A. Deanne Rogers

Feldspathic rocks on Mars: Compositional constraints from infrared spectroscopy and possible formation mechanisms

Rare feldspar-dominated surfaces on Mars were previously reported based on near-infrared (NIR) spectral data and were interpreted to consist of anorthosite or felsic rocks. Using thermal infrared (TIR) data over the feldspar detections with the largest areal extent in Nili Patera and Noachis Terra, we rule out felsic interpretations. Basaltic or anorthositic compositions are consistent with TIR measurements, but the geologic contexts for these regions do not support a plutonic origin. Laboratory NIR spectral measurements demonstrate that large plagioclase crystals (>~840 µm) can be detected in mixtures with as much as 50 vol % mafics, which is higher than the previously stated requirement of no more than 15% mafics. Thus, anorthositic or felsic interpretations need not be invoked for all NIR-based feldspar detections. Plagioclase-enriched basaltic eruptive products can be formed from Martian basalts through partial crystallization at the base of a thick crust, followed by low-pressure crystallization of the residual liquids.

Mid-infrared emission spectroscopy and visible/near-infrared reflectance spectroscopy of Fe-sulfate minerals

Abstract Sulfate minerals are important indicators for aqueous geochemical environments. The geology and mineralogy of Mars have been studied through the use of various remote-sensing techniques, including thermal (mid-infrared) emission and visible/near-infrared reflectance spectroscopies. Spectral analyses of spacecraft data (from orbital and landed missions) using these techniques have indicated the presence of sulfate minerals on Mars, including Fe-rich sulfates on the iron-rich planet. Each individual Fe-sulfate mineral can be used to constrain bulk chemistry and lends more information about the specific formational environment [e.g., Fe2+ sulfates are typically more water soluble than Fe3+ sulfates and their presence would imply a water-limited (and lower Eh) environment; Fe3+ sulfates form over a range of hydration levels and indicate further oxidation (biological or abiological) and increased acidification]. To enable better interpretation of past and future terrestrial or planetary data sets, with respect to the Fe-sulfates, we present a comprehensive collection of mid-infrared thermal emission (2000 to 220 cm-1; 5-45 μm) and visible/near-infrared (0.35-5 μm) spectra of 21 different ferrous- and ferric-iron sulfate minerals. Mid-infrared vibrational modes (for SO4, OH, H2O) are assigned to each thermal emissivity spectrum, and the electronic excitation and transfer bands and vibrational OH, H2O, and SO4 overtone and combination bands are assigned to the visible/near-infrared reflectance spectra. Presentation and characterization of these Fe-sulfate thermal emission and visible/near-infrared reflectance spectra will enable the specific chemical environments to be determined when individual Fe-sulfate minerals are identified.

Compositional provinces of Mars from statistical analyses of TES, GRS, OMEGA and CRISM data

We identified 10 distinct classes of mineral assemblage on Mars through statistical analyses of mineral abundances derived from Mars Global Surveyor Thermal Emission Spectrometer (TES) data at a spatial resolution of 8 pixels per degree. Two classes are new regions in Sinus Meridiani and northern Hellas basin. Except for crystalline hematite abundance, Sinus Meridiani exhibits compositional characteristics similar to Meridiani Planum; these two regions may share part of a common history. The northern margin of Hellas basin lacks olivine and high-Ca pyroxene compared to terrains just outside the Hellas outer ring; this may reflect a difference in crustal compositions and/or aqueous alteration. Hesperian highland volcanic terrains are largely mapped into one class. These terrains exhibit low-to-intermediate potassium and thorium concentrations (from Gamma Ray Spectrometer (GRS) data) compared to older highland terrains, indicating differences in the complexity of processes affecting mantle melts between these different-aged terrains. A previously reported, locally observed trend toward decreasing proportions of low-calcium pyroxene relative to total pyroxene with time is also apparent over the larger scales of our study. Spatial trends in olivine and pyroxene abundance are consistent with those observed in near-infrared data sets. Generally, regions that are distinct in TES data also exhibit distinct elemental characteristics in GRS data, suggesting that surficial coatings are not the primary control on TES mineralogical variations, but rather reflect regional differences in igneous and large-scale sedimentary/glacial processes. Distinct compositions measured over large, low-dust regions from multiple data sets indicate that global homogenization of unconsolidated surface materials has not occurred.

