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Patrick C. Mcguire - One of the best experts on this subject based on the ideXlab platform.
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Mineralogy of Juventae Chasma: Sulfates in the light‐toned mounds, mafic minerals in the bedrock, and Hydrated Silica and hydroxylated ferric sulfate on the plateau
Journal of Geophysical Research, 2009Co-Authors: Janice L Bishop, Catherine M. Weitz, N. K. Mckeown, Eldar Noe Dobrea, Mario Parente, Scott L. Murchie, Leah H. Roach, Patrick C. Mcguire, Christopher M. Rossi, Adrian J. BrownAbstract:[1] Juventae Chasma contains four light-toned sulfate-bearing mounds (denoted here as A–D from west to east) inside the trough, mafic outcrops at the base of the mounds and in the wall rock, and light-toned layered deposits of opal and ferric sulfates on the plateau. Hyperspectral visible/near-infrared Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectra were used to identify monoHydrated and polyHydrated sulfate (PHS) outcrops of layered material on the bright mounds. Most of the monoHydrated sulfate signatures closely resemble those of szomolnokite (FeSO4·H2O), characterized by a water band near 2.08 μm, while some areas exhibit spectral features more similar to those of kieserite (MgSO4·H2O), with a band centered closer to 2.13 μm. The largest PHS outcrops occur on the top of mound B, and their spectral features are most consistent with ferricopiapite, melanterite, and starkeyite, but a specific mineral cannot be uniquely identified at this time. Coordinated analyses of CRISM maps, Mars Orbiter Laser Altimeter elevations, and High Resolution Imaging Science Experiment images suggest that mounds A and B may have formed together and then eroded into separate mounds, while mounds C and D likely formed separately. Mafic minerals (low-Ca pyroxene, high-Ca pyroxene, and olivine) are observed in large ∼2–10 km wide outcrops in the wall rock and in smaller outcrops ∼50–500 m across at the floor of the canyon. Most of the wall rock is covered by at least a thin layer of dust and does not exhibit strong features characteristic of these minerals. The plateau region northwest of Juventae Chasma is characterized by an abundance of light-toned layered deposits. One region contains two spectrally unique phases exhibiting a highly stratified, terraced pattern. CRISM spectra of one unit eroded into swirling patterns with arc-like ridges exhibit a narrow 2.23-μm band assigned to hydroxylated ferric sulfate. A thin layer of a fractured material bearing an opaline Silica phase is observed at the contact between the older plateau unit and the younger hydroxylated ferric sulfate-bearing light-toned layered deposits. Hydrothermal processes may have produced an acidic environment that fostered formation of the Hydrated Silica and hydroxylated ferric sulfate units.
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mineralogy of juventae chasma sulfates in the light toned mounds mafic minerals in the bedrock and Hydrated Silica and hydroxylated ferric sulfate on the plateau
Journal of Geophysical Research, 2009Co-Authors: Eldar Noe Dobrea, Mario Parente, Leah H. Roach, Patrick C. Mcguire, J L Bishop, C M Weitz, S L MurchieAbstract:[1] Juventae Chasma contains four light-toned sulfate-bearing mounds (denoted here as A–D from west to east) inside the trough, mafic outcrops at the base of the mounds and in the wall rock, and light-toned layered deposits of opal and ferric sulfates on the plateau. Hyperspectral visible/near-infrared Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectra were used to identify monoHydrated and polyHydrated sulfate (PHS) outcrops of layered material on the bright mounds. Most of the monoHydrated sulfate signatures closely resemble those of szomolnokite (FeSO4·H2O), characterized by a water band near 2.08 μm, while some areas exhibit spectral features more similar to those of kieserite (MgSO4·H2O), with a band centered closer to 2.13 μm. The largest PHS outcrops occur on the top of mound B, and their spectral features are most consistent with ferricopiapite, melanterite, and starkeyite, but a specific mineral cannot be uniquely identified at this time. Coordinated analyses of CRISM maps, Mars Orbiter Laser Altimeter elevations, and High Resolution Imaging Science Experiment images suggest that mounds A and B may have formed together and then eroded into separate mounds, while mounds C and D likely formed separately. Mafic minerals (low-Ca pyroxene, high-Ca pyroxene, and olivine) are observed in large ∼2–10 km wide outcrops in the wall rock and in smaller outcrops ∼50–500 m across at the floor of the canyon. Most of the wall rock is covered by at least a thin layer of dust and does not exhibit strong features characteristic of these minerals. The plateau region northwest of Juventae Chasma is characterized by an abundance of light-toned layered deposits. One region contains two spectrally unique phases exhibiting a highly stratified, terraced pattern. CRISM spectra of one unit eroded into swirling patterns with arc-like ridges exhibit a narrow 2.23-μm band assigned to hydroxylated ferric sulfate. A thin layer of a fractured material bearing an opaline Silica phase is observed at the contact between the older plateau unit and the younger hydroxylated ferric sulfate-bearing light-toned layered deposits. Hydrothermal processes may have produced an acidic environment that fostered formation of the Hydrated Silica and hydroxylated ferric sulfate units.
