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501.
We show the presence of fractal ordering of copper grade in bore core data at short range in the Cadia Ridgeway porphyry deposit and measure its persistence after mining by monitoring the output of the... 相似文献
502.
503.
Dexter Perkins Elizabeth Y. Anthony 《Contributions to Mineralogy and Petrology》2011,162(6):1139-1157
In peridotites, olivine, clinopyroxene, and orthopyroxene are complex solid solutions with wide stability fields. Depending
mostly on bulk composition and pressure, these minerals may be accompanied by plagioclase (low pressure), spinel (moderate
pressure), or garnet (high pressure), resulting in 4-phase and rarer 5-phase assemblages. Although a particular mineral assemblage
is stable over a range of P–T, the compositions of the individual minerals vary with changing P–T conditions. Application
of standard geothermobarometers to olivine–clinopyroxene–orthopyroxene–spinel peridotites is problematic. An alternative approach
is to use a bulk rock composition to calculate equilibrium phase diagrams to determine the conditions under which a particular
assemblage is stable. This requires consideration of the 7-component system SiO2–Al2O3–Cr2O3–FeO–MgO–CaO–Na2O, internally consistent thermodynamic data for end members, and reliable mixing models for all mineral solutions. Experimental
studies in simpler systems, and solution models from the literature, permit derivation of multicomponent thermodynamic mixing
models for the key minerals. The models, when applied to xenoliths from Kilbourne Hole, constrain P and T of equilibration
and are less sensitive to mineral compositional variations, or uncertainty in activity models, than standard thermobarometry.
Our modeling provides the first tightly constrained pressure estimates for Kilbourne Hole, placing the xenoliths in the spinel
stability field at depths (30–45 km) that correspond to the uppermost mantle beneath the Rio Grande Rift. The fine-grained
equigranular lherzolite, porphyroclastic lherzolite, and some harzburgite-dunite specimens equilibrated at average conditions
of 11.5 Kbar-930°C, 12 Kbar-990°C, and 13 Kbar-1,080°C, respectively. The mantle beneath the Rio Grande Rift is layered; the
fine-grained equigranular lherzolite derives from relatively shallow depth (35 km average), and the porphyroclastic lherzolite
from slightly deeper levels. Lying 5–10 km beneath both lherzolites, the harzburgite-dunite represents a depth where melt
extraction has significantly altered mantle chemistry and where local thermodynamic equilibrium has not been maintained. 相似文献
504.
Composition of dissolved organic matter in groundwater 总被引:1,自引:0,他引:1
Groundwater constitutes a globally important source of freshwater for drinking water and other agricultural and industrial purposes, and is a prominent source of freshwater flowing into the coastal ocean. Therefore, understanding the chemical components of groundwater is relevant to both coastal and inland communities. We used electrospray ionization coupled with Fourier-transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) to examine dissolved organic compounds in groundwater prior to and after passage through a sediment-filled column containing microorganisms. The data revealed that an unexpectedly high proportion of organic compounds contained nitrogen and sulfur, possibly due to transport of surface waters from septic systems and rain events. We matched 292 chemical features, based on measured mass:charge (m/z) values, to compounds stored in the Kyoto Encyclopedia of Genes and Genomes (KEGG). A subset of these compounds (88) had only one structural isomer in KEGG, thus supporting tentative identification. Most identified elemental formulas were linked with metabolic pathways that produce polyketides or with secondary metabolites produced by plants. The presence of polyketides in groundwater is notable because of their anti-bacterial and anti-cancer properties. However, their relative abundance must be quantified with appropriate analyses to assess any implications for public health. 相似文献
505.
