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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Petrology and Geochemistry of D'Orbigny, Geochemistry of Sahara 99555, and the Origin of Angrites

We have done detailed petrologic study of the angrite, D'Orbigny, and geochemical study of it and Sahara 99555. D'Orbigny is an igneous-textured rock composed of Ca-rich olivine, Al-Ti-diopside-hedenbergite, subcalcic kirschsteinite, two generations of hercynitic spinel and anorthite, with the mesostasis phases ulv6spinel, Ca-phosphate, a silicophosphate phase and Fe-sulfide. We report an unknown Fe-Ca-Al-Ti-silicate phase in the mesostasis not previously found in angrites. One hercynitic spinel is a large, rounded homogeneous grain of a different composition than the euhedral and zoned grains. We believe the former is a xenocryst, the first such described from angrites. The mafic phases are highly zoned; mg# of cores for olivine are approx.64, and for clinopyroxene approx.58, and both are zoned to Mg-free rims. The Ca content of olivine increases with decreasing mg#, until olivine with approx.20 mole% Ca is overgrown by subcalcic kirschsteinite with Ca approx.30-35 mole%. Detailed zoning sequences in olivine-subcalcic kirschsteinite and clinopyroxene show slight compositional reversals. There is no mineralogic control that can explain these reversals, and we believe they were likely caused by local additions of more primitive melt during crystallization of D'Orbigny. D'Orbigny is the most ferroan angrite with a bulk rock mg# of 32. Compositionally, it is virtually identical to Sahara 99555; the first set of compositionally identical angrites. Comparison with the other angrites shows that there is no simple petrogenetic sequence, partial melting with or without fractional crystallization, that can explain the angrite suite. Angra dos Reis remains a very anomalous angrite. Angrites show no evidence for the brecciation, shock, or impact or thermal metamorphism that affected the HED suite and ordinary chondrites. This suggests the angrite parent body may have followed a fundamentally different evolutionary path than did these other parent bodies.

Mittlefehldt, David W.↗
NASA NTRS2000

Thermodynamics of Aqueous Organic Sulfur Compounds: A Key to the Organic Geochemistry of Hydrothermal Systems?

Hydrothermal environments are locations of varied geochemistry due to the disequilibrium between vent fluids and seawater. The disequilibrium geochemistry has been hypothesized to include reactions to synthesize organic compounds. Observations of the organic geochemistry of hydrothermal vent sites has received little attention. Experimental simulations of these environments, however, indicate that organic compounds may have difficulty forming in a purely aqueous environment. On the other hand, thiols. thioesters and disulfides have been implicated as reaction intermediates between CO or CO2 in experiments of carbon reduction in hydrothermal environments as well as in a variety of biological processes and other abiotic reactions (Wachtershauser, 1990, OLEB 20, 173; Heinen and Lauwers, 1996, OLEB 26, 13 1, Huber and Wachtershauser, 1997, Science 276, 245; Russell et al., 1998, in Thermophiles: The keys to molecular evolution and the origin of life?). The reduction of CO2 to thiols, for example, is observed using the FeS-H2S/FeS2 couple to provide the reducing power (see Schoonen et al., 1999, OLEB 29, 5). In addition, the enzyme involved in final stage of methanogenesis, coenzyme-M, is itself a thiol. Thus, organic sulfur compounds may hold the key to the organic chemistry leading to the origin of life at high temperatures. Understanding the biochemical processes of microorganisms that can live to temperatures at least as high as 113 C (Blochl et al., 1996, Extremophiles 1, 14) requires knowledge of the properties of the chemical reactions involved. In order to assess the role of aqueous organic sulfur compounds in hydrothermal organic geochemistry, we have been attempting to determine their thermodynamic properties. We have culled the literature to obtain the properties of organic sulfur compounds. We are able to calculate a number of essential properties, such as free energies of formation, from solubility data available in the literature together with standard properties of organic sulfur gases. However, a number of the properties for aqueous organic sulfur compounds have not been experimentally determined. Furthermore, most of thermodynamic data that are available are for 25 C and 1 bar. In order to determine reaction properties to temperatures and pressures appropriate to the hydrothermal conditions in which thermophilic organisms actually live, we use equations of state developed by Helgeson and co-workers (Helgeson et al., 1981, AJS 281, 1249). A key piece of information needed to go up in temperature is the partial molal heat capacity, which is one of the properties for which experimental data are unavailable for nearly all organic sulfur compounds. We have used correlation methods to determine the partial molal heat capacities and volumes of many organic solutes. These estimates allow us to asses the role of organic sulfur compounds during the reduction of carbon in hydrothermal settings. We will present these data, along with examples of the thermodynamic properties of reactions involving aqueous organic sulfur compounds.

