P13B-1290
Boundary Layer Models of Martian Hydrothermal Systems
Many geomorphic features on the surface of Mars, such as gullies, fans, paleolakes, outflow channels, and deltas, were likely caused by flowing water; however, the source of that water is disputed. One possible water source is a hydrothermal system driven by a magma intrusion. We investigated such hydrothermal systems by first developing analytical, steady state, two-dimensional, thermal boundary layer models in order to determine the mass and heat fluxes near the quasi-vertical boundaries of magma intrusions with heights ranging from 1 to 10 km. We analyzed the effects of various permeabilities and intrusion dimensions on the heat and mass fluxes generated by hydrothermal flow. Results showed, for example, that a 100 km long dike with a depth of 5 km injected into a highly permeable rock would produce |sim 1019 J/yr of heat and transport ~ 10 km3/yr of fluid. This and additional mass flux results were compared with hydrographs estimating the volumes of fluid outflow and durations of flow needed to form various observed geomorphic features. The hydrograph comparisons indicate that flow from such hydrothermal systems could be responsible for some fluvial features on Mars including gullies and stepped fans. The relatively small flow volumes suggest it is unlikely that the larger features were formed directly by out flowing hydrothermal fluids. However, additional fluid may result from the melting of subsurface ice as a result of hydrothermal heat transport.
P13B-1291
Continental-Scale Salt Tectonics on Mars and the Origin of Valles Marineris and Associated Outflow Channels
A synthesis of regional deformation patterns of the Thaumasia Plateau, Mars, leads to a new interpretation for regional deformation and the origin of Valles Marineris and associated outflow channels. The morphology of the Thaumasia Plateau is typical of thin-skinned deformation, akin to a "mega-slide," in which extensional deformation in Syria Planum and Noctis Labyrinthus connects via zones of lateral transtension — Claritas Fossae and Valles Marineris — to a broad zone of compressional uplift and shortening defined by truncated craters and thrust faults along the Coprates Rise and Thaumasia Highlands. However, the low regional slope (?1°) results in gravitational body forces that are too small to deform the basaltic lava flows conventionally thought to compose the flanks of the Tharsis volcanic province. Instead, we conclude that geothermal heating and topographic loading of extensive buried deposits of salts (or mixtures of salts, ice, and basaltic debris) would allow for weak detachments and large-scale gravity spreading. We propose that the generally linear chasmata of Valles Marineris reflect collapse and excavation along pre-existing extension fractures radial to Tharsis, reactivated as part of one lateral margin of the Thaumasia gravity spreading system. The other, dextral, lateral margin is a massive splay of extensional faults forming the Claritas Fossae, which resembles a trailing extensional imbricate fan. The compressional mountain belt defined by the Coprates Rise and Thaumasia Highlands forms the toe of the "mega-slide." Topographic observations and previous structural analyses reveal evidence for a failed volcanic plume below Syria Planum that could have provided both thermal energy and topographic potential for initiating regional deformation. Increased geothermal heating over time, or heating simply due to increasing depth in the crust due to continuing burial, would have contributed to flow of salt deposits, as well as formation of groundwater from melting ice and dewatering hydrous salts. We further propose that connection of overpressured groundwater from aquifers near the base of the detachment through the cryosphere to the martian surface created the outflow channels of Echus, Coprates and Juventae chasmata at relatively uniform source elevations along the northern margin of the "mega-slide" where regional groundwater flow would have been directed toward the surface. Our hypothesis provides a unifying framework to explain perplexing relationships between the rise of the Tharsis volcanic province, deformation of the Thaumasia Plateau, and the formation of Valles Marineris and associated outburst floods.
P13B-1292
A Sustained Greenhouse Climate on Mars following an Impact Event
The existence of craters of size 200 km and greater proves that large (30-250 km diameter) impacts were abundant in the early history of Mars. Injected water from three sources (the impactor, water innate to the crater, and from melting of the polar caps) provide periods of rain following such impacts. Very hot, global debris blankets are another consequence of these large impacts, and these layers create a thermal pulse that propagates into the subsurface, melting additional water. The melted and precipitated water and debris blanket combine to produce a temporarily altered climate. This research shows time-dependent modeled calculations of this altered climate, and focuses in particular on a possible "runaway" greenhouse state that might be initiated as a result of the additional heat and a sufficiently rapid supply of the melted and precipitated water to the atmosphere. Our model is a 1-D radiative-convective model coupled to a 1-D model of the regolith to calculate the evolution of the surface and subsurface temperatures. The effects of latent heating, cloud condensation, precipitation, and evaporation are included in the model. We also show mathematically how the effects of large asteroid or comet impacts can cause a planet to reach the runaway greenhouse state, and illustrate how this solution is part of a bi-stable climate solution for terrestrial planets. One solution is found when a planet cools from high temperature, the other when the planet warms from a cool state. The hot solution represents a planet in the runaway regime, while the cold solution represents a planet with most of its water condensed at the surface. If a planet cools from a large temperature perturbation, caused by a large impact, it is possible that the planet will remain stable in the runaway climate rather than returning to the low temperature climate state.