J. Teodorczyk - One of the best experts on this subject based on the ideXlab platform.
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thermal analysis of a Hydrated Silica sodium thiosulfate sulfur system
Journal of Thermal Analysis and Calorimetry, 2001Co-Authors: R Piekoś, Marek Wesolowski, J. TeodorczykAbstract:A system formed by concerted action of orthosilicic acid gelation and decomposition of sodium thiosulfate to afford highly dispersed elemental sulfur was studied by simultaneous methods, DTA, TG and DTG. A typical curve has been found to be an outcome of thermal processes associated with desorption of physically adsorbed water, condensation of surface silanol groups and thermal degradation of sodium thiosulfate. A large loss in mass over the lower temperature range was assigned to the loss of physically adsorbed water and condensation of silanol groups of the gel as indicated by accompanying strong endothermic effects. Subsequent strong exothermic effects were attributed to combustion of elemental sulfur embedded in the gel. Experiments were also conducted to control the extent of decomposition of the thiosulfate and generation of elemental sulfur by varying pH of thesilicic acid solution. These have shown that acidification of the silicic acid - sodium thiosulfate system with sulfuric acid fostered decomposition of the thiosulfate and raised the quantity of elemental sulfur.
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Thermal Analysis of a Hydrated Silica–Sodium Thiosulfate–Sulfur System
Journal of Thermal Analysis and Calorimetry, 2001Co-Authors: R. Piękoś, Marek Wesolowski, J. TeodorczykAbstract:A system formed by concerted action of orthosilicic acid gelation and decomposition of sodium thiosulfate to afford highly dispersed elemental sulfur was studied by simultaneous methods, DTA, TG and DTG. A typical curve has been found to be an outcome of thermal processes associated with desorption of physically adsorbed water, condensation of surface silanol groups and thermal degradation of sodium thiosulfate. A large loss in mass over the lower temperature range was assigned to the loss of physically adsorbed water and condensation of silanol groups of the gel as indicated by accompanying strong endothermic effects. Subsequent strong exothermic effects were attributed to combustion of elemental sulfur embedded in the gel. Experiments were also conducted to control the extent of decomposition of the thiosulfate and generation of elemental sulfur by varying pH of thesilicic acid solution. These have shown that acidification of the silicic acid - sodium thiosulfate system with sulfuric acid fostered decomposition of the thiosulfate and raised the quantity of elemental sulfur.
Janice L Bishop - One of the best experts on this subject based on the ideXlab platform.
