Pitfalls in geothermobarometry of eclogites: Fe<Superscript>3+</Superscript> and changes in the mineral chemistry of omphacite at ultrahigh pressures   总被引：1，自引：0，他引：1  

Alexander?ProyerEmail author  Edgar?Dachs  Catherine?McCammon 《Contributions to Mineralogy and Petrology》2004,147(3):305-318

The relatively low-variance mineral assemblage of a talc-kyanite eclogite from Dabie Shan enabled application of both conventional geothermobarometers (garnet-clinopyroxene geothermometer and the garnet-omphacite-phengite geobarometer) and a multi-equilibrium method to determine peak P-T conditions (THERMOCALC, average PT). The results were highly discrepant: 840 °C / 31.1 kbar vs. 590 °C / 29.8 kbar. Mössbauer spectroscopy showed that Fe³⁺/Fe_total in omphacite was significantly higher than the value obtained from standard formula recalculation. When the activities were corrected for Fe endmembers, geothermobarometry gave consistent results (606 °C / 31.3 kbar vs. 585 °C / 30.8 kbar). These are close to those obtained earlier by average PT, confirming the robustness of the multi-equilibrium approach. The high Fe³⁺ concentration in omphacite is best explained using a Ca-eskola endmember Ca_0.5[]_0.5AlSi₂O₆ and allowing corresponding vacancies in the omphacite structure.Editorial responsibility: W. Schreyer  相似文献   

The effect of the Jessica grounding on Galápagos reef fish communities adjacent to the wreck site     

Edgar GJ  Marshall PA  Mooney P 《Marine pollution bulletin》2003,47(7-8):296-302

The grounding of the oil tanker Jessica off San Cristóbal Island, Galápagos, resulted in generally elevated rather than depressed densities of fishes adjacent to the wreck site 15 weeks post spill. Species richness of fishes declined along transects out from the wreck; however, patterns were inconsistent for different depth strata, with the most clearly defined decline evident for the intermediate 5-7 m depth stratum. Fish species attracted to the immediate wreck site, most notably the surgeonfish Prionurus laticlavius, the damselfish Microspathodon dorsalis and the angelfish Holacanthus passer, were considered to be responding either to the heterogeneity provided by the wreck structure or elevated densities of macroalgae. The fish community at the wreck site lay outside the range of variation for other sites investigated in the region; however, contrary to predictions of grounding impacts, the fish assemblage immediately adjacent to the wreckage showed greater faunal similarity to reference sites than did fish assemblage at 60-90 m distance from the grounding.  相似文献   

Pollution embodied in trade: The Norwegian case   总被引：9，自引：0，他引：9  

Glen P. Peters  Edgar G. Hertwich 《Global Environmental Change》2006,16(4):379-387

With the increase in international trade, it is becoming increasingly important to accurately determine environmental impacts resulting from pollution embodied in trade. Many previous studies have unrealistically assumed that imports are produced with the technology of the importing country. For countries with diverging technology and energy mixes the likely errors are significant. This study uses a model that explicitly includes regional technology differences to the case of Norway. It is found that CO₂ emissions embodied in imports was 67% of Norway's domestic emissions. Around a half of this embodied pollution originates in developing countries, yet they represent only 10% of the value of Norwegian imports. In addition the carbon leakage from non-Annex I countries was at least 30%. We then argue that basing emission inventories on consumption, rather than production, may resolve not only issues related to international trade, but also provide greater flexibility towards pollution intensive resource endowments, emission reductions, and participation levels.  相似文献   

The Signature of Sea Spray in the Hexos Turbulent Heat Flux Data   总被引：7，自引：0，他引：7  

Edgar L Andreas  Janice Decosmo 《Boundary-Layer Meteorology》2002,103(2):303-333

The role of sea spray intransferring heat and moisture across the air-sea interface has remained elusive. Some studies have reported that sea spray does not affect the turbulent air-sea heat fluxes for 10-m wind speeds up to at least 25 m s^-1, while others have reported important spray contributions for wind speeds as low as 12 m s^-1. One goal of the HEXOS (Humidity Exchange over the Sea) program was to quantify spray's contribution to the turbulent air-sea heat fluxes, but original analyses of the HEXOS flux data found the spray signal to be too small to be reliably identified amid the scatter in the data. We look at the HEXOS data again in the context of the TOGA-COARE bulk flux algorithm and a sophisticated microphysical spray model. This combination of quality data andstate-of-the-art modelling reveals a distinct spray signature in virtually all HEXOS turbulent heat flux data collected in winds of 15 m s^-1 and higher. Spray effects are most evident in the latent heat flux data, where spray contributes roughly 10% of the total turbulent flux in winds of 10 m s^-1 and between 10 and 40% in winds of 15–18 m s^-1. The spray contribution to the total sensible heat flux is also at least 10% in winds above 15 m s^-1. These results lead to a new, unified parameterization for the turbulent air-sea heat fluxes that should be especially useful in high winds because it acknowledges both the interfacial and spray routes by which the sea exchanges heat and moisture with the atmosphere.  相似文献   

