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The peralkaline Kaffo albite—riebeckite granite is an albitised, low-temperature intrusion in Liruei Complex, one of the oldest of the ring-complexes in the Younger Granite province of Nigeria. Analyses of borehole samples from different parts of the intrusion show it to be compositionally heterogeneous, especially in respect of Si, Al, Na, K and F distribution and this, in part, can be correlated with the variable degree of albitisation. Isotopically the granite is a normal plutonic type with δ18 O values of , and albitisation does not seem to have been accompanied by exchange of isotopes between albitising fluid and the granite. Co-existing riebeckitic-arfvedsonite and aegirine pairs from borehole samples show extreme enrichment in Na and Fe; the amphibole also shows considerable substitution of Fe by Ti, Zn and Mn, and of OH by F. Isotopically the amphibole and pyroxene are different from others, having low, variable δ18 O values (+5.3–+6.4 and , respectively), and the fractionation value Δ Px — Am is always large, negative and constant (—). The low δ18 O values are considered to be due to special features of the crystal chemistry of the alkali amphiboles and pyroxenes, and the spread of each set of values may be due to sub-solidus isotope exchange between the minerals and albitising fluid. 相似文献
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Ken Durham 《Natural Hazards》2003,30(2):251-261
Cairns is exposed to the well-known natural hazards oftropical cyclone, flood, stormsurge and thunderstorm, but is also exposed to thelesser-known hazards of landslip, earthquake and dam break flooding. Recommendations fortreating the risks associated with these hazards have been made that will involve amulti-disciplinary approach to treatment strategies, require the cooperation of allthree levels of government, involve public utility authorities and private enterprise andinvolve the community as a whole.This paper summarises the suggested mitigation treatmentoptions, presented to the Cairns City Council and identified in the LocalGovernment Disaster Mitigation Project conducted in Cairns in 1999/2000 by theQueensland Department of Emergency Services. 相似文献
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Understanding the relative impacts of natural processes and human activities on the hydrology of the Central Rift Valley lakes,East Africa 
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下载免费PDF全文 Significant changes have been observed in the hydrology of Central Rift Valley (CRV) lakes in Ethiopia, East Africa as a result of both natural processes and human activities during the past three decades. This study applied an integrated approach (remote sensing, hydrologic modelling, and statistical analysis) to understand the relative effects of natural processes and human activities over a sparsely gauged CRV basin. Lake storage estimates were calculated from a hydrologic model constructed without inputs from human impacts such as water abstraction and compared with satellite‐based (observed) lake storage measurements to characterize the magnitude of human‐induced impacts. A non‐parametric Mann–Kendall test was used to detect the presence of climatic trends (e.g. a decreasing or increasing trends in precipitation), while the Standard Precipitation Index (SPI) analysis was used to assess the long‐term, inter‐annual climate variability within the basin. Results indicate human activities (e.g. abstraction) significantly contributed to the changes in the hydrology of the lakes, while no statistically significant climatic trend was seen in the basin, however inter‐annual natural climate variability, extreme dryness, and prolonged drought has negatively affected the lakes. The relative contributions of natural and human‐induced impacts on the lakes were quantified and evaluated by comparing hydrographs of the CRV lakes. Lake Abiyata has lost ~6.5 m in total lake height between 1985 and 2006, 70% (~4.5 m) of the loss has been attributed to human‐induced causes, whereas the remaining 30% is related to natural climate variability. The relative impact analysis utilized in this study could potentially be used to better plan and create effective water‐management practices in the basin and demonstrates the utility of this integrated methodology for similar studies assessing the relative natural and human‐induced impacts on lakes in data sparse areas. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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Thirty-one single crystals of synthetic forsterite, Fo100, were deformed in 69 compressional creep tests in a 0.1-MPa confining atmosphere of H2 + Ar. Temperature ranged from 1753 to 2023 K and stress σ (= σ1 - σ3) from 1.5 to 37.8 MPa. Steady-state creep under these conditions follows an empirical law of the form: strain rate where A, n, and Q are constants. General characteristics of Fo100 creep — uniformity of strain, shape change as a function of orientation of σ, relative deformation resistance of different orientations — match those of natural olivine single crystals of composition Fo92. Specific constants in the flow law, however, are distinctly new: for σ oriented along [111]c (equidistant from the three principal crystallographic axes), values for Fo100 are n = 2.9 ± 0.2 and Q = 0.67 ± 0.03 MJ/mol (160 ± 7 kcal/mol). A single law covers the range 3 < σ < 30 MPa and 1753 < T < 1953 K. Steady-state deformation is preceded by a transient period of strain softening. High strain rates at σ ? 10 MPa render the transient barely resolvable; it apparently displaces the steady-state flow law by approximately ?0.5% in strain. At σ ? 7.8 MPa, the amount of strain imparted to a sample of the [101]c orientation is typically <0.1% after one hour. 相似文献