Quantitative compositional analysis of sedimentary materials using thermal emission spectroscopy: 1. Application to sedimentary rocks

Thermal emission spectroscopy is used to determine the mineralogy of sandstone and mudstone rocks as part of an investigation of linear spectral mixing between sedimentary constituent phases. With widespread occurrences of sedimentary rocks on the surface of Mars, critical examination of the accuracy associated with quantitative models of mineral abundances derived from thermal emission spectra of sedimentary materials is necessary. Although thermal emission spectroscopy has been previously proven to be a viable technique to obtain quantitative mineralogy from igneous and metamorphic materials, sedimentary rocks, with natural variation of composition, compaction, and grain size, have yet to be examined. In this work, we present an analysis of the thermal emission spectral (~270–1650 cm−1) characteristics of a suite of 13 sandstones and 14 mudstones. X-ray diffraction and traditional point counting procedures were all evaluated in comparison with thermal emission spectroscopy. Results from this work are consistent with previous thermal emission spectroscopy studies and indicate that bulk rock mineral abundances can be estimated within 11.2% for detrital grains (i.e., quartz and feldspars) and 14.8% for all other mineral phases present in both sandstones and mudstones, in comparison to common in situ techniques used for determining bulk rock composition. Clay-sized to fine silt-sized grained phase identification is less accurate, with differences from the known ranging from ~5 to 24% on average. Nevertheless, linear least squares modeling of thermal emission spectra is an advantageous technique for determining abundances of detrital grains and sedimentary matrix and for providing a rapid classification of clastic rocks.

Thermal infrared and Raman microspectroscopy of moganite-bearing rocks

Abstract We present the first thermal infrared reflectance spectral characterization of moganite and mixtures of moganite with microcrystalline quartz. We find that for relatively high (>50%) abundances of moganite, the absolute reflectance for samples is significantly reduced. Using microscopic-Raman (~1 μm/pixel) measurements, we estimate the moganite content for various samples. We then compare Raman-derived moganite abundances with microscopic infrared reflectance (25 μm/pixel) spectra to determine the effects of increasing moganite abundance on thermal infrared spectra. We find that moganite is broadly spectrally similar to quartz with major reflectance maxima located between ~1030 and 1280 cm-1 and ~400 and 600 cm-1; but there are characteristic differences in the peak shapes, peak center positions, and especially the relative peak reflectance magnitudes. For regions with high (>50%) moganite content, the relative magntitudes of the reflectance maxima at 1157 and 1095 cm-1 (R1095/ R1157 band ratio) can be used to estimate the moganite content. This work demonstrates the utility of thermal infrared microspectroscopy in isolating phases that are intimately mixed in a sample, and has applications in planetary science, where constituent phases of quartz-rich sedimentary rocks can be identified using remote or in situ thermal infrared spectroscopy.

The association of hydrogen with sulfur on Mars across latitudes, longitudes, and compositional extremes

NASA/Jet Propulsion Lab; NASA Mars Data Analysis Program [NNX07AN96G, NNX10AQ23G]; MDAP grants [NNX12AG89G, NNX13AI98G]; LSUs College of Science and Geology and Geophysics

Amorphous salts formed from rapid dehydration of multicomponent chloride and ferric sulfate brines: Implications for Mars

Salts with high hydration states have the potential to maintain high levels of relative humidity (RH) in the near subsurface of Mars, even at moderate temperatures. These conditions could promote deliquescence of lower hydrates of ferric sulfate, chlorides, and other salts. Previous work on deliquesced ferric sulfates has shown that when these materials undergo rapid dehydration, such as that which would occur upon exposure to present day Martian surface conditions, an amorphous phase forms. However, the fate of deliquesced halides or mixed ferric sulfate-bearing brines are presently unknown. Here we present results of rapid dehydration experiments on Ca-, Na-, Mg- and Fe-chloride brines and multi-component (Fe2 (SO4)3 ± Ca, Na, Mg, Fe, Cl, HCO3) brines at ∼21°C, and characterize the dehydration products using visible/near-infrared (VNIR) reflectance spectroscopy, mid-infrared attenuated total reflectance spectroscopy, and X-ray diffraction (XRD) analysis. We find that rapid dehydration of many multicomponent brines can form amorphous solids or solids with an amorphous component, and that the presence of other elements affects the persistence of the amorphous phase under RH fluctuations. Of the pure chloride brines, only Fe-chloride formed an amorphous solid. XRD patterns of the multicomponent amorphous salts show changes in position, shape, and magnitude of the characteristic diffuse scattering observed in all amorphous materials that could be used to help constrain the composition of the amorphous salt. Amorphous salts deliquesce at lower RH values compared to their crystalline counterparts, opening up the possibility of their role in potential deliquescence-related geologic phenomena such as recurring slope lineae (RSLs) or soil induration. This work suggests that a wide range of aqueous mixed salt solutions can lead to the formation of amorphous salts and are possible for Mars; detailed studies of the formation mechanisms, stability and transformation behaviors of amorphous salts are necessary to further constrain their contribution to Martian surface materials.