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Stratigraphy and formation of clays, sulfates, and Hydrated Silica within a depression in Coprates Catena, Mars
Journal of Geophysical Research, 2016Co-Authors: Catherine M. Weitz, Janice L BishopAbstract:We investigate the morphology, mineralogy, and stratigraphy of light-toned layered deposits within a trough of Coprates Catena, centered at −15°N, 300°E. One of the deposits in the eastern portion of the trough contains numerous Hydrated minerals, including Al-phylloSilicates, Fe/Mg-phylloSilicates, Hydrated Silica, Hydrated sulfates, jarosite and acid alteration products characterized by a spectral doublet between 2.2 and 2.3 µm, and weakly Hydrated materials. The Al-phylloSilicates are observed both stratigraphically above and below the Fe/Mg-phylloSilicate unit, which is a rare and perhaps unique association on Mars. Most of the western light-toned layered deposit underlies a terraced fan. This deposit contains Hydrated materials, including Al-phylloSilicates and Fe/Mg-phylloSilicates. Dip measurements indicate that both the eastern and western deposits dip toward the center of the trough, indicating that they postdate formation of the trough and are consequently Late Hesperian or younger in age. Volcanic ash, most likely erupted during formation of the pit crater in the eastern portion of the trough, seems to best explain our observations for several of the units. Valleys sourced from water along the plateau may have flowed into the trough and altered the sediments, with changing aqueous chemistries over time resulting in the diverse range of mineralogies now observed in the eastern light-toned deposit. Our results reveal a complex sedimentary and aqueous history within the Coprates Catena trough, indicating that localized habitable conditions were possible relatively late in Martian history at a time when colder, drier conditions likely dominated the majority of the planet.
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Variability of rock texture and morphology correlated with the clay‐bearing units at Mawrth Vallis, Mars
Journal of Geophysical Research: Planets, 2013Co-Authors: N. K. Mckeown, Janice L Bishop, Eli A. SilverAbstract:[1] The clay units at Mawrth Vallis have been well-characterized in hyperspectral data; however, a similar study of high spatial resolution High Resolution Imaging Science Experiment (HiRISE) data has not been previously conducted. Here the textures of the clay units are described and related to mineralogy across the central Mawrth Vallis region. The nontronite-bearing rocks appear tan in HiRISE COLOR data and are polygonally fractured with polygons 2–5 m across. In some cases, the fractures appear wider and/or have darker fill or the rocks are a darker brown. The montmorillonite-bearing rocks appear blue with regular polygons 0.5–1.5 m across; sometimes, there are larger polygons surrounded by regular polygons, a square fracture pattern, or the color appears yellow or mottled blue-yellow. Kaolinite-rich rocks are the brightest outcrops and are nonpolygonally fractured. Regions with spectra consistent with Hydrated Silica or the ferrous mineral component do not have unique textures. Hydrated Silica-bearing rocks appear yellow or mottled with a regular polygonal texture or yellow with hummocky appearance with no polygons. It is also possible that dust/sand on the surface alters the montmorillonite spectrum to appear like that of Hydrated Silica. The ferrous component may be expressed as mottled coloring or as a bright fracture fill. The nontronite- and montmorillonite-bearing units have remarkably consistent textures in this region, allowing them to be uniquely identified in the Mawrth Vallis region in nonhyperspectral data sets such as CTX and HiRISE. The morphology of the polygons in these two units suggests that their formation is likely dominated by desiccation and controlled by composition.
