Geochemical constraints on magma processes in a peralkaline system: The Paisano volcano,west Texas     

William F. McDonough  Dennis O. Nelson 《Geochimica et cosmochimica acta》1984,48(12):2443-2455

Major and trace element data for a sequence of peralkaline silicic lavas and pyroclastic flows, exposed in the caldera wall of the Paisano volcano, west Texas, document systematic fractional crystallization during magmatic evolution and an open system, magma mixing event in the upper parts of the sequence. Stratigraphically lowest flows are comendite and comenditic quartz trachyte lavas and ash flow tufts. Overlying these units is a trachyte with compositional, textural and mineralogical features indicating that it is the product of magma-mixing; similar flows occur in other parts of the volcano at the same stratigraphic level. This composite trachyte is considered to be a mixture of mugearitic or mafic trachytic magma, derived from a similar source region which yielded the earlier caldera wall flows. Trace element concentrations of the post-trachyte comenditic quartz trachyte lavas suggest they were erupted from a chamber whose magma was diluted by an influx of mugearitic or mafic trachytic magma during a magma mixing event.Rayleigh fractionation calculations show that the comendites and comenditic quartz trachytes can be derived from a parental mugearite magma by 88% to 93% fractionation of dominantly plagioclase and alkali feldspar, with lesser amounts of clinopyroxene, magnetite and apatite. Zircon was not a significant fractionating phase. The composition, mineralogy and depth of the source region(s) which generated these magmas cannot be constrained from the present data set.  相似文献   

Forecasting errors: The importance of the decision-making context     

Robin L. Dennis 《Climatic change》1987,11(1-2):81-96

This article demonstrates the importance of context on forecast errors. It de J.scribes the development of an unrealistic transportation planning forecast for Denver, Colorado, noting its influence on air quality planning for Denver. The importance of two contextual features, procedural rationality and conflict of interest, to the introduction of error is discussed. The case described implies that different decision-making contexts define different rules of rationality, and substantive rationality may not fit the rules. The type of context and not necessarily a code of ethics will determine this.  相似文献   

Intra-field variability of scalar flux densities across a transition between a desert and an irrigated potato field     

Dennis D. Baldocchi  K. Shankar Rao 《Boundary-Layer Meteorology》1995,76(1-2):109-136

This paper reports on measurements of sensible and latent heat and CO₂ fluxes made over an irrigated potato field, growing next to a patch of desert. The study was conducted using two eddy correlation systems. One measurement system was located within the equilibrium boundary layer 800 m downwind from the edge of the potato field. The other measurement system was mobile and was placed at various downwind positions to probe the horizontal transition of vertical scalar fluxes. Latent (LE) and sensible (H) heat fluxes, measured at 4 m above the surface, exhibited marked variations with downwind distance over the field. Only after the fetch to height ratio exceeded 75 to 1 didLE andH become invariant with downwind distance. When latent and sensible heat fluxes were measured upwind of this threshold, significant advection of humidity-deficit occurred, causing a vertical flux divergence ofH andLE.The measured fluxes of momentum, heat, and moisture were compared with predictions from a second-order closure two-dimensional atmospheric boundary layer model. There is good agreement between measurements and model predictions. A soil-plant-atmosphere model was used to examine nonlinear feedbacks between humidity-deficits, stomatal conductance and evaporation. Data interpretation with this model revealed that the advection of hot dry air did not enhance surface evaporation rates near the upwind edge of the potato field, because of negative feedbacks among stomatal conductance, humidity-deficits, andLE. This finding is consistent with results from several recent studies.  相似文献   

Exploratory spectral analysis of hydrological times series     

A. Ian McLeod  K. W. Hipel 《Stochastic Environmental Research and Risk Assessment (SERRA)》1995,9(3):171-205

Current methods of estimation of the univariate spectral density are reviewed and some improvements are made. It is suggested that spectral analysis may perhaps be best thought of as another exploratory data analysis (EDA) tool which complements, rather than competes with, the popular ARMA model building approach. A new diagnostic check for ARMA model adequacy based on the nonparametric spectral density is introduced. Additionally, two new algorithms for fast computation of the autoregressive spectral density function are presented. For improving interpretation of results, a new style of plotting the spectral density function is suggested. Exploratory spectral analyses of a number of hydrological time series are performed and some interesting periodicities are suggested for further investigation. The application of spectral analysis to determine the possible existence of long memory in natural time series is discussed with respect to long riverflow, treering and mud varve series. Moreover, a comparison of the estimated spectral densities suggests the ARMA models fitted previously to these datasets adequately describe the low frequency component. Finally, the software and data used in this paper are available by anonymous ftp from fisher.stats.uwo.ca.  相似文献   

Short polarity intervals within the Matuyama: transitional field records from hydraulic piston cored sediments from the North Atlantic     

Brad M. Clement  Dennis V. Kent 《Earth and Planetary Science Letters》1987,81(2-3)

