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811.
Cristina P. De Campos Diego Perugini Werner Ertel-Ingrisch Donald B. Dingwell Giampiero Poli 《Contributions to Mineralogy and Petrology》2011,161(6):863-881
Magma mixing is common in the Earth. Understanding the dynamics of the mixing process is necessary for dealing with the likely
consequences of mixing events in the petrogenesis of igneous rocks and the physics of volcanic eruptive triggers. Here, a
new apparatus has been developed in order to perform chaotic mixing experiments in systems of melts with high viscosity contrast.
The apparatus consists of an outer and an inner cylinder, which can be independently rotated at finite strains to generate
chaotic streamlines. The two cylinder axes are offset. Experiments have been performed for ca. 2 h, at 1,400°C under laminar
fluid dynamic conditions (Re ~ 10−7). Two end-member silicate melt compositions were synthesized: (1) a peralkaline haplogranite and (2) a haplobasalt. The viscosity
ratio between these two melts was of the order of 103. Optical analysis of post-experimental samples reveals a complex pattern of mingled filaments forming a scale-invariant (i.e.
fractal) distribution down to the μm-scale, as commonly observed in natural samples. This is due to the development in space
and time of stretching and folding of the two melts. Chemical analysis shows strong non-linear correlations in inter-elemental
plots. The original end-member compositions have nearly entirely disappeared from the filaments. The generation of thin layers
of widely compositionally contrasting interfaces strongly enhances chemical diffusion producing a remarkable modulation of
compositional fields over a short-length scale. Notably, diffusive fractionation generates highly heterogeneous pockets of
melt, in which depletion or enrichment of chemical elements occur, depending on their potential to spread via chemical diffusion
within the magma mixing system. Results presented in this work offer new insights into the complexity of processes expected
to be operating during magma mixing and may have important petrological implications. In particular: (1) it is shown that,
in contrast with current thinking, rheologically contrasting magmas can mix (i.e. with large proportions of felsic magmas
and high viscosity ratios), thus extending significantly the spectrum of geological conditions under which magma mixing processes
can occur efficiently; (2) the mixing process cannot be modeled using the classical linear two-end-member mixing model; and
(3) the chemical compositions on short-length scales represent snapshots within the process of mixing and therefore may not
reflect the final composition of the magmatic system. This study implies that microanalysis on short-length scales may provide
misleading information on the parental composition of magmas. 相似文献
812.
Grain size is a fundamental property of sediments and is commonly used to describe sedimentary facies and classify sedimentary environments. Among the various conventional techniques utilized to determine grain‐size frequency distributions, sieving is the most widely applied procedure. The accuracy of such analyses is, among other factors, strongly dependent on the sieving time. However, despite a substantial amount of research in this field, optimal sieving times for different types of sediments have, to date, not been established. In this article, the influence of sieving time on grain‐size analyses of medium‐grained microtidal and mesotidal beach and dune sands has been determined. To assess the precision of important textural parameters, such as median grain size, sorting, skewness and kurtosis, an error analysis was carried out for different sieving times (2, 5, 10, 15 and 20 minutes). After calibrating the analytical and sampling methodologies, significant deviations were registered when sieving time was less than 10 minutes. However, such deviations were very small and grain‐size distributions remained almost identical for sieving times of 10 minutes and longer, relative errors being as low as 0% in some cases. 相似文献
813.
M.G. Vivanco M. Santiago M. Sánchez M.A. Clavero E. Borrás M. Ródenas F. Alacreu M. Vázquez E. Clemente R. Porras A. Muñoz A. Stein 《Atmósfera》2013,26(1):59-73
Secondary organic aerosols (SOA) constitute a significant fraction of the atmospheric particulate matter. Theses particles are formed as a consequence of the oxidation reaction of certain organic gases that leads to the formation of low-volatility compounds. As for other pollutants, air quality models allow the simulation of particle levels and thus models constitute a powerful tool in air quality management. Nevertheless, the accepted use of models must be based on the validation of its capacity to reproduce observed concentrations. Air monitoring sites provide measured information of a large variety of ambient pollutants. Unfortunately, measurements on SOA are not normally available, as current monitoring networks do not include instrumentation to distinguish primary from secondary sources of organic carbonaceous aerosol. This paper presents a set of photooxidation experiments performed in the European Photorreactor (EUPHORE) smog chamber (CEAM, Spain) under different experimental conditions to investigate SOA formation. The use of chambers allows the isolation of atmospheric chemistry and aerosol formation processes. Thus, although these measurements were obtained at initial precursor concentrations higher than those in atmospheric conditions, they constitute a valuable set of information for SOA model evaluation purposes. 相似文献
814.
