Diffuse gas emissions at the Ukinrek Maars,Alaska: Implications for magmatic degassing and volcanic monitoring     

William C. Evans  Deborah Bergfeld  Robert G. McGimsey  Andrew G. Hunt 《Applied Geochemistry》2009

Diffuse CO₂ efflux near the Ukinrek Maars, two small volcanic craters that formed in 1977 in a remote part of the Alaska Peninsula, was investigated using accumulation chamber measurements. High CO₂ efflux, in many places exceeding 1000 g m⁻² d⁻¹, was found in conspicuous zones of plant damage or kill that cover 30,000–50,000 m² in area. Total diffuse CO₂ emission was estimated at 21–44 t d⁻¹. Gas vents 3-km away at The Gas Rocks produce 0.5 t d⁻¹ of CO₂ that probably derives from the Ukinrek Maars basalt based on similar δ¹³C values (∼−6‰), ³He/⁴He ratios (5.9–7.2 R_A), and CO₂/³He ratios (1–2 × 10⁹) in the two areas. A lower ³He/⁴He ratio (2.7 R_A) and much higher CO₂/³He ratio (9 × 10¹⁰) in gas from the nearest arc-front volcanic center (Mount Peulik/Ugashik) provide a useful comparison. The large diffuse CO₂ emission at Ukinrek has important implications for magmatic degassing, subsurface gas transport, and local toxicity hazards. Gas–water–rock interactions play a major role in the location, magnitude and chemistry of the emissions.  相似文献   

Thermodynamic modeling assisted by multivariate statistical image analysis as a tool for unraveling metamorphic P-T-d evolution: an example from ilmenite-garnet-bearing metapelite of the Peloritani Mountains, Southern Italy     

Patrizia Fiannacca  Deborah Lo Pò  Gaetano Ortolano  Rosolino Cirrincione  Antonino Pezzino 《Mineralogy and Petrology》2012,106(3-4):151-171

An ilmenite-garnet-bearing schist from the medium-grade metapelite complex of the Mandanici Unit in the Peloritani Mountains has been investigated to constrain the P-T conditions attained in this sector of the southern European Hercynian chain. Microprobe investigations assisted by statistical handling of X-ray maps via principal component analysis allowed us to better elucidate the porphyroblast-matrix relationships, the geometry of the elemental distribution in garnet porphyroblasts and the average volume percentage of the reactant garnet during retrograde metamorphic evolution. Selected microprobe data were then used to constrain, by means of P-T pseudosections, the main P-T stages of the metamorphic evolution, using the XRF bulk-rock chemistry as the equilibrium chemical composition for the prograde and peak stages and an effective bulk-rock composition for the retrograde one. Peak metamorphic P-T estimates (~530?°C; 0.9?GPa) are consistent with a Hercynian crustal thickening stage at middle-lower crustal conditions, while subsequent evolution, constrained at 420–460?°C; 0.30–0.60?GPa, depicts a retrograde clockwise P-T trajectory linked to exhumation under likely extensional shearing conditions. The results obtained in this paper lead to envisage a new scenario for the crustal evolution of the Peloritani Mountains and stimulate a revision of previous interpretations in the light of the new investigation techniques.  相似文献   

Origin and Extent of Fresh Paleowaters on the Atlantic Continental Shelf, USA   总被引：3，自引：0，他引：3  

by Denis Cohen  Mark Person  Peng Wang  Carl W. Gable  Deborah Hutchinson  ee Marksamer  Brandon Dugan  Henk Kooi  Koos Groen  Daniel Lizarralde  Robert L. Evans  Frederick D. Day-Lewis  John W. Lane Jr. 《Ground water》2010,48(1):143-158

While the existence of relatively fresh groundwater sequestered within permeable, porous sediments beneath the Atlantic continental shelf of North and South America has been known for some time, these waters have never been assessed as a potential resource. This fresh water was likely emplaced during Pleistocene sea-level low stands when the shelf was exposed to meteoric recharge and by elevated recharge in areas overrun by the Laurentide ice sheet at high latitudes. To test this hypothesis, we present results from a high-resolution paleohydrologic model of groundwater flow, heat and solute transport, ice sheet loading, and sea level fluctuations for the continental shelf from New Jersey to Maine over the last 2 million years. Our analysis suggests that the presence of fresh to brackish water within shallow Miocene sands more than 100 km offshore of New Jersey was facilitated by discharge of submarine springs along Baltimore and Hudson Canyons where these shallow aquifers crop out. Recharge rates four times modern levels were computed for portions of New England's continental shelf that were overrun by the Laurentide ice sheet during the last glacial maximum. We estimate the volume of emplaced Pleistocene continental shelf fresh water (less than 1 ppt) to be 1300 km³ in New England. We also present estimates of continental shelf fresh water resources for the U.S. Atlantic eastern seaboard (10⁴ km³) and passive margins globally (3 × 10⁵ km³). The simulation results support the hypothesis that offshore fresh water is a potentially valuable, albeit nonrenewable resource for coastal megacities faced with growing water shortages.  相似文献   