Regional controls on geomorphology, hydrology, and ecosystem integrity in the Orinoco Delta, Venezuela     

Andrew G. Warne  Robert H. Meade  William A. White  Edgar H. Guevara  James Gibeaut  Rebecca C. Smyth  Andres Aslan  Thomas Tremblay 《Geomorphology》2002,44(3-4)

Interacting river discharge, tidal oscillation, and tropical rainfall across the 22,000 km² Orinoco delta plain support diverse fresh and brackish water ecosystems. To develop environmental baseline information for this largely unpopulated region, we evaluate major coastal plain, shallow marine, and river systems of northeastern South America, which serves to identify principal sources and controls of water and sediment flow into, through, and out of the Orinoco Delta.The regional analysis includes a summary of the geology, hydrodynamics, sediment dynamics, and geomorphic characteristics of the Orinoco drainage basin, river, and delta system. Because the Amazon River is a major source of sediment deposited along the Orinoco coast, we summarize Amazon water and sediment input to the northeastern South American littoral zone. We investigate sediment dynamics and geomorphology of the Guiana coast, where marine processes and Holocene history are similar to the Orinoco coast.Major factors controlling Orinoco Delta water and sediment dynamics include the pronounced annual flood discharge; the uneven distribution of water and sediment discharge across the delta plain; discharge of large volumes of water with low sediment concentrations through the Río Grande and Araguao distributaries; water and sediment dynamics associated with the Guayana littoral current along the northeastern South American coast; inflow of large volumes of Amazon sediment to the Orinoco coast; development of a fresh water plume seaward of Boca Grande; disruption of the Guayana Current by Trinidad, Boca de Serpientes, and Gulf of Paria; and the constriction at Boca de Serpientes.  相似文献   

Phase relations in the phlogopite-apatite system at 20 kbar; implications for the role of fluorine in mantle melting     

D. Vukadinovic  A. D. Edgar 《Contributions to Mineralogy and Petrology》1993,114(2):247-254

Phase relations have been determined at 20 kb in the simple, Fe-, Ti-free systems hydroxyphlogopite-hydroxyapatite and hydroxyfluorphlogopite-hydroxyfluorapatite in order to determine distribution of fluorine between phlogopite, apatite and melt under mantle conditions. No excess H₂O was present in the hydroxyphlogopite-hydroxyapatite system and the F/(OH) ratio was unity in the F-bearing system. Both systems are pseudobinary and contain forsterite at phlogopite-rich compositions. In the F-absent system, the minimum melting occurs at 1225°C and Phl₈₅Ap₁₅, whereas in the F-bearing system this temperature is 1260°C and Phl₆₆Ap₃₄. Phlogopite in the F-absent system has lower Al than in the F-bearing system with both showing Si+Mg=^[IV]Al+^[VI]Al as the principal substitution. Increase in CaO in forsterite increases with increasing apatite in the bulk composition and is more pronounced in the F-absent system. Distribution of fluorine between phlogopite and liquid and apatite and liquid shows that D _F ^(Phl/glass) ranges from 2–1.25 depending on temperature and bulk composition, whereas the D _F ^(Apat/glass) is about unity. These results suggest that fluorine will tend to remain in the solid phases rather than the melt during partial melting in the mantle. Hence the enrichment of fluorine in ultrapotassic magmas and its role in their evolution are constrained.  相似文献   

Using scintillation at two wavelengths to measure path-averaged heat fluxes in free convection     

Edgar L Andreas 《Boundary-Layer Meteorology》1991,54(1-2):167-182

Local free convection scaling is one of the obvious triumphs of boundary-layer similarity theory. In free convection, there is no dynamic velocity scale; the sensible and latent heat fluxes, therefore, scale directly with the temperature and humidity structure parameters C _t ² and C _q ². By using scintillation to measure the refractive index structure parameter C _n ² at two electromagnetic (EM) wavelengths, we can obtain C _t ² and C _q ² and, thus, in effect, measure path-averaged values of the sensible and latent heat fluxes. Here I describe this so-called two-wavelength method for free convection, derive quantitative guidelines for optimizing the method, and evaluate its potential accuracy. I show that the two-wavelength method works best when one EM wavelength is in the visible or infrared region and the other is in the millimeter or radio region. When the Bowen ratio is between -5 and -0.1 or between 0.1 and 5, the expected accuracy of the measured fluxes is ±10–20% — typical of what is possible with eddy-correlation measurements. With the two-wavelength method, however, the fluxes represent spatial averages.  相似文献   

