Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “hydrothermal fluids”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Terrestrial Aqueously Altered Magmatic Dike Forming Sulfate-Rich Hydrothermal Fluids to Constrain Martian Habitability

Intrusion of magma into a water-bearing crust can create a habitable hydrothermal environment, as seen on Earth. As the rock surrounding the intrusion is subjected to heat it can 1) release water, and different chemical species, from pre-existing minerals, and 2) interact with volatiles released from the cooling magma, which can create a geothermal brine with a distinct composition suitable for a range of chemotrophs. Hence, studying such environments on Earth is important in the search for life beyond our planet. The geothermal brine’s nature is dependent on the host rock and the magmatic properties. On Mars basaltic and sulfur-rich soils are dominant and therefore investigating basaltic magmatic interaction with sulfate-rich sediments and their associated habitats is key for recognizing potential habitats on Mars. The NASA Perseverance Rover at Jezero Crater has detected aqueously altered igneous rocks, potentially intrusive in origin, with secondary carbonates, sodium perchlorate and sulfates. Such an environment may have been habitable. Therefore, we investigate the intrusion of a magmatic dike into Jurassic sulfate-rich sediments from the San Rafael Swell, Utah, to reconstruct the geothermal fluids and assess their putative habitability.

B Baharier↗
NASA NTRS2004

Chicxulub Impact Melts: Geochemical Signatures of Target Lithology Mixing and Post-Impact Hydrothermal Fluid Processes

Impact melts within complex impact craters are generally homogeneous, unless they differentiated, contain immiscible melt components, or were hydrothermally altered while cooling. The details of these processes, however, and their chemical consequences, are poorly understood. The best opportunity to unravel them may lie with the Chicxulub impact structure, because it is the world s most pristine (albeit buried) large impact crater. The Chicxulub Scientific Drilling Project recovered approx. 100 meters of impactites in a continuous core from the Yaxcopoil-1 (YAX-1) borehole. This dramatically increased the amount of melt available for analyses, which was previously limited to two small samples N17 and N19) recovered from the Yucatan-6 (Y-6) borehole and one sample (N10) recovered from the Chicxulub-1 (C-1) borehole. In this study, we describe the chemical compositions of six melt samples over an approx. 40 m section of the core and compare them to previous melt samples from the Y-6 and C-1 boreholes.

Kring, David A.↗
NASA NTRS2003

Fine-grained Goethite as a Precursor for Martian Gray Hematite

Several isolated deposits of gray, crystalline hematite on Mars were discovered using data returned from the Thermal Emission Spectrometer (TES) instrument aboard the Mars Global Surveyor spacecraft. Christensen et al. provided five testable hypotheses regarding the formation of crystalline hematite on Mars: 1) low-temperature precipitation of Fe oxides/hydroxides from standing, oxygenated, Fe-rich water, followed by subsequent alteration to gray hematite, 2) low-temperature leaching of iron-bearing silicates and other materials leaving a Fe-rich residue laterite-style weathering) which is subsequently altered to gray hematite, 3) direct precipitation of gray hematite from Fe-rich circulating fluids of hydrothermal or other origin, 4) formation of gray hematitic surface coatings during weathering, and 5) thermal oxidation of magnetite-rich lavas. Since this initial work, several authors have examined the hematite deposits to determine their formation mechanism. Lane et al. cited the absence of a 390/ cm absorption in the martian hematite spectrum as evidence for platy hematite grains. Their model for the formation of the deposits includes deposition of any of a variety of iron oxides or oxyhydroxides by aqueous or hydrothermal fluids, burial and metamorphosis to gray platy hematite grains, and exhumation in recent times. Based on a detailed geomorphic examination of the Sinus Meridiani region, Hynek et al. conclude that the most likely method of hematite formation was either emplacement by a hydrothermal fluid or oxidation of a magnetite-rich pyroclastic deposit. Similarly, Arvidson et al., favor a model involving the alteration of pyroclastic deposits by aqueous or hydrothermal fluids. Finally, based on geochemical modeling and an examination of Aram Chaos, Catling and Moore favor emplacement by hydrothermal fluids with a minimum temperature of 100 C. Comparison of the average martian hematite spectrum measured by TES to hematite emissivity spectra for a variety of naturally occurring hematites shows small but potentially important differences. In particular, band shapes, positions and relative band emissivities of hematite spectra vary over the range of samples. These differences imply that the natural variability of thermal infrared hematite spectra has not been fully characterized, especially with respect to the reaction pathway and crystal structure.