The size of broad-line regions of low-luminosity active galactic nuclei     

Xue-Guang Zhang  Deborah Dultzin-Hacyan  Ting-Gui Wang 《Monthly notices of the Royal Astronomical Society》2007,374(2):691-696

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A Repository of Precision Flat Fields for High-Resolution MDI Continuum Data     

H. E. Potts  D. A. Diver 《Solar physics》2009,258(2):343-351

We describe an archive of high-precision MDI flat fields that can be used to refine most MDI high-resolution continuum data. The archive consists of many flat-field images representing different time ranges over the full operating period of SOHO. The residual flat-field error on the standard level 1.5/1.8 calibrated continuum images represents a significant proportion (25% – 100%) of the true data variation data on the quiet sun. Using the flat fields in this archive will reduce that error by a factor of 10 – 30, greatly increasing the accuracy of any tracking or photometric operations. The access, use and accuracy of these flat fields are described in this paper.  相似文献   

Isotopic and element exchange during serpentinization and metasomatism at the Atlantis Massif (MAR 30°N): Insights from B and Sr isotope data     

Chiara Boschi  Andrea Dini  Deborah S. Kelley 《Geochimica et cosmochimica acta》2008,72(7):1801-1823

The Lost City hydrothermal system at the southern Atlantis Massif (Mid-Atlantic Ridge, 30°N) provides a natural laboratory for studying serpentinization processes, the temporal evolution of ultramafic-hosted hydrothermal systems, and alteration conditions during formation and emplacement of an oceanic core complex. Here we present B, O, and Sr isotope data to investigate fluid/rock interaction and mass transfer during detachment faulting and exhumation of lithospheric sequences within the Atlantis Massif. Our data indicate that extensive serpentinization was a seawater-dominated process that occurred predominately at temperatures of 150-250 °C and at high integrated W/R ratios that led to a marked boron enrichment (34-91 ppm). Boron removal from seawater during serpentinization is positively correlated with changes in δ¹¹B (11-16‰) but shows no correlation with O-isotope composition. Modeling indicates that B concentrations and isotope values of the serpentinites are controlled by transient temperature-pH conditions. In contrast to prior studies, we conclude that low-temperature marine weathering processes are insignificant for boron geochemistry of the Atlantis Massif serpentinites. Talc- and amphibole-rich fault rocks formed within a zone of detachment faulting at temperatures of approximately 270-350 °C and at low W/R ratios. Talc formation in ultramafic domains in the massif was subsequent to an early stage of serpentinization and was controlled by the access of Si-rich fluids derived through seawater-gabbro interactions. Replacement of serpentine by talc resulted in boron loss and significant lowering of δ¹¹B values (9-10‰), which we model as the product of progressive extraction of boron. Our study provides new constraints on the boron geochemical cycle at oceanic spreading ridges and suggests that serpentinization associated with ultramafic-hosted hydrothermal systems may have important implications for the behavior of boron in subduction zone settings.  相似文献   

The non-oxidative dissolution of galena nanocrystals: Insights into mineral dissolution rates as a function of grain size, shape, and aggregation state   总被引：1，自引：0，他引：1  

Juan Liu  Deborah M. Aruguete  J. Donald Rimstidt 《Geochimica et cosmochimica acta》2008,72(24):5984-5996