Elizabeth A. Stanton 《Climatic change》2011,107(3-4):417-432
In a global climate policy debate fraught with differing understandings of right and wrong, the importance of making transparent the ethical assumptions used in climate-economics models cannot be overestimated. Negishi weighting is a key ethical assumption in climate-economics models, but it is virtually unknown to most model users. Negishi weights freeze the current distribution of income between world regions; without this constraint, IAMs that maximize global welfare would recommend an equalization of income across regions as part of their policy advice. With Negishi weights in place, these models instead recommend a course of action that would be optimal only in a world in which global income redistribution cannot and will not take place. This article describes the Negishi procedure and its origin in theoretical and applied welfare economics, and discusses the policy implications of the presentation and use of Negishi-weighted model results, as well as some alternatives to Negishi weighting in climate-economics models. 相似文献
506.
Francisco J. N��?ez-Corn�� Marta Rutz-L��pez V��ctor M��rquez-Ram��rez Carlos Su��rez-Plascencia Elizabeth Trejo-G��mez 《Pure and Applied Geophysics》2011,168(8-9):1293-1302
We present a fresh look at the source region of the 22 January 2003 M w 7.4 Armería earthquake, which occurred off the Pacific coast of the state of Colima, Mexico, near the town of Armería. The effects of this earthquake in the neighboring states of Colima and Jalisco were different and stronger than those of previous recent major earthquakes in the region. This earthquake and its aftershocks were recorded by two local telemetered seismograph networks (RESCO and RESJAL). From 22 January to 24 January 2003, no important seismicity was located on the plates interface, or within the Rivera Plate, and most epicenters were located west of the Armería River, which is the western border of the Colima Graben, and is located outside of the Colima Gap region. From 24 January to 31 January, the seismicity recorded by both networks showed a migration in depth, with an almost vertical offshore distribution between 4 and 24?km in depth. For this period, a seven-station portable digital seismograph network, equipped with three-component seismometers, was deployed in the epicentral area to study the aftershock sequence in detail. With this denser network more than 200 M L?>?2.0 aftershocks were recorded. The aftershock foci were deeper than those recorded during the early period and most of them locate on a hypothetical 12° dipping interface between the Rivera and North American Plates. Composite focal mechanism solutions for the aftershocks located during both periods indicate a reverse fault character that changes with time. Analysis of the new dataset still indicates that the earthquake was a shallow intraplate event. 相似文献
507.
Lead isotopes as tracers of anthropogenic pollution in urban topsoils of Mexico City 总被引:1,自引:0,他引:1
Ofelia Morton-Bermea María Teresa Rodríguez-Salazar Elizabeth Hernández-Alvarez Ma Elena García-Arreola Rufino Lozano-Santacruz 《Chemie der Erde / Geochemistry》2011,(2):189-195
A survey was performed to trace the main source of anthropogenic Pb pollution in Mexico City through Pb isotopic signatures (208Pb/204Pb, 206Pb/204Pb, 206Pb/207Pb, and 208Pb/207Pb) from 103 urban topsoil (0–5 cm) samples. Those were collected in the metropolitan area of Mexico City and compared with isotopic compositions of leaded gasoline (LG), domestic Pb ores (DLO) and parent rock (PR). The isotope ratios (IRs) of Pb were determined by inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) and total Pb concentration analyzed by wavelength dispersive X-ray fluorescence (WDXRF). The range of Pb concentrations levels in urban topsoil samples was 15–473 mg/kg. The IR values obtained for these samples were 37.965–39.718 (208Pb/204Pb), 18.375–19.204 (206Pb/204Pb), 1.177–1.218 (206Pb/207Pb) and 2.443–2.496 (208Pb/207Pb). Analyzed topsoil samples with low Pb content (<50 mg/kg) displayed high dispersion in 208Pb/204Pb values, which are determined by different natural sources. Samples with 51–200 mg/kg Pb content, shown low dispersion that revealed the mixing between the natural Pb and anthropogenic Pb. The assessment of the IR values shown that, as Pb concentration increases, a trend toward gasoline IR data has been observed. The results obtained by this research suggest that although the use of leaded petrol had been banned in Mexico since 1997, the Pb pollution in the urban topsoils due to the historical use of Pb in petrol is still significant. 相似文献
508.