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Mineralogy and stratigraphy of phylloSilicate‐bearing and dark mantling units in the greater Mawrth Vallis/west Arabia Terra area: Constraints on geological origin
Journal of Geophysical Research, 2010Co-Authors: E. Z. Noe Dobrea, Janice L Bishop, N. K. Mckeown, Christopher M. Rossi, Joseph R. Michalski, C. Heinlein, V. Hanus, François Poulet, R. J. F. MustardAbstract:[1] Analyses of MRO/CRISM images of the greater Mawrth Vallis region of Mars affirm the presence of two primary phylloSilicate assemblages throughout a region ∼1000 × 1000 km. These two units consist of an Fe/Mg-phylloSilicate assemblage overlain by an Al-phylloSilicate and Hydrated Silica assemblage. The lower unit contains Fe/Mg-smectites, sometimes combined with one or more of these other Fe/Mg-phylloSilicates: serpentine, chlorite, biotite, and/or vermiculite. It is more than 100 m thick and finely layered at meter scales. The upper unit includes Al-smectite, kaolin group minerals, and Hydrated Silica. It is tens of meters thick and finely layered as well. A common phylloSilicate stratigraphy and morphology is observed throughout the greater region wherever erosional windows are present. This suggests that the geologic processes forming these units must have occurred on at least a regional scale. Sinuous ridges (interpreted to be inverted channels) and narrow channels cut into the upper clay-bearing unit suggesting that aqueous processes were prevalent after, and possibly during, the deposition of the layered units. We propose that layered units may have been deposited at Mawrth Vallis and then subsequently altered to form the Hydrated units. The Fe/Mg-phylloSilicate assemblage is consistent with hydrothermal alteration or pedogenesis of mafic to ultramafic rocks. The Al-phylloSilicate/Hydrated Silica unit may have formed through alteration of felsic material or via leaching of basaltic material through pedogenic alteration or a mildly acidic environment. These phylloSilicate-bearing units are overlain by a darker, relatively unaltered, and indurated material that has probably experienced a complex geological history.
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Characterization of phylloSilicates observed in the central Mawrth Vallis region, Mars, their potential formational processes, and implications for past climate
Journal of Geophysical Research, 2009Co-Authors: N. K. Mckeown, Janice L Bishop, Bethany L. Ehlmann, Eldar Noe Dobrea, Mario Parente, John F. Mustard, Scott L. Murchie, Gregg A. Swayze, Jean-pierre Bibring, Eli A. SilverAbstract:Mawrth Vallis contains one of the largest exposures of phylloSilicates on Mars. Nontronite, montmorillonite, kaolinite, and Hydrated Silica have been identified throughout the region using data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). In addition, saponite has been identified in one observation within a crater. These individual minerals are identified and distinguished by features at 1.38–1.42, ∼1.91, and 2.17–2.41 μm. There are two main phylloSilicate units in the Mawrth Vallis region. The lowermost unit is nontronite bearing, unconformably overlain by an Al-phylloSilicate unit containing montmorillonite plus Hydrated Silica, with a thin layer of kaolinite plus Hydrated Silica at the top of the unit. These two units are draped by a spectrally unremarkable capping unit. Smectites generally form in neutral to alkaline environments, while kaolinite and Hydrated Silica typically form in slightly acidic conditions; thus, the observed phylloSilicates may reflect a change in aqueous chemistry. Spectra retrieved near the boundary between the nontronite and Al-phylloSilicate units exhibit a strong positive slope from 1 to 2 μm, likely from a ferrous component within the rock. This ferrous component indicates either rapid deposition in an oxidizing environment or reducing conditions. Formation of each of the phylloSilicate minerals identified requires liquid water, thus indicating a regional wet period in the Noachian when these units formed. The two main phylloSilicate units may be extensive layers of altered volcanic ash. Other potential formational processes include sediment deposition into a marine or lacustrine basin or pedogenesis.
