Oxygen deficient perovskites in the system CaSiO3–CaAlO2.5 and implications for the Earth’s interior     

U. W. Bläß  F. Langenhorst  D. J. Frost  F. Seifert 《Physics and Chemistry of Minerals》2007,34(6):363-376

Oxygen deficient perovskites of the system CaSiO₃–CaAlO_2.5 have been synthesised at high-pressure and -temperature conditions relevant to the Earth’s transition zone in order to investigate their stabilities in the Earth’s mantle and determine structural properties associated with vacancy incorporation. Two polysomes of thermodynamically stable defect perovskites with Ca(Al_0.4Si_0.6)O_2.8 and Ca(Al_0.5Si_0.5)O_2.75 stoichiometry have been identified. The ordering of oxygen defects into pseudo-cubic (111) layers results in well-ordered ten- or eightfold superstructures, respectively. At all other compositions examined, a metastable formation of perovskites has been observed instead, which are assumed to grow initially disordered. These are now characterised by tiny domains, formed due to subsequent ordering of vacancies along various pseudo-cubic {111} layers. Both ordered defect perovskites show a large P–T stability field ranging from about 9–18 GPa and 4–12 GPa, respectively. Microstructural TEM analyses revealed the presence of growth and ferroelastic twins, which indicate a phase transition from rhombohedral to monoclinic symmetry during quenching. Electron energy loss spectroscopy of Si and Al K edges point at the presence of tetrahedral, octahedral and maybe some pentacoordinated silicon, whereas aluminium is predominantly octahedrally coordinated with minor fractions in lower coordination. Observed properties are interpreted in terms of a new structural model, explaining the observed phase transition and formation of different twin laws as well as giving reasons for the development of such large superstructures. With respect to phase relations of the transition zone, the potential occurrence of such defect perovskites in the Earth’s interior is discussed.  相似文献   

Detecting infiltration and impacts of introduced water using strontium isotopes   总被引：3，自引：0，他引：3  

Brinck EL  Frost CD 《Ground water》2007,45(5):554-568

Water introduced to surface drainages, such as agricultural and roadway runoff, mine drainage, or coalbed natural gas (CBNG)-produced water, potentially can be of environmental concern. In order to mitigate potential environmental effects, it may be important to be able to trace water discharged to the surface as it infiltrates and interacts with near-surface aquifers. We have chosen to study water withdrawn during CBNG production for isotope tracing in the hyporheic zone because it poses a variety of economic, environmental, and policy issues in the Rocky Mountain states. Ground water quality must be protected as CBNG water is added to semiarid ecosystems. Strontium (Sr) isotopes are effective fingerprints of the aquifer from which water originates. In this study, CBNG water was found to have a higher (87)Sr/(86)Sr ratio than the local alluvial aquifer water. This measurable difference allows the strontium isotope ratio and concentration to be used as tracers of CBNG water following its discharge to the surface. The dissolution and mobilization of salts from soil are an important contributor to ground water quality degradation. In the Powder River basin of Wyoming, the soils are calcium carbonate-buffered systems. The chemical similarity of strontium to calcium allows it to substitute into calcium minerals and enabled us to use strontium isotopes to identify calcium salts mobilized from the soil. Strontium isotopes are an effective monitor of the source of ions and the volume and direction of introduced water flow in the hyporheic zone.  相似文献   

Petrologic constraints on the spatial distribution of crustal magma chambers,Atka Volcanic Center,central Aleutian arc     

James D. Myers  Bruce D. Marsh  Carol D. Frost  Jennifer A. Linton 《Contributions to Mineralogy and Petrology》2002,143(5):567-586

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THE CANYONLANDS METEORITE     

David E. Lange  Kent Frost  Paul P. Sipiera  Carleton B. Moore 《Meteoritics & planetary science》1974,9(4):271-280

The Canyonlands meteorite weighing 1,520 grams was found near the confluence of the Green and Colorado Rivers, Utah, near lat 38°11′N.; long 109°53′W. It is a shocked, brecciated H6 chondrite containing large black veins which do not differ in composition from the main chondritic mass. A black fusion crust remains on part of the meteorite.  相似文献   

Diagnostic monitoring of a changing environment: an alternative UK perspective     

Hardman-Mountford NJ  Allen JI  Frost MT  Hawkins SJ  Kendall MA  Mieszkowska N  Richardson KA  Somerfield PJ 《Marine pollution bulletin》2005,50(12):1463-1471