The mechanism of the reaction 1 tremolite+3 calcite+2 quartz =5 diopside+3 CO2+1 H2O: results of powder experiments     

Edgar Dachs  Paul Metz 《Contributions to Mineralogy and Petrology》1988,100(4):542-551

The mechanism of the reaction 1 tremolite +3 calcite+2 quartz=5 diopside+3 CO₂+1 H₂O was investigated at 2 and 5 kb, , using powder experiments lasting from 14 to 170 days. Because experiments were at high ratios of fluid to solids, the study identified the mechanism under surface-control conditions and thus establishes which reactant surface determines the kinetics. To achieve a diopside nucleation rate high enough to gain detectable reaction in the time of experimentation, the equilibrium boundary had to be overstepped by 30°–60° C at 5 kb. Experiments in which diopside successfully nucleated show that the reaction proceeds by a dissolution-crystallization mechanism. Experimentally-produced textures are presented in a series of SEM images and demonstrate that diopside nucleates and grows topotactically exclusively on tremolite. The mechanism of the forward reaction is modeled by a simplified scheme consisting of three processes, each comprising formation, transport and incorporation of 1) the Ca-, 2) the Mg-, and 3) the Si-bearing species in the fluid in response to dissolution of the reactants and crystallization of diopside. Using the dependence of the overall-reaction rate on the surface area of the reactants, it was experimentally determined that process 2) (dissolution of tremolite, transport of the Mg-bearing species in the fluid and crystallization of diopside) will be rate-limiting in most cases where metamorphism occurs in an internally controlled system. Due to the experimental design chosen, the dissolution of tremolite at the beginning of process 2) is rate-limiting in the experiments. The magnitude of the probable temperature-overstep necessary to achieve a significant nucleation rate during metamorphism is discussed on the basis of the experimental evidence and a simple nucleation rate model.  相似文献   

Stability of wadeite (Zr2K4Si6O18) under upper mantle conditions: Petrological implications     

M. Arima  A. D. Edgar 《Contributions to Mineralogy and Petrology》1980,72(2):191-195

Wadeite of composition Zr₂K₄Si₆O₁₈, synthesized at 1 atm, is stable between 12–25 kb at 800 °–1,250 ° C; conditions appropriate to those of partial melting of an anomalous K-enriched upper mantle. If published hypotheses for the generation of high potash mafic to ultramafic lavas based on partial melting of such an anomalous mantle are correct, wadeite is a possible K-bearing mineral, in addition to phlogopide and K-richterite, stable under mantle conditions. The restricted occurrence of wadeite to rocks of West Kimberley, Australia and Leucite Hills, Wyoming is believed to be due to their high K/Al and Zr contents relative to other high potash rocks. The cell constants of wadeite of Zr₂K₄Si₆O₁₈ composition are in agreement with those of natural Zr-rich wadeite and with the values predicted from synthetic wadeites with smaller tetravalents ions in the Zr site.  相似文献   

The application of a segmented tidal mixing model to the Great Bay Estuary,N.H.     

Wendell S. Brown  Edgar Arellano 《Estuaries and Coasts》1980,3(4):248-257

Measurements show that in general salt is vertically well-mixed everywhere in the Great Bay Estuary, New Hampshire except near the river entrances at the head of the estuary. Dyer and Taylor’s (1973) modified version of Ketchum’s segmented tidal prism model has been applied to the Great Bay Estuarine System in order to predict high and low water salinity distribution for a specified river flow. The theory has been modified here to account for the mixing which occurs at the junction of two branches of an estuary. The mixing parameter, which in this model is related to the tidal excursion of water in the estuary, has been determined for different segments in the estuary on the basis of a comparison between predictions and a comprehensive data set obtained for a low river flow period. Using a mixing parameter distribution based on the low river flow calibration procedure the salinity distribution has been predicted for high river flow. The resulting salinity distribution compares favorably with observations for most of the estuary. The corresponding flushing times for water parcels entering at the head of the estuary during periods of low and high river flow is 54.5 and 45.9 tidal cycles respectively.  相似文献