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Mineralogy of Juventae Chasma: Sulfates in the light‐toned mounds, mafic minerals in the bedrock, and Hydrated Silica and hydroxylated ferric sulfate on the plateau
Journal of Geophysical Research, 2009Co-Authors: Janice L Bishop, Catherine M. Weitz, N. K. Mckeown, Eldar Noe Dobrea, Mario Parente, Scott L. Murchie, Leah H. Roach, Patrick C. Mcguire, Christopher M. Rossi, Adrian J. BrownAbstract:[1] Juventae Chasma contains four light-toned sulfate-bearing mounds (denoted here as A–D from west to east) inside the trough, mafic outcrops at the base of the mounds and in the wall rock, and light-toned layered deposits of opal and ferric sulfates on the plateau. Hyperspectral visible/near-infrared Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectra were used to identify monoHydrated and polyHydrated sulfate (PHS) outcrops of layered material on the bright mounds. Most of the monoHydrated sulfate signatures closely resemble those of szomolnokite (FeSO4·H2O), characterized by a water band near 2.08 μm, while some areas exhibit spectral features more similar to those of kieserite (MgSO4·H2O), with a band centered closer to 2.13 μm. The largest PHS outcrops occur on the top of mound B, and their spectral features are most consistent with ferricopiapite, melanterite, and starkeyite, but a specific mineral cannot be uniquely identified at this time. Coordinated analyses of CRISM maps, Mars Orbiter Laser Altimeter elevations, and High Resolution Imaging Science Experiment images suggest that mounds A and B may have formed together and then eroded into separate mounds, while mounds C and D likely formed separately. Mafic minerals (low-Ca pyroxene, high-Ca pyroxene, and olivine) are observed in large ∼2–10 km wide outcrops in the wall rock and in smaller outcrops ∼50–500 m across at the floor of the canyon. Most of the wall rock is covered by at least a thin layer of dust and does not exhibit strong features characteristic of these minerals. The plateau region northwest of Juventae Chasma is characterized by an abundance of light-toned layered deposits. One region contains two spectrally unique phases exhibiting a highly stratified, terraced pattern. CRISM spectra of one unit eroded into swirling patterns with arc-like ridges exhibit a narrow 2.23-μm band assigned to hydroxylated ferric sulfate. A thin layer of a fractured material bearing an opaline Silica phase is observed at the contact between the older plateau unit and the younger hydroxylated ferric sulfate-bearing light-toned layered deposits. Hydrothermal processes may have produced an acidic environment that fostered formation of the Hydrated Silica and hydroxylated ferric sulfate units.
A. B. Yaroslavtsev - One of the best experts on this subject based on the ideXlab platform.
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Hybrid materials based on MF-4SK membranes and Hydrated Silica and zirconia with sulfonic acid-functionalized surface: transport properties and characteristics of DP-sensors in amino acid solutions with varying pH
Petroleum Chemistry, 2017Co-Authors: E. Yu. Safronova, A. V. Parshina, K. Yu. Yankina, E. A. Ryzhkova, Anna A. Lysova, Olga Bobreshova, A. B. YaroslavtsevAbstract:Hybrid ion-exchange membranes of MF-4SK brand containing Hydrated Silica and zirconia nanoparticles with sulfonic acid-functionalized surface have been synthesized. The effect of modification on the properties of materials in the proton and potassium forms and the characteristics of potentiometric sensors based on these materials have been studied. It has been found that membrane modification leads to an increase in the ionic conductivity compared with that of the unmodified MF-4SK sample and, in some cases, to a decrease in diffusion permeability. Variations in the cation transport selectivity provided by the modification of MF-4SK membrane have made it possible to decrease the sensitivity of sensors to interfering hydronium cations in an acid medium and increase the sensitivity to amino acid anions and zwitterions in an alkaline medium. Optimum membrane compositions for the determination of histidine cations at pH 7 have been selected.
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Hybrid materials based on MF-4SK membranes and Hydrated Silica and zirconia with sulfonic acid-functionalized surface: transport properties and characteristics of DP-sensors in amino acid solutions with varying pH
Petroleum Chemistry, 2017Co-Authors: E. Yu. Safronova, A. V. Parshina, K. Yu. Yankina, E. A. Ryzhkova, Anna A. Lysova, Olga Bobreshova, A. B. YaroslavtsevAbstract:Hybrid ion-exchange membranes of MF-4SK brand containing Hydrated Silica and zirconia nanoparticles with sulfonic acid-functionalized surface have been synthesized. The effect of modification on the properties of materials in the proton and potassium forms and the characteristics of potentiometric sensors based on these materials have been studied. It has been found that membrane modification leads to an increase in the ionic conductivity compared with that of the unmodified MF-4SK sample and, in some cases, to a decrease in diffusion permeability. Variations in the cation transport selectivity provided by the modification of MF-4SK membrane have made it possible to decrease the sensitivity of sensors to interfering hydronium cations in an acid medium and increase the sensitivity to amino acid anions and zwitterions in an alkaline medium. Optimum membrane compositions for the determination of histidine cations at pH < 7 and the simultaneous determination of potassium cations and methionine zwitterions and anions at pH > 7 have been selected.
