Pre-eruptive geochemistry of the ignimbrite-forming magmas of the Campanian Volcanic Zone, Southern Italy, determined from silicate melt inclusions     

J. D. Webster  F. Raia  C. Tappen  B. De Vivo 《Mineralogy and Petrology》2003,79(1-2):99-125

Summary ¶The Campanian Ignimbrite rock samples include two compositionally distinct populations of clinopyroxene phenocrysts, and the entrapped MI (melt inclusions) are also different in composition. The cores of the more MgO-enriched phenocrysts carry basaltic trachyandesite MI that contain >6wt.% MgO, whereas other phenocrysts contain MI with <4wt.% MgO. The MgO-enriched MI also contain comparatively greater abundances of F, CaO, TiO₂, P₂O₅, SO₂, and Sr and show marginally higher ratios of (CaO/Al₂O₃) than the low-MgO MI. Most of the high-MgO MI also contain comparatively more H₂O. The MgO-enriched MI are restricted to diopsidic clinopyroxenes and show minimal compositional variability, demonstrating that they were derived from a common magmatic source or sources. We interpret these MI to represent primary, mafic magma. In contrast, the more evolved, low-MgO melt inclusions, which are restricted to salitic clinopyroxenes, span the compositional range of trachyandesite to trachyte. The low-MgO fractions of Campanian Ignimbrite magma evolved via fractional crystallization with or without mingling or mixing with more primitive, high-MgO magma.Interestingly, the MI from the Giugliano sample also cluster into low-MgO and high-MgO fractions, and the evolutionary trends for major, minor, and trace elements mirror those exhibited by the Campanian Ignimbrite MI, suggesting that both magmas were derived from similar or the same source(s) and that the processes of magma evolution were equivalent for both magmas.The MI also indicate that the Campanian Ignimbrite and Giugliano magmas did not form by evolution of Taurano magma, because the geochemical trends expressing melt evolution of the former and latter magmas are too dissimilar. Most Taurano MI show higher (CaO/Al₂O₃) and contain less SiO₂, (Na₂O+K₂O), Cl, Li, Rb, Cs, Sr, Nb, Th, and U than the high-MgO and low-MgO Campanian Ignimbrite and Giugliano MI, indicating that the Taurano MI represent magmas which were much more primitive.Received July 15, 2002; revised version accepted March 27, 2003  相似文献   

Upward-thickening patterns and lateral continuity of Permian sand-rich turbidite channel fills, Laingsburg Karoo, South Africa   总被引：1，自引：0，他引：1  

Martin Grecula  Stephen S. Flint  Henry De V. Wickens†  Stephen D. Johnson‡ 《Sedimentology》2003,50(5):831-853

Abstract Analysis of extensive exposures of the Permian Laingsburg Formation, Karoo basin, South Africa, have enabled a detailed reconstruction of the base of slope stratigraphy and palaeoenvironments in a deep-water system characterized by a very narrow grain-size range (fine sandstone). The deposits include an ≈ 4 km wide and 80 m thick channel complex, fringed by sandy sheet deposits that extend laterally for at least 6 km across depositional strike. Within the channel complex, individual channel fills are marked by shallow basal erosion surfaces draped by thin, parallel-stratified beds of very fine sandstone and siltstone, interpreted as flow tails to largely bypassing flows. These thin beds are overlain by 0·4 to 5 m thick beds of structureless, fine-grained sandstone that represent the majority of the channel fills. The basal packages may be partially to completely removed by localized scour in the axial zone of the channel complex but can be mapped laterally into overbank areas where they thicken and are dominated by rippled fine sandstones with intercalated siltstones. Axial confinement resulted from subtle topography on the basin floor, whereby the lower, dense parts of the initially erosive and bypassing flows were partially confined in the lows and the more dilute, slower moving upper parts of the flows deposited sheet-like successions across slightly elevated overbank areas. The narrow grain-size distribution prohibited the formation ofcoarse-grained residual bypass deposits during the initial phases of channel formation. With decreasing magnitude, later flows became more depositional, filling remaining axial depressions with thick-bedded structureless sandstone. The smaller volumes of late-stage sediment were more axially focused, producing local scour-and-fill features and starvation of the overbank areas. Resulting grain-size vertical profiles are complex. The basal flow tail packages and overlying massive deposits form a thickening and slightly coarsening-upward trend in the channel fills. The overbank deposits show a thinning- and fining-upward profile as a result of less bypass plus late-stage starvation of sand. Application of traditional deep-water facies models could therefore potentially lead to erroneous interpretations of the channel complex as a prograding lobe and the overbank sheets as channel-fills.  相似文献   

