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.
Columbus crater in the Terra Sirenum region of the Martian southern highlands contains light‐toned layered deposits with interbedded sulfate and phyllosilicate minerals, a rare occurrence on Mars. ...Here we investigate in detail the morphology, thermophysical properties, mineralogy, and stratigraphy of these deposits; explore their regional context; and interpret the crater's aqueous history. Hydrated mineral‐bearing deposits occupy a discrete ring around the walls of Columbus crater and are also exposed beneath younger materials, possibly lava flows, on its floor. Widespread minerals identified in the crater include gypsum, polyhydrated and monohydrated Mg/Fe‐sulfates, and kaolinite; localized deposits consistent with montmorillonite, Fe/Mg‐phyllosilicates, jarosite, alunite, and crystalline ferric oxide or hydroxide are also detected. Thermal emission spectra suggest abundances of these minerals in the tens of percent range. Other craters in northwest Terra Sirenum also contain layered deposits and Al/Fe/Mg‐phyllosilicates, but sulfates have so far been found only in Columbus and Cross craters. The region's intercrater plains contain scattered exposures of Al‐phyllosilicates and one isolated mound with opaline silica, in addition to more common Fe/Mg‐phyllosilicates with chlorides. A Late Noachian age is estimated for the aqueous deposits in Columbus, coinciding with a period of inferred groundwater upwelling and evaporation, which (according to model results reported here) could have formed evaporites in Columbus and other craters in Terra Sirenum. Hypotheses for the origin of these deposits include groundwater cementation of crater‐filling sediments and/or direct precipitation from subaerial springs or in a deep (∼900 m) paleolake. Especially under the deep lake scenario, which we prefer, chemical gradients in Columbus crater may have created a habitable environment at this location on early Mars.
Phyllosilicates, a class of hydrous mineral first definitively identified on Mars by the OMEGA (Observatoire pour la Mineralogie, L'Eau, les Glaces et l'Activitié) instrument, preserve a record of ...the interaction of water with rocks on Mars. Global mapping showed that phyllosilicates are widespread but are apparently restricted to ancient terrains and a relatively narrow range of mineralogy (Fe/Mg and Al smectite clays). This was interpreted to indicate that phyllosilicate formation occurred during the Noachian (the earliest geological era of Mars), and that the conditions necessary for phyllosilicate formation (moderate to high pH and high water activity) were specific to surface environments during the earliest era of Mars's history. Here we report results from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) of phyllosilicate-rich regions. We expand the diversity of phyllosilicate mineralogy with the identification of kaolinite, chlorite and illite or muscovite, and a new class of hydrated silicate (hydrated silica). We observe diverse Fe/Mg-OH phyllosilicates and find that smectites such as nontronite and saponite are the most common, but chlorites are also present in some locations. Stratigraphic relationships in the Nili Fossae region show olivine-rich materials overlying phyllosilicate-bearing units, indicating the cessation of aqueous alteration before emplacement of the olivine-bearing unit. Hundreds of detections of Fe/Mg phyllosilicate in rims, ejecta and central peaks of craters in the southern highland Noachian cratered terrain indicate excavation of altered crust from depth. We also find phyllosilicate in sedimentary deposits clearly laid by water. These results point to a rich diversity of Noachian environments conducive to habitability.
The spectral properties of anhydrous carbonates and nitrates are dominated by strong, sharp vibrational bands due to the CO32− and NO3− anions observed as absorption bands in near‐infrared spectra, ...as Reststrahlen features or absorption bands in mid‐IR spectra, depending on particle size, and as peaks in Raman spectra. These spectral features provide a reliable means to identify the occurrence of carbonates and nitrates on planetary surfaces, which in turn contribute to our understanding of the environment and chemistry of planetary bodies. Four modes occur for carbonates and nitrates due to symmetric stretching (ν1), out‐of‐plane bending (ν2), asymmetric stretching (ν3), and in‐plane bending (ν4). The vibrational absorptions of these spectral features vary with the mineral structure and the size of the cation, where the calcite‐, dolomite‐, aragonite‐, and alkali‐type structures result in different spectral features. Mid‐IR bands for carbonates and nitrates occur from 1,040 to 1,105 cm−1 for ν1, from 810 to 906 cm−1 for ν2, from 1,275 to 1,590 cm−1 for ν3, and from 670 to 756 cm−1 for ν4. In Raman spectra the carbonate and nitrate absorptions are observed near 1,050–1,080 cm−1 for ν1, near 880 cm−1 for ν2, near 1,415–1,430 cm−1 for ν3, and near 680–700 cm−1 for ν4. NIR spectra include bands due to overtones and combinations at ∼1.75, 1.9, 2.0, 2.3, 2.5, 3.4, 4.0, and 4.6 μm for carbonates and ∼1.8, 2.0, 2.2, 2.4, 2.6, 3.5, 4.1, and 4.8 μm for nitrates. This study provides data for remote determination of carbonate and nitrate chemistry and will enable better characterization of these minerals on planetary bodies including Mars, Ceres, and Bennu.
Plain Language Summary
Carbonates are widespread minerals on Earth and have been identified as well on Mars, Ceres, near Earth asteroid (101955) Bennu, and in carbonaceous meteorites. Understanding the spectral properties of carbonates enables detection and characterization of this important mineral group. Furthermore, identifying the specific type of carbonate on planetary surfaces can help us constrain the geochemical environment of these planets or bodies. The spectral properties of nitrates are presented here as well because nitrates exhibit similar spectral features to carbonates due to their similar mineral structures. Nitrates are yet to be detected on planets other than Earth, but nitrogen has been detected on bodies in our Solar System and nitrates may be detected once researchers have access to their spectral properties.
