The structure and the phyllosilicates (chemistry, crystallinity and texture) of Talas Ala-Tau (Tien Shan, Kyrgyz Republic): comparison with more recent subduction complexes     

Isabel Abad  Gabriel Gutirrez-Alonso  Fernando Nieto  Igor Gertner  Alex Becker  Ana Cabero 《Tectonophysics》2003,365(1-4):103

Geological mapping and structural analysis of the Talas Ala Tau (Tien Shan, Kyrgyz Republic) have revealed a complex structure composed of folds with axial-plane cleavage and thrust faults verging towards the NE. The main structures of the range correspond to minor Tertiary and Carboniferous–Permian deformation superimposed on the main deformation event that took place during the Baikalian orogeny. The pervasive axial-plane cleavage diminishes in penetrativity from the hinterland to the foreland in both the Uzunakhmat and Karagoin sheets. The main thrusts developed phyllonitic shear-related rocks on the hangingwall immediately above the thrust planes. A crystal-chemical study of the phyllosilicates growth during the Baikalian deformation event along a cross-section revealed changes in the crystallinity, composition and lattice parameters of them. The phyllosilicates present in the Talas Ala Tau rocks were crystallized in very low-grade metamorphic conditions, that is below 300 °C, as indicated by their Kübler Index (KI), which decreases from SW towards the NE. Detailed TEM study of the phyllosilicates reveals a clear textural difference at the lattice level between samples with higher or lower KI parameters. There is also a clear difference in crystal-chemical parameters (KI and b) and composition between the phyllosilicates growth in relation to the axial-plane cleavage and the ones belonging to the thrust-related phyllonites. The first ones are more affected by the ferrimuscovitic vector than the phyllosilicates of phyllonites, closer to the theoretical phengitic component. Huge ranges of values of phengitic content of micas at sample level are interpreted as the result of a decompression path from at least 8 kbar. We propose a subduction geodynamic environment for the regional deformation and the origin of the phyllosilicates, as they are similar to those obtained in more recent accretionary complexes.  相似文献   

The circumstellar medium of the peculiar supernova SN1997ab     

Isabel Salamanca  Roberto Cid-Fernandes  Guillermo Tenorio-Tagle  Eduardo Telles  Roberto J. Terlevich  & Casiana Muñoz-Tuñón 《Monthly notices of the Royal Astronomical Society》1998,300(2):L17-L21

We report the detection of the slow-moving wind into which the compact supernova remnant SN 1997ab is expanding. Echelle spectroscopy provides clear evidence for a well-resolved narrow (full width at zero intensity, FWZI ∼180 km s⁻¹) P Cygni profile, both in Hα and Hβ, superimposed on the broad emission lines of this compact supernova remnant. From theoretical arguments we know that the broad and strong emission lines imply a circumstellar density ( n  ≥ 10⁷ cm⁻³). This, together with our detection, implies a massive and slow stellar wind experienced by the progenitor star shortly prior to the explosion.  相似文献   

Ion exchange between tectosilicates with the nepheline-kalsilite framework and molten MNO3 or MO (M = Li,Na, K,Ag)     

Isabel Sobrados  Michael Gregorkiewitz 《Physics and Chemistry of Minerals》1993,20(6):433-441

Natural nepheline, a synthetic Na-rich nepheline, and synthetic kalsilite were ion exchanged in molten MNO₃ or MCl (M = Li, Na, K, Ag) at 220–800° C. Crystalline products were characterized by wet chemical and electron microprobe analysis, single crystal and powder X-ray diffraction, and transmission electron microscopy and diffraction. Two new compounds were obtained: Li-exchanged nepheline with a formula near (Li,K_0.3,□)Li₃[Al₃(Al,Si)Si₄O₁₆] and a monoclinic unit cell with a = 951.0(6) b = 976.1(6) c = 822.9(5)pm γ = 119.15°, and Ag-exchanged nepheline with a formula near (K,Na,□)Ag₃[Al₃(Al,Si)Si₄O₁₆] and a hexagonal unit cell with a = 1007.4(8) c = 838.2(1.0) pm. Both compounds apparently retain the framework topology of the starting material. Ion exchange isotherms and structural data show that immiscibility between the end members is a general feature in the systems Na-Li, Na-Ag, and Na-K. For the system Na-K, a stepwise exchange is observed with (K,D)Na₃[Al₃(Al,Si)Si₄O₁₆] as an intermediate composition which has the nepheline structure and is miscible with the sodian end member (Na,□)Na₃[Al₃(Al,Si)Si₄O₁₆], but not with the potassian end member (K,□)₄[Al₃(Al,Si)Si₄O₁₆] which shows the kalsilite structure; there was no indication for the formation of trior tetrakalsilite (K/(K + Na)≈0.7) at the temperatures studied (350 and 800° C). The exact amount of vacancies □ on the alkali site depends upon the starting material and was found to be conserved during exchange, with ca 0–0.2 and 0.3–0.4 vacancies per 16 oxygen atoms for the synthetic and natural precursors, respectively. Thermodynamic interpretation of the Na-K exchange isotherms shows, as one important result, that the sodian end member is unstable with respect to the intermediate at K/(K+Na)≈0.25 by an amount of ca 45 kJ/mol Na in the large cavity at 800° C (52 kJ/mol at 350° C).  相似文献   

