Origin of collapsed pits and branched valleys surrounding the Ius chasma on Mars (original) (raw)
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Geomorphology of Ius Chasma, Valles Marineris, Mars
Journal of Maps, 2017
Cartographic products of the Martian trough system, Valles Marineris, are useful to identify the diversity and complexity of geological activity that has occurred there. A huge fraction of the processes that have shaped the surface of Mars are also concentrated there. A geomorphological map of Ius Chasma in western Valles Marineris is presented. The map is published in three sheets at 1:260,000. It was drawn on the basis of 100 Mars Reconnaissance Orbiter's Context Camera images of 12 m/pixel resolution, mosaiced using the USGS ISIS Planetary Image Processing Software, and subsequently mapped and interpreted for geomorphology in ArcGIS. The map displays 52 main geomorphological units of which some are further subdivided. They include both well-established features (e.g. spurand-gully morphology on trough walls, landslide scars, and deposits), and newly reported landforms (e.g. alluvial fans with dendritic channels, moraines in western Ius Chasma). The proposed classifications of landslide deposits, glacial landforms, and floor areas are more detailed than on any previous map of Valles Marineris. The Ius Chasma map is the first cartographic product presenting a full inventory of dune fields, impact craters, light-toned outcrops, and mass-wasting features.
Crater morphometry and modification in the Sinus Sabaeus and Margaritifer Sinus regions of Mars
Journal of Geophysical Research, 1997
Degraded craters in the southern highlands are indicative of an early martian climate much different than the present. Using a photoclinometric model, analyses of degraded crater morphometry have revealed the stages of crater modification and, for the first time, allow a quantitative assessment of the amount of material eroded in the highlands. Central peaks of fresh craters are removed early by degradational processes. The sharp rims of fresh craters also become rounded while the interior slopes become shallower. Continued degradation causes the crater rim to lower, and infilling produces a broad, flat crater floor. Contrary to earlier observations, the degree of rim modification does not appear to be dependent on the presence of ancient valley networks. During degradation, the diameter of the impact craters also increases due to backwasting. A simple algebraic model balancing the measured amount of infilling with that eroded from the interior slopes suggests that the crater diameters were enlarged by 7 to 10% initially, agreeing with prior observations. These models suggest that larger diameter (i.e., 50 km) craters were enlarged a greater amount than smaller diameter craters, which is opposite to what should be observed. To explain this discrepancy, a ~10m thick deposit, presumably aeolian in origin, must have been emplaced within the crater interiors following cessation of the degradational process. By the terminal stage of degradation, crater diameters appear to have been enlarged by 30%. In addition, a deposit ~60m average thickness must have been emplaced within these rimless craters to explain the discrepancy in crater enlargement. Because this deposit is contained only within the highly eroded, rimless craters, this material most likely originated from erosion of the surrounding terrain. The measured crater morphometry has allowed us to develop equations describing the amount of material eroded at any given stage of degradation. Applying these equations to craters within the Margaritifer Sinus and Sinus Sabaeus region indicates that an equivalent of ~200m of highland material was eroded and redistributed within the study area. Depending upon model chronology, degradation operated for either 400 or 600 million years, suggesting that erosion rates were on the order of ~0.0003 to 0.0005 mm/yr. These erosion rates are equivalent to those determined for terrestrial periglacial environments. Two-dimensional simulations of some possible degradational processes suggest that fluvial erosion and deposition combined with diffusional creep come closest to producing equivalent degrees of modification through the range of crater diameters investigated in this study (20 to 50 km). However, these processes are inefficient at producing the amount of crater enlargement observed, suggesting that crater interior slopes may have also been undermined by sapping. These results imply that geologic processes related to precipitation dominated the early martian environment. Our working hypothesis is that this precipitation was due to the presence of a primordial atmosphere which condensed and collapsed (i.e., precipitated) into the martian regolith; a process which ceased during the late Hesperian/early Amazonian (3.5 to 1.8 Ga).