Schulte, Mitchell↗
NASA NTRS2001

Thiols in Hydrothermal Solution: Standard Partial Molal Properties and Their Role in the Organic Geochemistry of Hydrothermal Environments

Modern seafloor hydrothermal systems are locations where great varieties of geochemistry occur due to the enormous disequilibrium between vent fluids and seawater. The disequilibrium geochemistry has been hypothesized to include reactions to synthesize organic compounds. Despite the incomplete understanding of the carbon budget in hydrothermal systems, the organic geochemistry of these sites has received little attention. Experimental simulations of these environments, however, indicate that organic compounds may have difficulty forming in a purely aqueous environment. On the other hand, thiols, thioesters and disulfides have been implicated as reaction intermediates between CO or CO2 in experiments of carbon reduction in hydrothermal environments, as well as in a variety of biological processes and other abiotic reactions. The reduction of CO2 to thesis, for example, is observed using the FeS-H2S/FeS2 couple to provide the reducing power. We have used recent advances in theoretical geochemistry to estimate the standard partial moral thermodynamic properties and parameters for the revised Helgeson-Kirkham-Flowers equation of state for aqueous straight-chain alkyl thesis. With these data and parameters we have evaluated the role that organic sulfur compounds may play as reaction intermediates during organic compound synthesis. We conclude that organic sulfur compounds may hold the key to the organic chemistry leading to the origin of life in hydrothermal settings. These results may also explain the presence of sulfur in a number of biomolecules present in ancient thermophilic microorganisms.

Schulte, Mitchell D.↗
NASA NTRS2017

Isotope Geochemistry for Comparative Planetology of Exoplanets

Isotope geochemistry has played a critical role in understanding processes at work in and the history of solar system bodies. Application of these techniques to exoplanets would be revolutionary and would allow comparative planetology with the formation and evolution of exoplanet systems. The roadmap for comparative planetology of the origins and workings of exoplanets involves isotopic geochemistry efforts in three areas: (1) technology development to expand observations of the isotopic composition of solar system bodies and expand observations to isotopic composition of exoplanet atmospheres; (2) theoretical modeling of how isotopes fractionate and the role they play in evolution of exoplanetary systems, atmospheres, surfaces and interiors; and (3) laboratory studies to constrain isotopic fractionation due to processes at work throughout the solar system.

atmosphere↗
NASA NTRS1972

Lunar carbon chemistry - Relations to and implications for terrestrial organic geochemistry.

Survey of the various ways in which studies of lunar carbon chemistry have beneficially affected terrestrial organic geochemistry. A lunar organic gas-analysis operating system is cited as the most important instrumental development in relation to terrestrial organic geochemistry. Improved methods of analysis and handling of organic samples are cited as another benefit derived from studies of lunar carbon chemistry. The problem of controlling contamination and minimizing organic vapors is considered, as well as the possibility of analyzing terrestrial samples by the techniques developed for lunar samples. A need for new methods of analyzing carbonaceous material which is insoluble in organic solvents is indicated.

Eglinton, G.↗
NASA NTRS1983

Precambrian organic geochemistry - Preservation of the record

A review of earlier studies is presented, and new results in Precambrian organic geochemistry are discussed. It is pointed out that two lines of evidence can be developed. One is based on structural organic chemistry, while the other is based on isotopic analyses. In the present investigation, the results of both structural and isotopic investigations of Precambrian organic matter are discussed. Processes and products related to organic geochemistry are examined, taking into account the carbon cycle, an approximate view of the principal pathways of carbon cycling associated with organic matter in the present global ecosystem, processes affecting sedimentary organic matter, and distribution and types of organic matter. Attention is given to chemical fossils in Precambrian sediments, kerogen analyses, the determination of the structural characteristics of kerogen, and data concerning the preservation of the Precambrian organic geochemical record.