T D Glotch↗
NASA NTRS1995

Geochemical constraints on chemolithoautotrophic reactions in hydrothermal systems

Thermodynamic calculations provide the means to quantify the chemical disequilibrium inherent in the mixing of reduced hydrothermal fluids with seawater. The chemical energy available for metabolic processes in these environments can be evaluated by taking into account the pressure and temperature dependence of the apparent standard Gibbs free energies of reactions in the S-H2-H2O system together with geochemical constraints on pH, activities of aqueous sulfur species and fugacities of H2 and/or O2. Using present-day mixing of hydrothermal fluids and seawater as a starting point, it is shown that each mole of H2S entering seawater from hydrothermal fluids represents about 200,000 calories of chemical energy for metabolic systems able to catalyze H2S oxidation. Extrapolating to the early Earth, which was likely to have had an atmosphere more reduced than at present, shows that this chemical energy may have been a factor of two or so less. Nevertheless, mixing of hydrothermal fluids with seawater would have been an abundant source of chemical energy, and an inevitable consequence of the presence of an ocean on an initially hot Earth. The amount of energy available was more than enough for organic synthesis from CO2 or CO, and/or polymer formation, indicating that the vicinity of hydrothermal systems at the sea floor was an ideal location for the emergence of the first chemolithoautotrophic metabolic systems.

Shock, Everett L.↗
NASA NTRS1988

Noble metals in mid-ocean ridge volcanism: A significant fractionation of gold with respect to platinum group metals

Hydrothermal precipitates, black smoker particulate, and massive sulphide dredge samples from the Explorer Ridge on the Juan de Fuca Plate and the TAG hydrothermal area on the Mid-Atlantic Ridge were analyzed for selected noble metals including Au, Ir and Pd by radiochemical neutron activation analysis. The preliminary results indicate that gold contents may reach the ppm range although values in the neighborhood of 100 to 200 ppb are more typical. The platinum group elements (PGE) represented by Ir and Pd are typically less than 0.02 ppb and less than 2 ppb respectively. These abundances represent a significant enrichment of gold relative to the PGE in comparison with average noble metal abundances in mid-ocean ridge basalts (MORB). A partial explanation of this distinctive fractionation can be found in the concepts of sulfur-saturation of basic magma in mid-ocean ridge (MOR) settings, and the origin of MOR hydrothermal fluids. Experimental and petrological data suggest that MORBs are sulfur-saturated at the time of magma generation and that an immiscible sulfide component remains in the mantle residue. Hence, MORBs are noble metal-poor, particularly with respect to PGE. Consequently, black smoker fluids can be expected to reflect the low Ir and Pd contents of the rock column. The average Au content of MORB is 1.3 ppb, and so the rock column is not significantly enriched in Au. The generation of fluids which precipitate solids with 200 ppb Au is apparently dependent on highly efficient fluid chemistry to mobilize Au from the rock column, high Au solubility in seawater hydrothermal fluids and efficient precipitation mechanisms to coprecipitate Au on Fe, Zn and Cu sulfides. Significant differences in these parameters appear to be the ultimate cause of the strong Au-PGE fractionation in the MOR setting. It does not appear from the current data base that MOR hydrothermal fluids are significant contributors to the Ir enrichment seen in Cretaceous-Tertiary boundary sediments.

Crocket, James H.↗
NASA NTRS2004

Lunar and Planetary Science XXXV: Impacts on Mars and Earth

The session "Impacts on Mars and Earth" included the following reports:A Timescale for Major Events in Early Mars Crustal Evolution; Impact Craters in Arabia Terra, Mars; Ancient Giant Basin/Aquifer System in the Arabia Region, Mars; Small Crater Morphology Within Gusev Crater and Isidis Planitia: Evidence for Widespread Secondaries on Mars; Martian Surface Properties: Inferences from Resolved Differences in Crater Geometries; Asymmetric Ramparts of Secondary Craters in Cerberus, Mars: Interpretation and Implications for Local Stratigraphy; Depth to Diameter Relationships of Craters in the High Latitudes (70 -80 ) of Mars: Implications for Geologic History of Those Areas; Impact Cratering on Mars: Search for Target Influence on Morphology; Starting Conditions for Hydrothermal Systems Underneath Martian Craters: Hydrocode Modeling; Impact-induced Hydrothermal System at the Sudbury Crater: Duration, Temperatures, Mechanics, and Biological Implications; Major and Trace Element Variations in Impact Crater Clay from Chicxulub, Lonar, and Mistastin, Implications for the Martian Soil; Stable Isotopes and Hydrothermal Fluid Source in the Yaxcopoil-1 Borehole, Chicxulub Impact Structure, Mexico; and Chicxulub Impact Melts: Geochemical Signatures of Target Lithology Mixing and Post-Impact Hydrothermal Fluid Processes.