P13B-1293
Geomorphologic Interpretation of Southwest Arabia Terra, Mars: Evidence of Regional, Long- Duration Fluvial Activity
Southwest Arabia Terra, Mars, is home to seven candidate Mars Science Laboratory (MSL) landing sites and is immediately north of the Mars Exploration Rover (MER) Opportunity in Meridiani Planum. Some of the strongest evidence for the past presence of liquid water exists in this region: the strong hematite signals from Meridiani revealed by the Thermal Emission Spectrometer (TES) as well as evidence of layering and analyses of rocks that must have formed in the presence of water by Opportunity. To better understand this region and the context for the potential MSL landing sites, a detailed geologic map was produced during the summer of 2007. The numerous exposed layers present in southwest Arabia Terra reveal a vast history of deposition and erosion. Of particular interest is the widespread geologic unit containing sinuous, inverted ridges of varying lengths, widths, and orientations. This ridge-forming unit appears to have once been dominant throughout much of the study region. Since its original formation, deposition and erosion have obscured or removed sections of this unit to produce the fragmented and discontinuous pattern that we see today. Analyses of these inverted ridges suggest that they are sedimentary in nature and are likely to be the cemented and hardened remains of ancient stream channels. One analog we are considering is that of a terrestrial megafan. Megafans, which are relatively new concepts in geology, are onshore sedimentary features laid down by rivers over extended periods of time. They are defined as major, regional geomorphic forms (similar to alluvial fans) that are greater than 100 kilometers in radius and typically have a slope of less than 1º. They differ from alluvial fans in main stream behavior; streams in alluvial fans will quickly split into numerous smaller streams while streams that form megafans remain as one continuous stream. The comparison of the ridged-unit to a terrestrial megafan is based on several features including the braided nature, sinuosity, and cross-cutting relationships of the inverted channels as well as the regional distribution of the entire unit across a plain of extremely low slopes. The hypothesis that the ridged-unit may be a remnant of a megafan would imply that liquid water was present in this area for an extended period of time. This would be consistent with other features suggesting that Southwest Arabia Terra has experienced of a long history of aqueous conditions (e.g., abundant rampart craters, ramparts with varying degrees of erosion, regional setting likely to have received run-off from the southern highlands and from possible extensions of the major obvious outflow channels to the west, and high abundances of near-surface hydrogen as measured by gamma-ray spectroscopy on Mars Odyssey which suggest the presence of significant ice/ fluids in the subsurface). The interpretation of possible megafans in Southwest Arabia Terra has implications for habitability in the Martian past. Long episodes of liquid water indicate that a denser atmosphere must have existed. In addition, liquid water is necessary for life as we know it to exist. MSL landing site candidates, such as Vernal Crater which are clearly associated with this ridged-unit, may have enhanced chances of having been habitable in the past if the proper conditions to produce a megafan once existed on Mars. Work is continuing to evaluate this possibility.
P13B-1294
The Volatile-Rich Attributes of two Deposits in a 15-km Crater on Utopia Planitia, Mars
Recent missions to Mars with diverse instrumentation have provided a new perspective on the Martian surface. These missions allow the characterization of over 40,000 impact craters larger than 5 km in diameter, showing a diverse cratering record with some unusual morphologies. We investigate three regions in the Acidalia, Arcadia, and Utopia Planitiae covering approximately 3 % of Mars' surface. A survey of Thermal Emission Imaging System (THEMIS) images revealed 14 craters with irregular, linear to circular depressions or pits on their cavity. Importantly, only three out of these 14 craters show deposits on their floors, perhaps due to volatile-rich material. We examine the nature of two deposits on a 15-km, pitted-floor crater located within Utopia Planitia at 40.9 N, 98.3 E. A close view of the crater's floor, using THEMIS visible data, uncovers a dark deposit in addition to a lighter- colored deposit, both with possible vents. The dark deposit extends in an elliptical shape with long and short axis about 7.4 km by 4.2 km in length. On the other hand, the lighter-colored deposit looks like it is emanating southward from the vent. Importantly, this deposit displays morphology typical of fluid flows with at least three identifiable lobes and a maximum extension of 2.1 km. Textural and albedo differences between both deposits indicate their composition may not be the same. Also, superposition of the light deposit on the dark deposit makes obvious their relative timing of formation. Based on the size and scarcity of these deposits among craters of the same size, we attribute their formation to aeolian deflation exposing near-surface ground ice in two steps. Deposits coming from both vents appear relatively unaffected by wind erosion. The surface of Mars has been extensible documented as one controlled by wind erosion and deposition. Thus, both deposits appear to be relatively young, post-impact modification, with the light deposit being the youngest. The formation of these deposits in recent times suggests they are related to aeolian processes on Mars rather than a period of high obliquity.