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Clifford E. Singer T. S. Gopi Rethinaraj Samuel Addy David Durham Murat Isik Madhu Khanna Brandon Kuehl Jianding Luo Wilma Quimio Kothavari Rajendran Donna Ramirez Ji Qiang Jürgen Scheffran T. Nedjla Tiouririne Junli Zhang 《Climatic change》2008,88(3-4):309-342
Probability distributions for carbon burning, atmospheric CO2, and global average temperature are produced by time series calibration of models of utility optimization and carbon and heat balance using log-linear production functions. Population growth is used to calibrate a logistically evolving index of development that influences production efficiency. Energy production efficiency also includes a coefficient that decreases linearly with decreasing carbon intensity of energy production. This carbon intensity is a piecewise linear function of fossil carbon depletion. That function is calibrated against historical data and extrapolated by sampling a set of hypotheses about the impact on the carbon intensity of energy production of depleting fluid fossil fuel resources and increasing cumulative carbon emissions. Atmospheric carbon balance is determined by a first order differential equation with carbon use rates and cumulative carbon use as drivers. Atmospheric CO2 is a driver in a similar heat balance. Periodic corrections are included where required to make residuals between data and model results indistinguishable from independently and identically distributed normal distributions according to statistical tests on finite Fourier power spectrum amplitudes and nearest neighbor correlations. Asymptotic approach to a sustainable non-fossil energy production is followed for a global disaggregation into a tropical/developing and temperate/more-developed region. The increase in the uncertainty of global average temperature increases nearly quadratically with the increase in the temperature from the present through the next two centuries. 相似文献
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Creep properties of single crystals of pure forsterite are compared with an earlier study on natural crystals of iron-bearing olivine (Fo92). The two compositions are found to have almost identical creep properties for the orientation, stresses and temperatures that were tested, forsterite being harder at comparable strain rate by approximately 14% in stress. These results can be interpreted to mean that iron is not an important creep variable for the single-crystal orientation, temperatures, and stress levels tested. However, possible differences between these specimens in hydrogen content and other impurities introduce ambiguities into this interpretation. 相似文献
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O. Jaoul C. Froidevaux W.B. Durham M. Michaut 《Earth and Planetary Science Letters》1980,47(3):391-397
The diffusivity of18O in forsterite Mg2SiO4 has been measured in the temperature range 1150–1600°C. The activation energy of oxygen self-diffusion in this silicate is found to equal0.32 ± 0.04MJ/mol(77 ± 10kcal/mol), and there is no dependence of the diffusivity upon the oxygen partial pressure surrounding the samples. The diffusion profiles were analysed either with an ion probe or by means of the18O(p, α)15N nuclear reaction. The latter method made use of a resonance in the nuclear cross-section in the case of diffusion profiles shorter than 100 nm (1000Å); for diffusion profiles up to 4 μm the same reaction was used, but in a non-resonant mode. New data on creep in forsterite and natural olivine are also given, including the influence of the oxygen partial pressurepO2 which is zero for forsterite and proportional to(pO2)16 for natural olivine. From this set of data we infer the possible relationship between diffusion and creep for these materials. This relationship may be more complicated than that predicted by simple climb mechanism. 相似文献
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A high-resolution underwater acoustic pulse-Doppler navigation system has been developed and tested at sea. The system provides continuous, highly accurate tracking of underwater and ocean-surface platforms in a fixed 50-km2navigation net. Three reference buoys, moored 20 m from the ocean bottom, provide the navigation net used by shipboard processing equipment. Each reference buoy contains an acoustic transponder, used to obtain the acoustic travel times from the transponder to the platform, and a continuous-tone beacon, used to obtain the Doppler shift due to platform motion. The system is capable of determining the position of a platform with respect to the reference net with an error of 2-3 m. The relative position of the platform on a fix-to-fix basis can be determined within several centimeters over short time intervals (approx 10 min). 相似文献