Source record↗
NASA NTRS1987

U, Th, and Pb isotopes in hot springs on the Juan de Fuca Ridge

Concentrations and isotopic compositions of U, Th, and Pb in three hydrothermal fluids from the Juan de Fuca Ridge were determined from samples obtained by the Alvin submersible. The samples were enriched in Pb and Th relative to deep-sea water, and were deficient in U. No clear relationship with Mg was found, suggesting nonideal mixing between the hot hydrothermal fluids and the cold ambient seawater. Values for U-234/U-238 have a seawater signature, and show a U-234 enrichment relative to the equilibrium value. The Pb isotopic composition has a uniform midocean ridge basalt signature, and it is suggested that Pb in these fluids may represent the best average value of the local oceanic crust.

Chen, J. H.↗
NASA NTRS1992

Chemical reaction path modeling of hydrothermal processes on Mars: Preliminary results

Hydrothermal processes are thought to have had significant roles in the development of surficial mineralogies and morphological features on Mars. For example, a significant proportion of the Martian soil could consist of the erosional products of hydrothermally altered impact melt sheets. In this model, impact-driven, vapor-dominated hydrothermal systems hydrothermally altered the surrounding rocks and transported volatiles such as S and Cl to the surface. Further support for impact-driven hydrothermal alteration on Mars was provided by studies of the Ries crater, Germany, where suevite deposits were extensively altered to montmorillonite clays by inferred low-temperature (100-130 C) hydrothermal fluids. It was also suggested that surface outflow from both impact-driven and volcano-driven hydrothermal systems could generate the valley networks, thereby eliminating the need for an early warm wet climate. We use computer-driven chemical reaction path calculation to model chemical processes which were likely associated with postulated Martian hydrothermal systems.

Plumlee, Geoffrey S.↗
NASA NTRS2008

Detection of Abiotic Methane in Terrestrial Continental Hydrothermal Systems: Implications for Methane on Mars

The recent detection of methane in the Martian atmosphere and the possibility that its origin could be attributed to biological activity, have highlighted the importance of understanding the mechanisms of methane formation and its usefulness as a biomarker. Much debate has centered on the source of the methane in hydrothermal fluids, whether it is formed biologically by microorganisms, diagenetically through the decomposition of sedimentary organic matter, or inorganically via reduction of CO2 at high temperatures. Ongoing research has now shown that much of the methane present in sea-floor hydrothermal systems is probably formed through inorganic CO2 reduction processes at very high temperatures (greater than 400 C). Experimental results have indicated that methane might form inorganically at temperatures lower still, however these results remain controversial. Currently, methane in continental hydrothermal systems is thought to be formed mainly through the breakdown of sedimentary organic matter and carbon isotope equilibrium between CO2 and CH4 is thought to be rarely present if at all. Based on isotopic measurements of CO2 and CH4 in two continental hydrothermal systems, we suggest that carbon isotope equilibration exists at temperatures as low as 155 C. This would indicate that methane is forming through abiotic CO2 reduction at lower temperatures than previously thought and could bolster arguments for an abiotic origin of the methane detected in the martian atmosphere.