P13B-1295
Bright Gully Deposits in Hale Crater and Implications for Recent Water
Hale Crater, a late Hesperian / early Amazonian [Cabrol N.A. et al., 2001 Icarus 154] 120 km x 150 km impact crater, hosts a large number of gullies with a variety of orientations. Gully distributions and orientations have strong implications for distinguishing between gully formation theories, which frequently depend on insolation or a local aquifer. Several of the gullies exhibit bright deposits that are unmodified at the scale, 0.26 - 0.31 cm/pixel, of images acquired by the High Resolution Imaging Science Experiment (HiRISE) aboard the Mars Reconnaissance Orbiter (MRO). Two recently formed bright gully deposits (BGDs) imaged by the Mars Orbiter Camera (MOC) at other locations were initially interpreted as evidence for water on the surface in recent years [Malin M.C. et al., 2006 Science 314]. One of these BGDs was modelled by Pelletier et al. [2007 submitted] who found that, although water could not be ruled out in the formation of the studied BGD, dry flow was sufficient. HiRISE has imaged several other unmodified BGDs around Mars, most of which occur on steep slopes (26-35°) [McEwen A.S. et al., 2007 Science in press] in fresh craters. The slopes of one section of Hale Crater with BGDs are closer to 19-20°, which suggests that it would be difficult for a dry debris flow to form the BGDs. We investigate the distribution and orientations of gullies and BGDs, as well as slope profiles, in Hale Crater. We present results of modeling the BGDs using Mars Orbiter Laser Altimeter (MOLA) topography and available imagery and evaluate the likelihood that the BGDs required or included water in their formation.
P13B-1296
Landform Simulations of Parana Basin, Mars
A landform evolution model is used to explore scenarios responsible for the late-Noachian early-Hesperian fluvial incision on the South Highlands. Simulation DEMs (Digital Elevation Models) are qualitatively and statistically compared to actual DEMs in order to evaluate working hypotheses. MOLA and THEMIS data sets were used to define and quantitatively investigate the valley networks debouching into Parana Basin in Eastern Margaritifer Sinus, Mars. Evaluation of various hypotheses for erosional processes responsible for observed valley erosion were simulated by MSLM (Mars Simulation Landscape Model developed by Howard). The overarching theme of this study is to compare geomorphic data with simulated models to evaluate the contrast in erosional style between the widespread, less channelized mid-Noachian erosion and the relatively limited, yet strongly focused erosion, fluvial, and otherwise, during the Noachian-Hesperian transition. We analyze specific features by statistical correlation and fitness between the features" morphometry and that of the results of model landscapes evolved under specific processes. The results of these quantitative best-fit analyses guide hypothesis generation and testing. Specifically, we focused on valley network placement, density, and depth of incision. In this work, an "original" topographic DEM for a study region is recreated from the extant topography. Various scenarios for runoff and sediment yield, surface induration, and episodic mantling are then simulated starting from the DEM. Suites of model runs explored the effects of discharge scaling, evaporative controls, emplacement of an indurated surface or capping unit, sediment size, and critical shear stress. Model results were statistically compared in terms of pattern and depth of incision with the extant topography for testing hypotheses for climate driven landform evolution. Specifically, elevation difference histograms, Chi-square analyses, and power spectrums were used to test model fitness. Runs with (1) discharge scaling similar to terrestrially arid to semi-arid environments, (2) modest evaporation rates and (3) an indurated capping unit 5 to 10m thick provide the best statistical and qualitative match to the actual surface. In conclusion, the use of landform evolution models provides insight into both process and timing of the evolution of the cratered highlands of Mars beyond using topographic data alone.
P13B-1297
Fluidization of Dry Material on Martian Gullies
Since their discovery many different theories have been put forward to explain the origin of Martian gullies. Each theory has certain weaknesses, however, and the formation of these features remains poorly understood. Distinctive morphologic variations exist that have often been ignored. Here we present experimental results that attempt to create Martian gullies through gaseous fluidization of CO2 using mixtures of dry granular material and CO2 ice. Using Mars Orbiter Camera (MOC), Thermal Emission Imaging System (THEMIS) and High Resolution Imaging Science Experiment (HiRise) 28 images and data, we identified 12 gullies with morphologic characteristics similar to those produced from our experiments. These gullies range occur at mid-latitude regions (33° to -71°) and at a range of elevations (-4800 to 2700 meters). Based on our experimental data and observations, we suggest that the formation of at least some gullies may be analogous to pyroclastics flows but colds. On Mars such flows may result from the accumulation of CO2 ice and dust on slopes during the winter. Increases in temperatures during the spring may cause the CO2 ice to sublime initiating slope failure and mass- wasting. The different elevation and latitudes in which we found gullies suggest that their existence can be explain by our model. Our scenario allows the formation of gullies in recent times and to a more extensive rank of latitude of what predict the models that require the liquid water presence. Our model also explains the occurrence of gullies at different orientations, temperatures, altitudes and probably different materials and slopes. We conclude that similar geomorphic features can be formed by different mechanisms, for example: gullies are formed by water flow on Earth but experiments results suggest that dust fluidization could be a valid mechanism on Mars.