N. Santillán Soto O.R. García Cueto S. Ojeda Benítez N. Velázquez Limón M. Quintero Núñez M. Schorr 《Atmósfera》2013,26(4):499-507
Solar radiation is one of the most important energy resources of our planet. The interest in its use as a renewable and clean energy to mitigate the greenhouse gases (GHG) effects has increased significantly. This paper evaluates the measurements of global solar radiation and its energy potential and presents a comparison between both of them, as an example of the effort to reduce GHG emissions. The measurements were made with pyranometers installed in the city of Mexicali, Baja California, located in northwestern Mexico, and the city of Yuma, Arizona, located in the southwestern United States. Separated by a distance of 96 km, both cities have a sustained development and are climatically similar, since they present numerous sunny days, extreme hot temperatures and little precipitation. The results presented show differences in their behavior and in the solar radiation measurement values, especially for the critical spring and summer seasons, with values 15.73% (0.042 kW/m2) higher in Mexicali with respect to Yuma. Energy power is estimated, and it is discussed with some variables as global solar radiation, rainfall, air temperature, relative humidity and climatology of clear, partly cloudy, and cloudy days. With this estimation, the solar energy used and GHG avoided is projected for Mexicali. It is assessed that 291 tons of GHG are prevented. The Mexicali values of potential energy are higher than those of Yuma; therefore, this solar and energy comparative study provides reasons to develop these technologies in Mexico, but solar technologies should be deployed also in Yuma. The measured data at the regional level demonstrate their importance, and the relevance of the proposed mitigation strategy for climate change. 相似文献
815.
J. Birkmann O. D. Cardona M. L. Carreño A. H. Barbat M. Pelling S. Schneiderbauer S. Kienberger M. Keiler D. Alexander P. Zeil T. Welle 《Natural Hazards》2013,67(2):193-211
The paper deals with the development of a general as well as integrative and holistic framework to systematize and assess vulnerability, risk and adaptation. The framework is a thinking tool meant as a heuristic that outlines key factors and different dimensions that need to be addressed when assessing vulnerability in the context of natural hazards and climate change. The approach underlines that the key factors of such a common framework are related to the exposure of a society or system to a hazard or stressor, the susceptibility of the system or community exposed, and its resilience and adaptive capacity. Additionally, it underlines the necessity to consider key factors and multiple thematic dimensions when assessing vulnerability in the context of natural and socio-natural hazards. In this regard, it shows key linkages between the different concepts used within the disaster risk management (DRM) and climate change adaptation (CCA) research. Further, it helps to illustrate the strong relationships between different concepts used in DRM and CCA. The framework is also a tool for communicating complexity and stresses the need for societal change in order to reduce risk and to promote adaptation. With regard to this, the policy relevance of the framework and first results of its application are outlined. Overall, the framework presented enhances the discussion on how to frame and link vulnerability, disaster risk, risk management and adaptation concepts. 相似文献
816.
Jordi Pujadas Josep Maria Casas Josep Anton Muñoz Francese Sabat 《Geodinamica Acta》2013,26(3):195-206
AbstractThe structure of the southern Pyrenees, east of the Albanyà fault (Empordà area), consists of several Alpine thrust sheets. From bottom upwards three main structural units can be distinguished : the Roc de Frausa, the Biure-Bac Grillera and the Figueres units. The former involves basement and Paleogene cover rocks. This unit is deformed by E-W trending kilometric-scale folds, its north dipping floor thrust represents the sole thrust in this area. The middle unit is formed by an incomplete Mesozoic succession overlain by Garumnian and Eocene sediments. Mesozoic rocks internal structure consists of an imbricate stack. The floor thrust dips to the south and climbs up section southwards. The upper unit exibits the most complete Mesozoic sequence. Its floor thrust is subhorizontal. The lower and middle units thrust in a piggy-back sequence. The upper unit was emplaced out of sequence.Lower Eocene sedimentation in the Biure-Bac Grillera unit was controlled by emergent imbricate thrusts and synchronic extensional faults. One of these faults (La Salut fault) represents the boundary between a platform domain in the footwall and a subsident trough in the hangingwall. Southward thrust propagation produces the inversion of these faults and the development of cleavage-related folds in their hangingwalls (buttressing effect). This inversion is also recorded by syntectonic deposits, which have been grouped in four depositional sequences. The lower sequences represent the filling on the hangingwall trough and the upper sequences the spreading of clastics to the south once the extensional movement ends. 相似文献
817.