Socki, Richard A.↗
NASA NTRS2016

FTIR Analysis of Water in Pyroxene and Plagioclase in ALH 84001 and Nakhlites

Determining the volatile budget of the interior of Mars is crucial for our understanding of that planet's formation, geodynamics, cooling history and the origin of its volcanism and atmosphere as well as its potential for life. Surficial water is evident from spacecraft and rover data in polar caps and the atmosphere, in the presence of river channels, and in the detection of water-bearing minerals. Meteorites, however, are our best candidates for estimating the amount of water present at depth, even if all are crustal samples. The last 10 years have seen a blooming of studies measuring water and halogens in Martian meteorites. The bulk of these studies target phosphate, a typically late-stage phase in the igneous Martian meteorites that potentially would concentrate incompatible element hydrogen (H quantified traditionally as "water", i.e., H2O concentrations in weight) near the end of the crystallization sequence. However, determining the amount of water, F, and Cl in the magma from which a phosphate crystallized from is not straightforward and in most instances not possible. On the other hand, phosphates have turned out to be very useful in identifying hydrothermal processes that could have added water while or after the magma flowed and crystallized. Another caveat of analyzing Martian meteorite phases for water is that shocked phases such as maskelynite and impact melts appear to have incorporated water from the Martian atmosphere, as evidenced by high H isotope ((delta)D) signatures, and therefore their water concentrations cannot be interpreted in terms of deep planetary processes. The best candidates for estimating the water content of the Martian interior have been melt inclusions (glass or amphibole-bearing) which the enclosing mineral (usually olivine) would have prevented from exchanging volatiles with the surroundings after crystallization. Even some of these, however, have high (delta)D, meaning they were affected by H exchange via impact events or with crustal reservoirs or hydrothermal fluids. Here, nominally anhydrous minerals (pyroxene, olivine, plagioclase, or maskelynite) in orthopyroxenite ALH 84001 and selected nakhlites are analyzed for water and major elements, in order to determine 1) whether they contain any water; 2) if they do, what controls its distribution (crystallization, degassing, hydrothermal or impact processes); and 3) if any of these measurements can be used to infer the water contents of the parent magma and their mantle sources. A shock-reverberation experiment was also performed on terrestrial orthopyroxenes (opx) to simulate the heavily shocked conditions of ALH 84001 (> 31 GPa [17]).

Peslier, A. H.↗
NASA NTRS1993

Laboratory simulated hydrothermal alteration of sedimentary organic matter from Guaymas Basin, Gulf of California

High temperature alteration of sedimentary organic matter associated with marine hydrothermal systems involves complex physical and chemical processes that are not easily measured in most natural systems. Many of these processes can be evaluated indirectly by examining the geochemistry of the hydrothermal system in the laboratory. In this investigation, an experimental organic geochemical approach to studying pyrolysis of sedimentary organic matter is applied to the hydrothermal system in the Guaymas Basin, Gulf of California. A general survey of hydrothermal oils and extractable organic matter (bitumen) in hydrothermally altered sediments identified several homologous series of alkanones associated with a high temperature hydrothermal origin. The alkanones range in carbon number from C11 to C30 with no carbon number preference. Alkan-2-ones are in highest concentrations, with lower amounts of 3-, 4-, 5- (and higher) homologs. The alkanones appear to be pyrolysis products synthesized under extreme hydrothermal conditions. Hydrous pyrolysis and confinement pyrolysis experiments were performed to simulate thermally enhanced diagenetic and catagenetic changes in the immature sedimentary organic matter. The extent of alteration was measured by monitoring the n-alkanes, acyclic isoprenoids, steroid and triterpenoid biomarkers, polycyclic aromatic hydrocarbons and alkanones. The results were compared to bitumen extracts from sediments which have been naturally altered by a sill intrusion and accompanied hydrothermal fluid flow. These pyrolysis experiments duplicated many of the organic matter transformations observed in the natural system. Full hopane and sterane maturation occurred after 48 hr in experiments at 330 deg C with low water/rock mass ratios (0.29). A variety of radical and ionic reactions are responsible for the organic compound conversions which occur under extreme hydrothermal conditions. Short duration pyrolysis experiments revealed that a portion of the hydrocarbons generated from kerogen was observed to go through alkene intermediates, and the rate of alkene isomerization was influenced by the ionic strength and catalytic mineral phases. Confinement of the organic pyrolysate to the bulk sediment accelerated the rates of the biomarker epimerization reactions, suggesting that these reactions are influenced strongly by the association of the inorganic matrix, and that the relative rates of some ionic and radical reactions can be influenced by the water/rock ratio during the pyrolysis experiments.

Leif, Roald N.↗
NASA NTRS1996

Hydrothermal systems as environments for the emergence of life

Analysis of the chemical disequilibrium provided by the mixing of hydrothermal fluids and seawater in present-day systems indicates that organic synthesis from CO2 or carbonic acid is thermodynamically favoured in the conditions in which hyperthermophilic microorganisms are known to live. These organisms lower the Gibbs free energy of the chemical mixture by synthesizing many of the components of their cells. Primary productivity is enormous in hydrothermal systems because it depends only on catalysis of thermodynamically favourable, exergonic reactions. It follows that hydrothermal systems may be the most favourable environments for life on Earth. This fact makes hydrothermal systems logical candidates for the location of the emergence of life, a speculation that is supported by genetic evidence that modern hyperthermophilic organisms are closer to a common ancestor than any other forms of life. The presence of hydrothermal systems on the early Earth would correspond to the presence of liquid water. Evidence that hydrothermal systems existed early in the history of Mars raises the possibility that life may have emerged on Mars as well. Redox reactions between water and rock establish the potential for organic synthesis in and around hydrothermal systems. Therefore, the single most important parameter for modelling the geochemical emergence of life on the early Earth or Mars is the composition of the rock which hosts the hydrothermal system.

