Evaluation of silica-water surface chemistry using NMR spectroscopy     

Susan A. Carroll  Robert S. MaxwellWilliam Bourcier  Sue MartinSuzy Hulsey 《Geochimica et cosmochimica acta》2002,66(6):913-926

We have combined traditional batch and flow-through dissolution experiments, multinuclear nuclear magnetic resonance (NMR) spectroscopy, and surface complexation modeling to re-evaluate amorphous silica reactivity as a function of solution pH and reaction affinity in NaCl and CsCl solutions. The NMR data suggest that changes in surface speciation are driven by solution pH and to a lesser extent alkali concentrations, and not by reaction time or saturation state. The ²⁹Si cross-polarization NMR results show that the concentration of silanol surface complexes decreases with increasing pH, suggesting that silanol sites polymerize to form siloxane bonds with increasing pH. Increases in silica surface charge are offset by sorption of alkali cations to ionized sites with increasing pH. It is the increase in these ionized sites that appears to control silica polymorph dissolution rates as a function of pH. The ²³Na and ¹³³Cs NMR results show that the alkali cations form outersphere surface complexes and that the concentration of these complexes increases with increasing pH. Changes in surface chemistry cannot explain decreases in dissolution rates as amorphous silica saturation is approached. We find no evidence for repolymerization of the silanol surface complexes to siloxane complexes at longer reaction times and constant pH.  相似文献   

Controls on accumulation of a volcaniclastic fan,Ruapehu composite volcano,New Zealand     

Beth A Palmer  Andrew M Purves  Sue L Donoghue 《Bulletin of Volcanology》1993,55(3):176-189

The Whangaehu fan is the youngest sedimentary component on the eastern ring plain surrounding Ruapehu volcano. Fan history comprises constructional (830–200 years bp) and dissectional (<200 years bp) phases. The constructional phase includes four aggradational periods associated with both syneruptive and inter-eruptive behavior. All four aggradational periods began when deposition by large lahars changed flow conditions on the fan from channelized to unchannelized. Subsequent behavior was a function of the rate of sediment influx to the fan. The rate of sediment influx, in turn, was controlled by frequency and magnitude of volcanic eruptions, short-term climate change, and the amount of sediment stored on the volcano flanks. Fanwide aggradation occurred when rates of sediment influx and deposition on the fan were high enough to maintaìn unchannelized flow conditions on the fan surface. Maintenance of an undissected surface required sedimentation from frequent and large lahars that prevented major dissection between events. These conditions were best met during major eruptive episodes when high frequency and magnitude eruptions blanketed the volcano flanks with tephra and rates of lahar initiation were high. During major eruptive episodes, volcanism is the primary control on sedimentation. Climatic variations do not influence sediment accumulation. Local aggradation occurred when lahars were too small to maintain unchannelized flow across the entire fan. In this case, only the major channel system received much sediment following the deposition from the initial lahar. This localized aggradation occurred if (1) the sediment reservoir on the flank was large enough for floods to bulk into debris flows and (2) sedimentation events were frequent enough to maintain sediment supply to only some parts of the fan. These conditions were met during both minor eruptive and inter-eruptive episodes. In both cases, a large sediment reservoir remained on the volcano flanks from previous major eruptive intervals. Periods of increased storm activity produced floods that bulked to relatively small debris flows. When the sediment reservoir was depleted, the fan entered the present dissectional phase. Syneruptive and noneruptive lahars are mostly channelized and sediment bypasses the fan. Fan deposits are rapidly reworked. This is the present case at Ruapehu, even though the volcano is in a minor eruptive episode and the climate favors generation of intense storm floods.  相似文献   

Geology of the platanares geothermal area, Departamento de Copán, Honduras     

Grant Heiken  Napoleon Ramos  Wendell Duffield  John Musgrave  Kenneth Wohletz  Sue Priest  James Aldrich  Wilmer Flores  Alexander Ritchie  Fraser Goff  Dean Eppler  Carlos Escobar 《Journal of Volcanology and Geothermal Research》1991,45(1-2)

The Platanares geothermal area, Departamento de Copán, Honduras, is located within a graben that is complexly faulted. The graben is bounded on the north by a highland composed of Paleozoic (?) metamorphic rocks in contact with Cretaceous - Tertiary redbeds of unknown thickness. These are unconformably overlain by Tertiary andesitic lavas, rhyolitic ignimbrites, and associated sedimentary rocks. The volcanic rocks are mostly older than 14 Ma, and thus are too old to represent the surface expression of an active crustal magma body. Thermal fluids that discharge in the area are heated during deep circulation of meteoric water along faults in a region of somewhat elevated heat flow. Geothermometry based upon the chemical composition of thermal fluids from hot springs and from geothermal gradient coreholes suggests that the reservoir equilibrated at temperatures as high as 225 to 240°C, within the Cretaceous redbed sequence. Three continuously cored geothermal gradient holes have been drilled; fluids of about 165°C have been produced from two drilled along a NW-trending fault zone, from depths of 250 to 680 m. A conductive thermal gradient of 139°C/km, at a depth of 400 m, was determined from the third well, drilled 0.6 km west of that fault zone. These data indicate that the Platanares geothermal area holds considerable promise for electrical generation by moderate- to hightemperature geothermal fluids.  相似文献   

Assessing the health effects of climate change in Alaska with community-based surveillance     

David L. Driscoll  Erica Mitchell  Rebecca Barker  Janet M. Johnston  Sue Renes 《Climatic change》2016,137(3-4):455-466

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Quantification of strain rate in the Western Alps using geodesy: comparisons with seismotectonics   总被引：1，自引：0，他引：1  

