A lunar rock of deep crustal origin: sample 76535     

R Gooley  Robin Brett  Jeff Warner  J.R Smyth 《Geochimica et cosmochimica acta》1974,38(9):1329-1339

Lunar sample 76535 is a coarse-grained troctolitic granulite exhibiting a texture indicative of long annealing times. It is composed of homogeneous crystals of plagioclase (58 per cent, An₉₆), olivine (37 per cent, Fo₈₈) and bronzite (4 per cent, En₈₆).Chromian spinel-bronzite-diopside (Wo₄₆En₅₀Fs₄) symplectic intergrowths commonly occur along olivine-plagioclase boundaries and as tiny inclusions within olivine grains. These symplectites apparently formed by a reaction of the type: . The reaction is related to the experimentally determined reaction of Kushiro and Yoder (1966). The enstatite content of the diopside coexisting with the bronzite indicates equilibration at about 1000°C. Thermodynamic calculations for 1000°C indicate that the symplectites formed at a minimum pressure of about 0.6 kb. Low alumina contents of the pyroxenes indicate equilibration near this minimum pressure.Clusters of the same assemblage found in the symplectic intergrowths, but containing accessory metal, troilite, Ca-phosphates, baddeleyite, plagioclase and/or K-feldspar occur sporadically throughout the rock. These apparent late stage products crystallized in the low temperature-high pressure region discussed above.Phase relations of co-existing metal phases indicate that the rock cooled at a few tens of degrees/my, corresponding to depths of 10–20 km below the lunar surface, in agreement with the above pressure estimate.We infer that 76535 represents an original cumulate deposited at a depth between about 10 and 30 km. The last liquid crystallized in the relatively high pressure-low temperature field opx + cpx + Al-Mg-chromite. Cooling was extremely slow and accompanied by extensive chemical and textural re-equilibration. Reaction to form the symplectites occurred during the late stages of re-equilibration.  相似文献   

Structural fabric of the Central Metasedimentary Belt of southern Ontario, Canada, from deep seismic profiling   总被引：1，自引：0，他引：1  

C.R. O'Dowd  D. Eaton  D. Forsyth  H.W. Asmis 《Tectonophysics》2004,388(1-4):145

The Central Metasedimentary Belt boundary tectonic zone (CMBbtz) is a 10–20-km-wide zone of intense structural deformation within the 1.3–1.0 Ga Grenville orogen of southeastern Canada. The crustal structure of the exposed CMBbtz has been well studied, but its sub-Phanerozoic location and geometry beneath the urban development and nuclear stations of the Toronto region are not well known. A new 75-km Lithoprobe reflection profile acquired close to Toronto provides a clear image of the CMBbtz as a panel of southeast-dipping reflections that extends with moderate dip (<25°) to mid-crustal depth (25 km). These dipping reflections truncate and (or) overprint a subhorizontal band of reflectivity at 21 km depth. The seismic line is oblique to the major structural trends; cross-dip analysis shows that the southeast-dipping reflections have a strike and dip of N13°E and 25°, whereas the “subhorizontal” reflections strike and dip at N65°E and 20°, respectively. Both of these bands of reflectivity can be correlated to magnetic anomalies in the CMBbtz or its immediate footwall. Magnetic anomalies with similar strike directions are well expressed within a distinct rhomboid-shaped region (106×109 km) in the subsurface of western Lake Ontario, herein named Mississauga domain. Taken together, the seismic and magnetic data are inconsistent with existing models, in which the CMBbtz is extrapolated beneath Lake Ontario along a linear magnetic anomaly. We propose a revised subsurface trace of the CMBbtz along the western edge of the Mississauga domain. Small earthquakes in western Lake Ontario appear to cluster along trends co-linear with ENE magnetic anomalies, suggesting a possible degree of basement tectonic control on local intraplate seismicity.  相似文献   

Backscattering from spherical elastic inclusions and accuracy of the Kirchhoff approximation for curved interfaces     