Journal of Geophysical Research, 2011
A basin-like area containing three interior layer deposits (ILDs) on the southern margin of Coprates Chasma was studied. We interpret the area as an ancestral basin and demonstrate that ILD deposition postdates the formation of the current wall rock slopes. The geometry of the ILD and the wall rock spurs form a catchment area between each ILD and the plateau to the south. Erosional remnants of extensive ash or dust layers deposited on the plateau south of Valles Marineris also crop out on the southern plateau of Coprates Chasma. A mass balance calculation suggests that the volume of each ILD is compatible with the volume of the ash or dust that would have been deposited within each catchment area. We propose that the ILDs likely formed by episodically washing such aerially deposited material down from chasma walls. Rifting of the Ius-Melas-Coprates graben opened the enclosed basin and removed any standing water. Faults within the ILDs are compatible with this chasm opening. Sulfates are associated with the ILDs and light-toned material on the basin floor. We suggest that they result from water alteration of preexisting deposits, though the timing of that alteration may predate or postdate the breaching of the basin. Scours within one ILD are similar to terrestrial glacial scours. During a period of high obliquity ice would accumulate in this region; hence we argue the scours are Martian glacial scours. A late deposited layer marks the end of the active local geological history between 100 My and 1 Gy.
Origin of circular collapsed landforms in the Chryse region of Mars
Icarus, 2016
The quasi-circular collapsed landforms occurring in the Chryse region of Mars share similar morpholog- ical characteristics, such as depth of collapse and polygonally fractured floors. Here, we present a statis- tical analysis of diameter, maximum and minimum depth, and amount of collapse of these features. Based on their morphometric characteristics, we find that these landforms have a common origin. In par- ticular, the investigated landforms show diameter-depth correlations similar to those that impact craters of equivalent diameters exhibit. We also find that the observed amount of collapse of the collected fea- tures is strongly correlated to their diameter. Furthermore, the linear relation between minimum filling and pristine depth of craters, the constant ratio between collapse and the amount of filling and the frac- tured and chaotic aspect of the filling agree with melting and subsequent collapse of an ice layer below a sediment layer. This interpretation is consistent with a buried sub-ice lake scenario, which is a non-climatic mechanism for producing and storing abundant liquid water under martian conditions.
Geology of the Melas Chasma landing site for the Mars Exploration Rover mission
Journal of Geophysical Research, 2003
The Melas Chasma landing site was considered a high-priority site for the Mars Exploration Rover (MER) mission because of the opportunity to land on and study potential layered sedimentary deposits. Though no longer considered a candidate site because of safety concerns, the site remains a scientifically interesting area that provides insight into the geologic history of Valles Marineris. Within the landing ellipse are dunes, landslide material, and unusual blocky deposits. The blocky deposits are composed of rounded blocks, some of which have meter-scale layering, and they show evidence of ductile deformation, including bending and distortion of coherent blocks around each other. The morphologic characteristics of the blocks are unique, and they appear to have no terrestrial analogue. However, the gross morphology of these blocky deposits and their superposition on adjacent wallrock is consistent with the blocks having been transported downslope. Given the existence of other large mass failures in the area, we propose the blocky deposits may also have originated from mass movement events. The size of the blocks coupled with the distances they traveled indicates high mobility. The distances the blocks were transported and their rounded, irregular shapes suggest either water in the source material or deposition in a subaqueous environment. The source for the main blocky deposit inside the landing ellipse is considered to be the wallrock to the south, while the other two blocky deposits have source regions along the northern canyon walls. The southern wallrock of Melas Chasma contains numerous valleys not seen elsewhere in Valles Marineris. The identification of valley networks along the southern wallrock suggests that a source of water existed below the surface of the plateau and produced the valleys after intersecting the edge of the exposed canyon walls.
Modeling the collapse of Hebes Chasma, Valles Marineris, Mars
Geological Society of America Bulletin, 2011
Physical modeling and detailed mapping of Hebes Chasma provide new insights into the crustal composition and origin of the Valles Marineris region of equatorial Mars. Hebes Chasma is a 315-km-long and 8-kmdeep closed depression containing distinctive landforms that include diapirs and extensive allochthonous fl ows that end in pits. A central puzzle of Hebes Chasma is how and where 10 5 km 3 of missing material disappeared. Our physical models tested the hypothesis that the chasma formed by collapse and removal of material from below. Gravity-driven collapse in the models reproduced all the chasma's main landforms as subsidence evolved from early sagging of the upper surface, to inward collapse and removal of material, to emergence of diapirs and low-gradient fl ows. The models and geologic evidence suggest that Hebes Mensa arched upward diapirically and raised deep stratigraphy almost level with the chasma rim. If the chasma indeed collapsed by subsurface drainage as occurred in the models, the upper 8-10 km of deposits at Hebes must have been solid to depths of ~5 km but viscous at greater depths. The materials removed could not have consisted mainly of basalt fl ows; instead, they probably were a mixture of hydrated and nonhydrated salts, water ice, liquid water, and insoluble (likely basaltic) particles. The proportions of these constituents are unknown but constrained because the material drained from the subsiding chasma and apparently contributed to the outburst fl oods released down neighboring Echus Chasma and Kasei Valles.