Bastien Delacou  Christian Sue  Jean-Mathieu Nocquet  Jean-Daniel Champagnac  Cécile Allanic  Martin Burkhard 《Swiss Journal of Geoscience》2008,101(2):377-385

The contrasted seismotectonic regime of the Western Alps is characterized by radial extension in the high chain, combined with local compressive areas at the foothill of the belt, and everywhere occurrence of transcurrent tectonics. Here, we compare this seismotectonic regime to a large-scale compilation of GPS measurements in the Western Alpine realm. Our analysis is based on the raw GPS database, which give the measured velocity field with respect to the so called “stable Europe”, and an interpolated velocity field, in order to smooth the database on a more regular mesh. Both strain rate and rotational components of the deformation are investigated. The strain rate field shows patch-like structure, with extensional areas located in the core and to the North of the belt and compressional areas located in its periphery. Although the GPS deformation fields (both raw and interpolated) are more spatially variable than the seismotectonic field, a good qualitative correlation is established with the seismotectonic regionalization of the deformation. The rotation rate fields (both raw and interpolated) present counterclockwise rotations in the innermost part of the belt and a surprising continuous zone of clockwise rotations following the arc-shape geometry of the Western Alps along their external border. We interpret this new result in term of a counterclockwise rotation of the Apulia plate with respect to the stable Europe. This tectonic scheme may induce clockwise rotations of crustal block along the large strike-slip fault system, which runs in the outer part of the belt, from the Rhône-Simplon fault to the Belledonne fault and Southeastward, to the High-Durance and Argentera fault.  相似文献   

Merged remotely sensed data for geomorphological investigations in deserts: examples from central Saudi Arabia   总被引：1，自引：0，他引：1  

Farhan Al-juaidi†  rew C Millington†  Sue J Mclaren† 《The Geographical journal》2003,169(2):117-130

Image merging has gained acceptance in geological remote sensing, however it has rarely been applied in geomorphology. We report on the usefulness of principal components substitution (PCS) to merge IRS panchromatic data with multispectral Thematic Mapper (TM) imagery, to map commonly encountered desert geomorphological features, and in relative age dating of alluvial surfaces. The merged data were applied to the identification and mapping of geomorphological features along two geolo-gically different mountain fronts in central Saudi Arabia. Two types of geomorphological maps have been created. A morphogenetic map that distinguishes between aeolian landforms, fluvial landforms, desert pavements, and gypsum crusts. Second, a morphochronological map, which shows the relative age of four geomorphic surfaces developed on an alluvial fan. The construction of the two maps is supported by field observations and laboratory measurements. Using the optimum index factor (OIF), a TM band 1, 5 and 7 image (of 20 merged composites) was found to be the optimum colour composite image for the geomorphological features in this arid environment. We discuss our findings in the context of the spatial and spectral properties required for applied geomorphological remote sensing.  相似文献   

Data and debate     

Sue Bowler 《Astronomy& Geophysics》2003,44(3):3.08-3.12

Sue Bowler draws together some of the NAM scientific sessions, to capture the flavour of this lively and popular meeting.  相似文献   

Zur Deutung der Vertikalbewegungen der Festländer und Meere     

Franz E. Sueß 《International Journal of Earth Sciences》1920,11(1-4):144-168

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The kinetic interactions of metal ions with humic acids     

Gregory R. Choppin  Sue B. Clark   《Marine Chemistry》1991,36(1-4)

Complexation of europium (III) and UO₂²⁺ by humic acid was found to be very fast (< 1 m). However, passage through ion exchange resin removed a fraction which decreased as the contact time increased over a 2–3 day period. The dissociation kinetics for UO₂²⁺-humate were described by an equation with five first order terms with rate constants ranging from 40.6 m⁻¹ to 5.64×10⁻³ m⁻¹. The percentage of UO₂²⁺ dissociating by the slower paths, comparable to that eluting with the humic acid through the ion exchange resin is assigned to internal site-bound cations (strong binding). The faster dissociating fraction corresponded roughly to the UO₂²⁺ removed by the cation exchange resin (weak binding). The time dependence of the weak to strong binding ratio was associated with change in the conformation of the macromolecular humic acid as the cations neutralized the charge repulsions of the anionic humate.  相似文献   

CO2 release due to impact devolatilization of carbonate: Results of shock experiments          下载免费PDF全文

Mary Sue Bell 《Meteoritics & planetary science》2016,51(4):619-646

A study of pure, single crystal calcite shocked to pressures from 9.0 to 60.8 GPa was conducted to address contradictory data for carbonate shock behavior. The recovered materials were analyzed optically and by transmission electron microscopy (TEM), as well as by thermogravimetry (TGA), X‐ray diffraction (XRD), and Raman‐spectroscopy. In thin section, progressive comminution of calcite is observed although grains remain birefringent to at least 60.8 GPa. TGA analysis reveals a positive correlation between percent of mass loss due to shock and increasing shock pressure (R = 0.77) and suggests that shock loading leads to the modest removal of structural volatiles in this pressure range. XRD patterns of shocked Iceland spar samples produce peaks that are qualitatively and quantitatively less intense, more diffuse, and shift to lower ^o2θ. However, the regularity observed in these shocked powder patterns suggests that structures with very uniform unit cell separations persist to shock pressures as high as 60.8 GPa. Raman spectral analyses indicate no band asymmetry and no systematic peak shifting or broadening. TEM micrographs display progressively diminishing crystallite domain sizes. Selected area electron diffraction (SAED) patterns reveal no signatures of amorphous material. These data show that essentially intact calcite is recovered at shock pressures up to 60.8 GPa with only slight mass loss (~7%). This work suggests that the amount of CO₂ gas derived from shock devolatilization of carbonate by large meteorite impacts into carbonate targets has been (substantially) overestimated.  相似文献