Analytical uncertainties in oxygen isotopic studies of hydrous silica have been investigated using a partial fluorination procedure in which fractional oxygen yields are achieved by reducing the amount of fluorine. Stepwise reaction of opaline silica results in a set of sequential oxygen fractions which show a wide range of δ18O values due to variable amounts of water, organic matter, and other impurities, δ-values for successive fractions in non-biogenic opal systematically increase as water is reacted away and then remain constant to within ±0.2%. as the remaining silica reacts, δ-values in biogenic silica increase similarly but then decrease when low 18O oxide(?) impurities begin to react.The troublesome water component in opal is readily removed by Stepwise fluorination. This technique allows more precise oxygen isotope analysis of non-biogenic opal-A, and may improve the analytical precision for biogenic silica and any silicate mineral containing a significant water component. 相似文献
The solubility of CO2CO fluids in a mid-ocean ridge basalt (morb) has been measured at 1200°C, 500–1500 bar, and oxygen fugacities between NNO and NNO-4. High oxygen fugacities, and thus CO2-rich fluids, were produced by using a starting material equilibrated at NNO, and Ag2C2O4 as the fluid source. Low oxygen fugacities were achieved by using graphite capsules, and MgCO3 as the fluid source. These graphite-saturated fluids have the lowest possibleC/O2CO ratio for a given pressure and temperature.
Experiments were run in a rapid-quench internally heated pressure vessel. Fluid compositions were measured using a simple vacuum technique and by Raman spectroscopy of fluid inclusions. The two techniques yielded comparable results. Fourier transform micro-infrared spectroscopy was used to identify and measure concentrations of dissolved volatiles in double-polished wafers of the quenched glasses. Carbonate was the only carbon-bearing species identified. Raman spectroscopic analysis of inclusion-free areas of glass confirmed the absence of dissolved molecular CO2, CO and carbon. The measured concentrations of dissolved CO2 in the glasses were proportional to the fugacity of CO2 during the experiments, calculated from the measured fluid compositions. The data were fit to the equationXCO2melt(ppm)= 0.492 fCO2 (bar).
The insolubility of CO, compared to CO2, may be related to the fact that dissolution of CO requires reduction of another species in the melt, whereas dissolution of CO2 does not. Due to the fact that CO will be an important component of natural CO fluids at low pressures and low oxygen fugacities, equilibrium dissolved CO2 contents will be less than calculated assuming pure CO2 fluids, but as theC/O2CO ratio in a pure CO fluid at fixed pressure and temperature is a direct function of oxygen fugacity, measurement of the oxygen fugacity of quenched glasses or trapped fluids in natural samples should allow saturation concentrations to be calculated. Dissolved CO2 contents of somemorb are less than expected if they were in equilibrium with pure CO2. These samples must, therefore, have been more reduced than average if they were fluid-saturated. Together with results from other studies of CO2 and H2O solubilities in basalt, the results of this study provide a comprehensive framework for modelling CO2 solution inmorb. 相似文献
Fifteen examples of quasi-periodic 2.8 GHz burst emission observed at the La Posta Astrogeophysical Observatory during the period December 1966 through May 1973 were identified. The periods of these events and those of 22 additional events previously reported in the literature were plotted against burst morphological parameters. The relationship between period and event energy was found to be considerably weaker than initially reported by Cribbens and Matthews. 相似文献
Rigorous equations in compact symbolic matrix notation are introduced to transform coordinates and velocities between ITRF
frames and modern GPS-based geocentric geodetic datums. The theory is general but, after neglecting higher than second-order
terms, it is shown that the equations revert to the formulation currently applied in most major continental datums. We discuss
several examples: the North American Datum of 1983 (NAD83), the European Terrestrial Reference System of 1989 (ETRS89), the Geodetic Datum of Australia of 1994 (GDA94), and the South American Geocentric Reference System (SIRGAS).