Developing an operational reference framework for fisheries management on the basis of a two-dimensional index of ecosystem impact     

Tudela  Sergi; Coll  Marta; Palomera  Isabel 《ICES Journal of Marine Science》2005,62(3):585-591

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Understanding spatial and temporal dynamics of key environmental characteristics in a mesotidal Atlantic estuary (Douro,NW Portugal)     

Isabel C. Azevedo  Pedro M. Duarte  Adriano A. Bordalo 《Estuarine, Coastal and Shelf Science》2008

Ecosystem management and decision making process are dependent of a good knowledge of ecosystem functioning. Conceptual models allow knowledge organization through representation of relationships between variables and processes, facilitating management decisions. In this study, spatial and temporal characterization of key environmental variables, as well as relationships between them, was studied aiming the design of a conceptual model of the Douro estuary. This temperate mesotidal estuary is limited upstream by a hydroelectric power dam that controls freshwater inflow and prevents the propagation of the tide upstream, which, in turn, influences water circulation and biogeochemical dynamics of the system. During one year, from December 2002 to December 2003, water column data were collected monthly at 10 stations along the estuary, during ebb and flood tides. Spatial and temporal variability of water column salinity, temperature, nutrients, phytoplankton biomass, total particulate matter (TPM), phytoplankton primary production (PP), faecal coliform bacteria (FC) and community respiration (CR) were analysed. Salinity stratification was assessed by means of the Estuary Number (Ne) and variation of this index as well as other key characteristics with river flow was analysed. Freshwater discharge controlled salinity stratification and freshwater residence time. Ne indicated that the Douro was stratified for river flows <300 m³ s⁻¹, and freshwater residence time was >1 day for the same conditions. A decaying exponential relationship between PP and river flow was found, whereas nitrate and TPM increased logarithmically and linearly, respectively, with river flow. Regarding spatial distribution, nitrate and PP decreased downstream, showing that the river was a source of nutrients and phytoplankton, while the opposite trend was found for TPM, FC, ammonium and CR. The latter increase was probably due to untreated sewage discharge in the urbanized middle and lower estuarine stretches. Reduction of nitrate coming from the watershed and of bacterial contamination in the urban stretches of this highly modified water body, according to the European Water Framework Directive, emerges as the main water quality issues for this estuarine ecosystem.  相似文献   

Magnetic imaging of the feeding system of oceanic volcanic islands: El Hierro (Canary Islands)     

Isabel Blanco-Montenegro  Iacopo Nicolosi  Alessandro Pignatelli  Massimo Chiappini 《Geophysical Journal International》2008,173(1):339-350

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Dynamics in the trophic structure of the macroinvertebrate community in a Mediterranean, temporary stream     

Maruxa Álvarez  Isabel Pardo 《Aquatic Sciences - Research Across Boundaries》2009,71(2):202-213

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Isotopic variability in a stream longitudinal gradient: implications for trophic ecology     

Noemi Costas  Isabel Pardo 《Aquatic Sciences - Research Across Boundaries》2015,77(2):231-260

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Crustacean assemblages in a polluted estuary from South-Western Spain     

J. Emilio Sánchez-Moyano  Isabel García-Asencio 《Marine pollution bulletin》2010,60(10):1890-1897

The spatial-temporal variation in crustacean assemblages of the Odiel-Tinto estuary, one of the most polluted areas in the world, was studied in 2000, 2002 and 2004. The crustacean assemblages were mainly established according to the natural gradient from estuarine to marine environment (based on water and sediment characteristics such as dissolved oxygen, salinity, granulometry or organic content). Pollutants such as copper, zinc or phosphates could also explain partially this pattern based on BIOENV and canonical correspondence analyses. However, there were clear symptoms of perturbation, mainly in the inner areas, such as a low number of species and a low abundance, especially in relation to the typical estuarine species (e.g. Cyathura carinata, Corophium spp.). This study provides baseline information which can be used as a reference point in a long-term perspective.  相似文献   

New spatial dimensions of global cityscapes: From reviewing existing concepts to a conceptual spatial approach     

Isabel Georg  Thomas Blaschke  Hannes Taubenböck 《地理学报(英文版)》2016,26(3):355-380

Current global urbanisation processes are leading to new forms of massive urban constellations. The conceptualisations and classifications of these, however, are often ambiguous, overlap or lag behind in scientific literature. This article examines whether there is a common denominator to define and delimitate–and ultimately map–these new dimensions of cityscapes. In an extensive literature review we analysed and juxtaposed some of the most common concepts such as megacity, megaregion or megalopolis. We observed that many concepts are abstract or unspecific, and for those concepts for which physical parameters exist, the parameters are neither properly defined nor used in standardised ways. While understandably concepts originate from various disciplines, the authors identify a need for more precise definition and use of parameters. We conclude that often, spatial patterns of large urban areas resemble each other considerably but the definitions vary so widely that these differences may surpass any inconsistencies in the spatial delimitation process. In other words, today we have tools such as earth observation data and Geographic Information Systems to parameterise if clear definitions are provided. This appears not to be the case. The limiting factor when delineating large urban areas seems to be a commonly agreed ontology.  相似文献