Rice cultivation in the Ebro Delta (Catalonia, Spain) has inverted the natural hydrological cycles of coastal lagoons and decreased water salinities for over 150 years. Adjustments in the water management practices—in terms of source and amount of freshwater inputs—have resulted in changes in the diversity, distribution and productivity of submerged angiosperms. Between the 1970s and late 1980s, a massive decline of the aquatic vegetation occurred in the Encanyissada–Clot and Tancada lagoons, but little information on the status is available after the recovery of macrophytes in the 1990s. Here, we evaluate the influence of salinity regimes resulting from current water management practices on the composition, distribution, seasonal abundance and flowering rates of submersed macrophytes, as well as on the occurrence of epiphyte and drift macroalgae blooms in three coastal lagoons. Our results show that Ruppia cirrhosa is the dominant species in the Encanyissada lagoon (185.97?±?29.74 g?DW?m?2?year?1; 12–27?‰ salinity) and the only plant species found in the Tancada lagoon (53.26?±?10.94 g?DW?m2?year?1; 16–28?‰ salinity). Flowering of R. cirrhosa (up to 1,011?±?121 flowers?m?2) was only observed within the Encanyissada and suggests that mesohaline summer conditions may favor these events. In contrast, low salinities in Clot lagoon (~3–12?‰) favor the development of Potamogeton pectinatus (130.53?±?13.79 g?DW?m2?year?1) with intersperse R. cirrhosa (8.58?±?1.71 g?DW?m?2) and mixed stands of P. pectinatus and Najas marina (up to ~57 g?DW?m?2?year?1) in some reduced areas. The peak biomasses observed during the study are 88 to 95 % lower than maximum values reported in the literature at similar salinities, and there is also little or no recovery in some areas compared to last reports more than 20 years ago. The main management actions to restore the natural diversity and productivity of submersed angiosperms, such as the recovering of the seagrass Zostera noltii, should be the increase of salinity during the period of rice cultivation, by reducing freshwater inputs and increasing flushing connections with the bays. 相似文献
818.
B. Garrido-Rodríguez D. Fernández-Calviño J. C. Nóvoa Muñoz M. Arias-Estévez M. Díaz-Raviña E. Álvarez-Rodríguez M. J. Fernández-Sanjurjo A. Núñez-Delgado 《International Journal of Environmental Science and Technology》2013,10(5):983-994
The aim of this study was to assess the influence of pH on copper mobilization in two copper-rich acid soils (from vineyard and mine) amended with crushed mussel shell. Crushed mussel shell amended soils (0–48 Mg ha?1) were subjected to the effect of several acid and alkali solutions in a batch experiment in order to study their copper release. Copper distribution was studied in decanted soils from batch experiments using a sequential extraction procedure, whereas the effect of crushed mussel shell on copper release kinetics was studied using a stirred flow reactor. When soils were treated with acid solutions, the copper mobilization from non-amended soils was significantly higher than from the amended samples. Major changes in copper fractionation were an increase of the acid soluble fraction in acid-treated vineyard soil samples with shell dose. For the mine soil, the oxidable fraction showed a relevant diminution in acid-treated samples at the highest crushed mussel shell dose. For both soils, copper desorption rates diminished up to 86 % at pH 3 when crushed mussel shell was added. At pH 5, copper release rate was very slow for both soils decreasing up to 98 % for the mine soil amended with the highest shell dose, whereas no differences were observed at pH 7 between amended and non-amended soils. Thus, crushed mussel shell addition could contribute to reduce potential hazard of copper-enriched soils under acidification events. 相似文献
819.
Michel Michaelovitch de Mahiques Rubens Cesar Lopes Figueira Alexandre Barbosa Salaroli Daniel Pavani Vicente Alves Cristina Gonçalves 《Environmental Earth Sciences》2013,68(4):1073-1087
The Cananéia–Iguape system consists of a complex of estuarine and lagoonal channels located in the coastal region of southeastern Brazil known as Lagamar, a Biosphere Reserve recognized by the United Nations Educational, Scientific and Cultural Organization (UNESCO) in 1991. The area suffered dramatic environmental changes along the last ca. 150 years initiated by the 1852 opening of an artificial channel, the Valo Grande, connecting the Ribeira de Iguape River to the estuarine system. Due to Au, Ag, Zn, and Pb mining activities that took place in the upstream regions of the Ribeira de Iguape River since the seventeenth century, the system has acted as a final destination of contaminated sediments. Analysis of cores located along the estuarine system revealed a history of contamination, with an increase of anthropogenic metal input between the decades of 1930 and 1990. The anthropogenic influence can be traced in locations as far as 20 km from the mouth of the artificial channel. 相似文献
820.
Eliseo Hernandez-Martinez Teresa Perez-Muñoz Jorge X. Velasco-Hernandez Armando Altamira-Areyan Luis Velasquillo-Martinez 《Mathematical Geosciences》2013,45(4):471-486
Well-log (radioactivity, density and resistivity) analysis constitutes a standard approach for inferring lithology from wells. However, due to inherent complexity of the signals (such as highly heterogeneous deep-water sedimentary sequences) lithology recognition is not straightforward. We used a rescaled range analysis, calibrated with cores, to recognize lithological patterns from signal recorded along wireline logs. The detected intervals coincide with zones of visual electro-facies associations proposed by geologist well-log interpreters. In addition, we propose a rescaled range multifractal analysis to identify ranges of well-log signal complexities, which could be related to sedimentary process variations at specific stratigraphic order cycles. 相似文献