Electronic Publication 相似文献
Multiple indicators of sublethal stress (bioindicators) were used to assess the health and condition of two important estuarine fish species in the Pamlico Sound estuary following extensive flooding from three sequential hurricanes that occurred during early fall 1999. Bioindicators ranging from the biochemical to the reproductive and organism-level were used to assess the health of southern flounder and spot in Pamlico Sound compared to the health of these same species sampled from a relatively unaffected references site in lower Core Sound. Many of the physiological, reproductive, immunological, histopathological, and general condition indices suggested that both species, and particularly spot, in Pamlico Sound were sublethally stressed and in poorer condition than fish sampled from Core Sound. The major environmental stressors causing these sublethal stress responses in Pamlico Sound fish appears to be those related to episodic hypoxic exposure or a combination of effects associated with hypoxic conditions such as alterations in preferred habitat and food availability. Although fish populations in Pamlico Sound do not appear to be severely damaged or impaired at this time, organisms that are sublethally stressed can incur increased vulnerability to additional or future stressors such as modified physicochemical regimes, changes in food and habitat availability, and increases in infectious pathogens. Because of the low flushing rate (~1 yr) of Pamlico Sound, recovery rate may be exceptionally slow, prolonging any adverse effects of altered nutrient regimes (such as hypoxia) on the health and fitness of resident fish populations. Flooding from the 1999 hurricanes may have contributed to the short-term health and condition of finfish species in Pamlico Sound and also influenced longer-term recovery and ecological status of this system. Longer-term manifestation of effects from flooding may be of particular concern as the frequency of hurricanes is expected to increase over the next few years and the accelerated uses of the coastal zone places further stress on estuarine resources. 相似文献
The structures of deuterated pyrochroite, Mn(OD)2 and β−Cο(OD)2 have been refined using the Rietveld method and neutron powder diffraction data collected in an opposed-anvil high pressure
(Paris-Edinburgh) cell from room pressure to 9 GPa. The equation of state for Mn(OD)2 was determined (K=41(3) GPa for fixed K′=4.7) and found to be consistent with previous studies of the isostructural brucite,
Mg(OD)2. The compressibility of β−Cο(OD)2 on the other hand is apparently anomalous. The c-axis initially decreases at 3 times the rate of decrease of the a-axis; the ratio decreases to about 1.5 at an estimated 6 GPa before increasing again beyond this pressure. There is no obvious
corresponding anomaly in the details of the atomic structure. In both materials there is an increase in the D-site disorder
with pressure. A split-site model for the D-positions best fits the data at pressures above 8 GPa. There is no statistically
significant increase in the O-D interatomic distance at increased pressure while the hydrogen bonding interaction D...O appears
to increase as this distance decreases and the O-D...O angle increases. The intramolecular O-D bond valences, determined indirectly
from the intermolecular D...O distances, decrease steadily for both materials as pressure is increased.
Received: 31 October 1996 / Revised, accepted: 27 February 1997 相似文献
Uplift rates of the Loyalty Islands (S.W. Pacific) have been determined from dating of raised coral terraces standing 2 to 7.5 m above sea level. The ages of the terraces on Ouvéa and Lifou correspond closely to previously documented periods of high sea levels at 120,000 and 180,000 yr BP. A +2-m terrace on Beautemps-Beaupré is considered to be beyond the range of the dating technique. The uplift rates of the various islands show a decrease toward the west. This lends support to the hypothesis of a lithospheric bulge of the leading edge of the Australian plate prior to its subduction at the level of the New Hebrides trench. 相似文献
Plagioclase in the range An2-An10 in a relatively undeformed Quartz—feldspar pegmatite is compared with similar material in a strongly deformed and recrystallized shear zone. Optical and transmission electron microscope observations and chemical data are discussed in terms of established mechanisms of strain induced recrystallization.Recrystallization occurs by the formation of subgrains from recovery, and their subsequent growth by boundary migration or coalescence by rotation. It is suggested that the recrystallization and grain growth are enhanced by a small increase in the anorthite content. Peristerite formation in the recrystallized grains is associated with the migration of high angle boundaries under upper greenschist facies conditions. 相似文献