David W. Eaton 《Geophysical Journal International》2006,166(3):1249-1258

The Kirchhoff (or tangent plane) approximation, derived from the theoretically complete Kirchhoff–Helmholtz integral representation for the seismic wavefield, has been used extensively for the analysis of seismic-wave scattering from irregular interfaces; however, the accuracy of this method for curved interfaces has not been rigorously established. This paper describes an efficient Kirchhoff algorithm to simulate scattered waves from an arbitrarily curved interface in an elastic medium. Synthetic seismograms computed using this algorithm are compared with exact synthetics computed using analytical formulae for scattering of plane P waves by a spherical elastic inclusion. A windowing technique is used to remove strong internal reverberations from the analytical solution. Although the Kirchhoff method tends to underestimate the total scattering intensity, the accuracy of the approximation improves with increasing value of the wavenumber-radius product, kR . The arrival times and pulse shapes of primary reflections from the sphere are well approximated using the Kirchhoff approach regardless of curvature of the scattering surface, but the amplitudes are significantly underestimated for kR ≤ 5. The results of this work provide some new guidelines to assess the accuracy of Kirchhoff-synthetic seismograms for curved interfaces.  相似文献   

LNAPL Volume Calculation: Parameter Estimation by Nonlinear Regression of Saturation Profiles     

Paul D. Lundegard  Brett S. Mudford 《Ground Water Monitoring & Remediation》1998,18(3):88-93

An estimation of the volume of light nonaqueous phase liquids (LNAPL) is often required during site assessment, remedial design, or litigation. LNAPL volume can be estimated by a strictly empirical approach whereby core samples, distributed throughout the vertical and lateral extent of LNAPL, are analyzed for LNAPL content, and these data are then integrated to compute a volume. Alternatively, if the LNAPL has obtained vertical equilibrium, the thickness of LNAPL in monitoring wells can be used to calculate of LNAPL in monitoring wells can be used to calculate LNAPL volume at the well locations if appropriate soil and LNAPL properties can be estimated.
A method is described for estimating key soil and LNAPL properties by nonlinear regression of vertical profiles of LNAPL saturation. The methods is relatively fast, cost effective, and amenable to quantitative analysis of uncertainty. Optionally, the method allows statistical determination of best-fit values for the Van Genuchten capillary parameters (n, α_oil-water and α_oil-air), residual water saturation and ANAPL density. The sensitivity of the method was investigated by fitting field LNAPL saturation profiles and then determining the variation in misfit (mean square residual) as a function of parameter value for each parameter. Using field data from a sandy aquifer, the fitting statistics were found to be highly sensitive to LNAPL density, α_oil-water and α_oil-air moderately sensitive to the Van Genuchten n value, and weakly sensitive to residual water saturation. The regression analysis also provides information that can be used to estimate uncertainty in the estimated parameters, which can then be used to estimate uncertainty in calculated values of specific volume.  相似文献   

Biological and Physical Attenuation of Endocrine Disruptors and Pharmaceuticals: Implications for Water Reuse   总被引：2，自引：0，他引：2  

Shane A. Snyder  Joseph Leising  Paul Westerhoff  Yeomin Yoon  Heath Mash  Brett Vanderford 《Ground Water Monitoring & Remediation》2004,24(2):108-118

A select group of endocrine disrupters, pharmaceuticals, and personal care products was studied to determine the degree of biological attenuation in water reuse applications. Laboratory investigations involved both batch reactors using biologically active sand and continuous flow simulated aquifer storage and recovery experiments. All laboratory experiments were conducted using Colorado River water spiked with various target compounds at concentrations between 10 and 100 ng/L. Field studies were also conducted to determine the occurrence and attenuation of target compounds in water reuse applications. Two golf courses irrigated with reuse water were studied to determine if turf applications led to contamination of nearby ground water. A waste water treatment facility that uses rapid infiltration basins seasonally was also tested to determine the degree of attenuation of detectable target compounds along a subsurface flowpath. A qualitative structural activity relationship model was applied to the target compounds to predict the general rate of aerobic biological degradation. Significant attenuation of many target compounds was observed in both laboratory and field experiments. Conversely, several compounds displayed limited removal during these studies. Field experiments were limited to detectable compounds and various nonbiological removal or concentration effects that may impact data interpretations, which are discussed in this paper. The predictive model was found to be moderately accurate within the confines of the project scope.  相似文献   

Symplectic integrators for long-term integrations in celestial mechanics     

Brett Gladman  Martin Duncan  Jeff Candy 《Celestial Mechanics and Dynamical Astronomy》1991,52(3):221-240

We discuss the use of symplectic integration algorithms in long-term integrations in the field of celestial mechanics. The methods' advantages and disadvantages (with respect to more common integration methods) are discussed. The numerical performance of the algorithms is evaluated using the 2-body and circular restricted 3-body problems. Symplectic integration methods have the advantages of linear phase error growth in the 2-body problem (unlike most other methods), good conservation of the integrals of the motion, good performance for moderately eccentric orbits, and ease of use. Its disadvantages include a relatively large number of force evaluations and an inability to continuously vary the step size.  相似文献   