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Theoretical and experimental investigation of diffusion permeability of hybrid MF-4SC membranes with Silica nanoparticles
Journal of Membrane Science, 2014Co-Authors: Anatoly Filippov, E. Yu. Safronova, A. B. YaroslavtsevAbstract:The diffusion permeability through hybrid materials based on a Nafion-type membrane and Hydrated Silica is investigated using the Nernst–Planck approach. A method of quantitative evaluation of physicochemical parameters (averaged and individual diffusion coefficients and averaged distribution coefficients of ion pairs in the membrane) of system “electrolyte solution–ion-exchange membrane–water” is developed. The parameters of hybrid membranes on the base of MF-4SC and Hydrated Silica are obtained from experimental data on diffusion permeability of HCl and NaCl solutions using theoretical calculations. It is shown that the dependence of computed diffusivities of sodium cation and proton upon SiO2 content has a minimum at 5% and 7%, respectively. At the same time experimental values of distribution coefficients of HCl and NaCl molecules reach the maximum at 1.5–3% of SiO2 content. The results obtained are in a good correlation with the physicochemical model of the limited elasticity of the membrane pore walls.
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Effect of surface modification with carbon-containing groups on the size, properties, and morphology of Silica particles
Inorganic Materials, 2012Co-Authors: E. Yu. Safronova, Anna A. Lysova, A. B. Il’in, A. B. YaroslavtsevAbstract:We report the properties of Hydrated Silica surface-modified with aminopropyl, 3-(2-imidazolin-1-yl)propyl, or 1H,1H,2H,2H-perfluorodecyl. The modifier groups reside on the surface of the Silica nanoparticles, as shown by NMR spectroscopy. We examine the effect of the nature and concentration of the modifier on the particle size and specific surface area of Silica. Thermal analysis results demonstrate that the modified materials are stable up to 430°C.
N. K. Mckeown - One of the best experts on this subject based on the ideXlab platform.
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Variability of rock texture and morphology correlated with the clay‐bearing units at Mawrth Vallis, Mars
Journal of Geophysical Research: Planets, 2013Co-Authors: N. K. Mckeown, Janice L Bishop, Eli A. SilverAbstract:[1] The clay units at Mawrth Vallis have been well-characterized in hyperspectral data; however, a similar study of high spatial resolution High Resolution Imaging Science Experiment (HiRISE) data has not been previously conducted. Here the textures of the clay units are described and related to mineralogy across the central Mawrth Vallis region. The nontronite-bearing rocks appear tan in HiRISE COLOR data and are polygonally fractured with polygons 2–5 m across. In some cases, the fractures appear wider and/or have darker fill or the rocks are a darker brown. The montmorillonite-bearing rocks appear blue with regular polygons 0.5–1.5 m across; sometimes, there are larger polygons surrounded by regular polygons, a square fracture pattern, or the color appears yellow or mottled blue-yellow. Kaolinite-rich rocks are the brightest outcrops and are nonpolygonally fractured. Regions with spectra consistent with Hydrated Silica or the ferrous mineral component do not have unique textures. Hydrated Silica-bearing rocks appear yellow or mottled with a regular polygonal texture or yellow with hummocky appearance with no polygons. It is also possible that dust/sand on the surface alters the montmorillonite spectrum to appear like that of Hydrated Silica. The ferrous component may be expressed as mottled coloring or as a bright fracture fill. The nontronite- and montmorillonite-bearing units have remarkably consistent textures in this region, allowing them to be uniquely identified in the Mawrth Vallis region in nonhyperspectral data sets such as CTX and HiRISE. The morphology of the polygons in these two units suggests that their formation is likely dominated by desiccation and controlled by composition.