Buried impact basin distribution on Mars: Contributions from crustal thickness data
[1] Crustal thickness data (derived from Mars Global Surveyor (MGS) gravity field and topographic data) exposes a number of circular thin areas (CTAs) that may represent deeply buried impact basins, which are often not visible in topography alone. A data set which combines quasi-circular depressions (QCDs) revealed by the Mars Orbiter Laser Altimeter (MOLA) on the MGS spacecraft with a population of non-QCD CTAs is a better estimate of the true crater retention ages of the buried surfaces of Mars. This study finds that all regions have older crater retention ages than previously thought based on QCDs alone. The highlands and lowlands appear to have the same basement crater retention age, but Tharsis is younger.
Discovery of a 450 km diameter, multi-ring basin on Mars through analysis of MOLA topographic data
Geophysical Research Letters, 1999
Mars Orbiter Laser Altimeter (MOLA) topographic data have revealed a previously unknown, 450 km wide, 2 km deep basin centered at 30N, 312W near the Phison Rupes. This basin, as large as and deeper than the obvious Cassini impact basin located 1000 km to the SW, is not apparent in the existing but good quality Viking imagery. Gridded MOLA data show the feature as a closed depression. Based on analysis of slope breaks readily visible in two MOLA profiles, we suggest this Phison Rupes Basin has three topographic rings with diameters approximately 350, 455 and 670 km. These rings outline a region of lower impact crater density and smoother inter-crater plains. Similar previously unknown features may exist elsewhere on Mars, and MOLA topographic data may be able to locate them. hard to derive from imagery, such as location of a main "topographic ring" marked by the maximum relief in basin rim materials [Frey et al., 1998a; 1999]. Here we demonstrate another important aspect of MOLA data: detection of moderate sized basins not readily apparent in imagery. We show there is a large, Cassini-size (diameter >400 km) basin in the Phison Rupes area of Arabia Terra (near 312W, 30N) which previous searches failed to find. MOLA profile data suggest this is a multi-ring basin of a size fairly common on Mars. That it was previously unknown suggests there may be more such structures waiting to be found.
Distribution and evolution of scalloped terrain in the southern hemisphere, Mars
Icarus, 2010
Scalloped depressions are a unique martian surface morphology found in the northern and southern hemisphere latitude-dependent dust and ice-rich surface mantles. These features exhibit a distinct asymmetric north-south slope profile, characterized by steep pole-facing scarps, flat floors and gentle equatorfacing slopes. We examined High Resolution Stereo Camera (HRSC) images of the southern hemisphere to determine their longitudinal distribution, which revealed that a majority of scalloped terrain is located in the region of the southern wall of the Hellas Basin and northern Malea Planum. A detailed map of this area was produced where scallops were found to contour the southern wall of the basin, and where the ice-rich mantle was seen to be thickest. Scalloped terrain is concentrated along the topographic highs near the Amphitrites and Peneus Paterae and areal extent and depth decreases with increasing depth into the basin. We also examined existing hypothesis for the formation and evolution of scalloped depressions using High Resolution Imaging Science Experiment (HiRISE) images and data from the Thermal Emission Imaging System-Infrared (THEMIS-IR) and the Thermal Emission Spectrometer (TES). Our approach provides regional context for the development of scalloped terrains within the southern hemisphere, and offers detailed evidence of scallop depressions forming around small cracks, presumably caused by thermal contraction. Morphometric measurements show that scalloped depressions can be as much as 40 m deep, with typical depths of between 10 and 20 m. Our observations of scallop formation and development in the southern hemisphere support a solar-insolation model proposed by previous researchers (e.g. press]). Observations made using HiRISE images suggest that scalloped depressions most likely form from small cracks in the mantle, which become larger and deeper through sublimation of interstitial ice from within the mantle. Sublimation is likely enhanced on equator-facing slopes because of increased solar insolation, which accounts for the asymmetric slope profile and hemispherical orientation and is demonstrated by THEMIS-IR images. We suggest that sublimation lag deposits can possibly be removed by dust devils or strong slope winds related to the Hellas Basin, offering an explanation as to why scalloped terrain is so abundant only in this area of the southern hemisphere. Daytime maximum summer temperatures suggest that sublimation in the study area of Malea Planum is possible under current conditions if the sublimation lag is removed. While it cannot be ruled out that scalloped terrain in Malea Planum is presently evolving, we attribute the extensive distribution to geologically recent obliquity excursions when conditions were more conducive to mesoscale modification of the ice-rich mantle.