Search results for "volcan"
showing 10 items of 899 documents
In situ and experimental evidence for acidic weathering of rocks and soils on Mars
2006
Experimental data for alteration of synthetic Martian basalts at pH=0-1 indicate that chemical fractionations at low pH are vastly different from those observed during terrestrial weathering. Rock analyses from Gusev crater are well described by the relationships apparent from low pH experimental alteration data. A model for rock surface alteration is developed which indicates that a leached alteration zone is present on rock surfaces at Gusev. This zone is not chemically fractionated to a large degree from the underlying rock interior, indicating that the rock surface alteration process has occurred at low fluid-to-rock ratio. The geochemistry of natural rock surfaces analyzed by APXS is c…
Characterization and petrologic interpretation of olivine-rich basalts at Gusev Crater, Mars
2006
Rocks on the floor of Gusev crater are basalts of uniform composition and mineralogy. Olivine, the only mineral to have been identified or inferred from data by all instruments on the Spirit rover, is especially abundant in these rocks. These picritic basalts are similar in many respects to certain Martian meteorites (olivine-phyric shergottites). The olivine megacrysts in both have intermediate compositions, with modal abundances ranging up to 20-30%. Associated minerals in both include low-calcium and high-calcium pyroxenes, plagioclase of intermediate composition, iron-titanium-chromium oxides, and phosphate. These rocks also share minor element trends, reflected in their nickel-magnesiu…
Lithologic composition of the Earth's continental surfaces derived from a new digital map emphasizing riverine material transfer
2005
[1] A new digital map of the lithology of the continental surfaces is proposed in vector mode (n ≈ 8300, reaggregated at 0.5° × 0.5° resolution) for 15 rock types (plus water and ice) targeted to surficial Earth system analysis (chemical weathering, land erosion, carbon cycling, sediment formation, riverine fluxes, aquifer typology, coastal erosion). These types include acid (0.98% at global scale) and basic (5.75%) volcanics, acid (7.23%) and basic (0.20%) plutonics, Precambrian basement (11.52%) and metamorphic rocks (4.07%), consolidated siliciclastic rocks (16.28%), mixed sedimentary (7.75%), carbonates (10.40%), semi- to un-consolidated sedimentary rocks (10.05%), alluvial deposits (15…
Worldwide distribution of continental rock lithology: Implications for the atmospheric/soil CO2uptake by continental weathering and alkalinity river …
2003
[1] The silicate rock weathering followed by the formation of carbonate rocks in the ocean, transfers CO2 from the atmosphere to the lithosphere. This CO2 uptake plays a major role in the regulation of atmospheric CO2 concentrations at the geologic timescale and is mainly controlled by the chemical properties of rocks. This leads us to develop the first world lithological map with a grid resolution of 1° × 1°. This paper analyzes the spatial distribution of the six main rock types by latitude, continents, and ocean drainage basins and for 49 large river basins. Coupling our digital map with the GEM-CO2 model, we have also calculated the amount of atmospheric/soil CO2 consumed by rock weathe…
Hydrogen in the gas plume of an open-vent volcano, Mount Etna, Italy
2011
[1] We report here on the first hydrogen determinations in the volcanic gas plume of Mount Etna, in Italy, which we obtained during periodic field surveys on the volcano's summit area with an upgraded MultiGAS. Using a specific (EZT3HYT) electrochemical sensor, we resolved H2 concentrations in the plume of 1–3 ppm above ambient (background) atmosphere and derived H2-SO2 and H2-H2O plume molar ratios of 0.002–0.044 (mean 0.013) and 0.0001–0.0042 (mean 0.0018), respectively. Taking the above H2-SO2 ratios in combination with a time-averaged SO2 flux of 1600 Gg yr−1, we evaluate that Etna contributes a time-averaged H2 flux of ∼0.65 Gg yr−1, suggesting that the volcanogenic contribution to the…
Overview of the Spirit Mars Exploration Rover Mission to Gusev Crater: Landing site to Backstay Rock in the Columbia Hills
2006
Spirit landed on the floor of Gusev Crater and conducted initial operations on soil covered, rock-strewn cratered plains underlain by olivine-bearing basalts. Plains surface rocks are covered by wind-blown dust and show evidence for surface enrichment of soluble species as vein and void-filling materials and coatings. The surface enrichment is the result of a minor amount of transport and deposition by aqueous processes. Layered granular deposits were discovered in the Columbia Hills, with outcrops that tend to dip conformably with the topography. The granular rocks are interpreted to be volcanic ash and/or impact ejecta deposits that have been modified by aqueous fluids during and/or after…
Soil sedimentology at Gusev Crater from Columbia Memorial Station to Winter Haven
2008
[1] A total of 3140 individual particles were examined in 31 soils along Spirit's traverse. Their size, shape, and texture were quantified and classified. They represent a unique record of 3 years of sedimentologic exploration from landing to sol 1085 covering the Plains Unit to Winter Haven where Spirit spent the Martian winter of 2006. Samples in the Plains Unit and Columbia Hills appear as reflecting contrasting textural domains. One is heterogeneous, with a continuum of angular-to-round particles of fine sand to pebble sizes that are generally dust covered and locally cemented in place. The second shows the effect of a dominant and ongoing dynamic aeolian process that redistributes a un…
Composition-resolved size distributions of volcanic aerosols in the Mt. Etna plumes
2008
Particle size distributions for soluble and insoluble species in Mt. Etna's summit plumes were measured across an extended size range (10 nm < d < 100 μm) using a combination of techniques. Automated scanning electron microscopy (QEMSCAN) was used to chemically analyze many thousands of insoluble particles (collected on pumped filters) allowing the relationships between particle size, shape, and composition to be investigated. The size distribution of fine silicate particles (d < 10 μm) was found to be lognormal, consistent with formation by bursting of gas bubbles at the surface of the magma. The compositions of fine silicate particles were found to vary between magmatic and nearl…
Geogenic and atmospheric sources for volatile organic compounds in fumarolic emissions from Mt. Etna and Vulcano Island (Sicily, Italy)
2012
[1] In this paper, fluid source(s) and processes controlling the chemical composition of volatile organic compounds (VOCs) in gas discharges from Mt. Etna and Vulcano Island (Sicily, Italy) were investigated. The main composition of the Etnean and Volcano gas emissions is produced by mixing, to various degrees, of magmatic and hydrothermal components. VOCs are dominated by alkanes, alkenes and aromatics, with minor, though significant, concentrations of O-, S- and Cl(F)-substituted compounds. The main mechanism for the production of alkanes is likely related to pyrolysis of organic-matter-bearing sediments that interact with the ascending magmatic fluids. Alkanes are then converted to alken…
Variation of H2O/CO2and CO2/SO2ratios of volcanic gases discharged by continuous degassing of Mount Etna volcano, Italy
2008
[1] We applied the Multi-GAS technique to measure compositions of the volcanic plumes continuously discharged from summit craters of Voragine, Northeast and Bocca Nuova at Mount Etna, in an attempt to estimate compositions of the source volcanic gases. The estimated CO2/SO2 and H2O/CO2 ratios of the volcanic gases show a large variation ranging from 0.6 to 30 and from 1 to 18, respectively. This variability overlaps with the compositional range of dissolved volatiles in melt inclusions and their coexisting bubbles in a magma chamber and can be caused by the low-pressure degassing of a magma with variable bubble content ranging from 0.3 to 15 wt.%. The variable bubble content in the magma is…