Incorporation of portable infrared spectral imaging into planetary geological field work: Analog studies at Kīlauea Volcano, Hawaii and Potrillo Volcanic Field, New Mexico

During geological work for future planetary missions, portable/hand-held infrared spectral imaging instruments have the potential to significantly benefit science objectives. We assess how ground-based infrared spectral imaging can be incorporated into geological field work in a planetary setting through a series of field campaigns at two analog sites: Kīlauea Volcano, Hawaii, and Potrillo Volcanic Field, New Mexico. For this study, we utilize thermal infrared emission spectroscopy (8–13 μm) because this wavelength range is sensitive to major silicate spectral features and covers the terrestrial atmospheric window; however, our conclusions are applicable to other forms of infrared imaging (e.g., near-infrared reflectance spectroscopy). We demonstrate the ways in which spectral imaging could potentially enhance the science return and/or efficiency of traditional geological field work. Benefits include the following: documentation of major compositional variations within scenes, the ability to detect visually subtle and/or concealed variability in (sub) units, and the ability to characterize remote and/or inaccessible outcrops. These advantages could help field workers rapidly document sample context and develop strategic work plans. Furthermore, ground-based imaging provides a critical link between orbital/aerial imaging scales and sampling scales. Last, infrared spectral imaging data may be combined with in situ measurement techniques, such as X-ray fluorescence, as well as other ground-based remote sensing techniques, such as LIDAR (Light Detection And Ranging), to maximize geological understanding of the work area. Plain Language Summary Future missions to planetary objects are expected to have increasingly more human and rover components in surface exploration. To aid the explorers in conducting scientific tasks, portable instruments will likely be invaluable. Currently, knowledge of instrument suitability and most effective incorporation strategies are not sufficiently developed. As one of the first steps in this development process, we assess the fundamental capabilities of portable imaging technique in providing critical information for geological field work on planetary surfaces. Portable imaging, operating in the thermal infrared (8–13 μm), captured crucial data regarding rock/mineral types at field sites analogous to planetary settings. Value brought forth by portable infrared imaging is substantial, and this technique has the potential to benefit effective geological field work, which may lead to maximizing scientific return from missions. This finding and accompanying analyses presented here serve as a foundation for further development of instruments and mission strategies.

Visible, near-infrared, and mid-infrared spectral characterization of Hawaiian fumarolic alteration near Kilauea's December 1974 flow: Implications for spectral discrimination of alteration environments on Mars

Abstract The December 1974 flow in the SW rift zone at Kilauea Volcano, Hawaii, has been established as a Mars analog due to its physical, chemical, and morphological properties, as well as its interaction with the outgassing plume from the primary Kilauea caldera. We focus on a solfatara site that consists of hydrothermally altered basalt and alteration products deposited in and around a passively degassing volcanic vent situated directly adjacent to the December 1974 flow on its northwest side. Reflectance spectra are acquired in the visible/near-infrared (VNIR) region and emission spectra in the mid-infrared (MIR) range to better understand the spectral properties of hydrothermally altered materials. The VNIR signatures are consistent with silica, Fe-oxides, and sulfates (Ca, Fe). Primarily silica-dominated spectral signatures are observed in the MIR and changes in spectral features between samples appear to be driven by grain size effects in this wavelength range. The nature of the sample coating and the thermal emission signatures exhibit variations that may be correlated with distance from the vent. Chemical analyses indicate that most surfaces are characterized by silica-rich material, Fe-oxides, and sulfates (Ca, Fe). The silica and Fe-oxide-dominated MIR/VNIR spectral signatures exhibited by the hydrothermally altered material in this study are distinct from the sulfate-dominated spectral signatures exhibited by previously studied low-temperature aqueous acid-sulfate weathered basaltic glass. This likely reflects a difference in open vs. closed system weathering, where mobile cations are removed from the altered surfaces in the fumarolic setting. This work provides a unique infrared spectral library that includes martian analog materials that were altered in an active terrestrial solfatara (hydrothermal) setting. Hydrothermal environments are of particular interest as they potentially indicate habitable conditions. Key constraints on the habitability and astrobiological potential of ancient aqueous environments are provided through detection and interpretation of secondary mineral assemblages; thus, spectral detection of fumarolic alteration assemblages observed from this study on Mars would suggest a region that could have hosted a habitable environment.