Adaptive management of the marine environment requires an understanding of the complex interactions within it. Establishing levels of natural variability within and between marine ecosystems is a necessary prerequisite to this process and requires a monitoring programme which takes account of the issues of time, space and scale. In this paper, we argue that an ecosystem approach to managing the marine environment should take direct account of climate change indicators at a regional level if it is to cope with the unprecedented change expected as a result of human impacts on the earth climate system. We discuss the purpose of environmental monitoring and the importance of maintaining long-term time series. Recommendations are made on the use of these data in conjunction with modern extrapolation and integration tools (e.g. ecosystem models, remote sensing) to provide a diagnostic approach to the management of marine ecosystems, based on adaptive indicators and dynamic baselines.  相似文献   

Strontium isotopic identification of water-rock interaction and ground water mixing   总被引：1，自引：0，他引：1  

Frost CD  Toner RN 《Ground water》2004,42(3):418-432

87Sr/86Sr ratios of ground waters in the Bighorn and Laramie basins' carbonate and carbonate-cemented aquifer systems, Wyoming, United States, reflect the distinctive strontium isotope signatures of the minerals in their respective aquifers. Well water samples from the Madison Aquifer (Bighorn Basin) have strontium isotopic ratios that match their carbonate host rocks. Casper Aquifer ground waters (Laramie Basin) have strontium isotopic ratios that differ from the bulk host rock; however, stepwise leaching of Casper Sandstone indicates that most of the strontium in Casper Aquifer ground waters is acquired from preferential dissolution of carbonate cement. Strontium isotope data from both Bighorn and Laramie basins, along with dye tracing experiments in the Bighorn Basin and tritium data from the Laramie Basin, suggest that waters in carbonate or carbonate-cemented aquifers acquire their strontium isotope composition very quickly--on the order of decades. Strontium isotopes were also used successfully to verify previously identified mixed Redbeds-Casper ground waters in the Laramie Basin. The strontium isotopic compositions of ground waters near Precambrian outcrops also suggest previously unrecognized mixing between Casper and Precambrian aquifers. These results demonstrate the utility of strontium isotopic ratio data in identifying ground water sources and aquifer interactions.  相似文献   

Evidence for high-pressure core-mantle differentiation from the metal-silicate partitioning of lithophile and weakly-siderophile elements     

Ute Mann  Daniel J. Frost  David C. Rubie 《Geochimica et cosmochimica acta》2009,73(24):7360-470

Liquid Fe metal-liquid silicate partition coefficients for the lithophile and weakly-siderophile elements Ta, Nb, V, Cr, Si, Mn, Ga, In and Zn have been measured in multianvil experiments performed from 2 to 24 GPa, 2023-2873 K and at oxygen fugacities of −1.3 to −4.2 log units relative to the iron-wüstite buffer. Compositional effects of light elements dissolved in the metal liquid (S, C) have been examined and experiments were performed in both graphite and MgO capsules, specifically to address the effect of C solubility in Fe-metal on siderophile element partitioning. The results were used to examine whether there is categorical evidence that a significant portion of metal-silicate equilibration occurred under very high pressures during core-mantle fractionation on Earth. Although the depletion of V from the mantle due to core formation is significantly greater than that of Nb, our results indicate that both elements have similar siderophile tendencies under reducing conditions at low pressures. With increasing pressure, however, Nb becomes less siderophile than V, implying that average metal-silicate equilibration pressures of at least 10-40 GPa are required to explain the Nb/V ratio of the mantle. Similarly the moderately-siderophile, volatile element ratios Ga/Mn and In/Zn are chondritic in the mantle but both volatility and core-mantle equilibration at low pressure would render these ratios strongly sub-chondritic. Our results indicate that pressures of metal-silicate partitioning exceeding 30-60 GPa would be required to render these element ratios chondritic in the mantle. These observations strongly indicate that metal-silicate equilibration must have occurred at high pressures, and therefore support core-formation models that involve deep magma oceans. Moreover, our results allow us to exclude models that envisage primarily low-pressure (<1 GPa) equilibration in relatively small planetary bodies. We also argue that the core cannot contain significant U as this would require metal-silicate equilibration at oxygen fugacities low enough for significant amounts of Ta to have also been extracted from the mantle. Likewise, as In is more siderophile than Pb but similarly volatile and also quite chalcophile it would have been difficult for Pb to enter the core without reversing the relative depletions of these elements in the mantle unless metal-silicate equilibration occurred at high pressures >20 GPa.  相似文献   