Non-NASA Center↗
NASA NTRS1996

Phenols in hydrothermal petroleums and sediment bitumen from Guaymas Basin, Gulf of California

The aliphatic, aromatic and polar (NSO) fractions of seabed petroleums and sediment bitumen extracts from the Guaymas Basin hydrothermal system have been analyzed by gas chromatography and gas chromatography-mass spectrometry (free and silylated). The oils were collected from the interiors and exteriors of high temperature hydrothermal vents and represent hydrothermal pyrolyzates that have migrated to the seafloor by hydrothermal fluid circulation. The downcore sediments are representative of both thermally unaltered and thermally altered sediments. The survey has revealed the presence of oxygenated compounds in samples with a high degree of thermal maturity. Phenols are one class of oxygenated compounds found in these samples. A group of methyl-, dimethyl- and trimethyl-isoprenoidyl phenols (C27-C29) is present in all of the seabed NSO fractions, with the methyl- and dimethyl-isoprenoidyl phenols occurring as major components, and a trimethyl-isoprenoidyl phenol as a minor component. A homologous series of n-alkylphenols (C13-C33) has also been found in the seabed petroleums. These phenols are most likely derived from the hydrothermal alteration of sedimentary organic matter. The n-alkylphenols are probably synthesized under hydrothermal conditions, but the isoprenoidyl phenols are probably hydrothermal alteration products of natural product precursors. The suites of phenols do not appear to be useful tracers of high temperature hydrothermal processes.

Non-NASA Center↗
NASA NTRS2001

The Biogeochemistry of Sulfur in Hydrothermal Systems

The incorporation of sulfur into many biomolecules likely dates back to the development of the earliest metabolic strategies. Sulfur is common in enzymes and co-enzymes and is an indispensable structural component in many peptides and proteins. Early metabolism may have been heavily influenced by the abundance of sulfide minerals in hydrothermal systems. The incorporation of sulfur into many biomolecules likely dates back to the development of the earliest metabolic strategies. Sulfur is common in enzymes and co-enzymes and is an indispensable structural component in many peptides and proteins. Early metabolism may have been heavily influenced by the abundance of sulfide minerals in hydrothermal systems. Understanding how sulfur became prevalent in biochemical processes and many biomolecules requires knowledge of the reaction properties of sulfur-bearing compounds. We have previously estimated thermodynamic data for thiols, the simplest organic sulfur compounds, at elevated temperatures and pressures. If life began in hydrothermal environments, it is especially important to understand reactions at elevated temperatures among sulfur-bearing compounds and other organic molecules essential for the origin and persistence of life. Here we examine reactions that may have formed amino acids with thiols as reaction intermediates in hypothetical early Earth hydrothermal environments. (There are two amino acids, cysteine and methionine, that contain sulfur.) Our calculations suggest that significant amounts of some amino acids were produced in early Earth hydrothermal fluids, given reasonable concentrations H2, NH3, H2S and CO. For example, preliminary results indicate that glycine activities as high as 1 mmol can be reached in these systems at 100 C. Alanine formation from propanethiol is also a favorable reaction. On the other hand, the calculated equilibrium log activities of cysteine and serine from propanethiol are -21 and -19, respectively, at 100 C. These results indicate that while amino acid formation with thiols as intermediates is favored in some cases, other mechanisms may have been necessary to produce significant amounts of other amino acids. Coupled with our previous results for thiols, these studies imply that sulfur may have been easily incorporated into the organic geochemistry of early Earth hydrothermal systems, leading to its widespread use in biomolecules. Formation of more complex biomolecules in hydrothermal systems may have required sulfur-bearing organic compounds as reaction intermediates.

