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 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   

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   

Spezielle regionalatlanten — erläutert an der kartographischen konzeption eines atlasses über die “optimale gestaltung der umweltbedingungen”     

Edgar Lehmann 《Geoforum》1973,4(3):59-62

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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   

Hydro‐morphologic Revision of the Cuautla Channel at Nayarit,Mexico     

Cuauhtemoc Franco Ochoa  Edgar Mendoza Baldwin  Rodolfo Silva Casarín  Gabriel Ruiz Martínez 《洁净——土壤、空气、水》2012,40(9):920-925

Pollution, habitat modification, and species migration are some of the results of human activities on natural environments which can be mitigated or compensated with proper planning. Irresponsibility or ignorance in planning coastal projects too often produces damage to natural systems which can be unpredictable and sometimes irrevocable. The specific site analyzed in this paper is the Cuautla littoral sub‐system which was originally a lagoon that diverted river water to other lagoons and estuaries, thus irrigating the Mexican Marismas Nacionales system, in the states of Nayarit and Sinaloa, Mexico. In the 1970s social and economic considerations motivated the construction of a small breaching canal from the sea to the lagoon. The subsequent growth of this channel was unforeseen and has produced an irreversible impact not only in the sub‐system but probably in the entire area of Marismas Nacionales. A lack of understanding of the present balances in the damaged system and of the impacts the changing morphology has on future change has created the need to study this area using numerical hydrodynamic simulation. The present distribution of water in the sub‐system was established and the governing processes were detected. By means of an analytical estimation of equilibrium conditions it was found that if nothing is done, the channel will continue eroding and the ecosystem will continue to degrade. Only by understanding the dramatic perturbations caused by the construction of the channel to the hydrologic and morphologic equilibriums can there be any hope of rescuing the ecosystem, including its human activities.  相似文献   

Characterization of Risks in Coastal Zones: A Review     

Mireille Escudero Castillo  Edgar Mendoza Baldwin  Rodolfo Silva Casarin  Gregorio Posada Vanegas  Maritza Arganis Juaréz 《洁净——土壤、空气、水》2012,40(9):894-905

Interest in sustainable development for the natural, socio‐economic, and cultural resources of coastal zones is growing worldwide. On the other hand, the range of threats to coastal zones increasingly posed by hydro‐meteorological natural phenomena has led to a trend in the analysis and assessment of risks to these areas. The available literature dealing with coastal risk assessment is quite wide, focusing mainly on the risk evaluation of coastal flooding and erosion resulting directly from the occurrence of extreme natural events. The risk assessment methodologies are usually specific to the conditions and available data of each country, society or location, though most have evolved to assess the risk concept more precisely and rigorously. However, there are still very few studies that present feasible and effective methodologies, which lead to the effective integration of risk analysis at all levels. In Mexico coastal risk analysis has barely begun despite our extensive coastline, which is highly vulnerable to the threat of tropical cyclones. This paper aims to give a broad view of the risk assessment methodologies which already exist, in order to provide a starting point for future efforts in Mexico and elsewhere.  相似文献   

Land cover change and carbon stores in a tropical montane cloud forest in the Sierra Madre Oriental,Mexico   总被引：1，自引：0，他引：1  

Edgar G.LEIJA-LOREDO  Numa P.PAVóN  Arturo SáNCHEZ-GONZáLEZ  Rodrigo RODRIGUEZ-LAGUNA  Gregorio áNGELES-PéREZ 《山地科学学报》2018,15(10):2136-2147

Tropical montane cloud forest is one of the ecosystems with the highest biomass worldwide, representing an important carbon store. Globally its deforestation index is –1.1%, but in Mexico it is higher than –3%. Carbon estimates are scarce globally, particularly in Mexico. The objective of this study was to simulate future land-cover scenarios for the Sierra Madre Oriental in Mexico, by analyzing past forest cover changes. Another objective was to estimate stored carbon in the two study areas. These objectives involve the generation of information that could be useful inputs to anti-deforestation public policy such as the REDD+ strategy. Remote sensing was used to measure land cover change and estimate carbon stocks. Satellite images from 2015, 2000 and 1986 were used, and Dinamica EGO freeware generatedmodels of future projections. Between 1986 and 2015, 5171 ha of forest were converted to pasture. The annual deforestation rates were –1.5% for Tlanchinol and –1.3% for the San Bartolo Tutotepec sites. Distance to roads and marginalization were highly correlated with deforestation. By 2030, an estimated 3608 ha of forest in these sites will have been converted to pasture. Stored carbon was estimated at 16.35 Mg C ha-1 for the Tlanchinol site and 12.7 Mg C ha-1 for the San Bartolo site. In the Sierra Madre Oriental deforestation due to land cover change(–1.4%) is higher than levels reported worldwide. Besides having high values of stored carbon(14.5 Mg C ha-1), these forests have high biodiversity. The models' outputs show that the deforestation process will continue if action is not taken to avoid the expansion of livestock pasturing. This can be done by paying incentives for forest conservation to the owners of the land. The results suggest that REDD+ is currently the most viable strategy for reducing deforestation rates in tropical montane cloud forests in Sierra Madre Oriental.  相似文献   

Petrogenesis of the gabbros from Mt. St. Hilaire,Quebec, Canada     

R. C. Greenwood  A. D. Edgar 《Geological Journal》1984,19(4):353-376

Mt. St. Hilaire occurs as a small funnel-shaped intrusion in the Monteregian petrographic province of Quebec and consists of alkali gabbros and later nepheline syenites. Based on field relations, petrography, and geochemistry, five types of gabbro are recognized. In order of intrusion these are: leucogabbro, foliated gabbro, kaersutite-biotite gabbro, kaersutite gabbro, and a gabbro-melagabbro series. Based on analyses of the early-forming ilmenite-titanomagnetite, the gabbros crystallized under high fO₂ conditions which lead to subsequent crystallization of olivines with high MnO contents. Fractionation of ilmenite and titanomagnetite was a major control on the Ti and A[TV]concentrations in the clinopyroxenes. Plagioclase compositions in the gabbros became richer in Ab contents in the sequence gabbro-melagabbro to leucogabbro. Whole-rock analyses suggest that the parental magma of alkali basaltic composition was fairly evolved prior to emplacement. Lack of olivine in the cumulate gabbro-melagabbros and low Ni and Cr in all gabbros may reflect either extreme olivine fractionation and/or a very low olivine content in the source material for these basalts. Differentiation of the gabbros occurred both pre- and post-emplacement, probably by a process of crystal-liquid fractionation at depths between 3-5 and 8 km. This is in accordance with geophysical measurements for other Monteregian intrusions. A model is presented for the mechanism of emplacement.  相似文献   

Laboratory investigation of pressure gradients induced by plunging breakers     

Adrián Pedrozo-Acuña  Amaia Ruiz de Alegría-Arzaburu  Alec Torres-Freyermuth  Edgar Mendoza  Rodolfo Silva 《Coastal Engineering》2011

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