Scaling and regionalization of flood flows in British Columbia,Canada     

Brett Eaton  Michael Church  Darren Ham 《水文研究》2002,16(16):3245-3263

A regionalization of flood data in British Columbia reveals a common scaling with drainage area over the range 0·5×10²<A_d<10⁴ km². This scaling is not a function of flood return period, which implies that simple scaling—consistent with a snowmelt‐dominated flow regime—applies to the province. The observed scale relation takes the form , similar to values reported in previous studies. The scaling relation identified was used to define the regional pattern of hydroclimatic variability for flood flows in British Columbia after discounting the effect of drainage area. The pattern was determined by kriging a scale‐independent runoff factor k for the mean annual flood, 5 year flood and 20 year flood. The analysis permits quantification of uncertainty of the estimates, which can be used in conjunction with the mapped k‐fields to calculate a mean and range for floods with the identified return period for ungauged basins. Owing to the sparsity of data, the precision is relatively poor. The standard error is generally less than 75% of the estimate in the southern half of the province, whereas in the northern half it is often between 75 and 100%. Examination of the relative increase in flood magnitude with increasing return period reveals spatially consistent but statistically insignificant differences. Flood magnitude tends to increase more rapidly in the western regions, where rain events may contribute to flood generation. The relative increase in flood magnitude with return period is consistently lower in the eastern mountain ranges, where snowmelt dominates the flood flow regime. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Development and validation of biocriteria using benthic macroinvertebrates for North Carolina estuarine waters     

Eaton L 《Marine pollution bulletin》2001,42(1):23-30

Biological criteria were developed to assess water quality in mesohaline and polyhaline estuarine waters in North Carolina. The criteria used a combination of three metrics: a new 'Hilsenhoff-type' biotic index incorporating the sensitivity to pollution of each taxon and its relative abundance, total number of taxa, and number of amphipod and caridean shrimp taxa. Agreement with an independent data set was 90%, as was within site repeatability of this biocriteria over a range of water qualities and salinities. The versatility of the biotic index is discussed relative to other sampling methods and in other parts of the world.  相似文献   

Spatial Analysis of Environmental Change Impacts on Wheat Production in Mid-Lower North, South Australia   总被引：1，自引：0，他引：1  

Qunying Luo  Brett Bryan  William Bellotti  Martin Williams 《Climatic change》2005,72(1-2):213-228

Three environmental change scenarios (the best scenario, the most likely scenario and the worst scenario) were used by the APSIM (Agricultural Production System sIMulator) Wheat module to study the possible impacts of future environmental change (climate change plus pCO₂ change) on wheat production in the Mid-Lower North of South Australia. GIS software was used to manage spatial-climate data and spatial-soil data and to present the results. Study results show that grain yield (kg ha⁻¹) was adversely affected under the worst environmental change scenario (−100% ∼ −42%) and the most likely environmental change scenario (−58% ∼ −3%). Grain nitrogen content (% N) either increased or decreased depending on the environmental change scenarios used and climate divisions (−25% ∼ +42%). Spatial variability was found for projected impact outcomes within climate divisions indicating the necessity of including the spatial distribution of soil properties in impact assessment.  相似文献   

Climate-change impacts on sagebrush habitat and West Nile virus transmission risk and conservation implications for greater sage-grouse     

Anne Schrag  Sarah Konrad  Scott Miller  Brett Walker  Steve Forrest 《GeoJournal》2011,76(5):561-575

Greater sage-grouse (Centrocercus urophasianus) are threatened by loss of sagebrush habitat and the spread of West Nile virus throughout much of their range in North America; yet, future impacts of climate change on these potential stressors have not been addressed. Here, we aim to quantify the potential impacts of climate change on the distribution of climatically suitable habitat for sagebrush and on transmission risk for West Nile virus in the eastern portion of the species’ range. We used Maxent to model the current and future climatically suitable habitat for two dominant sagebrush species in the study area, and we used a degree-day model to predict future West Nile virus transmission risk under likely climate-change scenarios. Our models suggest that areas with the highest future suitability for sagebrush habitat will be found in southwestern Wyoming and north-central Montana. The degree-day model suggests that greater sage-grouse in western portions of the study area, which are generally higher in elevation than where West Nile virus currently occurs, will see increasing risk of transmission in the future. We developed a spatially explicit map of suggested management actions based on our predictions that will aid in conservation of the species into the coming decades.  相似文献