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Mineralogy and stratigraphy of phylloSilicate‐bearing and dark mantling units in the greater Mawrth Vallis/west Arabia Terra area: Constraints on geological origin
Journal of Geophysical Research, 2010Co-Authors: E. Z. Noe Dobrea, Janice L Bishop, N. K. Mckeown, Christopher M. Rossi, Joseph R. Michalski, C. Heinlein, V. Hanus, François Poulet, R. J. F. MustardAbstract:[1] Analyses of MRO/CRISM images of the greater Mawrth Vallis region of Mars affirm the presence of two primary phylloSilicate assemblages throughout a region ∼1000 × 1000 km. These two units consist of an Fe/Mg-phylloSilicate assemblage overlain by an Al-phylloSilicate and Hydrated Silica assemblage. The lower unit contains Fe/Mg-smectites, sometimes combined with one or more of these other Fe/Mg-phylloSilicates: serpentine, chlorite, biotite, and/or vermiculite. It is more than 100 m thick and finely layered at meter scales. The upper unit includes Al-smectite, kaolin group minerals, and Hydrated Silica. It is tens of meters thick and finely layered as well. A common phylloSilicate stratigraphy and morphology is observed throughout the greater region wherever erosional windows are present. This suggests that the geologic processes forming these units must have occurred on at least a regional scale. Sinuous ridges (interpreted to be inverted channels) and narrow channels cut into the upper clay-bearing unit suggesting that aqueous processes were prevalent after, and possibly during, the deposition of the layered units. We propose that layered units may have been deposited at Mawrth Vallis and then subsequently altered to form the Hydrated units. The Fe/Mg-phylloSilicate assemblage is consistent with hydrothermal alteration or pedogenesis of mafic to ultramafic rocks. The Al-phylloSilicate/Hydrated Silica unit may have formed through alteration of felsic material or via leaching of basaltic material through pedogenic alteration or a mildly acidic environment. These phylloSilicate-bearing units are overlain by a darker, relatively unaltered, and indurated material that has probably experienced a complex geological history.
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Characterization of phylloSilicates observed in the central Mawrth Vallis region, Mars, their potential formational processes, and implications for past climate
Journal of Geophysical Research, 2009Co-Authors: N. K. Mckeown, Janice L Bishop, Bethany L. Ehlmann, Eldar Noe Dobrea, Mario Parente, John F. Mustard, Scott L. Murchie, Gregg A. Swayze, Jean-pierre Bibring, Eli A. SilverAbstract:Mawrth Vallis contains one of the largest exposures of phylloSilicates on Mars. Nontronite, montmorillonite, kaolinite, and Hydrated Silica have been identified throughout the region using data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). In addition, saponite has been identified in one observation within a crater. These individual minerals are identified and distinguished by features at 1.38–1.42, ∼1.91, and 2.17–2.41 μm. There are two main phylloSilicate units in the Mawrth Vallis region. The lowermost unit is nontronite bearing, unconformably overlain by an Al-phylloSilicate unit containing montmorillonite plus Hydrated Silica, with a thin layer of kaolinite plus Hydrated Silica at the top of the unit. These two units are draped by a spectrally unremarkable capping unit. Smectites generally form in neutral to alkaline environments, while kaolinite and Hydrated Silica typically form in slightly acidic conditions; thus, the observed phylloSilicates may reflect a change in aqueous chemistry. Spectra retrieved near the boundary between the nontronite and Al-phylloSilicate units exhibit a strong positive slope from 1 to 2 μm, likely from a ferrous component within the rock. This ferrous component indicates either rapid deposition in an oxidizing environment or reducing conditions. Formation of each of the phylloSilicate minerals identified requires liquid water, thus indicating a regional wet period in the Noachian when these units formed. The two main phylloSilicate units may be extensive layers of altered volcanic ash. Other potential formational processes include sediment deposition into a marine or lacustrine basin or pedogenesis.