Key Points
Spectral bands are presented for remote detection of anhydrous carbonates and nitrates
Mid‐IR band center comparisons for the ν3 vibration compared to the ν2 and ν4 vibrations enable identification of carbonate chemistry
NIR band center comparisons for ∼2.3 versus 2.5 μm, ∼2.3 versus 4 μm, and ∼3.4 versus 4 μm best enable identification of carbonate chemistry
Orbital topographic, image, and spectral data show that sulfate‐ and hematite‐bearing plains deposits similar to those explored by the MER rover Opportunity unconformably overlie the northeastern ...portion of the 160 km in diameter Miyamoto crater. Crater floor materials exhumed to the west of the contact exhibit CRISM and OMEGA NIR spectral signatures consistent with the presence of Fe/Mg‐rich smectite phyllosilicates. Based on superposition relationships, the phyllosilicate‐bearing deposits formed either in‐situ or were deposited on the floor of Miyamoto crater prior to the formation of the sulfate‐rich plains unit. These findings support the hypothesis that neutral pH aqueous conditions transitioned to a ground‐water driven acid sulfate system in the Sinus Meridiani region. The presence of both phyllosilicate and sulfate‐ and hematite‐bearing deposits within Miyamoto crater make it an attractive site for exploration by future rover missions.
Imaging spectroscopy is a tool that can be used to spectrally identify and spatially map materials based on their specific chemical bonds. Spectroscopic analysis requires significantly more ...sophistication than has been employed in conventional broadband remote sensing analysis. We describe a new system that is effective at material identification and mapping: a set of algorithms within an expert system decision‐making framework that we call Tetracorder. The expertise in the system has been derived from scientific knowledge of spectral identification. The expert system rules are implemented in a decision tree where multiple algorithms are applied to spectral analysis, additional expert rules and algorithms can be applied based on initial results, and more decisions are made until spectral analysis is complete. Because certain spectral features are indicative of specific chemical bonds in materials, the system can accurately identify and map those materials. In this paper we describe the framework of the decision making process used for spectral identification, describe specific spectral feature analysis algorithms, and give examples of what analyses and types of maps are possible with imaging spectroscopy data. We also present the expert system rules that describe which diagnostic spectral features are used in the decision making process for a set of spectra of minerals and other common materials. We demonstrate the applications of Tetracorder to identify and map surface minerals, to detect sources of acid rock drainage, and to map vegetation species, ice, melting snow, water, and water pollution, all with one set of expert system rules. Mineral mapping can aid in geologic mapping and fault detection and can provide a better understanding of weathering, mineralization, hydrothermal alteration, and other geologic processes. Environmental site assessment, such as mapping source areas of acid mine drainage, has resulted in the acceleration of site cleanup, saving millions of dollars and years in cleanup time. Imaging spectroscopy data and Tetracorder analysis can be used to study both terrestrial and planetary science problems. Imaging spectroscopy can be used to probe planetary systems, including their atmospheres, oceans, and land surfaces.
Natural and anthropogenic hazards have the potential to impact all aspects of society including its economy and the environment. Diagnostic data to inform decision-making are critical for hazard ...management whether for emergency response, routine monitoring or assessments of potential risks. Imaging spectroscopy (IS) has unique contributions to make via the ability to provide some key quantitative diagnostic information. In this paper, we examine a selection of key case histories representing the state of the art to gain an insight into the achievements and perspectives in the use of visible to shortwave infrared IS for the detection, assessment and monitoring of a selection of significant natural and anthropogenic hazards. The selected key case studies examined provide compelling evidence for the use of the IS technology and its ability to contribute diagnostic information currently unattainable from operational spaceborne Earth observation systems. User requirements for the applications were also evaluated. The evaluation showed that the projected launch of spaceborne IS sensors in the near-, mid and long term future, together with the increasing availability, quality and moderate cost of off the shelf sensors, the possibilities to couple unmanned autonomous systems with miniaturized sensors, should be able to meet these requirements. The challenges and opportunities for the scientific community in the future when such data become available will then be ensuring consistency between data from different sensors, developing techniques to efficiently handle, process, integrate and deliver the large volumes of data, and most importantly translating the data to information that meets specific needs of the user community in a form that can be digested/understood by them. The latter is especially important to transforming the technology from a scientific to an operational tool. Additionally, the information must be independently validated using current trusted practices and uncertainties quantified before IS derived measurement can be integrated into operational monitoring services.
The process of pyrite oxidation at the surface of mine waste may produce acidic water that is gradually neutralized as it drains away from the waste, depositing different Fe-bearing secondary ...minerals in roughly concentric zones that emanate from mine-waste piles. These Fe-bearing minerals are indicators of the geochemical conditions under which they form. Airborne and orbital imaging spectrometers can be used to map these mineral zones because each of these Fe-bearing secondary minerals is spectrally unique. In this way, imaging spectroscopy can be used to rapidly screen entire mining districts for potential sources of surface acid drainage and to detect acid producing minerals in mine waste or unmined rock outcrops. Spectral data from the AVIRIS instrument were used to evaluate mine waste at the California Gulch Superfund Site near Leadville, CO. Laboratory leach tests of surface samples show that leachate pH is most acidic and metals most mobile in samples from the inner jarosite zone and that leachate pH is near-neutral and metals least mobile in samples from the outer goethite zone.
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