Changes in seagrass food-web structure can shift the competitive balance between seagrass and algae, and may alter the flow
of energy from lower trophic levels to commercially important fish and crustaceans. Yet, trophic relationships in many seagrass
systems remain poorly resolved. We estimated the food web linkages among small predators, invertebrate mesograzers, and primary
producers in a Chesapeake Bay eelgrass (Zostera marina) bed by analyzing gut contents and stable C and N isotope ratios. Though trophic levels were relatively distinct, predators
varied in the proportion of mesograzers consumed relative to alternative prey, and some mesograzers consumed macrophytes or
exhibited intra-guild predation in addition to feeding on periphyton and detritus. These findings corroborate conclusions
from lab and mesocosm studies that the ecological impacts of mesograzers vary widely among species, and they emphasize the
need for taxonomic resolution and ecological information within seagrass epifaunal communities. 相似文献
509.
Amber Hardison Craig Tobias Jennifer Stanhope Elizabeth Canuel Iris Anderson 《Estuaries and Coasts》2011,34(2):243-255
The water–sediment interface is a dynamic zone where the benthic and pelagic environments are linked through exchange and
recycling of organic matter and nutrients. However, it is often difficult to measure rate processes in this zone. To that
end, we designed an experimental apparatus for continuous and homogeneous perfusion of sediment porewater with dissolved conservative
(SF6, Rhodamine WT dye) and isotopic (H13CO3− and 15NH4+) tracers to study nitrogen and carbon cycling by the sediment microbial community of shallow illuminated sediments. The perfusionator
consists of a 60-cm ID × 60-cm high cylinder that includes a reservoir for porewater at the base of the sediment column. Porewater
amended with conservative and stable isotopic tracers was pumped through a mixing reservoir and upward through the overlying
sediments. We tested the perfusionator in a laboratory setting, as part of an outdoor mesocosm array, and buried in coastal
sediments. Conservative and isotopic tracers demonstrated that the porewater tracers were distributed homogeneously through
the sediment column in all settings. The perfusionator was designed to introduce dissolved stable isotope tracers but is capable
of delivering any dissolved ionic, organic, or gaseous constituent. We see a potentially wide application of this technique
in the aquatic and marine sciences in laboratory and field settings. 相似文献
510.
Elizabeth M. Truswell 《Australian Journal of Earth Sciences》2013,60(3-4):343-356
Fifty‐three sea‐floor samples close to Antarctica collected by Douglas Mawson during the Australasian Antarctic Expedition of 1911–1914 have beeen analysed for recycled palynomorphs. The distribution of the recycled microfossils provides a broad guide to the position of hidden sedimentary sequences on the Antarctic continental margin. The samples were dredged off the East Antarctic coast between 91°E and 146°E. In three distinct ‐areas, concentrations of recycled palynomorphs suggest the presence nearby of eroding sedimentary sequences. Near the western edge of the Shackleton Ice Shelf the recycled suite suggests Early to Late Permian, Late Jurassic to mid‐Cretaceous, and Late Cretaceous to Early Tertiary sediments, with evidence for marine influence only in the Tertiary. Samples from the outer edge of the continental shelf and slope east of Cape Carr indicate Early Cretaceous and Late Cretaceous to Early Tertiary sequences, and the same age span is suggested by samples from the western side of the Mertz Glacier Tongue; in this area radio echosounding has suggested that inland sedimentary basins intersect the coast. The sedimentary sequence predicted for the Shackleton Ice Shelf area probably faced the open Indian Ocean, at least since the Mesozoic. Cretaceous sequences predicted for the other localities occur at points on the Antarctic coast where they would be expected on the basis of most reconstructions. The area east of Cape Carr has as its conjugate’ coast part of the Great Australian Bight Basin; that off the Mertz Glacier, the area west of the Otway Basin. At both these areas on the southern Australian margin thick Cretaceous rift‐valley sequences occur. 相似文献