The acidic, non-oxidative dissolution of galena (PbS) nanocrystals has been studied in detail using transmission electron microscopy (TEM) to follow the evolution of the size and shape of the nanocrystals before and after dissolution experiments, X-ray photoelectron spectroscopy (XPS) to follow particle chemistry, and dissolution rate analysis to compare dissolution rates between nanocrystalline and bulk galena. Dissolution characteristics were also studied as a function of nanocrystal access to bulk vs. confined solution due to the degree of proximity of next-nearest grains. Nearly monodisperse galena nanocyrstals with an average diameter of 14.4 nm were synthesized for this study, and samples were exposed to pH 3, deoxygenated HCl solutions for up to 3 h at 25 °C. Detailed XPS analysis showed the nanocrystals to be free of unwanted contamination, surface complexes, and oxidative artifacts, except for small amounts of lead-containing oxidation species in both pre- and post-dissolution samples which have been observed in fresh, natural bulk galena. Depending on the calculation methods used, galena nanocrystals, under the conditions of our experiments, dissolve at a surface area normalized rate of one to two orders of magnitude faster than bulk galena under similar conditions. We believe that this reflects the higher percentage of reactive surface area on nanocrystalline surfaces vs. surfaces on larger crystals. In addition, it was shown that {1 1 1} and {1 1 0} faces dissolve faster than {1 0 0} faces on nanocrystals, rationalized by the average coordination number of ions on each of these faces. Finally, dissolution was greatly inhibited for galena nanocrystal surfaces that were closely adjacent (1-2 nm, or less) to other nanocyrstals, a direct indication of the properties of aqueous solutions and ion transport in extremely confined spaces and relevant to dissolution variations that have been suspected within aggregates.  相似文献   

The Black Band Disease of Atlantic Reef Corals.   总被引：4，自引：0，他引：4  

Klaus  Rutzler  Deborah L.  Santavy Arnfried  Antonius 《Marine Ecology》1983,4(4):329-358

Abstract. The cyanophyte (Cyanobaclerium) that causes black band disease of Atlantic reef corals is described under the name Phormidium corallyticum , new species (family Oscillatoriaceae) , and its generic placement is discussed from the standpoint of the GEITLERian (classical) and D rouet systems. Distinguishing characters include densely interwoven filaments that form a blackish mat and trichomes without significant cell wall constrictions, almost isodiametric cells (4.2 μm mean width, 4.0μm mean length) tapering end cells, and thin (0.1 μm or less) mucilaginous wall coating. Transmission electron microscopy shows typical cyanophyte cell walls, sheath, nucleoplasm, and cytoplasmic inclusions, but an unusual thylakoid of straight, and, as seen in cell cross section, radiating lamellae. The dark coloration is due to a high concentration of phycocyanin and some phycoerythrin. The species is similar to Oscillatoria (= Phormidium) submembranacea , which differs in several morphological features and does not infect coral tissue. It is concluded that Phormidium should be used for this and related species that have external mucilage but not the distinct sheath found in Lyngbya.  相似文献   

Detection of mRNA sequences homologous to the human glutathione peroxidase and rat cytochrome P-450IVA1 genes in Mytilus edulis     

Peter Goldfarb  J.Andy Spry  Deborah Dunn  David Livingstone  Alan Wiseman  G.Gordon Gibson 《Marine environmental research》1989,28(1-4)

In this study we have used cloned gene probes for human glutathione peroxidase (GPX), rat cytochrome P-450IVA1 and rat cytochrome P-450IIE1 to detect homologous sequences in RNA from the hepato-pancreas of Mytilus edulis. The presence of sequences hybridising to the GPX and P-450IVA1 probes, but not to the P-450IIE1 probe, confirms the ancient origin of the former genes and indicates that conserved-sequence DNA probes from higher organisms can be used to examine the structure and function of genes of environmental interest in marine organisms.  相似文献   

Fault scarp identification in side-scan sonar and bathymetry images from the Mid-Atlantic Ridge using wavelet-based digital filters     

Sarah A. Little  Deborah K. Smith 《Marine Geophysical Researches》1996,18(6):741-755

Digital filters designed using wavelet theory are applied to high resolution deep-towed side-scan sonar data from the median valley walls, crestal mountains, and flanks of the Mid-Atlantic Ridge at 29°10 N. With proper tuning, the digital filters are able to identify the location, orientation, length, and width of highly reflective linear features in sonar images. These features are presumed to represent the acoustic backscatter from axis-facing normal faults. The fault locations obtained from the digital filters are well correlated with visual geologic interpretation of the images. The side-scan sonar images are also compared with swath bathymetry from the same area. The digitally filtered bathymetry images contain nine of the eleven faults identified by eye in the detailed geologic interpretation of the side-scan data. Faults with widths (measured perpendicular to their strike) of less than about 150 m are missed in the bathymetry analysis due to the coarser resolution of these data. This digital image processing technique demonstrates the potential of wavelet-based analysis to reduce subjectivity and labor involved in mapping and analyzing topographic features in side-scan sonar and bathymetric image data.  相似文献