater walls are phyllosilicate bearing. The intercrater plains contain remnants of a post‐Noachian thin, widespread, likely eolian mantle with an indurated surface. Plains near Hellas‐concentric escarpments to the north are more consistent with volcanic resurfacing. A 48 km crater nearby contains similar dark‐over‐light outcrops but no paleochannels. Our findings indicate that dark‐over‐light stratigraphy has diverse origins across Mars and that some dark‐toned plains with mafic mineralogy are not of igneous origin.

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Section: Discussionsupporting

confidence: 93%

Wind‐Eroded Crater Floors and Intercrater Plains, Terra Sabaea, Mars

et al. 2018

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“…The source of CO 2 levels in the hydrothermal fluids cannot be determined from this study, but it could come from either the Martian atmosphere or magma (Brown et al, ; Bultel et al, ). The hydrothermal experiments and their geochemical modeling show the strong link between the formation of carbonates and zeolites during hydrothermal alteration in the presence of CO 2 .…”

Section: Discussionmentioning

confidence: 95%

“…Interestingly, when the percentage of aqueous CO 2 increases and consequently the pH decreases, the content of trioctahedral chlorite increases in disfavor of the trioctahedral smectite content (Figures and ). The observation on the relative content of chlorite compared to smectite as a function of depth (Bultel et al, ; Carter et al, ; Loizeau et al, ; Sun & Milliken, ) could be related not only to burial diagenesis on Mars (Sun & Milliken, ) but also to fluid composition during hydrothermal alteration. Further experiments dedicated to this transformation using infrared and XRD characterization of the smectite/chlorite relative amounts in MLM will bring more constraints to the processes that led to this specific observation.…”

Section: Discussionmentioning

confidence: 99%

Dioctahedral Phyllosilicates Versus Zeolites and Carbonates Versus Zeolites Competitions as Constraints to Understanding Early Mars Alteration Conditions

et al. 2017

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Widespread occurrence of Fe,Mg‐phyllosilicates has been observed on Noachian Martian terrains. Therefore, the study of Fe,Mg‐phyllosilicate formation, in order to characterize early Martian environmental conditions, is of particular interest to the Martian community. Previous studies have shown that the investigation of Fe,Mg‐smectite formation alone helps to describe early Mars environmental conditions, but there are still large uncertainties in terms of pH range, oxic/anoxic conditions, etc. Interestingly, carbonates and/or zeolites have also been observed on Noachian surfaces in association with the Fe,Mg‐phyllosilicates. Consequently, the present study focuses on the dioctahedral/trioctahedral phyllosilicate/carbonate/zeolite formation as a function of various CO2 contents (100% N2, 10% CO2/90% N2, and 100% CO2), from a combined approach including closed system laboratory experiments for 3 weeks at 120°C and geochemical simulations. The experimental results show that as the CO2 content decreases, the amount of dioctahedral clay minerals decreases in favor of trioctahedral minerals. Carbonates and dioctahedral clay minerals are formed during the experiments with CO2. When Ca‐zeolites are formed, no carbonates and dioctahedral minerals are observed. Geochemical simulation aided in establishing pH as a key parameter in determining mineral formation patterns. Indeed, under acidic conditions dioctahedral clay minerals and carbonate minerals are formed, while trioctahedral clay minerals are formed in basic conditions with a neutral pH value of 5.98 at 120°C. Zeolites are favored from pH ≳ 7.2. The results obtained shed new light on the importance of dioctahedral clay minerals versus zeolites and carbonates versus zeolites competitions to better define the aqueous alteration processes throughout early Mars history.

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“…Spectra here suggest that these carbonates cooccur with phyllosilicates, and although all exhibit the four key absorptions listed in section 3.1 (e.g., Figure b), variation in the band positions makes it ambiguous whether these are Fe/Ca‐carbonates akin to those in the Huygens region, or more Mg‐rich carbonates as found ~600 km farther northeast in Libya Montes [ Bishop et al ., ], or a combination of both. Additional possible carbonate detections have been reported even farther east in Terra Tyrrhena [ Bultel et al ., ]. In the other direction, we find carbonates as far as 700 km southwest of Huygens, exposed in the walls of a cluster of eroded Noachian impact craters each ~40 km in diameter [ Irwin et al ., ].…”

Section: Huygens Basin Regionmentioning

confidence: 96%

Orbital evidence for more widespread carbonate‐bearing rocks on Mars

et al. 2016

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Carbonates are key minerals for understanding ancient Martian environments because they are indicators of potentially habitable, neutral-to-alkaline water and may be an important reservoir for paleoatmospheric CO 2 . Previous remote sensing studies have identified mostly Mg-rich carbonates, both in Martian dust and in a Late Noachian rock unit circumferential to the Isidis basin. Here we report evidence for older Fe-and/or Ca-rich carbonates exposed from the subsurface by impact craters and troughs. These carbonates are found in and around the Huygens basin northwest of Hellas, in western Noachis Terra between the Argyre basin and Valles Marineris, and in other isolated locations spread widely across the planet. In all cases they cooccur with or near phyllosilicates, and in Huygens basin specifically they occupy layered rocks exhumed from up to~5 km depth. We discuss factors that might explain their observed regional distribution, arguments for why carbonates may be even more widespread in Noachian materials than presently appreciated and what could be gained by targeting these carbonates for further study with future orbital or landed missions to Mars.

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Deep alteration between Hellas and Isidis Basins

Cited by 28 publications

References 84 publications

Wind‐Eroded Crater Floors and Intercrater Plains, Terra Sabaea, Mars

Wind‐Eroded Crater Floors and Intercrater Plains, Terra Sabaea, Mars

Dioctahedral Phyllosilicates Versus Zeolites and Carbonates Versus Zeolites Competitions as Constraints to Understanding Early Mars Alteration Conditions

Orbital evidence for more widespread carbonate‐bearing rocks on Mars

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