Hayes, J. M.↗
NASA NTRS1994

Spherical disharmonics in the Earth sciences and the spatial solution: Ridges, hotspots, slabs, geochemistry and tomography correlations

There is increasing use of statistical correlations between geophysical fields and between geochemical and geophysical fields in attempts to understand how the Earth works. Typically, such correlations have been based on spherical harmonic expansions. The expression of functions on the sphere as spherical harmonic series has many pitfalls, especially if the data are nonuniformly and/or sparsely sampled. Many of the difficulties involved in the use of spherical harmonic expansion techniques can be avoided through the use of spatial domain correlations, but this introduces other complications, such as the choice of a sampling lattice. Additionally, many geophysical and geochemical fields fail to satisfy the assumptions of standard statistical significance tests. This is especially problematic when the data values to be correlated with a geophysical field were collected at sample locations which themselves correlate with that field. This paper examines many correlations which have been claimed in the past between geochemistry and mantle tomography and between hotspot, ridge, and slab locations and tomography using both spherical harmonic coefficient correlations and spatial domain correlations. No conclusively significant correlations are found between isotopic geochemistry and mantle tomography. The Crough and Jurdy (short) hotspot location list shows statistically significant correlation with lowermost mantle tomography for degree 2 of the spherical harmonic expansion, but there are no statistically significant correlations in the spatial case. The Vogt (long) hotspot location list does not correlate with tomography anywhere in the mantle using either technique. Both hotspot lists show a strong correlation between hotspot locations and geoid highs when spatially correlated, but no correlations are revealed by spherical harmonic techniques. Ridge locations do not show any statistically significant correlations with tomography, slab locations, or the geoid; the strongest correlation is with lowermost mantle tomography, which is probably spurious. The most striking correlations are between mantle tomography and post-Pangean subducted slabs. The integrated locations of slabs correlate strongly with fast areas near the transition zone and the core-mantle boundary and with slow regions from 1022-1248 km depth. This seems to be consistent with the 'avalanching' downwellings which have been indicated by models of the mantle which include an endothermic phase transition at the 670-km discontinuity, although this is not a unique interpretation. Taken as a whole, these results suggest that slabs and associated cold downwellings are the dominant feature of mantle convection. Hotspot locations are no better correlated with lower mantle tomography than are ridge locations.

Ray, Terrill W.↗
NASA NTRS2001

Sedimentary Geochemistry of Martian Samples from the Pathfinder Mission

The purpose of this research project was to evaluate the APXS data collected on soils and rocks at the Pathfinder site in terms of sedimentary geochemistry. Below are described the major findings of this research: (1) An influential model to explain the chemical variation among Pathfinder soils and rocks is a two component mixing model where rocks of fairly uniform composition mix with soil of uniform composition; (2) The very strong positive correlation between MgO and SO, points to a control by a MgSO4 mineral however, spectroscopic data continue to suggest that Fe-sulfates, notably schwertmannite and jarosite, may be important components; (3) In an attempt to better understand the causes of complexities in mixing relationships, the possible influence of sedimentary transport has been evaluated; (4) Another aspect of this research has been to examine the possibility of sedimentary silica being a significant phase on Mars; and (5) On Earth, the geochemistry of sedimentary rocks has been used to constrain the chemical composition of the continental crust and an important part of this research was to evaluate this approach for Mars.

McLennan, Scott M.↗
NASA NTRSDate not supplied

Exploring the Geochemistry of Tholeiitic Basalts and Hyaloclastites Formed in Submarine Volcanoes for Comparison With Venus Lavas