Detailed sampling of two short magnetozones within the Matuyama Chronozone recorded at DSDP Site 609 (49.86°N, 335.77°E) confirms that one, the Cobb Mountain Subchronozone (1.12 Ma), is a very short, full normal polarity interval and that the other, the older interval, is a record of a geomagnetic excursion which occurred at approximately 1.55 Ma. The Cobb Mountain Subchron lasted approximately 25,000 years, one third the duration of the Jaramillo Subchron. The normal polarity interval is bounded by two transition zones which document an antisymmetry in the sequence of directions in the reverse to normal and normal to reverse polarity transitions. We interpret the antisymmetry as reflecting a dependence upon the sense of the reversal, without significant changes in the relative contributions of non-dipole terms. The polarity interval recorded at 1.55 Ma lasted only 8,800 years with what may be regarded as full polarity directions observed across only 3 cm of stratigraphic section. This feature is interpreted as an excursion of the geomagnetic field and appears to be correlative with the Gilsa Subchron. Similarities between the transition bounding these two magnetozones suggest that these features occur as the result of the same process or triggering mechanisms in the earth's outer core.  相似文献   

Cyclic Storage: A Preliminary Assessment     

Dennis P. Lettenmaier  Stephen J. Burges 《Ground water》1982,20(3):278-288

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A HYDROLOGICAL SIMULATION OF HAZARDOUS WASTE INJECTION IN THE MT. SIMON, OHIO     

Dennis J. Nealon 《Ground water》1982,20(3):348-349

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Book reviews     

Jesse H. Ausubel  Ronald L. Gilliland  John Opie  Stephen G. Warren  Robin L. Dennis  Paulette Middleton 《Climatic change》1982,4(3):313-322

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Orthodoxy and creativity in theories of mountain building before 1922     

Prof. Dr. John G. Dennis 《International Journal of Earth Sciences》1982,71(2):421-426

In the 1870s, theories of mountain building emerged from little more than speculation to inference based on a growing body of observation and documentation. This coincided with abandonment of models stressing uplift, and their replacement, in the new orthodoxy, by models in which earth contraction led to lateral compression in its outer shell. Nevertheless, perceived weaknesses in this model gave impetus to new theories, some emphasizing primary vertical movement, and others continental displacement or subcrustal flow. The rebel theories added to the understanding of earth processes in important ways, by drawing attention to the weaknesses in the prevailing orthodoxy. But, in 1922, the complete answer remained out of reach.

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Zusammenfassung Die siebziger Jahre des vorigen Jahrhunderts brachten den Anfang von wissenschaftlich fundierten Theorien der Gebirgsbildung. Diese Zeit sah auch den Übergang von Erhebungstheorien zur neuen Lehrmeinung, nach welcher Erdkontraktion zu lateralen Drucken in der Außenhülle der Erde führte. Erkannte Schwächen dieses Modells führten jedoch zu neuen Gegentheorien, von denen einige primäre Vertikalbewegungen in den Vordergrund stellten, während andere Kontinentalverschiebung oder Unterströmungen als den Motor der Gebirgsbildung sahen. Diese Gegentheorien haben den Fortschritt der Erdwissenschaften gefördert, indem sie auf Schwächen der herrschenden Lehrmeinung aufmerksam machten. Aber selbst zu Argands Zeit war ein völlig befriedigendes Modell noch gar nicht erreichbar.

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Résumé C'est dans les années 1870–1880 que commençaient à s'établir les premières théories vraiment scientifiques de l'orogenèse. C'était la décade qui marqua l'abandon des théories à base de soulèvement et le début du règne de la nouvelle orthodoxie d'après laquelle la contraction de la terre mène à la compression latérale d'une pellicule extérieure. Néansmoins, certaines faiblesses du nouveau modèle servaient d'élan à des théories rebelles dont quelques-unes soulignaient l'importance des soulèvements primaires, tandisque d'autres cherchaient le moteur de l'orogenèse dans la dérive des continents ou dans des courants dans une masse quasi-fluide subcrustale. Ces théories rebelles ont avancé la science en soulignant les faiblesses de l'orthodoxie. En fin de compte, une solution complètement satisfaisante ne paraissait pas encore pouvoir être atteinte à l'époque d'Argand.

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Optimal processing of satellite-derived magnetic anomaly data     

Malcolm G. McLeod 《Physics of the Earth and Planetary Interiors》1983,31(1):10-26

The statistical concept of the power spectrum has proven to be of great value in the analysis of time series and linear systems for which the inputs and outputs are functions of time. This paper shows how the concept can be extended to two-dimensional spatial power spectra and illustrates, by example, how the concept can be applied to the determination of optimal data processing methods for satellite-derived magnetic anomaly data and to the planning of missions to obtain such data.The analysis techniques indicated are applied to a data set and data processing procedure described by Mayhew et al. (1980). These authors describe magnetic anomaly data for Australia and surrounding ocean obtained by the polar orbit POGO series satellites. This paper shows that the data processing method used by these authors is approximately equivalent to an invariant two-dimensional linear filter and that it is reasonably close to optimal with respect to accuracy, though some possible improvements are suggested. Nevertheless, as is usual when filtering data, some real “signal” is unavoidably removed along with the “noise”, resulting in errors that can be quite large.A method for reducing these errors by using additional data from a medium inclination orbit satellite (for example, 60° inclination) is suggested.  相似文献