Evaluation of ferrous and ferric Mössbauer fractions. Part II     

S.G. Eeckhout  E. De Grave 《Physics and Chemistry of Minerals》2003,30(3):142-146

Mössbauer fractions f are reported for various ferrous- and/or ferric-containing oxides, hydroxides, silicates, and phosphates to extend the list previously reported by De Grave and Van Alboom (1991). The f fractions were evaluated from the experimental temperature dependencies of their center shifts, assuming the Debye model for the lattice vibrations. For most Fe²⁺ sites the characteristic Mössbauer or lattice temperatures Θ_M are in the range 300–400 K, while those for Fe³⁺ sites are close to or exceed 500 K, implying significantly higher f fractions for Fe³⁺ than for Fe²⁺, in particular at room temperature. A correlation between Θ_M and the coordination type, or, for a given valence state and coordination type, between Θ_M and the mineral type is, however, not obvious.  相似文献   

地球长波辐射 (OLR)遥感与重大自然灾害预测   总被引：27，自引：0，他引：27  

刘德富  康春丽 《地学前缘》2003,10(2):427-435

针对目前重大自然灾害 (如地震、洪水泛滥、火山喷发等 )还难能作出短期预测预警的现实状况 ,文中提出利用极轨卫星遥感所监测的“地气”系统射出长波辐射 (即OLR)信息 ,是可能攻克这一难关的突破口。文中不仅详细介绍了有关OLR数据的产出原理及其载荷卫星 (NOAA)运行的主要参数 ,而且还结合近年来发生的重大自然灾害实例 ,利用笔者研究的应用OLR提取灾前预测信息的3种方法 ,客观地给出了OLR时空变化图像。结果显示 ,在重大自然灾害事件发生前 ,在未来可能发生重灾的区域及其附近 ,OLR呈现出比周围区域更显著的辐射增强变化特征。这一特征的揭示 ,为利用卫星遥感技术预测未来可能发灾区域及时作出短期预测预警提供了一种新的途径。文末对目前有关强震前热红外异常成因的两种看法做了综合介绍和简要评述。  相似文献   

Present Observational Status of High Mass Pulsating Stars     

Peter De Cat 《Astrophysics and Space Science》2003,284(1):37-44

In this short review we present the current observationalstatus of high mass pulsating stars.We give an overview of the results of the first asteroseismicstudies performed for some of the best known Cepheiand slowly pulsating B stars and discuss the asteroseismicpotential of these pulsators for future ground-and space-based data-sets.  相似文献   

An Improved Method of Photometric Mode Identification: Applications to Slowly Pulsating B, β Cephei, δ Scuti and γ Doradus Stars     

M.-A. Dupret  R. Scuflaire  A. Noels  A. Thoul  R. Garrido  A. Moya  J. De Ridder  P. De Cat  C. Aerts 《Astrophysics and Space Science》2003,284(1):129-132

We present an improved version of the method of photometric mode identification based upon the inclusion of non-adiabatic eigenfunctions determined in the stellar atmosphere, according to the formalism recently proposed by Dupret et al. (2002).We apply our method to Cephei, Slowly Pulsating B, Scuti and Doradus stars. Besides identifying the degree of the pulsatingstars, our method is also a tool for improving the knowledge of stellar interiors and atmospheres, by imposing constraints on the metallicity for Cephei and SPBs, the characteristics of the superficial convection zone for Scuti and Doradus starsand the limb-darkening law.  相似文献   

Statistical Revision of the Moment Method     

Joris De Ridder  Geert Molenberghs  Conny Aerts 《Astrophysics and Space Science》2003,284(1):125-128

The moment method is a well known technique, which uses a time series ofthe first 3 moments of a spectral line, to estimate the (discrete) modeparameters and m. The method, contrary to Doppler imaging,also yields other interesting(real-valued) parameters such as the inclination angle i, or v sin i,during its identification procedure.In this paper, we are not only interested in the estimation of thesereal-valued parameters themselves but also inreliable estimates for their uncertainty.We designed a statistical formalism for the moment method based on theso-called generalized estimating equations (GEE). This formalismaims to estimate the uncertainty of the real-valued parameters taking intoaccount that the different moments of a line profile are correlated and –more importantly – that the uncertainty of the observed moments depends onthe pulsation parameters. The latter property of the moment method makesthe least-squares technique a poor choice to estimate the uncertainty ofthe real-valued parameters. We implemented the GEE method and presentan application to a high-resolution spectroscopic dataset of the slowly pulsating B star HD181558.  相似文献   