Modern Wyoming plant and pronghorn isoscapes and their implications for archaeology     

Jack N. Fenner  Carol D. Frost 《Journal of Geochemical Exploration》2009,102(3):149

Stable isotope ratios obtained from pronghorn teeth recovered from archaeological sites in southwestern Wyoming may provide information on past climate and hunter behavior. However, the interpretation of archaeological isotope values depends on pronghorn isotopic correlations with the environment and geography. To investigate these correlations, a series of modern Wyoming carbon, oxygen and strontium isoscapes are compared with recent temperature, humidity and geological variation. Results indicate that both pronghorn and sagebrush carbon, and to a lesser degree oxygen, isotope ratios are tied to relative humidity. Temperature is correlated with oxygen isotope ratios in sagebrush, but not pronghorn. Strontium isotope ratios in both sagebrush and pronghorn vary with geography, which in turn reflects variation in geology.  相似文献   

Intercalation of kaolinite with acetamide     

R. L. Frost  J. Kristof  G. N. Paroz  J. T. Kloprogge 《Physics and Chemistry of Minerals》1999,26(3):257-263

Upon intercalation of both ordered (low defect) and disordered (high defect) kaolinites with acetamide, two types of interaction are observed. Firstly, hydrogen bonding between the NH₂ groups of the acetamide with the siloxane oxygens is formed, as evidenced by the formation of two new bands at 3400 and 3509 cm^–1. Secondly, the appearance of additional bands at ∼3600 cm^–1 in both the infrared and Raman spectra of the acetamide intercalates is attributed to a second type of hydrogen bonding by the interaction of the C=O group and the inner surface hydroxyls. Changes in the intensity of the hydroxyl deformation modes in the 895 to 940 cm^–1 region are attributed to the changes in the hydrogen bonding of the kaolinite surfaces. It is proposed that the hydrogen bonding between the adjacent kaolinite layers is replaced with hydrogen bonding between both kaolinite surfaces and the acetamide molecule. Changes in the molecular structure of acetamide are observed upon intercalation. The amide 1 band is lost and replaced with a well-defined NH₂ deformation vibration. The loss of the amide 1 band is attributed the hydrogen bond formation between the amide hydrogens and the siloxane surface. The bands of the C=O group at 1680 and 1740 cm^–1 become a single band at 1680 cm^–1. The amide 2 band remains unchanged. The lack of intensity of the 1740 cm^–1 band is attributed to the formation of hydrogen bonding between the inner surface hydroxyl groups and the carbonyl group. Received: 4 February 1998/ Revised, accepted: 30 June 1998  相似文献   

Design and performance of a novel multi-function debris flow mitigation system in Wenjia Gully,Sichuan     

F.Z. Liu  Q. Xu  X.J. Dong  B. Yu  J.D. Frost  H.J. Li 《Landslides》2017,14(6):2089-2104

The post-earthquake debris flows in the Wenjia Gully led to the exposure of the shortcomings in the design of the original conventional debris flow mitigation system. A predicament for the Wenjia mitigation system is a large amount of loose material (est. 50 × 10⁶ m³) that has been deposited in the gully by the co-seismic landslide, providing abundant source material for debris flows under saturation. A novel design solution for the replacement mitigation system was proposed and constructed, and has exhibited excellent performance and resilience in subsequent debris flows. The design was governed by the three-phase philosophy of controlling water, sediment, and erosion. An Early Warning System (EWS) for debris flow that uses real-time field data was developed; it issues alerts based on the probabilistic and empirical correlations between rainfall and debris flows. This two-fold solution reduces energy of the debris flow by combining different mitigation measures while minimizing the impact through event forecasting and rapid public information sharing. Declines in the number and size of debris flows in the gully, with increased corresponding rainfall thresholds and mean rainfall intensity-duration (I-D) thresholds, indicate the high efficacy of the new mitigation system and a lowered debris flow susceptibility. This paper reports the design of the mitigation system and analyzes the characteristics of rainfall and debris flow events that occurred before and after implementation of the system; it evaluates the effectiveness of one of the most advanced debris flow mitigation systems in China.  相似文献