Underwater basaltic lavas exhibit distinct rock textures, mineralogy and morphological differences compared to those formed on land, primarily due to rapid cooling caused by contact with cold seawater instead of air and to high pressures – similar to Venus. The geomorphological similarities between terrestrial submarine volcanoes and some morphological classes of Venusian volcanoes have been investigated, but a comprehensive comparison in geochemical terms has yet to be conducted. Only three missions to Venus (Venera-13, Venera-14, and Vega-2) were able to report bulk composition of Venusian rocks, while other four missions (Venera-8, Venera-9, Venera-10, and Vega-1) provided limited geochemical information. Using X-Ray fluorescent (XRF) analysis, we saw that rocks analyzed on the surface of Venus are tholeiitic and alkalic basalts. This study, as part of the “Analogs for VENus's GEologically Recent Surfaces” (AVENGERS) initiative, aims to examine the possibility of seamounts/submarine volcanoes lavas serving as analogues to Venus lava geochemistry and morphology/formational processes. By sampling and analyzing submarine lavas from three distinct tectonic settings on Earth - hot-spot, convergent margins, and divergent margins - we will assess in which tectonic context the analogy with Venus is most comparable. Fieldwork will be conducted in further detail for submarine volcanoes located in Sicily, Hawaiʻi, and the Southern Pacific (Fiji, Vanuatu, Tonga, Samoa); we will use previously collected samples where these submarine areas are not accessible. Sampling efforts will target areas likely to yield submarine tholeiitic lavas and/or hyaloclastites. Samples collected during fieldwork will undergo detailed whole-rock geochemical analysis, including XRF, X-Ray diffraction (XRD) and Inductively Coupled Plasma Mass Spectrometry (ICPMS). Thin sections will be used to constrain differences in morphology/textures. The obtained geochemical data will then be compared with existing data on Venusian lava geochemistry, allowing for a comprehensive evaluation of potential analogies between submarine lavas from Earth and volcanic rocks on Venus. By elucidating these similarities and pinpointing specific tectonic contexts, our study has the potential to enhance our understanding of Venusian geology and the possibility of ephemeral plate tectonics on the planet.

N Mari↗
NASA NTRS2011

One-carbon (bio ?) Geochemistry in Subsurface Waters of the Serpentinizing Coast Range Ophiolite

Serpentinization - the aqueous alteration of ultramafic rocks - typically imparts a highly reducing and alkaline character to the reacting fluids. In turn, these can influence the speciation and potential for metabolism of one-carbon compounds in the system. We examined the aqueous geochemistry and assessed the biological potential of one-carbon compounds in the subsurface of the McLaughlin Natural Reserve (Coast Range Ophiolite, California, USA). Fluids from wells sunk at depths of 25-90 meters have pH values ranging from 9.7 to 11.5 and dissolved inorganic carbon (DIC concentrations) generally below 60 micromolar. Methane is present at concentrations up to 1.3 millimolar (approximately one-atmosphere saturation), and hydrogen concentrations are below 15 nanomolar, suggesting active consumption of H2 and production of CH4. However, methane production from CO2 is thermodynamically unfavorable under these conditions. Additionally, the speciation of DIC predominantly into carbonate at these high pH values creates a problem of carbon availability for any organisms that require CO2 (or bicarbonate) for catabolism or anabolism. A potential alternative is carbon monoxide, which is present in these waters at concentrations 2000-fold higher than equilibrium with atmospheric CO. CO is utilized in a variety of metabolisms, including methanogenesis, and bioavailability is not adversely affected by pH-dependent speciation (as for DIC). Methanogenesis from CO under in situ conditions is thermodynamically favorable and would satisfy biological energy requirements with respect to both Gibbs Energy yield and power.

McLaughlin Natural Reserve↗
NASA NTRS1967

Treatise in Organic Geochemistry

Survey on organic geochemistry origins and use of gas-liquid chromatography and mass spectrometry analyses of organic components isolated from crude oils and sediments

Mc Carthy, E. D.↗
NASA NTRS1968

Geochemistry of andesites.

Trace element geochemistry of calc-alkaline andesites, discussing crustal composition models and trace elements distribution

Taylor, S. R.↗
NASA NTRS1975

Mineralogy, petrology, and geochemistry of the lunar samples

The geochemistry of the bulk moon is considered, taking into account the large-scale chemical view of the lunar surface which has been obtained with the aid of three remote sensing experiments utilizing X-ray fluorescence, a gamma-ray spectrometer, and visible and near infrared reflectance measurements. Attention is also given to the regolith, the mare basins, and the lunar highlands and crust.

Warner, J.↗