Geochemical evidence for mixing of magmatic fluids with seawater,Nisyros hydrothermal system,Greece     

Tatjana?BrombachEmail author  Stefano?Caliro  Giovanni?Chiodini  Jens?Fiebig  Johannes?C.?Hunziker  Brunella?Raco 《Bulletin of Volcanology》2003,65(7):505-516

The chemical and isotopic compositions (δD_H2O, δ¹⁸O_H2O, δ¹⁸O_CO2, δ¹³C_CO2, δ³⁴S, and He/N₂ and He/Ar ratios) of fumarolic gases from Nisyros, Greece, indicate that both arc-type magmatic water and local seawater feed the hydrothermal system. Isotopic composition of the deep fluid is estimated to be +4.9±0.5‰ for δ¹⁸O and ?11±5‰ for δD corresponding to a magmatic water fraction of 0.7. Interpretation of the stable water isotopes was based on liquid–vapor separation conditions obtained through gas geothermometry. The H₂–Ar, H₂–N₂, and H₂–H₂O geothermometers suggest reservoir temperatures of 345±15 °C, in agreement with temperatures measured in deep geothermal wells, whereas a vapor/liquid separation temperature of 260±30 °C is indicated by gas equilibria in the H₂O–H₂–CO₂–CO–CH₄ system. The largest magmatic inputs seem to occur below the Stephanos–Polybotes Micros crater, whereas the marginal fumarolic areas of Phlegeton–Polybotes Megalos craters receive a smaller contribution of magmatic gases.  相似文献   

Effects on the Ionosphere Due to Phenomena Occurring Below it   总被引：4，自引：0，他引：4  

E. Kazimirovsky  M. Herraiz  B. A. De La Morena 《Surveys in Geophysics》2003,24(2):139-184

The terrestrial thermosphere and ionosphere form the most variable part of theEarth's atmosphere. Because our society depends on technological systems thatcan be affected by thermospheric and ionospheric phenomena, understanding,monitoring and ultimately forecasting the changes of the thermosphere–ionosphere system are of crucial importance to communications, navigation and the exploration of near-Earth space. The reason for the extreme variability of the thermosphere–ionosphere system isits rapid response to external forcing from various sources, i.e., thesolar ionizing flux, energetic charged particles and electric fields imposed via the interaction between the solar wind, magnetosphere and ionosphere, as well as coupling from below (meteorological influences) by the upward propagating, broad spectrum,internal atmospheric waves (planetary waves, tides, gravity waves) generated in thestratosphere and troposphere. Thunderstorms, typhoons, hurricanes, tornadoes andeven seismological events may also have observable consequences in the ionosphere.The release of trace gases due to human activity have the potential to cause changes inthe lower and the upper atmosphere.A brief overview is presented concerning the discoveries and experimentalresults that have confirmed that the ionosphere is subject to meteorologicalcontrol (especially for geomagnetic quiet conditions and for middle latitudes).D-region aeronomy, the winter anomaly of radiowave absorption, wave-liketravelling ionospheric disturbances, the non-zonality and regional peculiaritiesof lower thermospheric winds, sporadic-E occurrence and structure, spread-Fevents, the variability of ionospheric electron density profiles and Total ElectronContent, the variability of foF2, etc., should all be considered in connection withtropospheric and stratospheric processes. Ionospheric weather, as a part of spaceweather, (i.e., hour-to-hour and day-to-day variability of the ionospheric parameters)awaits explanation and prediction within the framework of the climatological, seasonal,and solar-cycle variations.  相似文献   

Covariance functions and models for complex-valued random fields   总被引：1，自引：1，他引：0  

S.?De IacoEmail author  M.?Palma  D.?Posa 《Stochastic Environmental Research and Risk Assessment (SERRA)》2003,17(3):145-156

In Geostatistics, primary interest often lies in the study of the spatial, or spatial-temporal, correlation of real-valued random fields, anyway complex-valued random field theory is surely a natural extension of the real domain. In such a case, it is useful to consider complex covariance functions which are composed of an even real part and an odd imaginary part. Generating complex covariance functions is not simple at all, but the procedure, developed in this paper, allows generating permissible covariance functions for complex-valued random fields in a straightforward way. In particular, by recalling the spectral representation of the covariance and translating the spectral density function by using a shifting factor, complex covariances are obtained. Some general aspects and properties of complex-valued random fields and their moments are pointed out and some examples are given.  相似文献