Schulte, Mitchell↗
NASA NTRS2000

Geology and geochemistry of paleosols developed on the Hekpoort Basalt, Pretoria Group, South Africa

The Hekpoort paleosols comprise a regional paleoweathering horizon developed on 2.224 +/- 0.021 Ga basaltic andesite lavas at the top of the Hekpoort Formation of the Pretoria Group, Transvaal Supergroup, South Africa. In five separate profiles, from outcrops along road cuts near Waterval Onder and the Daspoort Tunnel and in three drill cores from the Bank Break Area (BB3, BB8, and BB14), the top of the paleosol is a sericite-rich zone. The sericite zone grades downward into a chlorite-rich zone. In core BB8 and in the road cut at the Daspoort Tunnel, we sampled the underlying or parent basaltic andesite into which the chlorite zone grades. We did not obtain samples of the parent material at Waterval Onder and in cores BB3 and BB14, but chemical analyses indicate that the chlorite and sericite zones in these profiles derive from underlying lavas similar to the ones we sampled in core BB8 and at the Daspoort Tunnel. The presence of apparent rip-up clasts of the paleosol in the overlying ironstones of the Strubenkop Formation in the cores from Bank Break makes it very unlikely that most of the alteration was a result of interactions with hydrothermal fluids. Desiccation cracks at the top of the paleosol that were filled with sand during the deposition of the overlying sediments at Waterval Onder point to a subaerial weathering origin. Very little, if any, Al, Ti, Zr, V, or Cr moved a discernible distance during weathering of any of the five profiles. The vertical distribution of Fe, Mg, Mn, Ni, and Co indicates that these elements were largely removed from the top of the soil during weathering. The overall abundance of these elements in each of the profiles indicates that a significant fraction of the complement lost from the top subsequently reprecipitated in the lower portion of the soil as constituents of an Fe2(+) -rich smectite. The loss of Fe from the top of the soil during weathering of the Hekpoort paleosols indicates that atmospheric PO2 was less than 8 x 10(-4) atm about 2.22 Ga. Fe2(+) -rich smectite should only precipitate during soil formation if atmospheric PCO2 is less than or equal to 2 x 10(-2) atm (Rye, Kuo, and Holland, 1995). Ca and Na were largely lost during weathering. Some Na was apparently added to the sericite zone in cores BB3, BB8, and BB14 after weathering. All five profiles are enriched in K and Rb, and most are enriched in Ba. The distribution of these elements indicates that they all were added during post-weathering hydrothermal metasomatism. Rb-Sr analysis of the paleosol at the Daspoort Tunnel indicates that metasomatism last affected that profile 1.925 +/- 0.032 Ga (Macfarlane and Holland, 1991).

Non-NASA Center↗
NASA NTRS1981

The mineralogy and the isotopic composition of sulfur in hydrothermal sulfide/sulfate deposits on the East Pacific Rise, 21 deg N latitude

The mineralogy and isotopic composition of sulfur found in hydrothermal deposits associated with five groups of vents along the ridge axis of the East Pacific Rise near 21 deg N latitude are investigated. Solid samples of mixed sulfides and sulfates from mounds, chimneys and the surrounding sediment as well as fresh basaltic glass were examined with a portable X-ray fluorescence spectrometer and by scanning electron microscopy, X-ray diffractometry, and electron microprobe analysis. For the three vents of exit temperature close to 350 C, the chimneys are found to be rich in copper sulfides, while for those of temperatures around 300 C, zinc sulfide is found to predominate. The major sulfides found in the chimneys include wurtzite, chalcopyrite, pyrite and cubanite, with anhydrite the dominant sulfate. Significant mineralogical differences are found between active and inactive vents. The isotopic composition of sulfur in anhydrites from active vents is observed to be close to that of sea water and consistent with a derivation from sea water sulfate. The isotopic composition of sulfur in the sulfide minerals is explained in terms of precipitation from solutions with reduced sulfur derived from basalts or basaltic magmas, and sea water sulfate. Finally, the deposits are interpreted as the results of the mixing of H2S-dominated hydrothermal fluids with cold sea water near the sea floor.

Styrt, M. M.↗
NASA NTRS1984

Carbon and its isotopes in mid-oceanic basaltic glasses

Sample surface carbon, mantle carbon dioxide in vesicles, and mantle carbon dissolved in glasses, are the three carbon components evident in the 11 mid-oceanic basalts presently analyzed. The total carbon content may be controlled by the depth of the shallowest ridge magma chamber, and carbon isotopic fractionation accompanies magma degassing. Using He-3 and carbon data for submarine hydrothermal fluids, the present day midoceanic ridge carbon flux is approximately estimated to be 1.0 x 10 to the 13th g C/yr, requiring 8 Gyr to accumulate the earth's present crustal carbon inventory.

Des Marais, D. J.↗