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Mineralogy of Juventae Chasma: Sulfates in the light‐toned mounds, mafic minerals in the bedrock, and Hydrated Silica and hydroxylated ferric sulfate on the plateau
Journal of Geophysical Research, 2009Co-Authors: Janice L Bishop, Catherine M. Weitz, N. K. Mckeown, Eldar Noe Dobrea, Mario Parente, Scott L. Murchie, Leah H. Roach, Patrick C. Mcguire, Christopher M. Rossi, Adrian J. BrownAbstract:[1] Juventae Chasma contains four light-toned sulfate-bearing mounds (denoted here as A–D from west to east) inside the trough, mafic outcrops at the base of the mounds and in the wall rock, and light-toned layered deposits of opal and ferric sulfates on the plateau. Hyperspectral visible/near-infrared Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectra were used to identify monoHydrated and polyHydrated sulfate (PHS) outcrops of layered material on the bright mounds. Most of the monoHydrated sulfate signatures closely resemble those of szomolnokite (FeSO4·H2O), characterized by a water band near 2.08 μm, while some areas exhibit spectral features more similar to those of kieserite (MgSO4·H2O), with a band centered closer to 2.13 μm. The largest PHS outcrops occur on the top of mound B, and their spectral features are most consistent with ferricopiapite, melanterite, and starkeyite, but a specific mineral cannot be uniquely identified at this time. Coordinated analyses of CRISM maps, Mars Orbiter Laser Altimeter elevations, and High Resolution Imaging Science Experiment images suggest that mounds A and B may have formed together and then eroded into separate mounds, while mounds C and D likely formed separately. Mafic minerals (low-Ca pyroxene, high-Ca pyroxene, and olivine) are observed in large ∼2–10 km wide outcrops in the wall rock and in smaller outcrops ∼50–500 m across at the floor of the canyon. Most of the wall rock is covered by at least a thin layer of dust and does not exhibit strong features characteristic of these minerals. The plateau region northwest of Juventae Chasma is characterized by an abundance of light-toned layered deposits. One region contains two spectrally unique phases exhibiting a highly stratified, terraced pattern. CRISM spectra of one unit eroded into swirling patterns with arc-like ridges exhibit a narrow 2.23-μm band assigned to hydroxylated ferric sulfate. A thin layer of a fractured material bearing an opaline Silica phase is observed at the contact between the older plateau unit and the younger hydroxylated ferric sulfate-bearing light-toned layered deposits. Hydrothermal processes may have produced an acidic environment that fostered formation of the Hydrated Silica and hydroxylated ferric sulfate units.
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PhylloSilicate diversity and past aqueous activity revealed at Mawrth Vallis, Mars
Science (New York N.Y.), 2008Co-Authors: Janice L Bishop, Bethany L. Ehlmann, Ralph E. Milliken, N. K. Mckeown, Eldar Noe Dobrea, Mario Parente, Gregg A. Swayze, Joseph R. Michalski, F. Poulet, John F. MustardAbstract:Observations by the Mars Reconnaissance Orbiter/Compact Reconnaissance Imaging Spectrometer for Mars in the Mawrth Vallis region show several phylloSilicate species, indicating a wide range of past aqueous activity. Iron/magnesium (Fe/Mg)–smectite is observed in light-toned outcrops that probably formed via aqueous alteration of basalt of the ancient cratered terrain. This unit is overlain by rocks rich in Hydrated Silica, montmorillonite, and kaolinite that may have formed via subsequent leaching of Fe and Mg through extended aqueous events or a change in aqueous chemistry. A spectral feature attributed to an Fe^(2+) phase is present in many locations in the Mawrth Vallis region at the transition from Fe/Mg-smectite to aluminum/silicon (Al/Si)–rich units. Fe^(2+)-bearing materials in terrestrial sediments are typically associated with microorganisms or changes in pH or cations and could be explained here by hydrothermal activity. The stratigraphy of Fe/Mg-smectite overlain by a ferrous phase, Hydrated Silica, and then Al-phylloSilicates implies a complex aqueous history.
